Assessment of cyclic degradation effects in composite steel-concrete members

This paper investigates the inelastic behaviour of composite steel concrete beams, with particular emphasis on cyclic deterioration effects. A detailed continuum model is firstly developed to represent the hysteretic response of composite steel beam and concrete slab assemblages, validated against available experimental cyclic results on both steel and composite members. The proposed model is then adopted to perform detailed parametric assessments which are used to gain insights into the key response characteristics related to the inelastic cyclic performance of composite steel/concrete members, including their stiffness, capacity, and ductility. A synthetically generated numerical database is subsequently used to develop relationships governing the plastic rotation and cyclic degradation of dissipative composite beams as a function of the main geometric and material properties, with focus on members designed to European codified procedures. The deterioration effects are shown to be dependent on a number of key factors including, most significantly, the composite beam depth and the steel cross-section slenderness. In addition to the asymmetry in behaviour under sagging and hogging moments, it is shown that composite members typically exhibit 20% more degradation under cyclic loading compared to their bare steel counterparts. Importantly, the proposed cyclic degradation expressions for composite beams also enable the calibration of widely used uniaxial deterioration models which are suitable for implementation in computationally efficient nonlinear inelastic frame analysis for structural systems. These expressions also provide fundamental information required for idealised pushover representations for practical seismic assessment and design purposes.