Steel-concrete composite beams prestressed by external tendons: effects of material and geometric nonlinearities.

The analysis of externally post-tensioned beams is characterized by some specific issues related to the coupling between the local strain of the cable and the global deformation of the structure. Collapse modalities are influenced by the nonlinear behavior of materials and in many cases by non-negligible geometric nonlinear effects. The authors present a model for externally prestressed steel-concrete composite beams that includes geometric and material nonlinearities. The proposed model is based on the theory of small strains and moderate rotations obtained from the exact nonlinear theory. Comparisons with experimental tests are shown to validate the results obtained with the proposed formulation. Some numerical applications involving simply supported and two-span continuous composite beams post-tensioned with external cables are discussed to illustrate the nonlinear geometric effects and their influence on the ultimate capacity.