RE: seismic analysis dynamic and static difference

abhilashdoss sudhakar — Thu, 17 Dec 2020 06:15:17 GMT

In both the dynamic analysis method and static method, loads applied are same then why the total loads varying for all the three model ?

RE: seismic analysis dynamic and static difference

Sye — Thu, 17 Dec 2020 01:41:35 GMT

By default STAAD.Pro would give you 6 modes which would not be enough to get the minimum required 90% mass participation. So use a CUT OFF MODE SHAPE 50 command which would get you to close around 96 to 97% mass participation for the dynamic cases.

You should apply the masses in all 3 directions. You dynamic analysis model without reference loads need to have masses defined in Y as well.

If you have rigid diaphragms you should absolutely define those as part of the model as that would significantly change the lateral stiffness of the structure.

The total load defined for the mass type reference load model is about 10468 KN whereas for the dynamic analysis without the reference load, the total load considered for dynamic analysis is about 10499 KN.

The seismic weights that you have considered for the equivalent static in the dynamic model (without reference load) adds up to 9907 KN.

The seismic weight considered for the static seismic analysis in your static model is 9771 KN. So there are differences

Also you may want to check the direction factor used for the response spectrum loading as well. I see a value of 0.059 being considered. However based on your static seismic load definitions Z=0.16, I =1, and R=3. So seems like the factor Z/2 X I/R should be around 0.027

Last but not the least a static and a dynamic analysis is not going to produce the same results anyway.

RE: seismic analysis dynamic and static difference

abhilashdoss sudhakar — Wed, 16 Dec 2020 12:15:22 GMT

Any experts Answers ?