I'm really eager to have someone who can give me any advice. I've been trying to write a VBA code for STAAD Pro.

For some reason I need to pick a node but I don't know how...

How can I pick a node and get the node info during the VBA code is running?

I don't know where I should start from..

What I want to do is to record plates information. I can write a code to get that by selete all plates first and run the code but for some reason I need to do that one by one...

To do this I need to pick a node by clicking and recored the node numbers and do it many times.

Please give me some idea to pick a node by clicking and get the node information Thank you so much for you advice,

While I can look at the model with Stress Ratio values annotated next to the steel members that I have asked to be checked, when I do the member query (double clicking on the members) I don't see the Design Property and Steel Design boxes anymore. Why is that?

 Design Property and Steel Design tabs are not displayed for members which have not been designed. Are you sure you are clicking a member for which the design has been done? Sometimes, when ratios are annotated on the screen, the picture may become quite cluttered with data and in an effort to double click on a designed member, one may end up clicking on a member for which design has not been performed. So, first check that the member you are double-clicking has indeed been designed. If you are certain that STAAD has done the design and evidence of that exists in the analysis output file and in the postprocessing Unity Check tables, but still you are not able to see these tabs in the dialog box which comes up when you double click on the member, please send us your .std model and our support representatives will look into that.

STAAD is checking deflection for beams or girders for all the load combinations in my model. Is there a way to tell STAAD which load combination to check?

You have to use the LOAD LIST command to achieve this. Supposing you want to check deflection for combination cases 81 and 82. And assume that L/Deflection has a limit of 240. The command sequence required to achieve this is

LOAD LIST 81 82
PARAMETER
CODE AISC
DFF 240 ALL
CHECK CODE ALL

However, after these commands, you have to reset DFF to a very small number so that deflection does not become a criteria for any further design operations. That is because, once a parameter is specified in STAAD, it stays that way till it is changed again. So, after the above, you need to specify

PARAMETER
CODE AISC
DFF 1 ALL

The steel design output indicates a slenderness failure (KL/r exceeds allowable). Why? The axial force on the member is very small.

The code has requirements which say that the KL/r ratios for a member should not exceed certain allowable limits. For members subjected to tensile forces, the code suggests one limit, and for members subjected to compressive forces, there is another limit.

This check does not consider the amount of the axial force. It only looks at the sign of the force to determine if it is a tensile force or compressive force.

In most codes, this is the first check STAAD does on a member. If the member fails the check, no further calculations are done for that member.

So, STAAD performs these checks by default. However, the code does not offer any guidelines on what must be the minimum magnitude of the axial force for the member to become a candidate for this check.

So, in STAAD, two parameters are available - one called MAIN and another called TMAIN if you wish to bypass this check (TMAIN is available for some codes only). MAIN=1 is for bypassing the slenderness check in compression, and TMAIN=1 is for bypassing the slenderness check in tension.

I set my deflection limit to L/360, but the maximum deflection indicated in the summary of node displacements in PostProcessing shows a deflection of 1.5 inches. Isn't this above the limit that I set?

During steel design per the AISC ASD code, there are two types of deflection checks you can perform with STAAD. They are

1. Check for local deflection. This is usually applicable to members which are connected at both their ends to other members.
2. Check for the relative displacements between the nodes such as for a cantilever beam.

LOCAL DEFLECTION is defined as the maximum deflection between the 2 ends of the beam relative to a straight line connecting the 2 ends of that member in its deflected position.

If you go to

Help - Contents - Technical Reference - Commands and Input Instructions - Printing Section Displacements for Members

you will find a diagram indicating this is in figure 5.41.

To obtain more information on the difference between the 2 methods of deflection checking, please go to

Help - Contents - Technical Reference - American Steel Design - Design Parameters (which comes after Allowables per AISC code)

It will bring up section "2.4 Design Parameters"

At the end of the parameters table, you will see several notes. Please read Notes items 1 through 4 for the description of the two methods.

As you can see there, the default condition, which is also represented by a value of zero for the CAN parameter, is to perform the LOCAL DEFLECTION check.

Your question indicates that what you are looking for is a check of the nodal deflections. The cantilever style check STAAD offers is probably the solution for your problem. If so, specify the CAN parameter with a value of 1.

THE VALUE OF E FOR MEMBER NNN DOES NOT SEEM RIGHT. What does this mean?

The steel design output for several members is accompanied by the following warning message :

WARNING : THE VALUE OF E FOR MEMBER 21 DOES NOT SEEM RIGHT.

WARNING : THE VALUE OF E FOR MEMBER 22 DOES NOT SEEM RIGHT.

WARNING : THE VALUE OF E FOR MEMBER 23 DOES NOT SEEM RIGHT.

During steel design, there is a check for ensuring that the Modulus of Elasticity (E) specified for the member is within the range that is normal for steel. This is because, E is a crucial term that appears in many equations for calculating section capacities and the program wants you to know if the value appears to be abnormal.

In STAAD, you specify E either explicitly under the CONSTANTS command block or through the DEFINE MATERIAL block, as in the examples below.

Example 1 :

UNIT KIP INCH
CONSTANTS
E 29000 ALL
DENSITY 0.283E-3 ALL

Example 2 :

UNIT METER KNS
DEFINE MATERIAL START
ISOTROPIC STEEL
E 2.05e+008
POISSON 0.3
DENSITY 76.8195
ALPHA 1.2e-005
DAMP 0.03
END DEFINE MATERIAL
CONSTANTS
MATERIAL STEEL MEMBER 101 TO 121

So, if you are specifying an E value which is significantly different from that for steel, such as say, Aluminum, and then later asking the member to be designed according to a steel code, as in the following example, the above-mentioned warning message will appear.

UNIT FEET POUND
DEFINE MATERIAL START
ISOTROPIC ALUMINUM
E 1.44e+009
POISSON 0.33
DENSITY 169.344
ALPHA 1.28e-005
DAMP 0.03
END DEFINE MATERIAL

CONSTANTS
MATERIAL ALUMINUM MEMBER 21 TO 30

..
..
PARAMETER
CODE AISC
CHECK CODE MEMBER 21 TO 30

The KL/r value that STAAD reports for the Y axis for a single angle does not match what I get from my hand calculation. Can you explain why? 

For single angles, the local Y and Z axes are the principal axes as shown below:

The KL/r value is computed using ry and rz which are based on the principal axis system. Chances are that your handculation uses the geometric axes.

I have a large model with several hundred members which have been assigned steel sections. I am doing a code check and I want to find out which of those members have failed. Can I get a list of just those members without having to scroll through hundreds of pages of steel design output?

There are 2 methods for finding just those members which have failed the steel design checks.

1. From the Select menu, choose By Specification - All Failed beams. The members which fail the check will be highlighted. You can then isolate them into a New View to examine them in greater detail. Double click on those members or use Tools - Query - Member to access a dialog box with tabs called Steel Design and Design Property to see the cause of the failure along with allowable and actual stresses and critical conditions.
2. In the Post processing mode, go to the Beam page along the left side of the screen. One of the sub-pages will be Unity Check. A table will appear along the right side of the screen. One of the tabs of that table is Failed Members. Select this tab, and click on each row of the table to look at each such member individually.

I am running STAAD.Pro 2003. In the TRACK 2 output for the American LRFD code, I find some terms that I am not familiar with. Can you tell me what those are?

The terms reported in the TRACK 2 output for American LRFD are :

AX = Cross section Area.
AY : Area used in computing shear stresses along local Y axis.
AZ : Area used in computing shear stresses along local Z axis.
PY : Plastic Section modulus about local Y axis.
PZ : Plastic Section modulus about local Z axis.
RY : Radius of gyration about local Y axis.
RZ : Radius of gyration about local Z axis.

PNC : Axial compression capacity.

pnc : Axial compressive force used in critical condition.

PNT : Axial tensile capacity.

pnt : Axial tensile force used in critical condition.

MNZ : Nominal bending capacity about local Z axis.

mnz : Bending moment about local Z axis, used in critical condition.

MNY : Nominal bending capacity about local Y axis.

mny : Bending moment about local Y axis, used in critical condition.

VN : Shear capacity.

vn : Shear force associated with critical load case and section location.

DFF : Permissible limit for checking length to deflection ratio.

dff : Actual length to deflection ratio.

I am running STAAD.Pro 2002. In the TRACK 2 output for the AISC ASD code, I find some terms that I am not familiar with. Can you tell me what those are?

The terms reported in the TRACK 2 output for AISC ASD are :

AX = Cross section Area
AY : Area used in computing shear stresses along local Y axis
AZ : Area used in computing shear stresses along local Z axis
SY : Elastic Section modulus about local Y axis
SZ : Elastic Section modulus about local Z axis
RY : Radius of gyration about local Y axis
RZ : Radius of gyration about local Z axis

FA : Allowable axial stress. If failure condition involves axial tension, this is the allowable axial tensile stress. If failure condition involves axial compression, this is the allowable axial compressive stress.

fa : Actual axial stress.

FCZ : Allowable bending compressive stress about local Z axis.

FTZ : Allowable bending tensile stress about local Z axis.

FCY : Allowable bending compressive stress about local Y axis

FTY : Allowable bending tensile stress about local Y axis.

fbz : Actual bending stress about local Z axis, used in the design condition

fby : Actual bending stress about local Y axis, used in the design condition.

FV : Allowable shear stress.

Fey : Euler stress for buckling about local Y axis.

Fez : Euler stress for buckling about local Z axis.

DFF : Permissible limit for checking length to deflection ratio.

dff : Actual length to deflection ratio.

I am using STAAD.Pro 2003 and I want to use physical members to do a steel design. I know how to manually create physical members by selecting the individual members, right-clicking the mouse and choosing Form Member. But if I have hundreds of these members, can I do it faster?

In STAAD.Pro 2003, you can use the Auto-Form member option to let the program automatically create physical members for you. From the Member Design page in the Steel Design Mode, go to Member Design | Physical Members | Auto Form Members. The rules it uses to create physical members are as follows:

1. All elements must form a single continuous line. But they do not have to form a straight line. Thus curved members may be formed.
2. There must be a free end. Whilst curved members are allowed, they cannot form a closed loop.
3. All elements should have the same beta angle.
4. All elements must point in the same direction. Check with the orientation labels if necessary. Use the reverse element command on elements that point the wrong way.
5. None of the elements can be part of another member.
6. The section properties must be consistent at each element end. Elements can taper along their length, but where one element ends and the next starts, they must have the same section reference.
7. All elements must be made from the same material.
8. Vertical segments are converted into columns first.

I want STAAD.Pro to perform a steel design based on the LRFD 3rd Ed rather than the 2nd Edition. The output always says "LRFD 1994". How do I tell it what code to use?

If you wish to use LRFD 3rd Edition Code, you can write CODE LRFD3 when providing the design parameters.

The 3rd edition of the American LRFD steel code has been implemented along with the 2nd edition. In general, the principles outlined in the code for design for axial tension, compression, flexure, shear etc., are quite similar to those in earlier versions of the code. The major differences are in the form of incorporation of the Young’s modulus of steel in the various equations for determining various limits like slenderness and capacities.


Consequently, the general procedure used in STAAD for design of steel members per the AISC-LRFD code has not changed significantly. Users may refer to Section 2 of the STAAD.Pro Technical Reference manual for these procedures.


Those who wish to use the 1994 edition of the code can still do so by specifying the code name as:

CODE LRFD2

An example of commands used for performing design based on the new and old codes are as shown.


Example for the LRFD-2001 code (3rd Ed)


UNIT KIP INCH
PARAMETER
CODE LRFD


or

CODE LRFD3
FYLD 50 ALL
UNT 72 MEMBER 1 TO 10
UNB 72 MEMB 1 TO 10
MAIN 1.0 MEMB 17 20
SELECT MEMB 30 TO 40
CHECK CODE MEMB 1 TO 30

Example for the LRFD-1994 code (2nd Ed)

UNIT KIP INCH
PARAMETER
CODE LRFD2
FYLD 50 ALL
UNT 72 MEMBER 1 TO 10
UNB 72 MEMB 1 TO 10
MAIN 1.0 MEMB 17 20
SELECT MEMB 30 TO 40
CHECK CODE MEMB 1 TO 30

I am not sure how STAAD deals with the specifications of the unsupported length for top flange compression.

For example, if I have a truss whose top chord is laterally supported at every other node (i.e. two member lengths being unsupported), then should I highlight every two members (of the top chord) seperately and then tell the program to take their combined length as being unsupported, or should I highlight the entire top chord and then specify the correct unsupported length.

The value you specify for UNL is what STAAD uses for the expression Lb which you will find in Chapter F of the AISC ASD & LRFD codes. Starting from Version 2001, UNL has been replaced with UNT and UNB for these codes. If the Lb value for the top flange is different from that for the bottom flange, you have to specify the corresponding values for UNT & UNB.

So if the bracing points are at every alternate node, first determine the distance between the alternate nodes. Then assign that value for both beams which exist between those nodes.

For example, if you have

Member 5 connected between nodes 10 and 11, and is 6.5 ft long
Member 6 connected between nodes 11 and 12, and is 7.3 ft long

and both the top and bottom flanges are braced at nodes 10 & 12, you can assign

UNIT FEET
PARAMETER
CODE AISC
UNT 13.8 MEMB 5 6
UNB 13.8 MEMB 5 6

To assign these parameters using the GUI, while in the Modelling mode, select the Design page from the left side of the screen. Make sure the focus is on the Steel sub-page. On the right side, select the proper code name from the list box on the top. Click on the Define Parameters button along the bottom right side. In the dialog box which comes up, select the tab for UNT and UNB, specify the value, and assign it to the appropriate members.

I would like to perform code checking on a 8" x 2 1/2" x 10 Gage channel per the AISI Coldformed steel code. But this channel is not listed in the sections available in your database. Can I assign it using a user provided table?

At present, sections whose data is specified using a "User Provided Table" (see section 5.19 of the Technical reference manual for details) cannot be designed or checked per the AISI code. However, the following approach may be used to get around this limitation.

You may add your section to the STAAD AISI section database, so that your section becomes a permanent part of the database. This can be done using the following method.

From the Tools menu, select Modify Section database. The various steel databases available in the program will be listed in a dialog box. You will find ColdFormed (US) at the end of this list. Expand this list, and choose Channel with Lips or Channel without Lips as the case may be. On the right half of the dialog box, the Add option will become activated. Select that, and you will now be provided with an interface through which you can add your channel to the list. Save and Close it.

You can now go to the Commands menu, and choose Member property - Steel Table - AISI Table to obtain visual confirmation that this new section is permanently included among the list of channel sections. You should now be able to assign this new section to the members through the usual property pages and menus.

Increasing the NSF value in Steel Design does not change the Failure Ratio for a member, Why?

In the design input parameters, I set NSF to .85 for my steel design. The design output result showed a failure ratio of 1.063 on Member 1. I then proceeded to change the NSF parameter to 1.0. This time, the design output result showed the same failure ratio of 1.063. It seems that nothing has changed. I increased the net section factor by 0.15, but the stress ratio hasn't changed? 

The NSF value has an effect only on allowable axial tensile capacity, and the actual tensile stress.

If axial tension, or axial tension plus bending, are not what determine the critical condition, changing the value of NSF will not have any impact on the failure ratio. For example, if the critical failure condition for a member is compression, changing NSF will have no impact.

Check to see what the critical condition is. It will show up in the form of expressions such as:

AISC H1-1 or Slenderness, etc.

I ran my STAAD model and got an error message which stated that "This version does not design prismatic sections". What does this mean?

In the earlier versions of STAAD (STAAD-III), the code check for prismatic sections was done using allowable stresses which are arbitrarily chosen as 0.6 x Fy. However, this assumption of 0.6Fy was not based on any code specific requirements. The word PRISMATIC is meant to indicate a section of any arbitrary shape. But neither the AISC nor LRFD codes provide guidelines for design of arbitrary shapes. Section capacities are dependent upon aspects such as the width to thickness ratio of flanges and webs, lateral torsional buckling etc. From that standpoint, using an allowable stress of 0.6Fy for PRISMATIC sections was not always conservative.

A way around this limitation (lack of specific guidelines) would have been to use the rules of a known shape, such as a Wide Flange, for designing prismatic shapes. That would require knowledge of equivalent flange and web dimensions. When the properties are defined using the PRISMATIC option, there is no means to convey information such as dimensions of flanges or webs to the STAAD design facility. Hence, the design of PRISMATIC shapes is not supported in STAAD/Pro. You may get around this problem by defining the properties using the GENERAL section in a User Provided Table. For a GENERAL section, STAAD provides the means for providing dimensions of the components that are critical from the standpoint of computing allowable stresses. The allowable stresses for a GENERAL section are computed using the rules of a wide flange shape (I shape). As a result, the allowable stress value will be dependent on attributes such as dimensions of the cross section, length of the member, etc.

The KL/ry reported for a double angle does not match my hand calculations. I am designing the section per the AISC ASD 9th edition code.

For singly symmetric shapes such as Tees and Double Angles, the KL/r value for the Y axis is calculated by STAAD using the rules for flexural torsional buckling as explained in page 3-53 of the AISC ASD manual. It is not calculated as Ky multiplied by Ly divided by ry. 

I am using the composite beam design capabilities. But the output does not show any evidence of this design. Why?

There are 2 sets of data associated with analysing and designing a composite beam.

Step 1 : Define the member properties as a composite beam. To do this, one has to use the "TA CM" option as explained in Section 5.20.1 of the STAAD.Pro Technical reference Manual. For example, if member 1 is a composite beam made up of a 3.0 inch thick slab on top of a W18X35, and the grade of concrete is 4.0ksi, one would have to specify

UNIT INCH KIP
MEMBER PROPERTIES
1 TA CM W18X35 CT 3.0 FC 4.0

Step 2 : Parameters for steel design. This is what you find in Section 2.9 of the STAAD.Pro Technical reference Manual. These are the attributes which are to be used in the actual design equations, using the expression PARAMETER, as in,

PARAMETER
CODE AISC
BEAM 1 ALL
TRACK 2 ALL
FYLD 50 ALL
CMP 1 ALL
DR1 0.3 ALL
WID 60 ALL
FPC 4 ALL
THK 4 ALL
SHR 0 ALL
DIA 0.75 ALL
HGT 4 ALL
RBH 2 ALL
CHECK CODE ALL

The most important thing to note here is the usage of the parameter CMP. Unless it is set to 1.0, STAAD does not design the beam as a composite section. The beam will be designed as a pure steel beam section in the absence of the "CMP 1" parameter.

How does one change the value of the yield strength of steel?

FYLD is one of the items specified as parameters for steel design. The STAAD Technical Reference manual and International Design Codes manual contain information on specifying parameters for steel design.

There are example problems in the STAAD Example manual demonstrating how parameters are specified for design. The example below shows some typical post-analysis commands.

PERFORM ANALYSIS PRINT STATICS CHECK
PRINT MEMBER FORCES LIST 5 7
PRINT ELEMENT STRESSES LIST 10 TO 16
UNIT KIP INCH
PARAMETERS
CODE AISC
UNT 1.0 ALL
UNB 20.0 ALL
LY 60 MEMBER 36 40
LZ 60 MEMBER 36 40
FYLD 46.0 MEMBER 47 50
CHECK CODE ALL
FINISH

If you prefer to use the graphical method, this is how you can specify it. From the left side of the screen, select the Design page. Make sure the sub-page says Steel. On the right hand side of the screen, go to the top, and choose the appropriate code.

Select the members on the structure for which you wish to assign the FYLD parameter.

Then, on the bottom right hand side of the screen, you will find a button called Define Parameters. Click on that button. Select the FYLD tab. Specify the value, and click on Assign.

In STAAD/Pro 2000 and STAAD.Pro, I no longer see the UNL parameter for the AISC ASD and LRFD codes. Instead, I see the parameters UNT and UNB. Why?

In versions of STAAD prior to STAAD/Pro 2000, the mechanism for specifying the unsupported length of the compression flange was through the means of the UNL parameter. However, the drawback of this command is that if the value for the top flange is different from that of the bottom flange, there wasn't any means to communicate that information to STAAD.

Consequently, 2 new commands were introduced, namely, UNT and UNB.

UNT stands for the unsupported length of the TOP flange of the member for calculating the capacity in bending compression and bending tension.

UNB stands for the unsupported length of the BOTTOM flange for calculating the capacity in bending compression and bending tension.

To avoid the confusion that may arise from having 3 separate parameters to specify 2 items of input, we no longer mention the UNL parameter. However, to enable the current versions of STAAD to analyze input files created using the older versions of STAAD, the UNL parameter continues to work the way it did.

These 2 new parameters are to be used in place of UNL. If UNT/UNB is specified in addition to UNL, UNL will be ignored. If neither UNT nor UNB are specified, but UNL is specified, the value of UNL will be used for both top and bottom flange.

The steel design output for a tube section checked per the AISC ASD code indicates an SY and SZ substantially different from the values which are reported in the AISC publication. Why?

In steel design per the AISC ASD code, the elements of the cross section (flange, web etc.) have to be put through some tests per Chapter B of the code. These tests are required to classify the cross section into one of 3 types - Compact, Non-compact, Slender.

If a section is classified as slender, the allowable stresses on the section have to be determined per the rules of Appendix B of the code. For slender "stiffened elements", which is the type a tube falls into, the effective section properties have to be calculated and those effective properties must then be used in computing the actual stresses.

The extent of the cross section deemed effective depends on the bending moment on that section. It is very likely that for the critical load case, the effective properties are less than the gross section properties, which is why you see the reduced Sz and Sy in the output.

How can I check whether the story drift of the floors are within allowable limits?

If you have STAAD.Pro 2001 Build 1005 or Build 1006, you can specify a command called

PRINT STORY DRIFT

in your input file. Run the analysis. Then check your output file, The drift for each story will be reported. You will have to manually verify that this is within your allowable limits.

Utilizing DFF in STAAD only helps one check the local deflection. What if I want to check the drift of a column / beam frame?

If my joint displacement printout says that joint of a column/beam joint has moved 1.42 inch in the global X, then my drift ratio is 18x12/1.42 = 152.11, but the "dff" says 1072 for the same column, then where is the dff being measured?

When the DFF parameter is specified, the deflection checks during steel design are performed on the basis of so called "local axis deflection", not the nodal displacements in the global axis. For this reason, it is not possible to include storey drift checks into the steel design calculations at present.

If you want additional information on local axis deflection, please refer to example # 13, and Section 5.42 of the STAAD Technical Reference Manual.

Can I get STAAD to check deflection in both axes?

 Yes. However, rather than check the deflection for each axis independently, STAAD finds the resultant deflection "d" and compares the "L/d" (length to deflection ratio) against the allowable limit specified by you through the DFF parameter.

Will STAAD explicitly state that the beam has passed the deflection criteria?

When STAAD performs steel design (code checking as well as member selection), it checks several conditions required by the code. The one which gives rise to the highest unity check is the one determined as critical. If the deflection criteria ends up being the worst condition, you will see it being reported as the critical condition.

You can verify whether a member has passed the deflection check by looking at the terms "DFF" and "dff" in the steel design output. "DFF" is the value you input. "dff" is the value the program calculates as the actual "L/d" ratio. If "dff" is larger than "DFF", the member is deemed safe for deflection.

What are the design parameters which control deflection check?

1) DFF : This is the value which indicates the allowable limit for L/d ratio. For example, if a user wishes to instruct the program that L/d cannot be smaller than 900, the DFF value should be specified as 900. The default value for DFF is 0. In other words, if this parameter is not specified as an input, a deflection check will not be performed.

2) DJ1 and DJ2 : These 2 quantities affect the "L" as well as the "d" in the calculated L/d ratio. They represent node numbers that form the basis for determining L and d.

By default, DJ1 and DJ2 are the start and end nodes of the member for which the design is being performed, and "L" is the length of the member, namely, the distance between DJ1 and DJ2. However, if that member is a component segment of a larger beam, and the user wishes to instruct STAAD that the end nodes of the larger beam are to be used in the evaluation of L/d, then he/she may input DJ1 and DJ2 as the end nodes of the larger beam. Also, the "d" in L/d is calculated as the maximum local displacement of the member between the points DJ1 and DJ2. The definition of local displacement is available in Section 5.42 of the STAADPro Technical Reference Manual, as well as in Example problem # 13 in the STAADPro Examples Manual.

A pictorial representation of DJ1 and DJ2, as well additional information on these topics is available under the "Notes" section following Table 2.1 in Section 2.8 of the STAADPro Technical Reference Manual.

If you use the design parameter TRACK 2.0, you will see a term called "dff" in the STAAD output file. This terms stands for the actual length to deflection ratio computed by STAAD. If "dff" is smaller than "DFF", it means the member has violated the safety requirement for deflection, and will be treated as having failed.

THIS VERSION DOES NOT DESIGN TAPERED POLE SECTIONS (MEMBER 1). What does this error message mean?

 I am using tapered tubular section properties in my model. When I try to design those members using the AISC code.

The AISC code currently does not have the rules for designing tubular sections which are 6 sided, 8 sided, 12 sided, etc. That is why you cannot currently design them per the AISC code.

There is a code from ASCE called the ASCE publication # 72. That document contains the rules for designing these shapes. Those rules are implemented in STAAD's transmission tower code, and if you have purchased that code, you should be able to design them.

I am using STAAD to do steel design per the AISC code. For 2 members with similar cross sections, one passes, the other fails. Fact is, the one which fails has almost no load on it. The other is significantly more stressed but still passes. Is something wrong in the steel design calculations that STAAD is doing?

You will notice that, for the member which failed, the cause of the failure is reported using the phrase "L/R-EXCEEDS". This means that the member has failed the slenderness check.

When STAAD performs steel design on a member per the AISC code, it adopts the following sequence :

It first sets the allowable KL/r in compression to 200 and the allowable KL/r in tension to 300.

For the member being designed, it goes through all the active load cases to see if the member is subjected to axial compression and/or axial tension.

Next, it compares the actual KL/r against the allowable KL/r. If this check results in a FAILure, the member is declared as FAILed, and design for that member is immediately terminated. The requirement to check this condition is in Section B of the AISC specifications.

If the member passes the KL/r check, only then does the program go on to do the remainder of the checks such as axial compression + bending, shear, etc.

It must be noted that failure to satisfy the KL/r check is a reflection of the slenderness of the member, not the capacity of the section to carry the loads which act on it. Even if the axial load or bending moment acting on the member is a negligible quantity, the fact is, failure to satisfy KL/r will result in the member being declared as unsafe as per the code requirement.

If you do not want the KL/r condition to be checked, you can switch off that check using a parameter called MAIN. Set MAIN to 1.0 for a specific member and it won't be checked for slenderness. See Table 2.1 of the STAAD.Pro Technical Reference Manual for details.

What do the following parameters mean?

NSF 0.85 ALL
BEAM 1.0 ALL
KY 1.2 ALL
RATIO 0.9 ALL
LY 18 ALL
LZ 18 ALL
CHECK CODE ALL

NSF 0.85: This parameter is called Net Section Factor. One of the criteria used in determining the capacity of a section in Axial Tension is fracture of the net section. The capacity is calculated as NSF X Gross Area X Ultimate Tensile Strength of steel in tension

BEAM 1.0: This means the design or code checking of the member will be done by determining the safety of the member at a total of 13 points along the length of the member. Those 13 points are the start, the end, and 11 intermediate points along the length. If this parameter is not set, design will be performed by checking the safety at only those locations governed by the SECTION command.

KY 1.2: The KY value is used to determine the KL/r for the Y axis -
Ky multipled by Ly divided by Ry.

RATIO 0.9: The code requires one to check the safety of a member by verifying several interaction equations for compression, bending, tension, etc. The right hand side of these equations is usually 1.0. The RATIO parameter allows one to set the right hand side to the value of the RATIO parameter, in this case 0.9.

LY 18: The LY value is used in calculating the KL/r for the Y axis -
Ky multipled by Ly divided by Ry.

LZ 18: The LZ value is used in calculating the KL/r for the Z axis -
Kz multipled by Lz divided by Rz.

CHECK CODE ALL : For ALL members, the safety of the section is determined by evaluating the ratio of applied loading to section capacity as per the code requirements.

When one does the AISC code check or member selection, what are the calculations the program is performing?

The checks done as per the AISC ASD 9th edition code are :

1. Slenderness - Checks for KL/r limits per Chapter B
2. Local Buckling per Chapter B
3. Axial Compression + Bending per Section H
4. Axial Tension + Bending per Section H
5. Shear per Section F

When I run code checking [as per BS5950] of the steel prismatic members which were defined in the User Provided Table, I get the following message in my output file:

CHECK CODE ALL

DESIGN NOT PERFORMED WITH PRISMATIC PROPERTIES
USER-TABLE MAY BE USED TO DESIGN PRISMATIC SECTIONS

The program is not designing the steel members defined as "Prismatic" in the UP Table, whereas all other members defined otherwise as Tee, Channel etc are being designed. Also I couldn't understand the meaning of the last line "User-Table may be used to design prismatic sections".

Since PRISMATIC sections by definition are those whose section shape is not one of the standard shapes like a W, C, Angle, etc., there are no readily available rules in the code to follow. Due to this reason, prismatic shapes are presently not designed per the BS code nor the ACI code.

You may get around this problem by defining the properties using the GENERAL section in a User Provided Table. For a GENERAL section, STAAD provides the means for providing dimensions of the components that are critical from the standpoint of computing allowable stresses, such as flange, web, etc. The allowable stresses for a GENERAL section are computed using the rules of a wide flange shape (I shape). As a result, the allowable stress value will be dependent on attributes such as dimensions of the cross section, length of the member, etc.

I am using STAAD to perform steel design on a member per the AISC ASD code. I want the column to be designed based on an unbraced length of 20 ft. I have set the UNT and UNB values to 20 ft, but STAAD appears to consider only a 10 feet length in its KL/r calculations. How do I correct this problem?

The parameters UNT and UNB are for specifying the unsupported length of the compression flange for the purpose of computing allowable stresses in bending compression.

If you want to specify the unbraced length for the purpose of computing allowable stresses in axial compression, use the parameters LY and LZ. See Table 2.1 of the STAAD.Pro Technical Reference Manual for details.

How do I get a design parameter, say the RATIO parameter, to be applied only to certain load cases?

You would need to use the "LOAD LIST" command. For example, if you only were interested in the 1st, 3rd and 5th load cases for the RATIO parameter you would need to write:

LOAD LIST 1 3 5
RATIO 0.5

In your input file.

I run the analysis of a 3-D bridge truss model and requested a CODE CHECK of the members. The results of this code check do not correspond to my hand calculation results.

The results of this code check show some very strange numbers in as far as code ratio using AISC- H1-1 formulation is concerned. Reference result output for members number 62 to 74 for example. Other ratios do not seem right either.

If you look at the AISC equation H1-1, you will find that there are 2 terms in the denominator, called

(1-fa/Fey)

and

(1-fa/Fez)

If the value of fa equals or exceeds Fey or Fez (Euler stresses), the respective terms become zero or negative, which is not a desirable event. In such a situation, STAAD replaces that negative number with the value 0.0001. The consequence of this is that, that part of the interaction equation becomes magnified by 10000, which will cause the overall value of the left hand side of equation H1-1 to increase significantly.

The above scenario is what occurs in the case of several of the members in the list 62 to 74. If you want to obtain proof of this, you may do the following. Change the value of the TRACK parameter from 1 to 2, and you will get a more detailed design output. That output will include the values of fa, Fey, Fez, etc.

To remedy the problem, you need to use a larger cross section so that "fa" becomes smaller, or use one with a smaller KL/r value so that Fey and/or Fez become larger.

What is the LX parameter used for?

The LX is the parameter used in calculating the axial compression capacity for flexural torsional buckling 

The KL/r value that STAAD reports for a single angle member does not match my hand calculation. Design is per the AISC ASD 9th edition code.

A single angle is subjected to 2 buckling modes :

1. Column buckling. This is determined using the simple expressions (Ky.Ly/ry) and (Kz.Lz/rz), where ry and rz are the radii of gyration about the principal axes.
2. Flexural torsional buckling : This mode of buckling uses an equivalent KL/r, which is computed on the basis of equation (4-4) on page 5-311 of the AISC ASD 9th edition code. Generally, this mode of failure produces a higher KL/r than the ones from the column buckling mode.

You should check whether the flexural torsional buckling mode governs in your case. The KL/r calculated for the flexural torsional mode, if it happens to the largest of the 3 values, is reported only with a TRACK 1.0 detail of output. It does not get reported for TRACK 0 or TRACK 2 level of detail of output. In other words, if you want to see the KL/r in the flexural torsional buckling mode, use the parameter TRACK 1.0.

What are the SSY and SSZ parameters for AISC ASD based steel design?

SSY and SSZ are terms which dictate how sidesway criteria should be used in computing the Cm coefficients. For both of them, a value of 0.0 means sidesway is present for the corresponding axis, and, a value of 1.0 means sidesway is not present for the corresponding axis.

When SSY is set to 0.0, Cmy is set to 0.85 as per page 5-55 of AISC ASD.

When SSZ is set to 0.0, Cmz is set to 0.85 as per page 5-55 of AISC ASD.

When SSY is set to 1.0, Cmy is calculated as per the equations on page 5-55 of AISC ASD.

When SSZ is set to 1.0, Cmz is calculated as per the equations on page 5-55 of AISC ASD.

If the CMY parameter is specified (and the value is a valid one), that value is used, regardless of what the value of SSY is.

If the CMZ parameter specified (and the value is a valid one), that value is used, regardless of what the value of SSZ is.

The KL/ry reported for a T shape does not match my hand calculations. I am designing the section per the AISC ASD 9th edition code. 

For singly symmetric shapes such as Tees and Double Angles, the KL/r value for the Y axis is calculated by STAAD using the rules for flexural torsional buckling as explained in page 3-53 of the AISC ASD manual. It is not calculated as Ky multiplied by Ly divided by ry.

Can you provide me with some help on how I can include deflection check as one of the criteria in steel design?

Deflection of a beam or a column can be included as one of the criteria during code checking or member selection with most steel design codes in
STAAD. The ratio of length to maximum deflection of a beam (L/d ratio) will be calculated by STAAD. STAAD will then check that quantity against the allowable limit which the user specifies under the PARAMETERS option.

What are the design parameters which control deflection check ?

1. DFF : This is the value which indicates the allowable limit for L/d ratio. For example, if a user wishes to instruct the program that L/d
cannot be smaller than 900, the DFF value should be specified as 900. The default value for DFF is 0. In other words, if this parameter is not
specified as an input, a deflection check will not be performed.

2. DJ1 and DJ2 : These 2 quantities affect the "L" as well as the "d" in the calculated L/d ratio. They represent node numbers that form the basis for determining L and d.

By default, DJ1 and DJ2 are the start and end nodes of the member for which the design is being performed, and "L" is the length of the member, namely, the distance between DJ1 and DJ2. However, if that member is a component segment of a larger beam, and the user wishes to instruct STAAD that the end nodes of the larger beam are to be used in the evaluation of L/d, then
he/she may input DJ1 and DJ2 as the end nodes of the larger beam. Also, the "d" in L/d is calculated as the maximum local displacement of the member between the points DJ1 and DJ2. The definition of local displacement is available in Section 5.42 of the STAADPro Technical Reference Manual, as well as in Example problem # 13 in the STAADPro Examples Manual.

A pictorial representation of DJ1 and DJ2, as well additional information on these topics is available under the "Notes" section following Table 2.1 in Section 2.8 of the STAADPro Technical Reference Manual.

What are the results one gets from STAAD for the deflection check?

If the steel design parameter called TRACK is set to 2.0, the L/d ratio calculated for the member can be obtained in the STAAD output file. The value is reported against the term "dff". Notice that the expression is in lower-case letters as opposed to the upper-case "DFF" which stands for the allowable L/d.

If "dff" is smaller than "DFF", that means that the displacements exceeds the allowable limit, and that leads to the unity check exceeding 1.0. This is usually a cause for failure, unless the RATIO parameter is set to a value higher than 1.0. If "DFF" divided by "dff" exceeds the value of the parameter RATIO, the member is assumed to have failed the deflection check.

What are the limitations of this check?

Since the "d" in L/d is the local deflection, this approach is not applicable in the case of a member which deflects like a cantilever beam.
That is because, the maximum deflection in a cantilever beam is the absolute quantity at the free end, rather than the local deflection. Check whether STAAD offers a parameter called CAN for the code that you are designing to. If it is available, set CAN to 1 for a cantilever style deflection check.

Since the deflection which is checked is a span deflection and not a node displacement, the check is also not useful if the user wishes to limit story drift on a structure.

In the output for steel design, what does the term "dff" represent?

"dff" is the value of actual length divided by local deflection. The actual length value is the distance between the nodes DJ1 and DJ2 which default to the actual end nodes of the member. The deflection used is the maximum local deflection between the points DJ1 and DJ2. You can get the Max. Local Displacement value by looking at the output of the PRINT SECTION DISPLACEMENT command. The definition of DFF, DJ1 and DJ2 may be found in Table 2.1 of the Technical Reference Manual for STAAD/Pro.The word PRISMATIC is meant to indicate a section of any arbitrary shape. But the AISC code does not provide guidelines for design of arbitrary shapes.
Section capacities are dependent upon aspects such as the width to thickness ratio of flanges and webs, lateral torsional buckling etc. From that standpoint, using an allowable stress of 0.6Fy for PRISMATIC sections was not always conservative. 

In STAAD-III, I was able to get a steel design for members defined using the PRISMATIC property attribute per the AISC ASD code. I cannot do this in STAAD/Pro. Why?

In the earlier versions of STAAD, the code check for prismatic sections was done using allowable stresses which are arbitrarily chosen as 0.6 Fy. However, this assumption of 0.6Fy was not based on any code specific requirements.

The word PRISMATIC is meant to indicate a section of any arbitrary shape. But the AISC code does not provide guidelines for design of arbitrary shapes. Section capacities are dependent upon aspects such as the width to thickness ratio of flanges and webs, lateral torsional buckling etc. From that standpoint, using an allowable stress of 0.6Fy for PRISMATIC sections was not always conservative.

A way around this limitation (lack of specific guidelines) would have been to use the rules of a known shape, such as a Wide Flange, for designing prismatic shapes. That would require knowledge of equivalent flange and web dimensions. When the properties are defined using the PRISMATIC option, there is no means to convey information such as dimensions of flanges or webs to the STAAD design facility. Hence, the design of PRISMATIC shapes is not supported in STAAD/Pro.

You may get around this problem by defining the properties using the GENERAL section in a User Provided Table. For a GENERAL section, STAAD provides the means for providing dimensions of the components that are critical from the standpoint of computing allowable stresses. The allowable stresses for a GENERAL section are computed using the rules of a wide flange shape (I shape). As a result, the allowable stress value will be dependent on attributes such as dimensions of the cross section, length of the member, etc.

In the context of design, what is meant by the term Ratio?

In steel design, the Pass/Fail status of a member is determined according to various conditions. According to most design codes, the member has to be checked for failure against axial compression and axial tension, slenderness, compressive & tensile stresses caused by axial compressive force + bending moments, failure caused by shear stresses, etc. For each of these conditions, determination of whether the member is safe or unsafe is done by checking whether the actual values due to the loading exceed or are less than the allowable values. The amount by which the member is stressed for each of these conditions is quantified in the form of the Ratio. For example, take the case of equation H1-1 of Section H of the AISC-89 specifications. The number obtained by computing the left hand side of that equation is the Ratio corresponding to that equation.

I have multiple sets of design in the same STAAD file and I am only able to see the results for the final set in the Postprocessing mode (GUI). How can I view the results for all design sets in the GUI ?

The postprocessing Beam >Unity Check page can report the design results only for the final set of design. This is a limitation in STAAD.Pro as the program architecture does not allow that results of multiple design sets to be made available at the same time graphically. The analysis output file is the only place where you can view results for all design sets. The only way to view the results of a previous design cycle graphically is 

1. to go to the editor and comment out the subsequent design sets and rerun the analysis
2. reverse the order for the design data blocks so that the set, for which the GUI data is needed, becomes the last set.     

How is the shear stress calculated in STAAD.Pro for AISC design code ? 

The shear stress calculated by STAAD is the maximum shear stress by default which is based on the standard formula VQ/Ib, where

V = Shear force

Q = Moment of area of the part of the cross section that
is above ( or below ) the plane where shear stress is being calculated, about
the neutral axis

I = Moment of Inertia

b= Width of the section at the plane where the stress is
being calculated

So the term Ib/Q is reported as the shear area that corresponds to this shear stress calculation.

If required one can get STAAD to calculate the average shear stress instead of the maximum. There is a SHE design parameter that can be used to influence how STAAD calculates the shear stress. When the parameter is set to 0 ( default ), stress is calculated as mentioned above. However when this parameter is set to 1, average shear stress will be calculated based on the formula V/Ay (or Az ) where Ay or Az are the shear area for the cross section.  

Do you have a plan that STAAD.Pro implements AISI 2007 edition?

AISI 2007 code is being developed, but as part of the STAAD(X) project rather than STAAD.Pro. It should be released in mid next year (2014).

See Also

Product TechNotes and FAQs

Structural Product TechNotes And FAQs

External Links

Bentley Technical Support KnowledgeBase

Bentley LEARN Server

Comments or Corrections?

Bentley's Technical Support Group requests that you please confine any comments you have on this Wiki entry to this "Comments or Corrections?" section. THANK YOU!

Regarding 1st Observation:
You have pointed out correctly. The code is silent on the design rules on design of slender section. There is no specific rules for the calculation for bending capacities for slender section. STAAD.Pro only perform design of Slender I sections with non-slender flange. In the case of, slender section subjected to bending, moment is taken by flanges alone. Design bending strength would be calculated with effective elastic modulus disregarding the contribution of web of the section.

Regarding 1st Observation:
STAAD.Pro deals with the member design. The main requirement of Aseismic design is to achieve ductility requirement. Section 12 of IS-800-2007 deals with detailing against Earth Quake loads. This section also stipulates certain requirement at the time of providing bracings in the model as you have mentioned. There requirement has to be achieved while modelling the members and their feasibility has to be checked after designing them. The judgement has to be done by the users. There is following criteria:

The aforementioned criteria has to be achieved during IS:1893 Seismicanalysis either in Design lateral force method of Response Spectrum method.

We got the following query from the user:

I have a model where I want to generate windload using STAAD.Pro Wind Definition. The program is generating wind loadcorrectly in the nodes of enclosed panels. I do not want loads to be generatedat the nodes which is on the beam. I used exposure factor zero on those nodes.If I remove the exposure factor, the program is generating Wind loading on the nodes. On using the exposure factors, the program is just ignoring the loads on the nodes. It is not redistributing the loads. Please suggest an alternate Process

for me its a input editor and concrete designer, it can export reinf. details to autocad

Created by Surojit Ghosh

This excel macro can be used to extract the total number of nodes selected in a STAAD.Pro model and also the selected node numbers. For example, if you select 4 nodes in your model and run this macro, total number of nodes selected in the model will be reported as 4 and the node number of those four nodes will be reported in the excel.

The following is the VB macro working in the background.

Private Sub CommandButton1_Click()

Dim numno As Long

Dim node() As Long

Dim i As Integer

Set objOpenSTAAD = GetObject(, "STAADPro.OpenSTAAD")

numno = objOpenSTAAD.Geometry.GetNoOfSelectedNodes

Cells(2, 2).Value = numno

ReDim node(numno - 1) As Long

For i = 1 To numno

objOpenSTAAD.Geometry.GetSelectedNodes node, 0

Cells(3 + i, 2).Value = node(i - 1)

Next

Set objOpenSTAAD = Nothing

End Sub

To run this macro, first open the STAAD.Pro model. Select the node (or nodes) and then click on the “Selected Nodes” tab in excel.

When you open this excel, you may receive a security warning message. Please click on the following link for more details about the procedure to activate the macro.

http://communities.bentley.com/products/structural/structural_analysis___design/m/structural_analysis_and_design_gallery/254111.aspx

The coordinates of the selected nodes can be extracted using the Geometry.GetNodeCoordinates function.

Collapse Mechanism in RCC members can be in the following category: 

Bond Failure: Brittle

Shear Failure: Brittle

Flexural Failure

Brittle: if over-reinforced section (compression failure)

Ductile: if under-reinforced section (tension failure)

Hence, We need to ensure that bond failure does not take place. Shearfailure does not precede flexural yielding. Beam is under-reinforced. IS:13920 code has stipulated this condition. In Clause-6.2.2, it says- the minimum steel ratio on any face of a flexural member should not exceed  row, max=0.025

Failure of RC Section : This may be in the following form: 

Yielding of tension bars- this type of failure is having the following category-

• Ductile
• Tension failure
• Under-reinforcedsection

Crushing of compression concrete this-type of failure is having the following category- 

• Brittle
• Compression failure
• Over-reinforced section failure

Tension failure more likely if:

• Less tension reinforcement
• Morecompression reinforcement
• Higher grade of concrete
• Lowergrade of steel
• Lower value of axial compression

Section ductility increases as- 

• Grade of concrete improves
• Grade of steel reduces
• Tension steel reduces
• Compression steel increases
• Axial compression  force reduces 

Generally, columns are less ductile than beams.

Capacity Design Concept:

• The chain has both ductile and brittle elements.
• To ensure ductile failure, we must ensure that the ductile link yields before any of the brittle links fails.

For instance, in a RC member:    

 
Shear failure is brittle      
Flexural failure can be made ductile      
Element must yield in flexure and not fail in shear

Capacity Design of Frames:  

We need to consider the following: 

• Choose yield mechanism
• Locate desirable hinge locations
• Estimate reasonable design seismic force on the building
• Design the members at hinge locations (upper bound type)
• Assess the member forces at other locations under the action of “capacity” force
• Design other locations for that force; need not detail these for high ductility

Materials in RC Members:  

Concrete and steel have very different characteristics

Steel ductile: strain capacity: ~12% to 25%

Concrete brittle: strain capacity: ~0.35%

Confinement of concrete:

It considerably improves its strain capacity:

Main Steps:

• Weak Girder – Strong Column Philosophy
• Shear Failure Prevented by Special Calculations (Capacity Design Method)
• Good Development Length
• Regions Likely to have Hinges Confined with Closely-spaced and Closed Stirrups

To ensure ductility: 

• Correct collapse mechanism
• Adequate ductility at locations likely to form hinge in collapse mechanism
• Need sufficient member ductility to ensure adequate structural ductility.
• Prevent brittle failure mechanisms to take place prior to ductile yielding

Storey collapse Mechanism: 

• Columns require too much ductility
• Columns are difficult to make ductile
• Collapse in column may lead to failure of whole structure.

Beam –Hinge Mechanism (Sway Mechanism):

Preferred mechanism

Ensure that beams yield before columns do

Strong Column –Weak Beam Design

my comment above was based on STAAD Pro 2005, FYI

This eSeminar was originally presented on July 30th, 2013 

You can view the recording online at our BeConnected site. (coming soon)

The following are the product-related questions and corresponding answers from the eSeminar.

ISM/Structural Synchronizer:

Can I model a structure in RAM Structural System and transfer it to STAAD?

Yes, with ISM you can create a model in one program and transfer that model to the other. This capability is available for the RAM products, STAAD, AECOsim Building Designer, ProStructures, and AutoPIPE, among others, as well as non-Bentley products such as Tekla and Revit. For more information see: http://communities.bentley.com/products/structural/w/structural__wiki/integrated-structural-modeling-home.aspx and: http://www.bentley.com/en-US/Products/Structural+Analysis+and+Design/ISM/

How do you transfer load data from RAM Structural System to STAAD and CSI Software?

Currently only the geometry is transferred from the RAM Structural System to the ISM repository, so once the geometry has then been imported into STAAD it would be necessary to define the loads in STAAD. We intend to implement the transfer of loads in a future enhancement to the ISM capabilities. Note however that gravity beam reactions are transferred through ISM, for use in the creation of the floor plan drawings. Also note that the ability to transfer foundation reactions for use in STAAD Foundation Advanced is currently being implemented. The CSI software does not have the capability of extracting data from an ISM repository.

When you do not accept the updated BIM import, can the originator of the change be notified, or is there always the discrepancy between the two models?

As explained in the webinar, the Structural Synchronizer acts as a “Gatekeeper”, giving the engineer control over whether or not the changes made in one application will be transferred to the other application. If changes are ‘rejected’ the originator of the change is not automatically notified; it is expected that the engineer will communicate those concerns directly with the architect or contractor or whomever made the change, if necessary. Related to that, one feature of the Structural Synchronizer that is particularly powerful is the ability to roll back to any previous version of that ISM repository. Thus if changes were made in error and committed to the ISM model they can be easily removed by rolling back to the previous version of the ISM model.

What if you do not have admin rights on your machine? Is there a way to fully utilize the benefits of the ISM process without having admin rights? Most of our in-house engineers do not have admin rights. 

It is not necessary for the engineer to have Admin rights, but the ISM repository must reside in a directory for which they have permission to modify files. This could be the same directory, for example, as where the RAM Structural System models or STAAD models are stored, where they already have permission.

Bentley has other structural analysis programs like LARS and LEAP CONSPAN. Will those programs be able to access ISM?

Although not currently available, the intent is to implement the ISM capability, or something similar, into the Bentley bridge design products, especially LEAP and RM Bridge. Some investigative work has already been done on that.

Where do you download the ISM export for Revit?

Downloads for the ISM Structural Synchronizer and for the ISM Revit plug-in can be found at: http://communities.bentley.com/products/structural/w/structural__wiki/integrated-structural-modeling-home.aspx

Use of BIM on the LAX Project:

Were other team members using other software such as Revit and if so, how was that handled to keep the production moving forward?

The team used Revit. The steel fabricator used their own in-house BIM software. Navisworks was used for the clash detection. There were no notable difficulties with integrating the various models and performing the coordination.

Who is responsible for the BIM model data during the update process, the author of the edit or the recipient of the edited data?

Each discipline was responsible to make modifications to their respective models to incorporate agreed upon modifications emanating from the clash detection process.

Analysis and Design Programs used on the LAX Project:

Why was RAM Structural System not used for the lateral stability design rather than changing to STAAD.Pro?

The RAM Structural System is special purpose software specifically for buildings. The advantage of this specialization is that it allows building models to be created very quickly, and the analysis and design can be very comprehensive without requiring time-consuming input by the engineer. The disadvantage is that it doesn’t handle some complex geometries such as the curved roofs and curved and non-orthogonal trusses that were prominent in the LAX project. While the RAM Structural System can easily handle even very complicated framing in plan, as well as sloping roofs and sloping columns, the modeling of the curved trusses would have been very tedious; thus it was more productive to use the RAM Structural System for the bulk of the elements in the structure where feasible but to turn to STAAD and other programs where necessary for the more complicated geometries. The RAM Structural System was particularly useful for the design of the composite and noncomposite floor beams, design of the numerous beams with web openings, and in the investigation of the floors for vibration. STAAD was useful in the analysis and design of the complex trusses and for member studies.

Why was SAP 2000 used in the LAX project beside STAAD?

STAAD and SAP 2000 were both used. JAMA decided to use SAP 2000 in cases where we would need to interface with our in-house post-processing programs.

Can you touch on STAAD.Pro on complex framing?

STAAD.Pro is general purpose software, capable of modeling virtually any structural configuration, with a wide variety of elements. It is routinely used in buildings, stadiums, transmission towers, plants, nuclear power plants and containment vessels, as well as dams, culverts, etc. So it has the ability to model, analyze and design complex framing, and is capable of performing advanced analyses.

RAM Structural System:

How were nodal loads (say MEP loads) added to lateral members at different points in RAM Frame?

Gravity point, line and surface loads are modeled in the Modeler by creating a table of loads with their magnitudes and then placing them in their proper location on the floor layout. The loads are then automatically distributed to the gravity and lateral members considering the deck type and direction (one-way or two-way decks). Live Load Reduction where applicable is automatically calculated and applied to the live loads. Wind and seismic loads can be manually defined as nodal loads and assigned to nodes on the frames, or more usefully they can be automatically generated and applied to the frames.

How was diaphragm stiffness correctly modeled in RAM Frame?

For the LAX project, since RAM Frame was not used for the lateral analysis it was not necessary to model the diaphragm in-plane stiffness. However, when performing lateral analysis RAM Frame does offer the engineer several options for specifying the diaphragm stiffness. Here is a very brief explanation. The simplest and most common option is to specify that the diaphragm is “Rigid”; when this option is selected the diaphragm distributes the story forces to the various frame members based on their relative stiffnesses. A more rigorous option is to specify that the diaphragm is “Semi-rigid”; this requires that the engineer specify the diaphragm properties (effective E, thickness, Poisson’s ratio, etc.), the program meshes the diaphragm, and the analysis considers the diaphragm flexibility in the distribution of the lateral forces to the frame members. For both “Rigid” and “Semi-rigid” diaphragms the code requirements for 5% eccentricity for accidental torsion are automatically included if desired. An option unique to RAM Frame is the ability to specify the diaphragm as “Pseudo-Flexible”; for this option the engineer assigns the percent of the story force that is to be distributed to each frame. This is useful in the case of roof diaphragms, for example, that have very little diaphragm stiffness, and these percentages could be based on tributary area or tributary exposure, or whatever the engineer feels is appropriate. The program then uses these percentages to determine and automatically apply nodal loads to the frames.

Is it possible to model cold formed joists back to back in RAM Structural System for 2D floor systems?

Based on the loading, span and design criteria specified by the user, Steel Joists can be selected from tables of sizes (e.g., 16K2 or 40LH16) and Joist Girder labels can be determined (e.g., 24G6N11.2k). The Steel Joist sizes and load capacities are listed in simple tables provided with the program, and can be easily customized. The supplied joist tables do not include doubled up joists, but the tables could be easily modified by the user to include them; it would merely be necessary to include entries in the tables with joist labels indicating double joists (such as 2-16K2), with load capacity values equal to twice those listed for the single joists.

RAM Connection:

What percentage of the joints was designed by RAM Connection?

JAMA did not use RAM Connection. JAMA has in-house programs for connections.

Does RAM Connection design per the British codes?

Yes, the connection design requirements of BS 5950-1:2000 are included for the design of shear and moment connections, but not for gusset plates (brace connections) or baseplates.

RAM Concept Training:

I'm looking for more tutorials for RAM Concept, other than the ones that came with the program. Are there any training services available or additional tutorials?

Bentley offers an extensive set of Live and On-Demand courses for all of its products. Information on these can be found at: http://learn.bentley.com/app/Public

For courses specific to RAM Concept, see: http://learn.bentley.com/app/Public/ViewLearningPathWithMasterCourseExpanded?lpId=100127&mcId=100205

Useful wikis and blogs can be found on the Be Communities website. Search for the product that you are interested in: http://communities.bentley.com

Be Inspired Awards:

How do we learn more about last year’s Be Inspired Award winner and finalists in the Structural category, and the 2013 event this October in London? 

Bentley is proud to have received a number of great use cases for this category. The Innovation in Structural Engineering finalists and winner were outstanding uses of Bentley products for their structural projects. Consider attending the 2013 event in London this October. And consider submitting your innovative project in the Spring of 2014! More information can be found at: www.bentley.com/beinspired.

About This eSeminar:

How do we get Continuing Education Credits? How can I get a certificate of attendance for CEU’s?

Bentley Learning Units (BLU), Bentley Institute’s equivalent to Professional Development Hours (PDH), are granted for the live and recorded eSeminar. Within 2-4 weeks of watching the presentation, Learning Units are added to your transcript. To access your transcript, go to: http://www.bentley.com/en-US/Training/Products/Resources/History/

On the "My Learning History" page, there is a detailed how-to guide related to Learning Units and transcripts, in addition to the link to the user’s online transcript. In most states, users can submit their Bentley transcripts for consideration for continuing education credit toward their registration renewals.

How do I view this eSeminar again or share it with a colleague?

This event along with the live Q&A was recorded, and it is available online. (coming soon)

The following TechNotes and FAQs are provided as a reference by Bentley's Technical Support Group.

Licensing & Installation

• Configuring Structural Products For SELECT Server
• Accessing SELECTservices Online And Downloading Files
• Manually Removing Bentley IEG Licensing Software
• Viewing And Checking In Licenses Using The Site Administration Page
• [[Using Bentley Structural Products Offline]]
• [[Structural Products Compatibility With 64 Bit Operating Systems]]
• [[Non-Interactive Installation Of Structural Products]]
• [[Performing A Clean Installation]]
• [[Structural Products Licensing FAQ]]
• [[Recommended Computer Specifications For Structural Products]]
• [["Another installation is already in progress, you must complete the installation first"]]

 

STAAD.Pro

• [[Member Tension And Combination Load Cases TN]]
• [[2066 | STAAD.Pro Developing The Model FAQ]]
• [[STAAD.Pro General FAQ]]
• [[STAAD.Pro Result Diagram FAQ]]
• [[STAAD.Pro Load Generation FAQ]]
• [[STAAD.Pro Member Specification FAQ]]
• [[STAAD.Pro Time History Analysis FAQ]]
• [[STAAD.Pro Response Spectrum FAQ]]
• [[STAAD.Pro Plates And Solid Elements FAQ]]
• [[STAAD.Pro Eigen Solution FAQ]]
• [[2046 | STAAD.Pro Instability And Zero Stiffness FAQ]]
• [[STAAD.Pro PDELTA Analysis FAQ]]
• [[STAAD.Pro Steel Design FAQ]]
• [[STAAD.Pro Concrete Design FAQ]]
• [[STAAD.Pro Timber Design FAQ]]
• [[STAAD.Pro Aluminum Design FAQ]]
• [[STAAD.Pro Miscellaneous FAQ]]
• [[2676 | STAAD.Pro Driver Downloads FAQ]]
• [[2764 | STAAD.Pro Tutorials FAQ]]
• [[2750 | STAAD.Pro Wall Analysis For Dams TN]]
• [[OpenSTAAD FAQ]]
• STAAD.Pro Postprocessing FAQ

STAAD.Foundation

• [[STAAD.Foundation Downloads]]

RAM Structural System

Release Notes

• RAM Structural System Release Notes

TechNotes and FAQs

General

• RAMSS Installation FAQ
• RAM Defaults Guide
• RAMSS Files FAQ
• [[RAM SS File-Open Troubleshooting [TN] ]]
• RAM Table Editing
• RAM SS 3D Viewer FAQ
• RAMSS Polygon Intersection Error
• RAM SS Analysis Types
• RAMSS Two Way Decks
• RAMSS Common Framing Table Errors

RAM Modeler

• RAMSS Modeling FAQ
• RAM SS Walls FAQ
• Importing DXF Files into RAM SS

RAM Steel

• RAMSS Gravity Loads FAQ
• RAMSS Beams FAQ
• RAMSS Joists FAQ
• RAMSS Columns FAQ

RAM Frame

• RAM Frame Troubleshooting
• RAMSS Eigenvalue Error
• RAM Frame Meshing and Segmentation
• RAM Instability In Finite Element Analysis
• RAM Frame P-Delta
• RAM SS Semirigid Diaphragms
• RAMSS Pseudo Flexible Diaphragms FAQ
• RAMSS Truss Modeling And Design
• RAMSS Wind Loads FAQ
• RAMSS Seismic Loads FAQ
• RAMSS Dynamic Modal Analysis FAQ
• RAMSS Tension Only FAQ
• Star Seismic Buckling Restrained Braces
• CoreBrace™ Buckling Restrained Braces
• RAM Frame AISC 360 Stability Analysis and Design

Revit Link

• RAM Structural System Revit Link

RAM DataAccess

• What is RAM DataAccess?

RAM Elements

NOTE: RAM Advanse is now RAM Elements

Release Notes

• RAM Elements Release Notes

TechNotes and FAQs

• RAM Elements Importing from RAM SS FAQ
• RAM Instability In Finite Element Analysis
• Creating custom elements in RAM Elements
• [[RAM Advanse Load Combos FAQ|RAM Elements Advanse Load Combos FAQ]]
• Ram Elements Shells FAQ
• RAM Elements Masonry Wall FAQ
• RAM Elements Unbraced Lengths
• RAM Elements Effective Length Factors
• RAM Elements AISC Stability

RAM Connection

Release Notes

• RAM Connection Release Notes

TechNotes and FAQs

• [[RAM Connection is installed, but the Connection button fails to appear in RAM Elements]]

RAM Concept

Release Notes

• RAM Concept Release Notes

TechNotes and FAQs

• RAM Concept-RAM Structural System Integration TN
• RAM Concept T-Beams and Axial Force TN
• RAM Concept Lateral Self Equilibrium Analysis TN
• RAM Concept Design Strips TN
• RAM Concept Load History Calc Options TN
• [[RAM ConceptCapabilities and ModelingFAQ|RAM Concept Capabilities and Modeling FAQ]]
• RAM Concept Files FAQ
• RAM Concept Plans And Perspectives FAQ
• RAM Concept Structure FAQ
• RAM Concept Tendons FAQ
• RAM Concept Loading FAQ
• RAM Concept Shear Reinforcement FAQ

AutoPIPE

Release Notes

• AutoPIPE Release Notes

TechNotes and FAQs

• AutoPIPE New User Guide
• AutoPIPE User Tips
• AutoPIPE Modeling Pipe-Structure Interaction
• AutoPIPE Compressor Vibration Method
• AutoPIPE CAD To Stress Integration
• AutoPIPE Model Wind Sway On A Pipe Rack
• AutoPIPE M-S Stress Level In Code Stress Combinations
• AutoPIPE Pipe Stress Programs
• AutoPIPE FAQ

Structural Modeler
PowerStructural Modeler
Structural DocumentationCenter

• Technotes have been moved to Structural Drafting and Detailing

See Also

Product TechNotes and FAQs

External Links

STAAD.Pro from Bentley

Structural Analysis and Design Products

Comments or Corrections?

Bentley's Technical Support Group requests that you please confine any comments you have on this Wiki entry to this "Comments or Corrections?" section. THANK YOU!

This Client Server article is republished in its entirety from 2008 for reference purposes.

By Phil RiegelTechnical Support Analyst
11 September 2009 Modified: 24 November 2009

Reference Loads is a powerful tool in STAAD.Pro that expands users’ options for setting up load cases and improves their overall efficiency. Reference Loads are useful because they are not explicitly solved during the analysis, but rather exist only as building blocks to be included in creating primary load cases. In this sense one can think of Reference Loads as “load definitions.”

They are particularly helpful for large models, which often contain many load cases that do not require analysis in their own right, including seismic, wind, or live load acting alone. Users can create multiple reference loads and then have STAAD.Pro solve only a limited number of “real” load cases. By limiting the loads examined, the user can significantly reduce the time required for analysis.>

Reference Loads are defined in the General -> Load & Definitions page of the Modeling Mode, which can be accessed by clicking the appropriate tabs on the left-hand side of the screen (circled in Figure 1):

 
Figure 1

In the Definitions section, the Reference Loads are listed as follows:

To add a new Reference Load case, select "Reference Load Definitions" in the Load & Definition dialog box and click Add. Inputting the title for the Reference Load case and the number is done in the same manner as when creating primary load cases.

Once a Reference Load case has been created, follow these steps to input load items. This process, too, is exactly the same as for primary load cases:

1. Select a Reference Load to highlight it,
2. Click Add to open the Add New Reference Load Items dialog box, 
3. Define the load items, selecting from the list of loads on the left,
4. Assign the load item to the appropriate entities (nodes/members/etc.) in the model.

At this point the Reference Load definition is complete. The next step is to include the Reference Loads in primary load cases, as follows:

1. Select a primary load case and click Add,
2. Click the load item Repeat Load -> Reference Load,
3. Select the required defined Reference Load cases and click [>] to include them in the current primary load case. Clicking [>>] will include all defined Reference Load cases. You can add appropriate combination factors for each reference load.

The format of the definition of a Reference Load (i) in the data file is as follows:

DEFINE REFERENCE LOADS

LOAD R(i) LOADTYPE (type) TITLE REF LOAD CASE 1

(Load items)

....

END DEFINE REFERENCE LOADS

The format of a reference to a Reference Load in a primary load (j) case is as follows:

LOAD (j) LOADTYPE (type) TITLE LOAD CASE 1

REFERENCE LOAD

R(i) 1.0

Reference Loads are very helpful when creating a seismic load definition. Consider, for example, a situation in which the dead loads have been defined as Reference Loads. Instead of manually inputting the dead loads a second time in the seismic definition, you can simply refer to the Reference Load case, which is listed in the seismic definition dialog box as seen below.

See Also

Client Server Archive 

Comments or Corrections?

Bentley's Technical Support Group requests that you please confine any comments you have on this Wiki entry to this "Comments or Corrections?" section. THANK YOU!

Overview

I understand that one should use the REPEAT LOAD command and not the LOAD COMBINATION command when analysing a model for cases where the MEMBER TENSION or MEMBER COMPRESSION command has been used. Talking about load combinations, in Section 5.35 of the STAAD Technical Reference Manual, notes Item (2) mentions that the LOAD COMBINATION command is inappropriate for a PDELTA analysis, and that one should use REPEAT LOADs instead. This appears to be true for NON-LINEAR analysis also. Why?

Primary Load Cases

A primary load case is one where the load data is directly specified by the user in the form of member loads, joint loads, temperature loads, element pressure loads, etc. It is characterized by the fact that the data generally follow a title which has the syntax

LOAD n

where "n" is the load case number. For example,

LOAD 3

MEMBER LOAD

2 UNI GY -3.4

JOINT LOAD

10 FX 12.5



LOAD 4

ELEMENT LOAD

23 PR GY -1.2



LOAD 5

TEMPERATURE LOAD

15 17 TEMP 40.0 -25.0

Combination Load Case

Here, the user does not directly specify the load data, but instead asks the program to add up the results of the component cases - which are defined prior to the combination case - after factoring them by the user specified factors. It is characterized by the title which has the syntax

LOAD COMBINATION n

where "n" is the case number of the combination load case.

LOAD COMBINATION 40

3 1.2 4 1.6 5 1.3

REPEAT LOAD Type

A Repeat Load type is a Primary load case. That is because, when the program runs into this command, it physically creates the load data for this case by assembling together the load information from all the component load cases (after factoring them by the respective load factors) which the user wants to "REPEAT". Thus, when you specify

LOAD 10

REPEAT LOAD

4 1.4 5 1.7

STAAD creates a physical load case called 10 whose contents will include all of the data of load case 4 factored by 1.4, and all of the data of load case 5 factored by 1.7.
If we use the same data used in the definition of the primary load case above, STAAD internally converts the REPEAT LOAD case 10 to the following :

LOAD 10

ELEMENT LOAD

23 PR GY -1.68

TEMPERATURE LOAD

15 17 TEMP 68.0 -42.5

What is the difference between a REPEAT LOAD case and LOAD COMBINATION?

The difference lies in the way STAAD goes about calculating the results - joint displacements, member forces and support reactions. For a load combination case, STAAD simply ALGEBRAICALLY COMBINES THE RESULTS of the component cases after factoring them. In the example shown above, it

gathers the results of load case 3, factors them by 1.2,

gathers the results of load case 4, factors them by 1.6,

gathers the results of load case 5, factors them by 1.3,

and adds them all together. In other words, in order to obtain the results of load 10, it has no need to know what exactly is it that constitues load cases 3, 4 and 5. It just needs to know what the results of those cases are. Thus, the structure is NOT actually analysed for a combination load case. With a REPEAT LOAD case however, the procedure followed is that which occurs for any other primary load case. A load vector {P} is first created, and later, that load vector gets pre-multiplied by the inverted stiffness matrix.

[Kinv] {P}

to obtain the joint displacements. Those displacements are then used to calculate the member forces and support reactions. Thus, the structure IS analysed for that load case {P}.

Why should the difference in the way STAAD treats a REPEAT LOAD case vs. a COMBINATION LOAD case matter? 

Normally, if you are doing a linear static analysis - which is what a PERFORM ANALYSIS command does - it should make no difference whether you specify REPEAT or COMBINATION. However, if you are doing a PDELTA analysis, or a NONLINEAR analysis, or cases involving MEMBER TENSION and MEMBER COMPRESSION, etc., it matters. That is because, in those situations, the results of those individual cases acting simultaneously IS NOT the same as the summation of the results of those individual cases acting alone. In other words,

(Results of Load A) + (Results of Load B) is not equal to (Results of Load (A+B))

Take the case of a PDelta analysis. The P-Delta effect comes about from the interaction of the vertical load and the horizontal load. If they do not act simultaneously, there is no P-Delta effect. And the only way to make them act simultaneously is to get the program to compute the displacement with both loads being present in a single load case. A REPEAT LOAD case achieves that. A COMBINATION load case does not.

See Also

Product TechNotes and FAQs

Structural Product TechNotes And FAQs

External Links

Bentley Technical Support KnowledgeBase

Bentley LEARN Server

Comments or Corrections?

Bentley's Technical Support Group requests that you please confine any comments you have on this Wiki entry to this "Comments or Corrections?" section. THANK YOU!

Overview

The purpose of this document is to help engineers analyze and design walls for dams using Bentley's STAAD.Pro V8i.

STAAD.Pro is the professional's choice for steel, concrete, timber, aluminum and cold-formed steel design of low and high-rise buildings, culverts, petrochemical plants, tunnels, bridges, piles and much more. It is a general purpose structural analysis and design tool. This general purpose nature of STAAD.Pro V8i allows engineers to model and analyze variety of structures but at the same time often leads to the question, How? The intent of this document is to answer how to model a wall of a dam in the STAAD interface.

Walls of dams are usually very thick speaking relatively to the other dimensions. These walls are modeled using solid elements in STAAD.Pro V8i.

Hoover Dam (Ref. U. S. Department of the Interior, The Bureau of Reclamation) 

Creating the Wall Geometry/Structural Analysis

The advanced drawing generation tools included in STAAD.Pro can make the model generation task very easy. The wall geometry in STAAD.Pro can be constructed in many ways:

1. STAAD.Pro user interface
2. Structure Wizard
3. Using a DXF import (importing a dxf MicroStation or AutoCAD drawing. Only line or plates can
   be imported using this technique)
4. OpenSTAAD customization etc.

Figure 1 illustrates a wall geometry that was created using the STAAD.Pro interface. This type of wall geometry can be easily created using the solid element tool and the circular repeat command.

Figure 1: Wall FEM model created using STAAD.PRO V8i 

Hydrostatic Loading

STAAD.Pro V8i's automatic hydrostatic load generator will help generate pressure loads on the wall surface as illustrated in Figure 2. The user has the option of applying the pressure loads with respect to the local coordinate axis of the plates or the global coordinate axis of the model.

The following two load cases will be created in this example:

Loading Type		Components
Dead Load		Self weight of the structure
Live Load		Hydrostatic load applied on the structure + Self weight of the structure

Figure 2: Water pressure acting on wall 

Analysis Results

STAAD.Pro V8i will calculate the element stresses at the center and at the joints of the solid element which can help engineers design the walls appropriately. The items that are printed are:

• Normal Stresses : SXX, SYY and SZZ
• Shear Stresses : SXY, SYZ and SZX
• Principal stresses : S1, S2 and S3.
• Von Mises stresses 

Figure 3: Deflected shape of structure along with SXX normal stress distribution diagram. 

The integration of the graphical contour plots with the element stress tables help engineers easily find the stress values in any stress concentration area. 

Figure 4: Wall opening SXX normal stresses 

The wall of the dam may be resting on soil. STAAD.Pro V8i's automatic foundation support generator generates spring supports for plate elements based on the sub-grade modules provided by the engineer. These springs could be compression-only springs and as a result of this a true stability analysis can be performed on the structure. The base pressure diagrams presented in Figure 5 are generated due to the soil spring supports underneath the wall. The maximum base pressure can be compared to the soil bearing capacity. 

Figure 5: Wall base pressure distribution diagram. 

See Also

Product TechNotes and FAQs

STAAD.Pro

External Links

Bentley Technical Support KnowledgeBase

Bentley LEARN Server

Comments or Corrections?

Bentley's Technical Support Group requests that you please confine any comments you have on this Wiki entry to this "Comments or Corrections?" section. THANK YOU!

The technotes and FAQs in this section cover various topics that pertain to STAAD.Pro.

Frequently Asked Questions ( FAQs )

• [[STAAD.Pro [FAQ] ]]
• [[OpenSTAAD [FAQ] ]]

TechNotes

• STAAD.Pro Technotes [TN]

Known Issues

• [[STAAD.Pro Known Issues]]

Other Related Pages

• [[Pushover Analysis of Steel Structure using STAAD]]
• [[Reference Loads An Introduction [CS] ]]
• [[STAAD.Pro IS800 2007 Verification Examples]]

Pushover Analysis

of

Steel Structure using STAAD 

 By

Bentley Systems

Mr. Kalavagunta Sreedhar)

                                                            Definition

Pushover Analysis option will allow engineers to perform pushover analysis as per FEMA 356 : 2000 and ATC 40. Pushover analysis is a static, nonlinear procedure using simplified nonlinear technique to estimate seismic structural deformations. It is an incremental static analysis used to determine the force-displacement relationship, or the capacity curve, for a structure or structural element.

The analysis involves applying horizontal loads, in a prescribed pattern, to the structure incrementally, i.e. pushing the structure and plotting the total applied shear force and associated lateral displacement at each increment, until the structure or collapse condition.

Purpose of Pushover Analysis

It is expected that most buildings rehabilitated in accordance with a standard, would perform within the desired levels when subjected to the design earthquakes. Structures designed according to the existing seismic codes provide minimum safety to preserve life and in a major earthquake, they assure at least gravity-load-bearing elements of non-essential facilities will still function and provide some margin of safety. However, compliance with the standard does not guarantee such performance. They typically do not address performance of non-structural components neither provide differences in performance between different structural systems. This is because it cannot accurately estimate the inelastic strength and deformation of each member due to linear elastic analysis. Although an elastic analysis gives a good indication of elastic capacity of structures and indicates where first yielding will occur, it cannot predict failure mechanisms and account for redistribution of forces during progressive yielding.

To overcome this disadvantages different nonlinear static analysis method is used to estimate the inelastic seismic performance of structures, and as the result, the structural safety can be secured against an earthquake. Inelastic analysis procedures help demonstrate how buildings really work by identifying modes of failure and the potential for progressive collapse. The use of inelastic procedures for design and evaluation helps engineers to understand how structures will behave when subjected to major earthquakes, where it is assumed that the elastic capacity of the structure will be exceeded. This resolves some of the uncertainties associated with code and elastic procedures. The overall capacity of a structure depends on the strength and deformation capacities of the individual components of the structure. In order to determine capacities beyond the elastic limit  some form of nonlinear analysis, like Pushover Analysis, is required.

Theory on which it is based

There are two nonlinear procedures using pushover methods:  

a)       Capacity Spectrum Method,

b)       Displacement Coefficient Method. 

In STAAD Displacement Coefficient method has been followed.

Displacement CoefficientMethod is to find target displacement which is the maximum displacement that the structure is likely to be experienced during the design earthquake. It provides a numerical process for estimating the displacement demand on the structure, by using a bilinear representation of capacity curve and a series of modification factors, or coefficients, to calculate a target displacement. Refer Section 3.3.3.3.2 of FEMA 356: 2000 for detailed description of calculation of target displacement

Types of non-linearity 

Both geometric and material non-linearities are considered in this static nonlinear pushover analysis.

Geometric non-linearity 

This is a type of non-linearity where the structure is still elastic, but the effects of large deflections cause the geometry of the structure to change, so that linear elastic theory breaks down. Typical problems that lie in this category are the elastic instability of structures, such as in the Euler bulking of struts and the large deflection analysis of a beam-column member. In general, it can be said that for geometrical non-linearity, an axially applied compressive force in   a member decreases its bending stiffness, but an axially applied tensile force increases its bending stiffness. In addition, P-Delta effect is also included in this concept.

Material non-linearity 

In this type of non-linearity, material undergoes plastic deformation. Material non-linearity can be modeled as discrete hinges at a number of locations along the length of a frame (beam or column) element and a discrete hinge for a brace element as discrete material fibers distributed over the cross-section of the element, or as a series of material points throughout the element.

Frame element hinge properties

Discrete hinge properties for frame elements are based on FEMA-356 criteria as per Section 5.5.2.2.2.  

Figure1.6 Generalized Force-Deformation Relationship for Components

• Point A is the origin
• Point B represents yielding. No deformation occurs in the hinge up to point B, regardless of the deformation value specified for point B. The displacement (rotation or axial elongation as the case may be) will be subtracted from the displacements at points C, D and E. Only plastic deformation beyond point B will be exhibited by hinge.
• Point C represents ultimate capacity of plastic hinge. At this point hinge strength degradation begins (hinge starts shedding load) until it reaches point D.
• Point D represents the residual strength of the plastic hinge. Beyond point D the component responds with substantially strength to point E.
• Point E represnts total failure. At deformation greater than point E the plastic hinge will drop load to zero.

This diagram represent for those component actions which are ductile (e.g. Hinge formation for bending moment about local z axis of beam). For force-controlled action, Type 3 curve is followed. Refer Table C2-1 of FEMA 356 : 2000 for examples of possible deformation-controlled and force-controlled actions.

Lateral Load Distribution as per Section 3.3.3.2.3 Chapter 3 FEMA 356

 Lateral load can be applied by following three methods.

 Method 1 

The vertical distribution of the base shear shall be as specified in this section for all buildings. The lateral load applied at any floor level x shall be determined in accordance with equation (1-8-1) and equation (1-8-2):

                                 F_x= C_vxV                          …………………………. (1-8-1)

where    

                                                    w_xh^k_x

                                C_vx= --------------------   …………………………. (1-8-2)

    n

  S w_ih^k_i

  i = 1

Method 2

 A vertical distribution proportional to the shape of the fundamental mode in the direction under consideration is performed. Use of this distribution shall be permitted only when more than 75% of the  total mass participates in the fundamental mode in the direction under consideration, and the uniform distribution is also used. 

                                                w_x F_x

                                F_x= --------------- V

   _n

 S   w_i F_i

  ^{i = 1}

Method 3 

A vertical distribution is performed consisting of lateral forces at each level proportional to the total mass at each level . 

                                              w_x

                                F_x= --------- V

                                         _n

                                        S   w_i

                                                              ^{i = 1}

where,

C_vx          =  Vertical distribution factor

k              =  2.0 for T 2.5 seconds≥

=  1.0 for T 0.5 seconds≤

     Linear interpolation shall be used to calculate values of for intermediate values of k for                 

     intermediate values of T.

V            =  User defined base shear

w_i           =  Portion of the total building weight W located on or assigned to floor level i

w_x           =  Portion of the total building weight W located on or assigned to floor level x

h_i            =  Height (in ft) from the base to floor level i

h_x           =  Height (in ft) from the base to floor level x

F_x                =  Amplitude of mode a floor level  x

Masses

The method involves 2 matrices – the stiffness matrix and the mass matrix.

The stiffness matrix, usually called the [K] matrix, is assembled using data such as member and element lengths, member and element properties, modules of elasticity, poison’s ratio, member and element release, member offsets, support information, etc.

For assembling the mass matrix, called the [M] matrix, the input is weights, not masses. Internally, STAAD will convert weights to masses by dividing the input by “g” the acceleration due to gravity.

Example.

Illustrate the procedure and results find the bellow STAAD example

STAAD PLANE

START JOB INFORMATION

ENGINEER DATE 07-Oct-05

END JOB INFORMATION

INPUT WIDTH 79

UNIT INCHES KIP

JOINT COORDINATES

1 0 0 0; 2 0 118.11 0; 3 118.11 118.11 0; 4 118.11 0 0; 5 0 236.22 0;

6 118.11 236.22 0; 7 0 354.331 0; 8 118.11 354.331 0; 9 0 472.441 0;

10 118.11 472.441 0; 11 236.22 118.11 0; 12 236.22 0 0; 13 236.22 236.22 0;

14 236.22 354.331 0; 15 236.22 472.441 0;

MEMBER INCIDENCES

1 1 2; 2 2 3; 3 3 4; 4 2 5; 5 5 6; 6 6 3; 7 5 7; 8 7 8; 9 8 6; 10 7 9; 11 9 10;

12 10 8; 13 3 11; 14 6 13; 15 8 14; 16 10 15; 17 11 12; 18 13 11; 19 14 13;

20 15 14;

DEFINE MATERIAL START

ISOTROPIC STEEL

E 29732.7

POISSON 0.3

DENSITY 0.000283

ALPHA 1.2e-005

DAMP 0.03

END DEFINE MATERIAL

MEMBER PROPERTY AMERICAN

2 5 13 14 TABLE ST W16X26

8 11 15 16 TABLE ST W16X26

1 3 4 6 17 18 TABLE ST W24X55

7 9 10 12 19 20 TABLE ST W24X55

CONSTANTS

MATERIAL STEEL ALL

SUPPORTS

1 4 12 FIXED

DEFINE PUSHOVER DATA

FRAME 2

FYE 36.000000 ALL

GNONL 1

DISP X 15 JOINT 10

LDSTEP 250

SPECTRUM PARAMETERS

DAMPING 5.0000

SC 1

SS 1

S1 1

SAVE LOADSTEP RESULT DISP 0.010000

END PUSHOVER DATA

LOAD 1 LOADTYPE Gravity  

SELFWEIGHT Y -1

MEMBER LOAD

2 5 8 11 13 TO 16 UNI GY -.4

PERFORM PUSHOVER ANALYSIS

FINISH

Figure 1: Capacity Curve for a Structure in STAAD.Pro V8i

Figure 2: Deflected shape at specified displacement for a Structure in STAAD.Pro V8i

Figure 4: Beam Hinge results for a Structure in STAAD.Pro V8i

STAAD Results

            P R O B L E M   S T A T I S T I C S

     NUMBER OF JOINTS/MEMBER+ELEMENTS/SUPPORTS =    15/    20/     3

           SOLVER USED IS THE IN-CORE ADVANCED SOLVER

     TOTAL PRIMARY LOAD CASES =    1, TOTAL DEGREES OF FREEDOM =     36

 NUMBER OF MODES REQUESTED              =     1

 NUMBER OF EXISTING MASSES IN THE MODEL =    24

 NUMBER OF MODES THAT WILL BE USED      =     1

    STAAD PLANE                                              -- PAGE NO.    3

               CALCULATED FREQUENCIES FOR LOAD CASE       2

       MODE            FREQUENCY(CYCLES/SEC)         PERIOD(SEC)

         1                       1.292                  0.77396

                     MASS  PARTICIPATION FACTORS IN PERCENT

           MODE    X     Y     Z     SUMM-X   SUMM-Y   SUMM-Z

             1   79.94  0.00  0.00   79.944    0.000    0.000

This page contains a list of TechNotes related to STAAD.Pro

Member Tension And Combination Load Cases [TN]

Pushover Analysis of Steel Structure using STAAD (TN)

Reference Loads An Introduction [CS]

STAAD.Pro Wall Analysis For Dams [TN]

Please somebody help me with this.

I' ve been trying to write a code to gather plates information I pick.

As you can see below my code, I can get the selected plates information such as plate number and thickness and node numbers.

There are two more things I really really really want to do.

First, I want to display this information on a Dialogue window.

Second, I want to select more plates and keep adding the information to the Dialogue window.

Please somebody be my hero,

'====================================

Sub Main()
 Dim objOpenSTAAD As Object
 Dim SelPlatesNo As Long, PlateNo As Long, SelPlates() As Long
 Dim NodeA As Long, NodeB As Long, NodeC As Long, NodeD As Long
 Dim CoordX As Double, CoordY  As Double, CoordZ  As Double
  Set objOpenSTAAD = GetObject(, "StaadPro.OpenSTAAD")

SelPlatesNo = objOpenSTAAD.Geometry.GetNoOfSelectedPlates
  If (SelPlatesNo > 0) Then
ReDim SelPlates(SelPlatesNo) As Long
End If
If (SelPlatesNo = 0) Then
MsgBox "Select Plate !!" , , " Warning "
Exit Sub
End If

objOpenSTAAD.Geometry.GetSelectedPlates SelPlates
 Dim PlateData As String, PThickness(3) As Double

   For i = 0 To SelPlatesNo-1
       objOpenSTAAD.Property.GetPlateThickness(SelPlates(i) , PThickness)
       pthk = CCur(PThickness(0))*1000
     'Get a Plate Number
    PlateNo= Join(Array(SelPlates(i)))
      'Print  Plate Number, Thickness and Node Nubers, ex) 123, 6 (395 17 864 863)
    GetPlateNodeNo PlateNo, NodeA, NodeB, NodeC, NodeD
    If NodeD = 0 Then :PlateData =  PlateNo & ", " & pthk & " (" & NodeA & " " & NodeB & " " & NodeC & ")"
    If NodeD <> 0 Then:PlateData =  PlateNo & ", " & pthk & " (" & NodeA & " " & NodeB & " " & NodeC & " " & NodeD & ")"
       'Debug.Print  PlateData & vbCr
       PlateData1 = PlateData1 + PlateData & vbCr
    Next i
    MsgBox PlateData1
End Sub

Sub GetPlateNodeNo(PlateNo As Long, ByRef NodeA As Long, ByRef  NodeB As Long, ByRef  NodeC As Long, ByRef  NodeD As Long )
  Dim objOpenSTAAD As Object
  Set objOpenSTAAD = GetObject( , "StaadPro.OpenSTAAD")
  objOpenSTAAD.Geometry.GetPlateIncidence PlateNo, NodeA, NodeB, NodeC, NodeD
End Sub

Is it possible to specify a displacement and then have STAAD analyze a frame to give me a corresponding load (the load that would have been required to produce that displacement)?

You first need to know the pattern or arrangement of the loading which will eventually cause the displacement you wish to see. This is because, there can be millions of loading arrangements which cause that amount of displacement at that node, so one needs to have an idea of which of those patterns is the one that one wants. By pattern, we are talking of details like, is the load going to consist of concentrated forces at nodes, or distributed and trapezoidal loads on members, or pressures on plates, etc. For example, any of these loads will cause a certain amount of displacement at a node along a certain direction.

So, a unit load analysis would be the best approach for solving this kind of a problem. That means, all the components of the loading pattern would be represented by unit loads. Let us say that by applying a member load of 100 pounds/ft, you get 0.4 inches of displacement along global X at node 43. So, if the final desired displacement at node 43 along X is say, 1.2 inches, the applied load should be simply (1.2/0.4)*100 = 300 pounds/ft.

I am applying a UBC seismic load on a bridge. The analysis engine reports an error message which says that:

EITHER NA OR NV FACTOR HAS NOT BEEN SPECIFIED

WHILE SEISMIC ZONE HAS BEEN SPECIFIED AS 4.

This is due to the fact that, for your model, STAAD looks at the data under the DEFINE UBC LOAD command and concludes that you intend to analyse the structure per the UBC 1997 code. It then checks whether all the required parameters have been specified for that code, and detects that NA and NV are missing. You perhaps have an input similar to the one below :

DEFINE UBC LOAD
ZONE 0.4 I 1 RWX 12 RWZ 12 STYP 1.2 PX 0.2626 PZ 0.2626

For Zone 4, Na and Nv are two of the fundamental parameters necessary to calculate the base shear. If you look at Tables 16-Q and 16-R on pages 2-34 & 2-35 of the UBC 1997 code, you will find that for Zone 4, the coefficients Ca and Cv are dependent on Na and Nv.

So, specify the NA and NV parameters, so that the commands look similar to the one below :

DEFINE UBC LOAD
ZONE 0.4 I 1 RWX 12 RWZ 12 STYP 1.2 NA 1.6 NV 1.6 PX 0.2626 PZ 0.2626

I would like to create a REPEAT LOAD case whose constituent load cases are themselves REPEAT LOAD cases. Is this allowed?

You can do this if you have STAAD.Pro version 2002 or later. An example of this is shown below.

LOADING 1
SELFWEIGHT Y -1.0

LOAD 2
REPEAT LOAD
1 1.0
JOINT LOAD
4 5 FY -15. ; 11 FY -35.

LOAD 3
REPEAT LOAD
2 1.0
MEMB LOAD
8 TO 13 UNI Y -0.9 ; 6 UNI GY -1.2

LOAD 4
SELFWEIGHT Y -1.0
JOINT LOAD
4 5 FY -15. ; 11 FY -35.
MEMB LOAD
8 TO 13 UNI Y -0.9 ; 6 UNI GY -1.2

PERF ANALY
LOAD LIST 3 4
PRINT *** RES
FINISH

In the above example, load case 3 repeats load case 2, which in turn repeats load case 1.

After determining the lateral loads using Staad UBC seismic analysis in a first file, I note down the lateral loads computed at each joint. In a second separate file with the same frame model, I apply the lateral loads from the first file combining them with the gravity loads and perform the analysis. I consider this procedure of mine very tedious in case of a 3D high rise building most specifically in view of the first file. Is there any shorter procedure for this? Please take note that I am using the Command File Editor.

There is absolutely no need for you to take the lateral load data from the output of the first file, and insert it as input into the second file. In STAAD, once the lateral loads due to UBC or IBC are generated, they are automatically available for combining with gravity loads, or any other loads for that matter. Consequently, there are 2 ways in which this combination can be achieved, and each is demonstrated below :

Method 1 :
Generate the lateral load in one load case. Specify the gravity load in another load case. Then, combine the two in a load combination case.

LOAD 1 - GENERATE LATERAL LOADS DUE TO UBC ALONG X
UBC X 1.0

LOAD 2 - SPECIFY GRAVITY LOADS
SELFWEIGHT Y -1.0
MEMBER LOAD
1 TO 25 UNI GY -1.2
JOINT LOAD
10 39 FY -10.0

LOAD COMBINATION 3 - COMBINE THE LATERAL AND GRAVITY LOADS IN ONE CASE
1 1.0 2 1.0

Method 2 :
Create a single load case in which the lateral forces are generated, and gravity loads are specified.

LOAD 1 - LATERAL LOADS + GRAVITY LOADS
UBC X 1.0
SELFWEIGHT Y -1.0
MEMBER LOAD
1 TO 25 UNI GY -1.2
JOINT LOAD
10 39 FY -10.0

I am trying to analyse a structure which consists of a large dia pipe supported at discrete points. I am unable to get STAAD to analyse this for UBC loads.

When the UBC committee came up with the recommendations for analysing structures subjected to earthquakes, the type of structures they had in mind were conventional style buildings where the base of the model, namely, the points where the supports are located is at the lowest elevation with respect to the rest of the model.

If you look at the UBC procedure, it involves computation of the base shear, which then has to be distributed over the height of the building, so that one can then calculate the inter-story shears. A certain amount of the weight gets lumped at the highest point of the building, and the rest gets distributed along the height. In other words, the principle is that a mass at any height of the building is subjected to an acceleration and the force caused by the acceleration is represented by a concentrated force where the mass is located. The summation of all such forces at a given floor cause the columns beneath that floor to be subjected to a shear force.

When you talk of a model like a pipe which is defined as line members attached to several collinear nodes, all of which are at the same elevation, the UBC rules become impossible to apply. The fact is, to analyse your structure for seismic effects, you do not even need the elaborate procedure of the UBC code. You can take the selfweight, and any imposed loads on the pipe, and apply them along a horizontal direction like X or Z with a factor, and you will get what is normally expected in a seismic analysis.

So, you just have to have

LOAD 2
SELF X n

where n is a number like 1.5, which represents that there is a net force of 1.5 times the weight of the structure acting along the X direction due to an earthquake. For better handling of the distributed loads, you might want to consider defining several nodes along the length of the pipe, between supports.

I am modelling a steel building consisting of columns and beams. The floor slab is a non-structural entity which, though capable of carrying the loads acting on itself, is not meant to be an integral part of the framing system. It merely transmits the load to the beam-column grid.  There are uniform area loads on the floor (think of the load as wooden pallets supporting boxes of paper). Since the slab is not part of the structural model, is there a way to tell the program to transmit the load to the beams without manually figuring out the beam loads on my own?

STAAD's FLOOR LOAD option is ideally suited for such cases. This is a facility where you specify the load as a pressure, and the program converts the pressure to individual beam loads. Thus, the input required from the user is very simple - load intensity in the form of pressure, and the region of the structure in terms of X, Y and Z coordinates in space, of the area over which the pressure acts.

In the process of converting the pressure to beam loads, STAAD will consider the empty space between criss-crossing beams (in plan view) to be panels, similar to the squares of a chess board. The load on each panel is then tranferred to beams surrounding the panel, using a triangular or trapezoidal load distribution method.

Additional information on this facility is available in example problem 15 in the examples manual, and section 5.32.4 in the STAAD.Pro Technical Reference manual.

When does one use FLOOR LOAD and when does one use ELEMENT LOAD?

When modelling a grid system made up of horziontal beams and the slabs which span between the beams, we have found that there are 2 approaches that users take :

1) They model the beams only, and do not include the slabs in the model. However, they take into account the large inplane stiffness of the slab by using the master-slave relationship to tie together the nodes of the deck so that a rigid diaphragm effect is simulated for the horizontal plane at the slab level.

2) They model the slabs along with the beams. The slabs are modelled using plate elements.

The question that arises is, how does one account for the distributed loading (load per area of floor) which is present on top of the slab?

If you model the structure using method (1), the load can be assumed to be transferred directly on to the beams. The slab-beam grillage is assumed to be made up of a number of panels, similar to the squares of a chess board. The load on each panel is then tranferred to beams surrounding the panel, using a triangular or trapezoidal load distribution method. You can do this in STAAD by defining the load intensity in the FLOOR LOAD command. In other words, the pressure load on the slabs (which are not included in the model) are converted to individual beam loads by utilizing the FLOOR LOAD facility.

In method (2), the fact that the slab is part of the model makes it very easy to handle the load. The load can be applied on individual elements using the ELEMENT LOAD facility. The connectivity between the beams and elements ensures that the load will flow from the plates to the beams through the columns to the supports.

 What is the difference between the LOAD COMB & REPEAT LOAD commands?

The difference lies in the way STAAD goes about calculating the results - joint displacements, member forces and support reactions. For a load combination case, STAAD simply ALGEBRAICALLY COMBINES THE RESULTS of the component cases after factoring them. In other words, for example, in order to obtain the results of load 10, it has no need to know what exactly is it that constitutes load cases 3, 4 and 5. It just needs to know what the results of those cases are. Thus, the structure is NOT actually analysed for a combination load case. With a REPEAT LOAD case however, the procedure followed is that which occurs for any other primary load case. A load vector {P} is first created, and later, that load vector gets pre-multiplied by the inverted stiffness matrix.

I am modelling an elevated silo which will be used for storing grain. The columns which support the structure are modelled as members and the walls of the silo (containment part of the structure) are modelled using plate elements. The silo has vertical and sloping walls. The loads on the structure consist of the weight of the grain contained in the silo. What is the best method for applying the load when the silo is full of grain? As pressure loads on the inside? How should the load be applied on the sloping walls?

There are 2 segments of the tank which have to be individually considered for application of the load.

The vertical walls
------------------

The material in the tank, especially if it is a fluid, will exert a lateral pressure on the vertical walls of the tank. This pressure load can be applied on the tank using the ELEMENT PRESSURE load facility. You can use one of 2 options to do this.

a) A uniform pressure. If you take any individual element on the wall, if you know the pressure intensity at the top edge, and the pressure intensity at the bottom edge, the average of these 2 intensities can be applied as a constant pressure on the entire surface of the element, as in the following example :

45 PRESSURE -3.5

Since the load is along the local Z axis of the element, you do not have to specify the axis name in the above command since local Z is the default for the axis. The load value must be accompanied by the proper sign (positive or negative) which accounts for whether the load acts along or opposite to the direction of the local Z axis.

b) A trapezoidally varying pressure.

In case (a) above, we decided to take the average of the pressures at the top and bottom edges, and thus obtain a uniform pressure. However, this is not absolutely necessary. The load can be applied as a trapezoidal load, in which case, the TRAP option is used and the intensities at the top and bottom edges must be specified. An example of that is

45 PRESSURE TRAP Y -4.5 -2.5

In this example, it is assumed that the local Y axis of element 45 is along the vertical direction, and thus the trapezoidal variation is along the local Y. The load itself acts perpendicular to the surface of the element, and hence along local Z. If local Y is in the same sense as global Y, -4.5 indicates the intensity at the lower edge, and -2.5 indicates the intensity at the upper edge.

If the vertical wall has many divisions along the vertical direction, there will be several "horizontal rings" of elements. Every element contained in a ring has the same intensity at its top and bottom edge. That means, the top & bottom intensity for each of those rings will have to be manually calculated. There is a facility in the STAAD.Pro GUI to simplify this task. From the top of the screen, select Commands - Loading - Load Commands - Element - Hydrostatic Trapezoidal, and provide the intensities at the top and bottom edges of the vertical wall. The program will use the linear interpolation method to find the intensity at each intermediate division, and then create the individual element TRAPEZOIDAL loads.

The sloping walls
-----------------

The load on the elements which make up these walls is derived from the weight of the column of material directly above these elements, and acts along the global vertical downward direction. Since the element TRAP load facility that is available in STAAD allows a load to be applied only along the local Z axis, and since local Z is not parallel to any of the global directions, the TRAP load option cannot be used here. Hence, one will have to apply these as uniform pressure loads, the value of which has to be calculated for each sloping element as the average of the intensities at the 4 nodes of that element. There is no generation facility currently available in the program to automate this task.

I modeled a curved beam using cylindrical coordinates and tried to run a moving load over the curved beam. STAAD.Pro is not allowing me to do this. Why?

Moving load on curved beams is not supported by the DEFINE MOVING LOAD command in STAAD.Pro. The STAAD moving load generator assumes:
1)All loads are acting in the negative global vertical (Y or Z) direction. The user is advised to set up the structure model accordingly.
2)Resultant direction of movement is determined from the X, Y and Z increments of movements as provided by the user.

However, STAAD.beava, an automated bridge load generator, can handle moving loads for curved or custom-defined bridge decks with beams and plates. It also generates a 3D influence surface based on displacements, support reactions, beam forces or plate stresses for any point on the bridge. The critical loading patterns and critical vehicle position will be identified as well. STAAD.beava is an integrated module in the STAAD.Pro environment.

What is the significance of the Rw Value in the UBC code?

The UBC 1997 code defines Rw as a Numerical Coefficient representative of the inherent overstrength and global ductility capacity of lateral-force resisting systems.

It is to be used in the equation for computing base shear. Its values are dependent on the type of lateral-force resisting system in the building, such as whether the system is a Light-framed wall with shear panels or Shear wall made of concrete or a special moment resisting frame, etc.

Values of Rw are listed in Tables 16-N and 16-P of the UBC 1994 and 1997 codes.

How is the wind load calculated/generated for a structure in STAAD.Pro ? What is the exposure factor calculated and how is it calculated? In 2002, I hear you can now define your own "panels"? What does this mean?

The DEFINE WIND LOAD command may be used to define the parameters for automatic generation of wind loads on the structure. The user needs to define the intensity and corresponding heights along with the exposure factors. If the exposure factor is not defined, the program takes the default value as 1.0.

A value of 1.0 means that the wind force may be applied on the full influence area associated with the joints if they are also exposed to the wind load direction.
All loads and heights are in the current unit system. In the list of intensities, the first value of intensity (p1) acts from the ground level up to the first height. The second intensity (p2) acts in the global vertical direction between the first two heights (h1 and h2) and so on. The program assumes that the ground level has the lowest global vertical coordinate of any joint entered for the structure.

The exposure factor (e) is the fraction of the influence area associated with the joint(s) on which the load may act if it is also exposed to the wind load. Total load on a particular joint is calculated as follows.

JOINT LOAD = (Exposure Factor) x (Influence Area) x (Wind Intensity).

Exposure factor (User specified) = (Fraction of Influence Area) x (influence width for joint).

In STAAD.Pro 2002, the built-in wind load generation facility has been enhanced to allow the user to specify the actual panels of the building which are exposed to the wind. This user-level control will now allow the user to obtain a more accurate distribution of wind forces, especially when the exposed surface of the building lies in several vertical zones, each reset from the one below or the one above, in terms of the direction of wind force. Further, the basic algorithm for detecting the shape of the panels and the amount of load which should be calculated for the panel corners too has undergone significant improvements. The parameters for definition of the wind load types are described in Section 5.31.3 of the STAAD.PRO Technical Reference Manual. The relevant extracts from Section 5.32.12 of the STAAD.Pro Technical Reference Manual, where the method for applying wind loading in the form of a data in load cases has been explained, is provided below. Note that areas bounded by beam members (and ground), and exposed to the wind, are used to define loaded areas (plates and solids are ignored). The loads generated are applied only at the joints at vertices of the bounded areas. For example, in the following set of commands:

DEFINE WIND LOAD
TYPE 1
INTENSITY 0.1 0.12 HEIGHT 100 200
EXP 0.6 JOI 1 TO 25 BY 7 29 TO 37 BY 4 22 23
TYPE 2
INT 0.1 0.12 HEIGHT 100 900
EXP 0.3 YR 0 500
LOAD 1
SELF Y -1.0
LOAD 2
WIND LOAD Z 1.2 TYPE 2 ZR 10 11
LOAD 3
WIND LOAD X TYPE 1 XR 7 8

A minus sign indicates that suction occurs on the other side of the selected structure. If all of the members are selected and X (or Z) is used and the factor is positive, then the exposed surfaces facing in the -x (or -z) direction will be loaded in the positive x (or z) direction (normal wind in positive direction). If X and a negative factor is used, then the exposed surfaces facing in the +x direction will be loaded in the negative x direction (normal wind in negative direction). [If -X is entered and a negative factor, then the exposed surfaces facing in the -x direction will be loaded in the negative x direction (suction). If -X is entered and a positive factor, then the exposed surfaces facing in the +x direction will be loaded in the positive x direction (suction).] A member list or a range of coordinate values (in global system) may be used. All members which have both end coordinates within the range are assumed to be candidates for defining a surface which may be loaded if the surface is exposed to the wind. The loading will be in the form of joint loads (not member loads). 1, 2 or 3 ranges can be entered to form a "layer", "tube" or "box" for selecting members in the combined ranges. Use ranges to speed up the calculations on larger models.

It is advisable not to use the SET Z UP command in a model with wind load. A closed surface is generated by the program based on the members in the ranges above and their end joints. The area within this closed surface is determined and the share of this area (influence area) for each node in the list is then calculated. The individual bounded areas must be planar surfaces, to a close tolerance, or they will not be loaded. Hence, one should make sure that the members/joints that are exposed to the wind make up a closed surface (ground may form an edge of the closed surface). Without a proper closed surface, the area calculated for the region may be indeterminate and the joint force values may be erroneous. Consequently, the number of exposed joints should be at least 3.

I am using the moving load generation. The truck that I am specifying is so wide (dimension perpendicular to direction of traffic) that within the width of one lane of traffic, there are 3 or more parallel beams along the direction of traffic. How does STAAD determine how the truck load should be converted to beam loads?

Based on the data you provide under the DEFINE MOVING LOAD command, each truck is treated as a set of axles. If the WIDTH option is NOT specified, each axle is assumed to be comprised of 1 tire. If the WIDTH option is specified, each axle is assumed to be comprised of 2 tires.

The program looks at each tire independently. For any given tire, it looks for one longitudinal beam to the left of the tire, and another longitudinal beam to the right of the tire. Then it distributes the tire weight on those 2 beams as though the tire is located on a simply supported cross beam that spans the two longitudinal members on either side.

Thus, even if a lane spans across 3 longitudinal beams or for that matter several beams, the above approach ensures that the tire weights get properly applied on the correct set of beams as concentrated member loads.

You can get a listing of these concentrated member loads by using the command:
PERFORM ANALYSIS PRINT LOAD DATA

For moving load generation, does STAAD provide the location of all the moving point loads in terms of member number and distance from the start of the member?

Yes. Please use the PRINT LOAD DATA option with your PERFORM ANALYSIS command and you will get the information in your output file.

How does STAAD consider the moving load over the beams if the load is not applied over a beam exactly?

If a wheel falls inside a panel composed of beams on either side of the wheel running parallel to the direction of movement of the vehicle, the load is distributed on the 2 beams as simply supported reactions. Hence, if the wheel load is 10 kips, and if the distance from the wheel to the beam on the left is 7 ft, and the distance to the beam on the right is 3 ft, the beam on the left gets a 3 kip load, and the beam on the right gets a 7 kip load.

If we have a wind load on a bracing system (perpendicular to the bracing plane), can we apply the wind loading directly to the brace as a uniform load instead of resolving the force into point loads? How does Staad handle this type of loading on members that are declared trusses?

If a transverse load such as a uniform distributed load or a concentrated force is applied on a truss member, STAAD converts it to the equivalent concentrated shears at the 2 ends of the member. The member end force output will show them as shears on the member under the output terms SHEAR-Y or SHEAR-Z depending on the local axis direction the load is applied in.

However, if you determine the equivalent end shears and apply them as joint loads instead, and not as a member load, the truss members at that node will not experience any shear force due to that load.

I am using the moving load generation facility to generate a set of load cases for a truck moving on a bridge. Can STAAD provide the support reactions for the critical position that produces the maximum effects on the system flooring?

This would require that the support reactions for all generated load cases be produced in a report form sorted in a descending order based upon the specific support reaction criteria we are interested in, such as the FY force, or the MZ moment.

To get this report, first run the analysis. Go to the Post processing mode. Select the support node(s) at which you want the information you are seeking. From the top of the screen, select Report | Support Reactions. In the dialog box that comes up, select the degree of freedom (FY, MZ, etc.) which should be used as the criteria for sorting. Set the sorting order (high to low or low to high). From the loading tab, select the load cases that you want considered. Click on OK. A report of the results will be displayed in tabular form.

I have some distributed loads on some members of the model. I would like to consider the weights due to these loads in the base shear calculation for UBC load generation. Can you explain the process for doing this?

When analysing a structure for UBC loads, there 2 stages in the input. The first stage is the one where one defines data such as the various parameters (zone factor, importance factor, soil structure interaction factor, etc.) as well as the weights. In terms of the STAAD command language, it is initiated using the DEFINE UBC LOAD command, and an example for this may be found in Example 14 of the STAAD.Pro Examples manual.

Graphically, one may assign the data in the following manner.

Select the beam or beams you want to assign the distributed weights to. Next, from the top of the screen, select Commands | Loading | Define Load | Seismic Load. In the Parameters tab, select the type, and enter the relevant
values for the parameters. Press the "Save" button. A new tab called "Weights" should come up. Press the "Member Weight" button. For the loading type, choose UNI, enter the distributed weight value, distances to where the load starts and the load ends, and press "OK". Press the "Assign" button to actually assign them to the selected members. Finally, press the "Close" button.

What is JOINT WEIGHT? I'm trying to learn how to use the seismic load generator and I don't see anything explaining what JOINT WEIGHT is or what it is used for.

In the block of commands which fall under the DEFINE UBC LOAD heading or any of the other ones like AIJ, 1893, etc., the weight data which goes into the calculation of the total weight consists of

SELFWEIGHT

MEMBER WEIGHT

JOINT WEIGHT

If at any of the joints of the structure, there are any weights which you want included in the total weight calculation, you specify them using the JOINT WEIGHT option.

How do I get STAAD to automatically combine static load cases with load cases generated using the MOVING LOAD generation facility?

You should use the option called ADD LOAD along with the LOAD GENERATION command.

Shown below is an example:

DEFINE MOVING LOAD
TYPE 1 LOAD 20. 20. 10. DISTANCE 10. 5. WIDTH 10.
LOAD 1 STATIC LOAD
SELF Y -1.0

* GENERATE MOVING LOADS AND ADD THE SELFWEIGHT
* LOAD TO EACH GENERATED LOAD CASE

LOAD GENERATION 10 ADD LOAD 1
TYPE 1 7.5 0. 0. ZI 10.
PERFORM ANALYSIS PRINT LOAD DATA

How to calculate the temperature parameter f1 and f2  for applying temperature load on the
structure?

You have to know three temperatures :
 
1) the stress-free temperature, which is the temperature that the structure was at when it was constructed or installed.  Call it A.
 
2) The temperature of the top fiber (the fiber that is farthest along the positive direction of the local Z axis of elements and local Y axis for beam). Call it B.
 
3) The temperature of the bottom fiber (the fiber that is farthest along the negative direction of the local Z axis of element and local Y axis for beam). Call it C.
 
When you specify the temperature load, the command is
member-list TEMPERATURE f1 f2
where
 
f1 = (B+C)/2 - A
 
f2 = B-C
 
f1 is the temperature that causes axial elongation / shrinkage along the longitudinal axis (local X of the member, and, local X and Y axes for the plate element).
 
 f2 is the temperature responsible for inducing bending in the member and element.
 
Also, refer to article 5.32.6 of the Technical Reference Manual of Staad.pro

I have multiple structures modeled in STAAD with varying heights and I want to use the Automatic Seismic Load Generation in STAAD. Can STAAD still properly distribute the seismic forces even though my structures are disjointed ?

STAAD.Pro Seismic Load Generation should not be used in this case. If the structures are independent of each other, you should have 3 separate models and do seismic load generation on each model separately.

I defined dead and live loads as reference load cases and I used these cases for specifying seismic weights as part of my seismic load definition. Do I have to re-define the dead loads and live loads as part of the seismic load case ?

Related question : I defined dead loads, live loads for seismic weight calculation as part of my seismic load definition. Do I again need to specify the dead and live loads as part of the seismic load cases ?

No you do not need to. Once the seismic weight is defined ( either through reference load or through the various seismic weight definition options ) as part of the seismic load definition, the software is able to figure out the total seismic weight. You do not need to redefine. Doing so would apply these as additional loads to the ones already defined. 

Can STAAD automatically calculate the seismic forces both in horizontal and vertical direction required by ASCE as shown next 

E = (Rho) x Q_E (+/-) 0.2 x S_DS x D

The seismic load generation in STAAD only calculates the horizontal portion Q_E. The factors like Rho or the vertical effect factors like 0.2SDS has to be calculated manually and applied as factors to the appropriate loads when defining load combinations. 

See Also

Product TechNotes and FAQs

Structural Product TechNotes And FAQs

External Links

Bentley Technical Support KnowledgeBase

Bentley LEARN Server

Comments or Corrections?

Bentley's Technical Support Group requests that you please confine any comments you have on this Wiki entry to this "Comments or Corrections?" section. THANK YOU!

I have uploaded the model through the secure file upload.

Hi,

You can use a button shown in the screenshot. It becomes available once you select some text lines in the editor.

Regards,

Modestas