A NOVEL FINITE ELEMENT MODEL FOR RC STRUCTURAL WALLS

With the implementation of performance-based methodologies in modern seismic codes and assessment/rehabilitation guidelines, reliable modeling of the nonlinear seismic response of reinforced concrete (RC) structural walls has recently gained much importance among both researchers and engineers. However, typical fiber-based modeling approaches, which are currently used in the vast majority of real-life performance-based design applications, fail to consider critical behavioral characteristics of walls, such as plane sections not remaining plane (especially in walls with non-rectangular cross-sections), development of nonlinear shear deformations, shear ductility, shear strength and stiffness (defined mechanically versus using code equations), the influence of shear on flexural ductility, and the influence of flexural ductility on shear strength (shear-flexure interaction behavior). Improved modeling approaches are needed to accurately, using a mechanical approach, the generalized seismic response characteristics of RC walls at both global (load vs. displacement behavior, load capacity) and local (deformation and strain) response levels. Accordingly, this paper aims to summarize a recent research effort aimed to develop, experimentally-validate, and implement into OpenSees, a relatively simple yet robust finite element modeling methodology for RC walls. A novel finite element model formulation, referred to as the Layered Fixed-Strut-Angle-Finite Element (LFSAFE) model, will be introduced. Working principles of the model, including its hysteretic in-plane membrane behavior, its layered-shell out-of-plane formulation, and definition of its drilling degrees of freedom (that allow connectivity with beams or coupling beams), will be described. OpenSees implementation of the model and experimental validation of the model will also be presented via simulation of quasi-static tests conducted on wall specimens with U-shaped cross-sections as well shake table (E-Defense) tests conducted on full-scale buildings. The LFSAFE model will, therefore, be presented as a reliable and experimentally-validated candidate to be used in nonlinear response history analysis of structural systems incorporating RC walls, in which the critical seismic response characteristics of walls are simulated in a purely mechanical manner, as opposed to using code-prescribed equations or code-recommended performance criteria.