Strength of prestressed concrete beams in torsion

An analytical model with tension softening for the prediction of the capaci ty of prestressed concrete beams under pure torsion and under torsion combi ned with shear and flexure is introduced. The proposed approach employs bil inear stress-strain relationship with post cracking tension softening branc h for the concrete in tension and special failure criteria for biaxial stre ss states. Further for the solution of the governing equations a special nu merical scheme is adopted which can be applied to elements with practically any cross-section since it utilizes a numerical mapping. The proposed meth od is mainly applied to plain prestressed concrete elements, but is also ap plicable to prestressed concrete beams with light transverse reinforcement. The aim of the present work is twofold; first, the validation of the appro ach by comparison between experimental results and analytical predictions a nd second, a parametrical study of the influence of concentric and eccentri c prestressing on the torsional capacity of concrete elements and the inter action between torsion and shear for various levels of prestressing. The re sults of this investigation presented in the form of interaction curves, ar e compared to experimental results and code provisions.