Impact of lean-on bracing layouts on system stiffness behavior

Stability is a critical limit state for bridges during construction and requires the installation of intermediate bracing, typically that of cross-frames with single-angle members, to prevent lateral torsional buckling. These stability braces are often a cause of concern in skewed bridge systems due to the increased difficulty of installation and long-term maintenance issues caused by fatigue stresses. Removal of cross-frame diagonals in strategically selected bays has become an attractive design option, leveraging on lean-on bracing concepts already utilized in frames in the building industry. When utilized correctly, lean-on bracing can increase the pliability of bracing lines during construction-easing erection, reducing fabrication costs, and minimizing long-term fatigue issues. Past studies on lean-on bracing such as TxDOT Project 0-1772 and 5-1772, have provided initial design guidance on cross-frames distribution, and the corresponding stiffness and strength behavior of the cross-frames installed alongside lean-on struts. However, these initial investigations are not without limitations which have led to the necessity of improved design guidance on lean-on bracing behavior. This dissertation addresses the uncertainties regarding the impact of cross-frame distribution on the individual system stiffness components and the overall behavior of lean-on bracing systems. The performance of several cross-frame configurations was analyzed using finite element analysis to codify new design guidance on bracing layouts. The chapters included in this dissertation provide an in-depth look at the methodologies and parametric studies conducted as well as a summary of the behaviors in the form of actionable design recommendations.