Auto Seismic Analysis in STAAD PRO

Hi Sanjay,

No, it is not necessary to add Joint Weights in a seismic definition.  The joint weight option is provided for instances where it may be convenient to use.  One example that comes to mind is modeling the weight associated with connection material used in large gusset/bracing connections. 

Fortunately, the procedure for applying seismic loads is the same regardless of the material/construction type.

Note that a new build of STAAD.Pro is now available for downloading from the SELECT site.  It goes by the name STAAD.Pro V8i SELECT Series 1 and has the build number 20.07.06.23.

Cheers,

Chris

 

Dear Chris,

Thanks for your reply to my querry, I am attaching a STAAD file of seismic analysis done by me, please check, If I have done it correctly.

Thanks for your help,

regards,

Sanjay

Hi Sanjay,

It looks like your model will work.  I am not familiar with the analysis requirements stipulated by IS 1893, but I am accustomed to seeing P-Delta analyses performed for concrete structures.  So this would be a something for you to investigate.

If it turns out that you decide to implement a P-Delta analysis, then your load combinations should be created by using the REPEAT LOAD specification as opposed to the LOAD COMB spec.  (REPEAT LOAD instructs the program to analyze the constituent load cases concurrently, for the proper determination of P-Delta effects, whereas LOAD COMB simply instructs the program to combine the results of the constituent load cases analyzed independently.)

And if you implement the REPEAT LOAD specs, then you will want to issue a PERFORM ANALYSIS and CHANGE command after each of your IS 1893 seismic load cases.

 

Cheers,

Chris

Dear Chris,

Thanks for your reply, I haven't used P-Delta Analysis so far. I will look further regarding P-Delta Analysis. If you have run my staad file, you may notice that, I am getting more column steel area in upper floors as compare to lower floors in few columns. Is it normal in case of seismic analysi?

thanks & best regards,

-Sanjay

Hi Sanjay,

When I look at the version of the model you posted below, there are some columns where the moment due to lateral load is not significantly larger at the lower levels than it is at the upper levels.  Thinking in terms of the shape of a typical column interaction diagram, I suppose it is possible that for a given moment value, the reinforcing requirements could actually be REDUCED as the design axial load is increased.  This could be represented by the shift indicated on the interaction diagram below.  In any case, your question underscores the importance of establishing the proper P-Delta analysis procedure with REPEAT LOAD cases before going too far with any concrete design results.

 

Regards,

Chris

Hi Chris, Thanks for your information. Could you update my STAAD Input file with P-Delta Analysis Parameter? 

thanks and best regards,

Sanjay 

 

Hi Chris, Thanks for your information. Could you update my STAAD Input file with P-Delta Analysis Parameter? 

thanks and best regards,

Sanjay 

 

Hi Chris, Thanks for your information. Could you update my STAAD Input file with P-Delta Analysis Parameter? 

thanks and best regards,

Sanjay 

 

Sanjay,

I made some modifications to the attached version of your model.  They include a PDELTA analysis command, converting your LOAD COMB statements to REPEAT LOADs, adding PERFORM ANALYSIS and CHANGE commands after your two seismic load cases, and inserting the SET NL command to specify the total number of primary load cases, now that this has become a "multiple analysis" model.

This should give you a good start on incorporating a technically correct PDELTA analysis.

Cheers,

Chris

Dear Chris,

Thanks for the update in input file. I ran the file, but its giving syntax error in floor weight, when I ran the analysis, it shows one error:

187. PDELTA 35 ANALYSIS SMALLDELTA

*** ERROR *** ABOVE LINE CONTAINS ERRONEOUS DATA.
 what could be the reason?

regards,

Sanjay

 

My pleasure Sanjay.  There are a couple of things to look for to diagnose the Error. 

First, be sure you are running the most current version, because no errors are reported in the most current version.  If your service agreement is current, you can download and install the latest version from the website.  If you are running a version earlier than 20.07.xx.yy, then it is probably not recognizing the SMALLDELTA portion of the PDELTA command.  Just try deleting that one word, save, and see if that will run.

Next, be aware that the FLOOR load command will always produce a Warning, whether or not there is a problem with your particular use of the command.  The Warning is there to remind us that the algorithm used to apply FLOOR loads can produce unexpected results if it is applied to an area that includes and inside corners.  It is always best to visually inspect the loads that are actually applied by the FLOOR load command to ensure that they are as expected.  If you ever have any trouble with it, the best thing to do is to break it into more commands that each apply to smaller areas within the model, and to make sure that each of the smaller areas is convex in shape.

Cheers,

Chris

Thanks Chris, I am using Staad Pro 2006, probably the commands are not supported in this version.. I will check with the latest updates. regards, Sanjay