Seismic Loadings (STAAD Pro V8i - 20.07.09.31)

Hi,

I have questions regarding the seismic issues. Thanks so much for the help.

Q1:
what are differences between the GZ direction and one-way distribution on
member (please see the screen shot attached)?

Q2:
Which one is making sense for lateral loading – uniform or parabolic?

I
got uniform loading if I select one-way distribution which makes sense and I
got parabolic loading if it is not selected but I will get some
untouched/unselected areas (see screen-shot attached).

The
example I found in the Bentley website is only using IBC LOAD Z1 but I have the
floor mass loading (including DL, LL and equipment loads etc…).  Can someone please show me some good examples
how to model the seismic for building? I appreciate your help.

Please
see the screen-shots attached for more info.

Seismic QA.std
  • ONE option relates to oneway type distribution and towards 1 would mean the load would be distributed to members 1 and the others parallel to member 1, if that is what you are asking. The FLOOR option on the other hand would do a two way type distribution. From the diagrams that you provided, it seems like there may be issues with the formation of closed panels. There is an example model named “examp14_UBC97.STD” showing UBC seismic load generation. This file is provided with the software and you will find it within C:\SProV8i\STAAD\Examp\US folder in your machine. Although it deals with UBC code but the same principle is applicable for other codes as well.



  • Thanks Sye,

    After looking at the example 14, some questions came to me. Please advise.  Thanks,

    Q1: Shall I define the UBC/IBC load in X or Z directions ONLY (i.e. IBC LOAD X1 or Z1)?  Do I need to define the YRANGE under seismic load?  Does the program calculate the lateral loads based on the weight of the floor properties and DL, LL and equipment loads I input?

    Q2: I need to get the uniform lateral loads applied on the floor - how can I get it without select one-way toward a member?

    Q3: Can you please help me to find out the formation of closed panels for the diagrams (the unselected areas)?  I tried but I had no clues.  (see attached file)

    Seismic QA.std
  • IBC loads can be generated in X and Z directions and you have done that correctly. However you do not have to define the one way loads for defining the IBC loads. If you do, these will be applied as additional loads on the structure in addition to the seismic load. For the seismic load to be generated, the seismic weight needs to be defined as part of the seismic definition. The FLOOR WEIGHT and SELFWEIGHT defined as part of the seismic definition would be the total weight that the software would use to calculate the base shear. If there are additional loads that you would like to consider for calculation of seismic weight, you need to add these as part of the seismic definition.

    For one way load to work, you have to have quadrilateral panels which is not true for the portion where the generation is failing.

    There are no beam elements connected between nodes 8 and 159 which is leading to an L shaped panel and causing the two way floor load generation to fail for load 3. If it is an oversight and you have an actual beam there, you may add it. Else you may define a dummy member between the nodes 8 and 159 and assign it a dummy material having a low E and a zero density. This would allow the two way floor load generation to work. I added a member 4418 and assigned it the same property as member 714.

    Also I noted that the pressure applied as part of load case 3 is 20 kip/ft2 which seems very high. Please check for any inconsistency between units and value used. For the FLOOR WEIGHT I changed the value to 0.2 Kip/ft2.

    A modified file is attached.



    Answer Verified By: Ming-Hung Teng