A fiber beam element based on plastic and damage models for prestressed concrete structures

Modeling of prestressed concrete beams and their degrading processes are relevant issues in the assessment of existing structures and infrastructures, particularly for bridges. This work focuses on the formulation and validation of a fiber beam finite element for prestressed concrete structural elements that accounts for nonlinear material behavior and time-dependent phenomena. The element is a 3D Timoshenko beam that follows a force -based approach. A fiber discretization of the cross-section is used to model concrete, steel reinforcements and prestressing cables based on damage and plasticity for concrete, and plasticity for steel through three-dimensional constitutive laws. The steel fibers are fully bonded. Strain-softening in the concrete requires an appropriate regularization procedure. The tendons are treated as additional fibers with prestressing applied as initial strain of the relevant fibers. No additional discretization is required except for the description of the tendons' profile. Time-dependent phenomena such as creep, shrinkage and cable relaxation are taken into account. The proposed model is implemented in the OpenSees computational framework to carry out specific validation tests and demonstrate the element potential.