huangyhg

looking for opinions on the best wa
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?
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
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.

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