The development of tubular eccentrically braced frames links for the seismic retrofit of braced steel bridge piers

There are many steel truss bridges in the United States and other countries that were constructed prior to 1940 when seismic demands on structures were not well understood. Many of these bridges are now considered seismically vulnerable. Contributing significantly to their undesirable seismic performance are the steel piers that support the superstructure. These piers typically have bracing members that are made up of channels or angles that are tied together with steel lacings and rivets. Recent experimental investigations have shown that such structural members can suffer severe local buckling, rapid strength degradation, and limited ductility, when subjected to cyclic loading. Therefore, it is necessary to develop retrofit strategies for these piers that focus on protecting, strengthening, or increasing the ductility of the existing brace members.; This report describes, categorizes, and uses selected qualitative measures to rate various retrofit strategies for steel truss bridge piers. Promising retrofit strategies that require fundamental research before they can be properly implemented are then identified. One such strategy is an eccentrically braced frame where the link is not subject to lateral torsional buckling. This is desirable since eccentrically braced frames have been shown to exhibit excellent seismic performance, and if lateral bracing of the link can be avoided, they can be implemented in bridge piers where lateral bracing can be difficult to provide.; Design equations were derived for links of eccentrically braced frames with hybrid rectangular cross-sections (hybrid meaning that the webs and flanges may have different yield stresses) accounting for compactness and stiffener spacings. Using the derived design equations, a proof-of-concept experimental study was designed and conducted. It is found that the hybrid rectangular link shows stable and ductile cyclic behavior with no sign of lateral torsional buckling, in the absence of lateral bracing.; A finite element parametric study was performed to investigate the effects of key design parameters for rectangular link cross-sections on link rotation capacity, energy dissipation, and overstrength. The models for the parametric study were validated by comparison with the proof-of-concept experimental study. Results of this parametric study are used to revise the proposed design recommendations and provide insight into the behavior of tubular links.; A second experimental program was then developed. This program tests fourteen links with cross-sections that were at the revised limits for web and flange compactness and four different link lengths. (Abstract shortened by UMI.)...