Moment transfer from flat slabs to columns 1

[hockley]

Hi there - I am a structural engineer with what is rather a basic question relating to the design of reinforced concrete flat slabs and columns. The ISTRUCTE publication "Manual for the Design of Reinforced Concrete Building Structures" gives guidlines for the design of such elements but I am unclear as to the stage at which the ability of the slab to transmit the out-of balance design moments to the columns is checked.

I would be grateful if you could point me to a reference that gives details of the mechanism assumed for the tranfer of moments from the slab to the columns and to a method of checking the capacity of this mechanism.

The background to this question is that I am invoved in the conversion of an existing building where we are cutting holes in the slabs. Once the holes are cut we will be left with a strip of slab running parallel to a set of perimeter columns that is effectively cantilevering from the columns. Whilst I suspect that the columns can carry this moment, I have my doubts, given the original reinforcement details, about the ability of the slab to transfer these moments to the columns and would like to check this explicitly.

Any pointers you can give will be gratefully received.

With best regards,
Matthew Hockley

 

[JAE]

I think the PCA Notes on ACI 318 has some design examples. You can find this publication at the PCA website here:

PCA Notes

 

[pappyirl]

The slab is assumed to transfer the moment to the columns via torsion on the 2 sides of the column perpindicular to the edge and directly through the face of the column. The width of this strip and max transferable moment is determined from BS-8110 clause 3.7.4.2. The moment capacity will be determined by the amount of reinforcement within this strip.

A good guide to this is found in CIRIA Report 10 "Design of reinforced concrete flat slabs to BS-8110".

 

[dik]

Out of curiosity, did a search of CIRIA and came up with the following... Do they ever have a list of publications...

http://www.ciria.org/acatalog/Publications.html