An analysis procedure to facilitate performance-based design of steel moment frame buildings with reduced beam section joints

During the 1994 Northridge, CA earthquake weldments in the beam-to-column connection failed, revealing deficiencies in the structural steel design codes. One result of the failures has been a push for improved analysis techniques that give information about the response of a structure to loading in addition to information about capacity provided in existing design codes. In order to develop reasonable design methods, the structural engineering community must describe the constitutive behavior of a structure under lateral loading and identify and quantify its potential failure modes. The focus of this study is to address the former of these two issues for moment resisting frames (MRFs) with reduced beam sections (RBSs).; To the end of developing analytical methods for a nonlinear dynamic structural analysis (one component of a performance-based design), a MRF subassemblage constitutive model has been defined. The subassemblage load-displacement relationship is determined using mechanics of materials theory by isolating the contribution of the frame's components (RBS, panel zone, and elastic portions of the beam and column). The model has been verified analytically via finite element analysis and experimentally via tests of full-scale beam-column subassemblage specimens. The end result of the modeling is a computationally efficient FORTRAN program that accurately predicts the constitutive behavior of a MRF with a RBS.; The utility of the MRF constitutive model is demonstrated in a nonlinear dynamic analysis of a hypothetical 13-story office building in Southern California. Unlike a traditional multi-degree of freedom dynamic analysis, the degrees of freedom fall at the mid-story height because of the MRF subassemblage geometry. The element constitutive relationship is then used to determine the inelastic stiffness matrix for the dynamic analysis. By predicting the component contribution to the hysteretic response, the analysis might be easily coupled with local failure analyses once reasonable methods are developed to determine weldment fracture and RBS local buckling.