Concentrated Moment on Concrete slab
Concentrated Moment on Concrete slab
(OP)
Hi,
I'm checking a 10" slab for the installation of jib cranes. The jib cranes will apply a concentrated moment on the slab, near mid-span. The jib cranes will be located in several places; sometimes in column strip, others in the middle strip.
How much of the slab contributes to the resistance of this concentrated moment? The base plate is about 24"x24". The slab span is abour 24ft in each direction.
The Canadian code doesn't offer anything, and textbooks seem to ignore concentrated moments/loads on slabs.
Thanks
I'm checking a 10" slab for the installation of jib cranes. The jib cranes will apply a concentrated moment on the slab, near mid-span. The jib cranes will be located in several places; sometimes in column strip, others in the middle strip.
How much of the slab contributes to the resistance of this concentrated moment? The base plate is about 24"x24". The slab span is abour 24ft in each direction.
The Canadian code doesn't offer anything, and textbooks seem to ignore concentrated moments/loads on slabs.
Thanks






RE: Concentrated Moment on Concrete slab
ANY FOOL CAN DESIGN A STRUCTURE. IT TAKES AN ENGINEER TO DESIGN A CONNECTION."
RE: Concentrated Moment on Concrete slab
ANY FOOL CAN DESIGN A STRUCTURE. IT TAKES AN ENGINEER TO DESIGN A CONNECTION."
RE: Concentrated Moment on Concrete slab
Are you attaching the jib crane to the slab with through bolts?
BA
RE: Concentrated Moment on Concrete slab
Is this slab new or existing?
RE: Concentrated Moment on Concrete slab
If not, we would likely go with a bunch of long adhesive anchors. We don't have access to the slab underside; there is a large water tank directly below that covers the entire floor area.
RE: Concentrated Moment on Concrete slab
If the jib is located in the middle of a middle strip, there is probably no top steel, so you have to ensure that the combined stress is not tensile in the immediate vicinity of the jib base.
You also have to ensure that the combined tensile stress on the bottom does not exceed the capacity of the bottom steel.
BA
RE: Concentrated Moment on Concrete slab
RE: Concentrated Moment on Concrete slab
I ignored distributing the moment. I checked the 610mm wide slab strip directly below the base plate only. The top bars in that width are sufficient.
The moment is not very large. The factored moment that the jib crane put into the slab is about 11.3 kN.m. When I checked service load stresses, the net tensile stress (jib crane tension minus dead load compression) was less than the cracking stress of the concrete, but I don't want to rely on that. Without the top steel present, I would have tried to have the jib cranes moved (they are not installed yet).
csd72: I checked punching and we are OK
The jib cranes are not very large; they will not carry more than 1000 lbs.
Thanks for the tips everyone.
RE: Concentrated Moment on Concrete slab
I was thinking more of the moment component of the punching shear, i.e you have an increased punching shear on the shear boundary where the plate is bearing on the slab.