Structural response, health monitoring, and performance evaluation of CFRP post-tensioned, in-service, long-span, precast/prestressed box girder bridges

Abstract

Two severely deteriorated long-span, precast, prestressed, box-girder bridges, located in Defiance, Ohio, were selected by the Federal Highway Administration’s (FHWA’s) Innovative Bridge Research and Construction Program for rehabilitation using advanced carbon fiber polymer (CFRP) composite materials, full-scale live-load testing, and long-term structural health monitoring. The root cause of deterioration was an improper deck drainage scheme, which had enabled the de-icing salts and water to corrode the prestressing strands and spall the concrete. Sika’s CFRP stress-head system, a post-tensioned and bonded external strengthening technique, was utilized to restore the original load carrying capacity of the deteriorated beams. An integral component of the rehabilitation plan was a long-term, structural health monitoring system (SHM), installed to monitor the performance of selected beams on the bridges. The structural health monitoring system consisted of vibrating wire strain gages with integrated thermistors to monitor changes in strain and temperature on 11 beams on the bridges. The data compiled reveal that compression is induced in the bottom of the deteriorated beams, thereby improving the load-carrying capacity. The use of the external Stress Head post-tensioning system proved to be a viable and effective means to strengthen a deficient box girder bridge. In addition, a series of full-scale live load tests were conducted prior to and following the completion of bridge rehabilitations. Strain transducers were employed to monitor the structural response under the multiple passes of truck loads. An overview of the compilation of the short-term live load test results and long-term structural health monitoring data is presented in this manuscript. The behavior of both bridges in terms of strain response history is summarized.