Time-dependent deflection of composite concrete slabs

Relatively little research has been reported on the time-dependent in-service behavior of composite concrete slabs with profiled steel decking as permanent formwork, and little guidance is available for calculating long-term deflections. The drying shrinkage profile through the thickness of a composite slab is greatly affected by the impermeable steel deck at the slab soffit, but this has not yet been quantified satisfactorily. This paper presents the results of longterm laboratory tests on composite slabs subjected to both drying shrinkage and sustained loads. Based on laboratory measurements, a design model for the shrinkage strain profile through the thickness of a slab is proposed. In addition, an existing analytical model developed by the authors to calculate the time-dependent deflection of composite slabs is used to calculate the final deflection of the test slabs. The calculated deflections are shown to be in good agreement with the experimental measurements. © 2014, American Concrete Institute.