Partial-interaction analysis of composite beam/column members

Abstract

Members in which two or more elements are bolted together to form composite structures that are stronger, stiffer, and more ductile than the sum of the individual elements are now commonly used in practice, not only for new structures but also, more recently, for the retrofitting of existing structures. The shear connectors that are used to tie the elements together rely on slip, that is partial interaction, to transfer the longitudinal shear. This makes the behavior of composite structures complex, so that most composite structures are designed assuming no slip, full interaction, which gives an upper bound to the strength and stiffness. In order to determine the true strength, to estimate the amount of slip to prevent fracture of shear connectors due to excessive slip, and to ensure that plated reinforced concrete columns can achieve their required seismic ductility, it is necessary to allow for slip in the mathematical model. In this paper, the classic linearelastic partial-interaction theory for composite steel and concrete beams is extended to allow for axial forces, as occur in plated reinforced concrete columns and prestressed composite beams, and also to allow for boundary conditions associated with plastic hinges. Furthermore, a set of generic parameters that govern the fundamental response of the composite members is developed that can be used for the eventual formation of design guides and procedures.