Algorithm for Hysteresis Analysis of Prestressed‐Concrete Frames

The descending part of the hysteretic load‐deformation history of a structure with softening behavior discloses important structural properties such as strength, ductility, residual deformation, hysteresis loop shape, and energy‐dissipation capacity, especially under earthquake conditions. In the present paper, a finite‐element algorithm for hysteresis analysis of bonded and unbonded prestressed‐concrete frames subjected to arbitrary loading history including postultimate descending portion is put forward. One‐dimensional constitutive models for concrete, tendon, and reinforcing steel are proposed. The crack‐contact effect is included in the constitutive model for concrete. A bond‐slip relation between tendon and grout is suggested. A method for implementing the bond‐slip relation into the element in which tendons are embedded is also put forward. Being of self‐correcting incremental type, the algorithm incorporates both increment‐force and increment‐displacement procedures whose transition from one into the other is automatically performed according to the variations of the hysteresis curve. The results of laboratory tests of three prestressed‐concrete frames are reported. Comparison of computed results with experimental ones shows good agreement.