Software Patterns for Nonlinear Beam-Column Models

A framework for simulating the material and geometric nonlinear response of frame members is developed from the equations of beam mechanics. The implementation of a beam-column finite element is reduced to the state determination procedure for a basic system that displaces and rotates with the element. An abstraction for geometric nonlinearity represents the kinematic and equilibrium transformations between the basic and global reference systems, while an abstraction for force-deformation response represents material nonlinearity for the basic system. Separate objects encapsulate material stress-strain behavior and cross-sectional integration in order to increase the modeling flexibility for computing the response of fiber-discretized cross sections. Multiple forms of distributed plasticity in beam-column elements are incorporated in the framework through objects that encapsulate one-dimensional quadrature rules. Software design patterns are utilized to create complex beam-column simulation models by composition of basic building blocks. The modeling flexibility of the software design is demonstrated through the simulation of a reinforced concrete column.