concrete slab diaphragm transfers horizontal load in the XY plane to the core, but does not restrain beams

[james.schembri]

Afternoon,

Please make reference to the attached model. the proposed structure is composed of a steel frame with an RC core. The steel frame shall be designed to withstand the vertical imposed loads, the RC slabs which lie within the thickness of the steel frame, shall be used to restrain the steel beams against LTB and most importantly transfer horizontal loads (mainly wind) from the cladding panels to the RC wall.

I have attached the model for reference. As you can note:

Wind pressures are high, however their relative pressure maps make sense:

 

from the nodal displacements the model appears to be behaving correctly, with the wind load causing a twist in the building.

 

However the member displacements show that the horizontal load form the facade panels are being resisted by the steel beams, causing large deflections in the weaker axis.

In reality this displacement would be 0 since the concrete slab would restrain the member. 

Currently the slab is modeled as  one-way partially stiffened in X-Y. This model allows for the right vertical load transfer from slabs to beams, but offers no restraint to horizontal deflections of the members. 

Is there a way of restraining the beams against horizontal load by the slab diaphragm?

[Krzysztof_Wasik · Accepted solution]

Hi @james.schembri 

Diaphragms used for slab generation do not have finite elements. In that case diaphragm is built between nodes in slab plane. If there is long continuous beam with no intermediate nodes only endnodes are connected by diaphragm simulated by beam. You can add intermediate nodes along beams in slabs plane using Edit >Divide option. It is enough to defined nodes along beams (without physical beams division).

Even one node defined along such beams (divisin into 2 parts) reduces deflection significantly.

[james.schembri]

Thanks for that.