Low Base Shear Dynamic Analysis

[CorporalToe]

Hello, I am currently modeling a build into SAP2000 and I am getting a low base shear after performing a Linear Dynamic Analysis on my model. It is 50% of the base shear that I calculated using the Elastic Static Force Procedure.

Is this a cause for concern? And that does the low base shear mean? Is it because of the stiffness in my building?

 

[haynewp]

Check your building code assuming nothing is wrong with the model. There is a minimum of 80% or 85% of the equivalent lateral force procedure base shear in what I use.

 

[CorporalToe]

You are right the limit is 80%. I’m just more concerned if my model is acting wrong. Is it normal for a model to spit out a base shear that is 50% lower then ESFP?

 

[haynewp]

It depends on what you have. I've gotten an even lower % for base shears for flexible structures. But there may be something wrong with the model and the lower shear is from an error affecting the stiffness calculation.

 

[driftLimiter]

Have you adequately scaled the dynamic inputs? You didn't say whether your doing response spectrum analysis or time history, but for either one you need to pay attention to the scaling of the input spectra, or acceleration time history respectively. Finally as is mentioned above, you need to check that your scaling provides at least a certain % of the ELF base shear.