Nonlinear Finite Element Analyses of Steel/FRP-Reinforced Concrete Beams by Using a Novel Composite Beam Element

A simple displacement-based one-dimensional two-node layered composite beam element with only two degrees of freedom per node is developed based on Timoshenko's composite beam functions for nonlinear finite element analyses of steel/FRP-reinforced concrete beams in this paper. Timoshenko's composite beam functions are employed to represent the displacement interpolation functions, and thus the element gives a unified formulation for both slender and moderately deep composite beams and the notorious shear-locking problem is avoided naturally. Geometric nonlinearity and material nonlinearity are included in the new model, and tension-stiffening effect after cracking is also accounted for. The proposed composite beam element is validated against numerical examples, and it is demonstrated to be accurate and effective for analyses of slender and moderately deep composite beams even with very coarse meshes. The element is then employed to analyse the nonlinear structural behaviour of composite steel/FRP-reinforced concrete beams with different parameters, such as different types of reinforcing bars (steel, GFRP, CFRP and BFRP) and different ratios of reinforcement, and the influences of these parameters on the structural behaviour are investigated. The progressive cracking processes of the concrete beams with the increase of loading are also modelled using the proposed element and the results are presented in this paper.