Nonlinear Analysis of Steel Frames with Semi-rigid Connections Using the Capacity Spectrum Method

This report summarizes the development and application of a computeraided system for the inelastic analysis, evaluation, and design of threedimensional steel frames with sp.mi-rigid connections under static loading. Main components of the work include: (1) development of a model to represent the nonlinear moment-rotation response of partially restrained connections, (2) development of a matrix-based method for incorporating the connection model in a nonlinear finite element program for framed structures, (3) implementation of the connection model in CU-STAND, a workstation based program for interactive analysis and design of steel t ... ·!lmed structures, (4) computer implementation of the capacity spectrum met~od for estimating inelastic seismic response using modal analysis, and (5) demonstration of the system for sensitivity studies on the inelastic response of a planar frame with semi-rigid connections. The connection mod~l is based on a four parameter power equation. Based on calibration to existing experimental data, sets of normalized parameters are proposed for use where more exact values based on test data are not available. Through a case study. overall frame response is found to be relatively insensitive to variations in the connection response parameters. The case study also includes application of the capacity spectrum method to investigate the inelastic limit state under seismic loading and comparisons are made with results based on equivalent static code-based loading.