Etabs Model Troubleshooting - Storey Shear decreases down the Building

[efFeb]

Good Afternoon,
I am reviewing an etabs model for a coworker and doing some troubleshooting. One thing that stands out to me is that the storey shear force appears to be decreasing down the height of the building, when considering the response spectrum cases:


This seems odd to me and I am trying to find if there may be an error causing this. I've tried experimenting with turning off P-delta, deleting all columns, deleting any null areas and cladding beams, and havent managed to get rid of this effect. Does anyone have any thoughts of what might not be quite right in the model that might be causing this or what other sort of troubleshooting steps might be wise to take?
Thanks so much,

 

[KootK]

The effect make be accurate. You are, after all, doing the RSA in part to capture vibration modes higher than the first.

 

[Harbringer80]

I think KootK nailed it. It looks like you have an inflection point around level 12. Squint your eyes and look at mode 3 below.

Also, curious do you have a podium around level 5? It looks like a big change in stiffness.

 

[milkshakelake]

Are you getting something similar with wind?

 

[JoshPlumSE]

This is also one of the reasons why RSA results often have to get "scaled" back up to some percentage of the equivalent lateral force base shear.

 

[human909]

Shouldn't you generally expect greater storey shear forces at the top? Kootk and Harbringer80 have touch on the reasons why. Other more simplistic codified approaches allocate higher percentages of the base shear to higher floors than lower floors.