State Transformation Procedures for Fiber Beam-Column Element in Inelastic Dynamic Time History Analysis for Moment-Resisting Frames

Based on full understanding of the characteristics of sparse distribution of inelastic deformation in the ends of beams and columns of moment-resisting frames subjected to strong earthquakes, state transformation procedures (STPs) for fiber beam-column elements are proposed to accelerate inelastic time history analysis of moment-resisting frames. In STPs, as a default, all sections in fiber beam-column elements are simply simulated by predetermined linear moment versus curvature-resisting force models until nonlinearity occurs. Once nonlinearity develops, these linear models will be replaced smoothly with those determined by corresponding nonlinear fiber sections. Section state judgment and state transformation of STPs for either displacement- or force-based fiber beam-column elements are discussed in detail, as well as an assessment of computational efficiency. The effects of some factors on the acceleration ratio of analysis using STPs are comprehensively investigated on two example moment-resisting frames, i.e., a reinforced concrete (RC) frame and a steel frame. The results from the example study indicate that the proposed STP is computationally efficient both for RC and steel frames with remarkably high accuracy, especially for RC frames, even with high peak ground acceleration (PGA) levels. The so-called acceleration ratio of STP, compared with ordinary procedures, is closely related to the transformation ratio, which increases with an increasing PGA level. Lower transformation ratios could yield more desirable efficiency. In addition, the computational efficiency of STPs can also be affected by some other factors, e.g., the type of materials, numerical integration scheme, number of integration points, type of fiber beam-column elements, spectral characteristics of earthquakes, etc.