Pushover Analisys

Question

Hello, 
 
 This is my 3rd thread and seems that no one from Bently staff seems to bother to give me a reply. I am still writing to try my luck once more. 
 
 I am applying a pushover analysis on a steel structure. But I am stuck at the application of hinge properties. Apparently FEMA has a default linear Moment-rotation curve, hence I want to add a new curve. But I do not know how to define the Yield Moment and Yield Rotation. Also when it comes to apply the hinge properties for braces how do I do it because braces need another type of hinge but StaadPro appears to have only Moment-Rotation type of hinge. 
 Can anyone help (is Benltly Forum still operating?)

Kris Sathia · Accepted Answer

Your question: 
 
2) Also, I am using the Select/Group commands to have STAAD design steel members. After Select/Group I have included a Perform Analysis and Design Check Commands, which the program does against the new set of cross sections that it itself picked, I suppose. But still the design check in Post Processor/Beams/Unity Check shows Failing members, and not just by a little. Some members have ratios over 2.0! How can sections chosen by Staad itself not pass the design check, while Staad could have chosen even higher sections. 
 
Answer: 
 
You can get around this problem with the help of the RATIO parameter. Set its value to a number like 0.75 or 0.8 prior to the SELECT command, and, set it back to 1.0 just before the CHECK CODE command. 
 
An example of this is 
 
 PERFORM ANALYSIS 
 LOAD LIST 11 TO 15 
 PARAMETER 
 CODE AISC 
 RATIO 0.75 ALL 
 SELECT ALL 
 GROUP MEMBER 1 TO 8 
 GROUP MEMBER 21 TO 25 
 GROUP MEMBER 33 TO 37 
 
 LOAD LIST 11 TO 15 
 PERFORM ANALYSIS 
 LOAD LIST 11 TO 15 
 PARAMETER 
 CODE AISC 
 RATIO 1.0 ALL 
 CHECK CODE ALL 
 
Now, if you go to Analyze - Run Analysis, the Select command will use a ratio of 0.75 and the Check Code command will use a ratio of 1.0. If a member still fails, you can go back and change the ratio command again. You can use it selectively, if you want. You could specify several ratio commands so that, for example, for the member selection of channels, the program uses a ratio of 0.7, for the angles it uses 0.6, etc.

Kris Sathia · Answer

In section 4.5.2 of the Pushover Analysis documentation, you can find the description and an example for the input that needs to be specified for a user-defined moment hinge. 
 
If you have a data set you wish to specify and if you can upload it to this thread, we can provide you with a sample model containing that data. 
 
For braces, we assume you are looking for an axial hinge. Such a hinge is not available in STAAD at present. 
 
We were not able to find any other post created by you on the BE Communities forum on this topic. If you can provide us the link to those, we will look into those.

Kris Sathia · Answer

This is the answer to your question on the output for Steel Design. 
 
Do the following. 
 
From the File menu, choose Report Setup. 
 
Under the drop down list called Available, choose Steel Design Detail. 
 
Go to the tab called Ranges. 
 
You will find a Radio button against the term Ranges. Switch it on. In the text box for Beams/Plates/Solids, type in the list of members for which you want the Steel Design output to be reported. 
 
Close the dialog box. 
 
Go back to the File menu and choose Print Preview Report. 
 
The report will be presented only for those members that you choose under the Ranges tab.

Kris Sathia · Answer

You asked: 
 
And one more thing, when I use a SELECT command, is the deflection check against the results for the new sections or for the old ones? 
 
Answer: 
 
During the member selection phase, the program first calculates the L/d ratio (L = distance between the points DJ1 and DJ2, and, d being the maximum deflection between those nodes). If that L/d happens to be smaller than the value of the DFF parameter, it indicates that a larger section needs to be selected. The program will then look for a section whose IZ is at least as large or larger than a value called "A" where 
 
A = IZ of the section used in the analysis * B 
 
B = DFF / (L/d) 
 
Thus, if the member's deflection exceeds the limit imposed by the DFF value, a section with a greater IZ is chosen. 
 
If the deflection is smaller than the limit dictated by the DFF, then the member selection is governed only by the strength checks.

Kris Sathia · Answer

You asked: 
 The thing is that I want the answer for all my members but I want the answers organised in physical members not for all those smaller elements. If this is not possible the question may be - which of the smaller elements would represent the answer for all the member? 
 Answer: 
 In the batch mode (or "old method" as you have described it), the output will be presented for all members in the list for the SELECT or a CHECK CODE command. 
 If you want to check the highest ratio from among the segments of a physical member, and do that graphically, the following method should work: 
 First, select all the components of the physical member. Click the right mouse button on the drawing area, choose New View - Create a New window for the view. Go to the Results page on top of the screen, and choose Utilization Ratio. The number will appear as a label on the individual segments. 
 If you want to find which segment has received the largest section, then, the GROUP command you have used is the right approach, and you should examine the output file to see that section name. You will find statements like the following 
 GROUPING BASED ON MEMBER 1 (ST W14X99 ) LIST= 1.... 
 The above statement means that the segments in the list for the GROUP command have been assigned a W14X99 (same as the one chosen for member 1) because it happens to be the largest section from among the those in that list.

Kris Sathia · Answer

While it may seem like a shortcoming of the program, an examination of the method used in member selection will enable us to realize that it is not easy to arrive at a final set of sections without several iterations, especially for large structures. The steps involved in member selection are described at the following link 
 Procedure used in STAAD for Member Selection 
 Note that the selected section is optimum only from the standpoint of the recent analysis. Since a new analysis has to be done following the selection, the new stiffness distribution in the structure will determine the extent to which the forces change in the members. Also, a new section also means a new weight, which too will affect the forces in the members. 
 Another layer of complexity is added when a GROUPing operation is done following the MEMBER SELECTION. Grouping can inadvertantly cause a safe section to be replaced by an unsafe section. For example, consider a physical member made up of members 1 and 2. Let us assume that during member selection, a W14X61 (AX = 17.9, IZ = 640) was selected for member 1, a W12X65 for member 2 (AX = 19.1, IZ = 533). Observe that the area and hence the weight of the W12X65 is larger than that of the W14X61. But the W14X61 has a larger IZ and hence a larger section modulus than the W12X65. When a grouping is performed, both members will receive a W12X65 since it is the heavier one. But if bending about Z is the critical condition for member 1, by replacing the W14X61 with a W12X65, an unsafe section is being chosen for it. 
 The method I suggested earlier, which is use the RATIO parameter is the most effective method I have seen to minimize the number of iterations. Something similar is automatically done by the program if the command SELECT OPTIMIZED is specified. But I am not sure if it is any superior to the one I suggested earlier.

Modestas · Answer

This Wiki post should answer your question: http://communities.bentley.com/products/structural/structural_analysis___design/w/structural_analysis_and_design__wiki/16165.limiting-section-assignment-or-member-selection-to-specific-cross-sections 
 
In addition, I would suggest you to create a new Forum thread if your new question or issue is not related to the original question of the forum thread.

Andi · Answer

Thank you very much Modestas, this was really helpful. 
 
And, sorry I will open a new thread next time. 
 
Regards, 
 
Skerdi

Sye · Answer

Pushover analysis in STAAD.Pro is limited to steel structures only. So you cannot have a material by a different name. You should however be able to modify the value of E for STEEL and the analysis should work. I have attached an example file with E value of approx. 210 GPa used for steel. 
 
 ExampPush01.std

Sudip Narayan Choudhury · Answer

I think the input is ok. The SGR and the TORSION parameter does not really help in the Deflection check - and so it was not necessary to be specified. The torsional deformations are not be included in the deflection check. TRACK 4 is very important - which you have included. Please let me or Kris know if you have nay further questions.

Sudip Narayan Choudhury