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.