Fracture Damage Assessment and Monitoring of Cable Stayed Bridge Tie Down Anchorages

摘要

CTLGroup and Michael Baker Jr engineers assisted the West Virginia DOT in evaluating and monitoring the causes and consequences of tie down anchor bolt fractures at the Veterans Memorial Cable Stayed Bridge. Starting in 2004, cracks had been discovered in several of the 20, 3-inch diameter threaded anchor bolts encompassing the 2 anchorage arrays, during periodic bridge inspections by the Michael Baker inspection team lead by one of the authors. This cracking prompted the need for progressively more frequent inspections and emergency-basis bolt repairs. The structural evaluation and monitoring program served as the basis for development of design criteria for interim and permanent structural repairs. The structural evaluation program described in this paper included: estimation of load distribution and variation in the anchor bolts using vibration methods; monitoring of strain fluctuation in all 20 anchor bolts and the cable stayed superstructure linkage, using an automated structural health monitoring system, including implementation of real time alerts signaling potential bolt fracture; and fracture analysis of broken bolts to determine fracture origins and potential causes for the observed failures. Based on anchorage structural behavior data gathered using the structural monitoring system, over an 8-month interval, designs for both interim and permanent tie down anchorage structural retrofits were developed by Michael Baker and HNTB. Repairs commenced in November, 2008 and were completed May, 2009.