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This study presents an experimental investigation on composite beams (CB) to explore the effectiveness of adding external post-tensioning (EPT) force, as a strengthening technique, on the monotonic flexural performance of composite samples. Two experiments on CB were conducted under three-point loading. High-strength steel strands post-tensioned to 46% of the ultimate strength were used to apply the EPT. Moreover, a finite element (FE) model is developed to present numerical investigations on the monotonic and fatigue behaviors of the CB with and without EPT by considering the slip between the concrete slabs and steel beams as well as the fatigue deterioration in the concrete slabs. A FE parametric study is conducted using the proposed FE model to investigate the effect of steel beam grade, tendon eccentricity, span-to-depth ratio, and fatigue loading. The optimum span-to-depth ratio to obtain the maximum contribution of the EPT force in improving the CB capacities is 9.0. [ABSTRACT FROM AUTHOR]

A two-node beam element formulation with eight degrees of freedom was developed and implemented into MATLAB to simulate the nonlinear behavior of the composite. The beam element includes the reinforced concrete slab, the concrete reinforcement, the steel beam, and the shear connectors. One dimension-softening model was used to simulate the concrete, the bilinear isotropic plastic model was used to simulate the steel, and a multi-linear spring was used to simulate the partial shear connectivity. Experimental results were used to validate the numerical model, which was able to closely predict the experimental response by a 2% difference. The model was able to simulate several material nonlinearities such as the plasticity of the steel beam and cracking and crushing of concrete slab. A parametric study was performed to investigate the effects of strength of shear connector, concrete slab thickness, steel beam depth, and the concrete compressive strength on the overall response of steel–concrete composite beams. It was found that the variation in shear connector strength significantly affects the response of the composite beams. In addition, the composite beam stiffness and strength increased with the increase of the steel beam depth, significantly. [ABSTRACT FROM AUTHOR]