Software frameworks for the computational simulation of structural systems

The performance-based engineering paradigm requires advanced algorithms and numerical models to simulate the response of structural systems to the complex loadings induced by seismic excitations. In addition, performance-based engineering incorporates parameter sensitivity in structural simulation to identify the controlling parameters and the most significant sources of uncertainty during each phase of the structural design and assessment process. Flexible and reusable software designs and implementations are required to support the performance-based engineering methodology for structural simulation. The modeling hierarchy for the nonlinear finite element analysis of structural systems consists of three levels: global, element, and material. For the frame finite element models commonly used in structural simulation, the element level is decomposed further to the geometric transformation and the basic system, and a distinction is made between stress resultant and stress-strain models at the material level. Software abstractions represent each level in the modeling hierarchy and software design patterns permit complex implementations of force-based beam-column element, section constitutive, material stress-strain, and uniaxial hysteretic behavior to be built from simpler, reusable components. Plastic hinge integration methods for force-based beam-column elements overcome the problems with non-objectivity and localization posed by distributed plasticity integration methods. An optimal plastic hinge integration method, derived from the Gauss-Radau quadrature rule, integrates deformations over a characteristic length at the element ends and maintains the correct numerical solution for linear curvature distributions. The derivation of the response sensitivity with respect to material and geometric parameters in the force-based element formulation shows the effect the integration method has on the element response. The software design associates a beam-column element with several integration methods and includes response sensitivity computations. At the global level, the software design incorporates accelerated Newton algorithms for the efficient solution of the structural equilibrium equations. The rate of convergence for these methods is comparable to that of conventional Newton methods, while reducing the number of matrix factorizations required to reach equilibrium. The simulated response of a multi-story reinforced concrete structure demonstrates the modeling capability and the computational scalability of the software framework for the nonlinear finite element analysis of structural systems.