Wendel Michael Sebastian

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

Abstract 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.

Nonlinear influence of contraflexure migration on near-curtailment stresses in hyperstatic FRP-laminated steel members

The flexural characteristics of hyperstatic steel members with adhesively bonded Fibre reinforced polymer (FRP) laminates are considered. It is shown that, during elasto-plastic activity, the migration of the points of contraflexure along such members has two nonlinear effects on the stresses in both the laminate and the adhesive. First, the lengths of laminate traversed by these migrating points undergo reversal of axial stress from tension to compression, which exposes the laminate to potential buckling. Second, the bond stresses in the adhesive near laminate curtailment increase dramatically, and so may initiate brittle failure near curtailment by separation of the laminate from the steel member. Nonlinear finite element (FE) analyses are used to illustrate both these effects. The FE model is verified by comparison with published data, and is then used to analyse an isostatic and a hyperstatic FRP-laminated steel member. The results show that the above nonlinear influences are pronounced in the hyperstatic member, but are absent from the isostatic member. Tapering of both the laminate and adhesive profiles near curtailment of the laminate is investigated as a potential means of reducing these effects in the hyperstatic member. Finally, the implications of the above effects for the performance of hyperstatic FRP-laminated steel members in practice, are discussed.

Ductility requirements in connections of composite flexural structures

Abstract The provision of adequate shear connection between the tension and compression-resisting components of composite flexural members is essential to the robust performance of such structural members under load. If the combined capacity of all the connections in a given composite member is to be exploited at the ultimate load of the member, there is a requirement for the connections to possess some measure of ductility, because the shear force capacities of the connections will typically be activated before the member ultimate load is attained. In this paper, finite element (FE) analyses of a composite member comprising an I-section steel beam connected to a concrete slab are used to show that the required level of connection ductility is parasitic on the compliance of the connections. In order to clearly identify the nonlinear influence of plastification of the connections on overall member behaviour, the relative properties of the connections, the slab and the beam are such that the concrete and steel exhibit little and no nonlinearity up to the peak loads here considered. The analyses reveal that, when the ultimate load of the composite member is attained, the required ductility in the connections must increase as the compliance of the connections decreases. By contrast, it is seen that, en route to attaining the ultimate load, the connection ductility required to just achieve yield of all connections increases as connection compliance increases. The implications of the FE results for the performance of steel–concrete and timber–concrete composite members at the serviceability and ultimate limit states are discussed.

Interpretation of sensor data from in situ tests on a transversely bonded fibre-reinforced polymer road bridge

The Frampton Cotterell fibre-reinforced polymer road bridge deck comprises pultruded glass-fibre-reinforced polymer units which are laid longitudinally and are adhesively bonded transversely, in contrast to previous glass-fibre-reinforced polymer deck bridges where the pultruded units were laid transversely. This novel layout dictates that transverse distribution of live loading occurs only through the deck’s flanges and entails possible transverse tension which should be controlled to avoid cracks through the bonded deck–deck joints. This article assesses these structural actions by interpreting strains and deflections recorded during lorry testing of the bridge. Transverse distribution is evaluated by comparing transverse profiles of recorded longitudinal strains and of predicted longitudinal moments, with the conclusions qualitatively reinforced using a deflected surface based on the test recordings. Evidence of the deck acting as a continuum free of propagating joint cracks comes from the fact that the strains recorded during complementary lorry runs along the bridge satisfy the superposition principle and that the recorded strain influence lines replicate an idiosyncratic feature of the moment influence line without redistribution effects. That feature was then exploited to inform the strategy for a braking test which produced valuable vibration data for the bridge. Test data integrity is corroborated by cross checking deflections recorded from different types of sensors. It is concluded that since longitudinal placement of pultruded decks enhances the versatility of fibre-reinforced polymer bridges, this sensor layout and data interpretation process may form part of a wider strategy for health monitoring of such bridges.