Updating of Bending Moment Design Coefficients for RC Slabs

Most of the coefficients for the design of reinforced concrete rectangular slabs, recommended in the current provisions of design codes worldwide, do not include the case of slab cast monolithically with their supporting beams, some were computed with approximated methods in plates supported on rigid beams, and some of them are underestimated. Consequently, insufficient steel reinforcement areas may be computed with the available coefficients, which is unsafe. To guarantee safe designs of reinforced one-way and two-way concrete rectangular slabs with the coefficient method, the updating of the simplified flexural moment coefficients, computed with computational mechanics, is performed in this paper. These computed coefficients are compared with the regulatory coefficients recommended in the current provisions of design codes worldwide. It is shown that approximately 50% of the current provided design coefficients are underestimated, so they must be updated to guaranty the structural stability and integrity of slabs. The slabs, columns and supporting beams were modelled with shells and frames FE, respectively, in the software SAP2000. The strain energy was the criterion to choose an appropriate FE mesh size in such a way that the slab models yield accurate results. Seven types of panels are studied, considering two types of construction: slabs cast monolithically and not cast monolithically with their supporting beams. Additionally, two types of supports were modelled: flexible supports and rigid supports; in the former, panels are supported on principal beams with vertical supports at the intersection of the beams and in the latter, panels are supported on confined masonry walls. A comparative design example of a slab with six panels, using both the current provided design coefficients and the proposed coefficients, is presented, where the panels designed with the latter coefficients require more reinforcement than those designed with the former coefficients. Consequently, safer designs are obtained with the proposed coefficients.