Nonlinear proportionality of shear-bond stress to shear force in partially plastic regions of asymmetric FRC-laminated steel member

This paper focuses on the elastic–plastic flexural characteristics of hybrid members comprising I-section steel beams with adhesively bonded fiber reinforced composite (FRC) laminates. Specifically, predictive models are presented for the shear-bond stresses developed within the adhesive layer. The asymmetry of the hybrid section, due to the presence of the laminate, is shown to have two important consequencies, namely that two parameters are required to fully define the elastic–plastic behavior, and that there is a progressive migration of the neutral axis towards the laminate as elastic– plastic flexure of the section increases. Five different phases of elastic–plastic flexure are identified. Analytically exact two-parameter predictive models, which incorporate the nomadic tendencies of the neutral axis, are derived for the shear-bond stresses associated with each phase. The models reveal that, in contrast to fully elastic flexure, shear-bond stress is nonlinearly proportional to shear force during elastic–plastic behavior. Predictions from the models are compared with test data from the laboratory and with predictions from a finite element program, for FRC-laminated I-section steel beams under both distributed loads and point loads. These comparisons show that two elastic–plastic phases, each defined by axial stress redistribution within the tension steel flange, stimulate rapidly varying shear-bond stresses in the adhesive. The capabilities of the models are highlighted, and areas open for further work are discussed