Uplift on hollowcore slab

[CHADENGFL]

I have a 17 ft. span 6" deep hollowcore slab with 2" topping for an open canopy wing, so the ASCE 7-10 wind uplift used is the overhang area for pressure (approx. 78 psf ultimate uplift). The specialty engineer submitted gravity load calcs only. Despite a net downward dead load, as the slab self-weight is relieved could critical tension stress in the unreinforced top of slab develop depending on the negative precamber balanced by the slab self weight? Therefore am I not reasonable to demand uplift stress calcs. I have no problem with stability (W+D) per ASCE 7-10.

 

[JedClampett]

Are you sure you're using the right Effective Wind Area? For a 17 foot span your EWA is near 100 square feet. Seems like 78 psf is a bit high.
But back to your point, if there is a net uplift, you should check uplift moment on the hollowcore plus the attachment details. But the net uplift will be small, so the calculations should be pretty easy.

 

[spats]

You most likely have WWR in the topping that could be used for uplift.

 

[CHADENGFL]

My wind design is for south florida: ASCE 7-10; Basic Wind Speed = 170 mph; Rick Category II; mean roof height = 13 ft.; Enclosed Building. As you mentioned, my tributary area is approximately 100 ft^2 (96.3 ft^2), but I'm using the eave overhang pressure, since the carwash is open on 3 sides (effectively a propped overhang). The 78 psf gross uplift pressure mentioned is the ultimate wind pressure, my main concern would be the immediate deflection when the uplift load unloads the hollow-core / topping dead weight, whose net deflection need to remain below 0.425 in. (L/480)for serviceability requirements. The Florida Building Code 2010's allowable stress load combination: D + 0.6W self-adjusts for the ASCE 7-10 ultimate uplift pressure, versus 47.3 psf uplift allowable service pressure if ASCE 7-10 had still used allowable pressures, and the load combination: D + W would have remained for load deflection calculations in the Florida Building Code.

 

[hokie66]

The "specialty engineer" may not have been aware of your uplift loading condition. Uplift does not commonly control on concrete slabs, so when it does, the designer needs to be informed. Tell him/her that you have a loading condition that hasn't been considered, and needs further design. Top strands can be provided.