Avoid transmission of moment between suspended slab and lift core during lateral analysis in ETABS

[nathan7]

Hi all

I'm performing the lateral analysis of a 40 storey building in Etabs. The structure is an office with central core and perimeter columns. The slab is 300 post tensioned.

the lift core is the only element resisting the lateral loads. I want to make sure that the connection between the slab and the core is a pinned connection with no transmission of moment (the builder wants to use ferrules with very limited capacity). By achieving a pinned connection I am ensuring that the slab and the perimeter columns are not contributing resisting the lateral loads and the natural frequency of the tower will be influenced only by the core.

I'm currently modelling this by drawing a 1m strip of slab around the core with zero stiffnesses, alternatively I can draw a series of voids with small beams in between the voids connecting the slab to the core.

Look forward to other suggestions on how to model the slab in order to avoid transmission of moment between core and slab.

Thanks

 

[slickdeals]

There are two ways to do this.

1. Isolate your perimeter columns (pin them top and bottom), so that they have no flexural stiffness.
2. Assign your floor element as a "membrane" instead of a "shell", so that the slab has no flexural stiffness.

My preference is to go with Option 2.

 

[nathan7]

Thanks slickdeals, i will try this