Flexible Moment Connections for Unbraced Frames Subject to Lateral Forces — A Return to Simplicity

It seems that there has been confusion among structural engineers about the type of construction referred to in the AISC Load and Resistance Factor Design Specification for Structural Steel Buildings (AISC, 2000), since 1986, as Partially Restrained or PR. The general concept has been of interest to the authors for many years and has been the topic of several of their papers. The purpose of this paper is to reacquaint the profession with a longstanding and successfully applied approach to structural steel frame design, herein called "Flexible Moment Connections (FMC)," and to compare this approach to the Specification-defined PR approach. In addition, the goal is to show that although much has changed in the profession, including specifications and the tools for their application, FMC design remains an acceptable and economical approach for steel structures.