Shear Resisting Mechanisms and Capacity Equations for Composite Truss Beams

This paper deals with the development of shear capacity equations for composite truss beams (CTBs). These equations are obtained from a purposely developed mechanics-based shear model. As opposed to commonly used approaches for the design of these structural elements, where the shear capacity is attained when the first pair of web steel bars yields, in this case the shear capacity is expressed as that causing $n$ pairs of web steel bars to yield before concrete crushes. In this way, the performance of CTBs is maximized. Two different capacity equations are proposed: one, derived from an analytical method, explicitly takes into account the contribution of concrete to shear capacity, and the other, following most current codes, does not consider such contribution. The accuracy of the proposed capacity equations has been verified against the results of nonlinear analyses and experimental tests conceived and conducted to this aim. The comparison confirmed both the consistency of the proposed mechanical model with the experimental observations, and the capability of the capacity equations to predict the shear capacity of CTBs.