Point Load on One-Way Slab

[ForrestLowell]

I have a floor system with steel beams 6 feet on center and a 12 inch concrete slab on top of them. The steel beems span about 20 feet so the slab acts like a one-way slab. In addition to live and dead loads, during construction I am going to have some pretty large point loads from small mobile cranes that will be driving around to lift equipment into place. How do I treat a point load on a one-way slab system? Everything I can find in the codes and books always assumes that there is a uniform load. But I have point loads. What I want to do, and my calculation checker is not agreeing with, is take my point load and distribute it over a width of 4 times the slab thickness. This is what they do in the ACI 318 (13.2.4, 8.10.2) for composite beams, on each side of the web they extend the effective area of flange 4 times the slab thickness on either side. I don't have a composite beam, but I was hoping to use this rationale to justify my effective width. Basically I want to slice my one-way slab into widths 4 feet wide for analysis of point loads. Obviously I will still consider my dead and live loads over the whole 4 foot width. In addition to your opinion any information backing your position would be helpful, so my checker and I can come to a concensus. Thanks for the help! I am just out of college and starting to understand how much I did not learn there.

 

[structuresguy]

Well, don't know if this helps, but here is how United Steel Deck tells us to deal with point loads on a concrete slab on metal deck.

http://www.njb-united.com/usd/ddds/data33.pdf

 

[JAE]

See my response here: thread507-223271

 

[sdz]

Assuming you aren't using a finite element program one way is set out in "Strip Method of Design": Arno Hillerborg: ISBN 9780721010120 (I think this is correct).

Basically you can use a two way distribution patch to distribute the point load over a larger area and then carry that distributed load on a one way strip, with final design moments obtained by superposition.

Simple really.