shear heads and effective length

[LeoD]

Im looking at an existing two way slab, that seems to be underdesigned for the given loadings on the design documents. The slab uses some steel beams for shear heads @ the columns. Does anyone know if these shear heads can be used to reduce the effective length for the span? I am aware of the contribution of negative moment capacity that ACI permits, but I am having problems with the positive moments as well. Any thoughts or Knowlege of this mater would be greatly appreciated.

Thanks,
Leo Doyer

 

[jec67]

"Reinforced Concrete" by James MacGregor has an excellent discussion regarding the history of two-way slabs. In a nutshell, many older slabs were not designed for the loadings as prescribed by current ACI requirements. I do not know the age of the slab you are investigating, but I have encountered similar problems with two-way slabs constructed in the 1930's and '40s.

I am by no means an expert, but I do not believe that you can reduce the span for the shear heads. Again, MacGregor's book is an excellent reference for this matter.

Good luck.