The ANSI/AISC 360-10 Appendix-6 provisions provide limited guidance on the bracing requirements for beam-columns. In cases involving point (nodal) or shear panel (relative) lateral bracing only, these provisions simply sum the corresponding strength and stiffness requirements for column and beam bracing. Based on prior research evidence, it is expected that this approach is accurate to conservative when the requirements can be logically added. However, in many practical beam-column bracing situations, the requirements cannot be logically added. This is because of the importance of the brace and transverse load position through the cross-section depth, as well as the fact that both torsional and lateral restraint can be important attributes of the general bracing problem. These attributes of the bracing problem can cause the current beam-column bracing requirement predictions to be unconservative. In addition, limited guidance is available in the broader literature at the current time regarding the appropriate consideration of combined lateral and torsional bracing of I-section beams and beam-columns. Nevertheless, this situation is quite common, particularly for beam-columns, since it is rare that separate and independent lateral bracing systems would be provided for both flanges. More complete guidance is needed for the proper consideration of combined bracing of I-section beams and beam-columns in structural design. This research focuses on a reasonably comprehensive evaluation of the bracing strength and stiffness requirements for doubly-symmetric I-section beams and beam-columns using refined Finite Element Analysis (FEA) test simulation. The research builds on recent simulation studies of the basic bracing behavior of beams subjected to uniform bending. Various cases of beam members subjected to moment gradient are considered first. This is followed by a wide range of studies of beam-column members subjected to constant axial load and uniform bending as well as axial load combined with moment gradient loading. A range of unbraced lengths are considered resulting in different levels of plasticity at the member strength limit states. In addition, various bracing configurations are addressed including point (nodal) lateral, shear panel (relative) lateral, point torsional, combined point lateral and point torsional, and combined shear panel lateral and point torsional bracing.

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.

The objective of this research is to evaluate the stiffness and strength demands on flange braces in metal building systems. This objective is accomplished by a targeted study of the effects of various attributes of metal building systems not fully addressed in existing bracing design procedures. Special emphasis is placed on attributes such as unequal brace spacing and stiffness, end brace point flexibility, nonprismatic member geometry, special requirements at knee joints and the specific configuration of combined girt/purlin, flange diagonal, diaphragm and X bracing systems used in metal building construction. A sub-objective of the research is the demonstration of how virtual test simulation via full nonlinear finite element analysis may be applied to solve a structural engineering research problem that would be difficult to address by any other means. When conducted properly, virtual test simulation can serve as a valuable companion to experimental testing since attributes such as residual stresses and critical geometric imperfections can be controlled precisely and with relative ease in virtual test simulation. Both highly simplified and more complex but relatively rigorous procedures are considered, with the ultimate goal being improved economy and safety of flange stability bracing in metal buildings.