Prestressing with Unbonded Internal or External Tendons: Analysis and Computer Model

A method of analysis is presented to predict the behavior of prestressed concrete structures with internal or external tendons up to ultimate. The structure is modeled as an assemblage of plane frame members connected at nodes. The prestressing tendon is treated as a member with a small moment of inertia connected to the structural nodes with short arms. Because the centroidal axis changes with cracking and time-dependent effects, the nodes are located on an arbitrarily chosen axis called the reference axis. The analysis includes the effects of tension stiffening, and geometric and material nonlinearities. Any nonlinear stress–strain relationship for concrete and reinforcements can be applied. The analysis accounts for friction and slip of external tendons at deviators, variation of tendon eccentricity with applied load (geometric nonlinearity), and opening of joints in precast segmental construction. The computer program developed to perform the analysis method is verified using experiments on simple and continuous beams with internal or external tendons.