Cyclic Testing of Built-Up Steel Shear Links for the New Bay Bridge

Abstract

Tests were conducted on two prototype steel shear links for the main tower of the new San Francisco-Oakland Bay self-anchored suspension bridge to evaluate the link force and deformation capacities. The links were built-up wide-flange sections, designed to yield in shear. A quasi-static loading protocol was used to test the links in reverse curvature, simulating the expected seismic demand. The link capacities exceeded the predicted demands from the Safety Evaluation Earthquake. The specimens behaved in a ductile manner until small cracks initiated at the end of the vertical fillet welds connecting the intermediate stiffeners to the link web. As the cracks propagated further, brittle fracture of the web ensued. The maximum shear strength was nearly twice the expected yield shear strength, a significantly higher overstrength than current codes recognize. Alleviating the stress concentration on the vertical fillet welds of the intermediate web stiffeners is necessary to avoid brittle fracture and to increase the link deformation capacity. Analysis showed that offsetting the fillet welds from the web-flange-stiffener intersection reduced the demand at the end of the weld.