RETROFIT OF A THREE-SPAN SLAB BRIDGE WITH FIBER REINFORCED POLYMER SYSTEMS--TESTING AND RATING

A 45-year old, three-span reinforced concrete slab bridge with insufficient capacity was retrofitted with 76.2- and 127-mm wide bonded carbon fiber-reinforced polymer (FRP) plates, 102-mm wide bonded carbon FRP plates with mechanical anchors at the ends, and bonded carbon FRP fabrics. The use of four systems in one bridge provided a unique opportunity to evaluate field installation issues and to examine the long-term performance of each system under identical traffic and environmental conditions. Using controlled truckload tests, the response of the bridge before retrofitting, shortly after retrofitting, and after one year of service was measured. The stiffness of the FRP systems was small in comparison to the stiffness of the bridge deck, and accordingly the measured deflections did not change noticeably after retrofitting. The measured strains suggest participation of the FRP systems, and more importantly, the strength of the retrofitted bridge was increased. A detailed 3D finite-element model of the original and retrofitted bridge was developed and calibrated based on the measured deflections. The model was used to predict more accurately the demands for computing the rating factors. The addition of FRP plates and fabrics led to a 22% increase in the rating factor and corresponding load limits. During a one-year period, traffic loading and environmental exposure did not apparently affect the performance of the FRP systems. The increased capacity and acceptable performance of the FRP systems enabled the engineers to remove the load limits in order to resume normal traffic. Future tests are necessary to monitor the long-term behavior of the FRP systems.