Looking for opinions on the best wa

[prblmfxr]

Looking for opinions on the best way to analyze the following situation:

One-way concrete slab reinforced top & bottom both ways, 6 1/2" thick with 1" Kalman topping (7 1/2" thick total).

Slab supported by WF steel beams @ 6'-8" O.C. with top flange embedded in slab (no shear studs). Beams frame into WF steel girders spaced @ 20'-0" O.C. with top flange embedded in slab (no shear studs). Beams & girders frame into steel columns on a 20' by 20' grid. Slab designed (and confirmed) for 500 psf LL and 100 psf DL.

The problem: the floor is used as a warehouse area, using heavy-duty storage racks typically used on slabs-on-grade. Obviously, the storage rack legs create high point loads on the slab. How can I get accurate results for shear, moment, deflection based on this point loading. I need to know if the floor is being overloaded.

It seems to me that applying the loads over a 1' strip of slab and analyzing as a 1' wide conc. beam would be way to conservative. Am I right or wrong? Any suggestions?

 

[FrankHartzell]

AASHTO Specsfor Highway bridges cover point loads on concrete slabs. Also see many concrete texts,e.g.,"Design of Concrete Structures, Nilson & Winter,11th Ed.

Be sure to check slab for punching shear.

Frank hartzell
frank.hartzell@jacobs.com

 

[JAE]

To space the point loads by hand, I would agree with Frank and simply use the AASHTO equation:

The concentrated load is spread over a distance E

E = (4 + 0.06 x S) but not more than 7 feet (or, I would add, the center to center spacing of the posts).

S = span, ft.
Alternatively, you could use a finite element analysis on the slab, modeling the beams and girders, and get moment contours.

In either case, you should check punching shear through the slab per ACI 11.12.