مهدی نعمت زاده افروزی

In this research, prestressed concrete-encased CFST beams that incorporate CFST in the compression zone to improve the concrete strength, and prestressed strands in the tension zone to control cracks in reinforced concrete beams are numerically investigated. On account of the insufficient research and the unknown behavior of these beams, the study objective is the finite element analysis of parameters which are not feasible to be examined through experimental specimens such as the stress of steel and concrete, shear span-to-depth ratio, loading pattern, load transfer mechanism, in addition to longitudinal rebar ratio, prestressed strand ratio, core concrete ratio, and the steel tube ratio indices. Hence, the experimental study has been done to validate the nonlinear finite element modeling and a full-scale model is constructed to explore the flexural behavior of beams. The numerical results indicate the increasing effect of prestressed strand, longitudinal rebar, steel tube, and core concrete ratios, on the ultimate moment. The gain in the prestressed strand and longitudinal rebar ratios further escalate the flexural stiffness. Among investigated indices, the prestressed strand ratio has the greatest influence on elevating the flexural strength, the displacement ductility, and the entire absorbed energy. This is associated with the effect of the prestressed strand in improving the core concrete confinement, the tension zone crack control, and the cross section strengthening at the tension zone. Subsequently, a strut-and-tie model is proposed for the load transfer mechanism of beams. In addition, as the failure mode changes from flexural–shear to flexural, the ultimate moment capacity increases.