Reinforced and prestressed concrete beams subjected to shear and torsion

Today, the nonlinear finite element method is commonly used by practicing engineers, although design and assessment for shear and torsion in reinforced concrete structures are still made using methods based on sectional forces. By modelling the shear behaviour, using 3D nonlinear FEM, higher load carrying capacity and more favourable load distribution was shown, compared to conventional analysis. A modelling method using four-node curved shell elements with embedded reinforcement was evaluated in this study. Tests of reinforced and prestressed beams loaded in bending, shear and torsion were simulated. The increase in shear capacity, in addition to the reinforcement contribution, was modelled with a relationship for concrete in tension according to the modified compression field theory and compared with the use of a relationship related to the fracture energy of plain concrete. The results show that evaluations of the load-carrying capacity or crack width will be on the safe side, if only the fracture energy is used to define the concrete in tension.