Experiments, analysis, and design improvement for new-generation buckling-restrained braces (brbs)
T h e U n i v e r s i t y o f U t a h G r a d u a t e S c h o o l STATEMENT OF DISSERTATION APPROVAL The dissertation of Wenjing Xu has been approved by the following supervisory committee members: Pantelides, Chris P. , Chair ABSTRACT Buckling-restrained braces (BRBs) are widely used in new and existing buildings to enhance their performance during large earthquakes. The new generation BRB has connection plates welded perpendicular to core plates, which makes the manufacturing easier compared
... ng easier compared to current construction. The new generation BRB has two connection plates on each end, which makes the pinned end, bolted end, and welded end much easier to construct and connect the BRB to buildings. Nine full-scale experiments carried out in this research demonstrates the ability of new generation BRBs to perform equally well as current generation BRBs. Research has been done for the buckling force of the core plate and the contact force between concrete and core plate for conventional BRBs, but specific equations for buckling force and contact force considering the friction between concrete and core plates have been developed when the core plate buckles in a number of waves for strong-axis buckling. A theory based on the strut-and-tie model was developed to predict strong or weak axis buckling for a given BRB. In addition, finite element models were developed which are compared to the analytical results for determining the occurrence of strong-axis or weak-axis buckling, as well as the magnitude buckling load. Allowable ratio of lateral force to BRB axial compressive capacity for a certain casing length and cross-section is determined using finite element analysis, at which BRBs can deform up to 2% interstory drift without global buckling. Simulation of the iv hysteretic performance of the nine BRBs tested in full-scale experiments is carried out using finite element analysis with quasistatic cyclic loads, and the results are then compared to the experiments. Finally, the factors which effected the out-of-plane buckling of the gusset plate in one of the experiments are investigated and measures to prevent this are offered.