Evaluation of Steel Girder Bridge Strengthened with Carbon Fiber–Reinforced Polymer Posttension Bars

This project investigated the effectiveness of carbon fiber–reinforced polymer (CFRP) composite materials to strengthen an existing, structurally deficient steel girder bridge. The bridge selected for strengthening with the CFRP posttensioning system is a three-span continuous steel stringer bridge on IA-141 approximately 1.6 mi west of Bayard, Iowa. The research program consisted of several tasks, and the main emphasis was the installation of the strengthening system and associated field testing. The bridge was instrumented to measure strain at selected critical locations and tested before installation of the posttensioning system, shortly following posttensioning, and after approximately 1 and 2 years of service to assess changes in behavior resulting from the addition of the posttensioning system and time. During the application of the posttensioning strengthening system, strain was measured to investigate the response of the bridge to the applied posttensioning forces. After the last follow-up test was completed, the posttensioning force was removed (and reapplied) to investigate any loss of posttensioning force that may have occurred during the 2-year period. In general, the installation of the posttensioning system required no special equipment or training other than access equipment, an acetylene torch to remove a portion of several diaphragms, and a hydraulic jack. A three-person crew was able to install the system in just over 1 day. On the basis of an analysis performed by using an HS-20 truck, it was found that the posttensioning strengthening system reduced the dead and live load induced moments by approximately 3% to 5%, allowing the bridge to carry additional live load.