Time-History Analysis-Base Shear vs Internal Shear

[lutein]

I am running a fast non-linear analysis (FNA) in SAP2000 on a simple shear wall building. I noticed that the base shear is much larger than the summation of internal shear, almost 2.5 times more. This is very weird. Is this normal or what could I have missed in the analysis?

Thanks for your input in advance.

 

[WARose]

That is somewhat unusual as non-linear analysis sometimes results in less force being applied at the foundation than is actually generated.

The main thing that comes to my mind (since you are doing an analysis that takes into account the dynamic characteristics of the system) is it could be an issue with transmissibility. At certain frequency ratios (i.e. forcing frequency to supporting system), the amount of force transmitted to the foundation can be greater than what is applied.