Built-up shear links as energy dissipators for seismic protection bridges

The use of shear links as hysteretic energy dissipators in eccentrically braced frames for buildings has become an attractive means of reducing the lateral demands imposed by large earthquakes.; The purpose of the large-scale experiments was to determine the deformation capacity, maximum resistance and ultimate failure mode of built-up shear links by applying incrementally increasing cyclic plastic deformations. Two experiments utilizing conventional A709 Grade 345 MPa (50 ksi ) steel confirmed the viability of built-up sections where the deformation capacity exceeded the minimum specified by the AISC Seismic Provisions for rolled shapes. High performance steel A709 HPS 485W (70W) was utilized to further extend the design options for built-up shear links. The results of the experiments illustrated the suitability of using this grade of steel for seismic applications as the ultimate failure mode and deformation capacity were similar to the conventional steel grade links. Typical failure mode initiated with cracks in the web at the stiffener connections and propagated along the heat affected zone leading to progressive web tearing and ultimate failure at approximately 0.12 rad. The nominal design shear capacity of the links was the same, yet the ultimate shear strength was found to be significantly less for the link utilizing high performance steel. The overstrength ratio for the high performance steel link was 1.4 as compared to approximately 2.0 for the conventional grade links.; Low yield point (LYP) steels with specified yield strengths of 100 MPa (14.5 ksi) and 225 MPa (33 ksi) were utilized to develop three types of shear links with low web compactness and without stiffeners. Two types of deformation history were used to evaluate these types of shear links; incremental cyclic and near-fault histories. The links exhibited ductile hysteretic behavior under both deformation histories, with the ultimate deformation capacity of approximately 0.20 rad significantly exceeding the links where stiffeners were used. The improved deformation capacity was achieved by eliminating welding from the web of the link and reducing the plastic shear strain demand as a direct result of excluding intermediate stiffeners. However, the shear strength was found to vary among the different designs, with recorded overstrength ratios ranging from 1.9 to 4.9. The latter case resulted in connection failure prior to reaching the ultimate deformation capacity in those cases, emphasizing the need for accurate estimation of overstrength. (Abstract shortened by UMI.)...