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Moment comparison of modeling wall on top of beams

Moment comparison of modeling wall on top of beams

Moment comparison of modeling wall on top of beams

Hello all,

I am using ETABS concrete frame design to give me the moments and shear values needed to design my beam. In this case, there is a wall on top of the beam and I have compared the moments for the following:

Case 1: No modifiers
Pos moment ~ 20.2 k-ft
Neg moment ~ -35.4 k-ft

Case 2: Changed the walls in-plane stiffness to 0.01 (F11 & F12)
Pos moment ~ 70 k-ft
Neg moment ~ -163.4 k-ft

Based on these results, I would expect to see the moments on case 2 but this would mean that I would design my beam assuming no composite action between the wall and beams – however, we normally indicate on our structural notes to not impose loads until concrete members attain the specified compressive strength. This leads me to thinking that my approach is rather conservative and that in reality, the beam will be supported during construction while they pour the walls – meaning, there is composite action.

Overall, I am curious to see how other engineers go about designing beams with walls on top in structural softwares.

Thanks and appreciate any insight/comments.

RE: Moment comparison of modeling wall on top of beams

Etabs is considering the stiffness in the distribution of the loads to the beam. If there are no load transfer issues - this becomes a local problem to the beam only.

If the wall is a load bearing wall, then modeling it becomes important for the design of the building. If it is only a cladding wall, then it could be replaced with a line load instead.

I would probably back-check this section of the design with hand calculations and bracket my design across all iterations.

RE: Moment comparison of modeling wall on top of beams

Generally speaking I would design the beam as if the wall isn't composite, and then sleep easy at night knowing it is likely composite.

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