Torsional Brace Strength Requirements for Steel I-Girder Systems

Abstract

Effective stability bracing of beams can be achieved by either preventing lateral movement of the compression flange or restraining twist of the beam cross section. Bracing that restrains twist is aptly referred to as torsional bracing. Adequate stability bracing must satisfy both stiffness and strength requirements. The torsional brace strength requirement in the latest edition of the AISC specification (2016) was significantly changed from the previous edition of the specification (2010). This paper presents a parametric study on the strength requirements of beam torsional bracing. An overview of the many factors affecting bracing behavior is provided. The paper demonstrates that the latest expression results in brace strength predictions that can be significantly nonconservative. The paper recommends a return to the strength provisions provided in previous editions of the specification.