Steel moment frames: resolution of recent seismic detailing and material shape issues

Abstract

An area of heightened interest after the 1994 Northridge earthquake was the seismic ductility of steel moment frame connections. Work by the Federal Emergency Management Agency (FEMA) and Seismic Analysis Code (SAC), American Institute of Steel Construction Inc. (AISC) and many others over the last few years has expanded knowledge in a number of areas and provided a set of new and modified connection details for improved seismic performance. Some of the more popular connection types, such as the new reduced beam section (RBS) detail, will be described more fully later. Questions about the performance characteristics of the k-area region of wide-flange steel shapes were also addressed by AISC. Such regions contain variations in mechanical properties due to cold forming during the mill straightening process. Localized material properties in this region, such as strain hardening, yield and ultimate strengths, ductility and toughness are known to become altered. An extensive research effort sponsored by AISC was initiated to study the effects and performance of the k-area region is nearing completion. Such studies, conducted at four different universities, evaluated the cyclic inelastic strain behavior of rolled steel shapes, the performance characteristics of rotary and gag-straightened rolled column sections, assessed beam-to-column joint assemblies and updated the standard shape material properties database for improved design and reliability. This paper gives an overview of new seismic connection details for moment frames and summarizes the results of the k-area research effort.