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Report No.: CCEER-04-8

Title: Built-up Shear Links as Energy Dissipaters for Seismic Protection of Bridges

Authors: Peter Dusicka, Ahmad Itani and Ian Buckle

Date: November 2004

Sponsoring Agency: California Department of Transportation (CalTrans) and Federal Highway Administration (FHWA)

Performing Organization:
Department of Civil Engineering/258
University of Nevada, Reno
Reno, NV 89557

Abstract:

A variety of applications of built-up shear links can be realized for the seismic protection of bridges. The objective of this research was to investigate the inelastic behavior of built-up shear links through the use of large-scale experiments and detailed numerical analyses. 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 grade steel confirmed the viability of utilizing built-up sections. The use of high performance steel was then implemented to further extend the design options and illustrate the suitability of this grade for seismic applications. Low yield point steels 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 significantly exceeding the links where stiffeners were used. The improved performance was a direct result of excluding intermediate stiffeners which eliminated welds and reduced shear strain demand. However, the shear strength was found to vary among the different designs. The major shear strength contribution was found to relate to the grade of steel and minor shear strength contributions were found by parametric numerical studies to originate from the web the flanges as well as the stiffeners. These results led to the development of a relationship for plastic shear strength of built-up shear links that reflected the trends obtained from the parametric studies. An expression was developed that effectively correlated with experimental results and conservatively estimated the shear link overstrength. Based on the results of the experimental and numerical research, built-up shear links were shown to be effective hysteretic energy dissipators. The importance of estimating the link overstrength was illustrated and design recommendations developed.

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