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high steel ratio in the roof floor of buildings

high steel ratio in the roof floor of buildings

Hi guys,
when analysing a roof slab, edge columns will absorb unbalanced momenta which will result in a high reinforcement ratio since the compression carried by thee colums are not enough to counteract the tensile forces caused by the moment.
if we look at the below floors, reinforcement will be much less since the moments are smaller cz the columns is continious and the axial force is increased.
Do u generally increase the reinforcement in the roof or do u assign end releases for the edge columns (not a big fan of releases) ??

RE: high steel ratio in the roof floor of buildings

in continuation to the above , the below is the method i follow:
i design the roof slab and assign releases to the edge or corner column so no unbalanced moment is carried to the column.
however, since some minimum top reinforcenent will be located above these columns and this reinforcement will be responsible of carrying some moment to the column, i assign 0.35 as stiffness modifiers to the edge columns. The reinforrcement will decrease but at the end , the column will be designed to carry some moment although the slab is designed as e
pinned edges.
any comments ??

RE: high steel ratio in the roof floor of buildings

I hope you still design the slab/column connections for the elastic bending moment that they joint tries to develop, before it falls down.

RE: high steel ratio in the roof floor of buildings

how do u proceed Rapt for such case ?

RE: high steel ratio in the roof floor of buildings

Check punching shear assuming the full moment is transferred to the column!

RE: high steel ratio in the roof floor of buildings

Ok i fogot to mention that if the columns are not intersected by perimeter beams, i check the punching shear assuming full moment is transfered, make sure that no brittle failure will occur, then rerun the model with pinned edges. the thing is that i dont want to pass from 1% as steel ratio in the columns in the below story to 3 or 4 or sometimes greater ratios For the top of the building.

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