Assessment of basic steel I-section beam bracing requirements by test simulation
Prado, Evan Peter
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Appendix 6 of the ANSI/AISC 360-10 Specification provides methods for assessing the required stiffness and strength for basic bracing of columns and of beams. Substantial evidence exists showing that the Appendix 6 equations provide an accurate characterization of the stability bracing requirements, particularly when various refinements from the AISC Commentary are employed. Nevertheless, the development of these equations is based largely on elastic stability theory and various practical approximations are invoked to make the equations useful for design. Some of the important approximations relate to the handling of member inelasticity as well as the influence of member continuity across brace point locations. To the knowledge of the author, no comprehensive studies have been conducted to date to evaluate the specific nature of these approximations. Furthermore, the current Appendix 6 provisions do not recognize the benefits of combined lateral and torsional bracing. Limited prior research studies have shown substantial reduction in the demands on the individual bracing components by using them in combination. This thesis presents a methodical and comprehensive study of basic beam bracing behavior via refined FEA test simulation. Various point (nodal) lateral, shear panel (relative) lateral, point torsional, combined point lateral and point torsional, and combined shear panel lateral and point torsional bracing cases are studied for representative beams subjected to uniform bending. Detailed comparisons to the current Appendix 6 rules are provided, where applicable, and recommendations for improvements are forwarded. Specific questions addressed in this research are: • What is the effect of inelasticity on the bracing response and requirements? • What is the influence of member continuity across the brace points on the bracing response and requirements? • What are the benefits of combined torsional and lateral bracing when the lateral bracing is placed on the compression flange versus when it is placed on the tension flange.