Strengthening of Bridge Slabs with Frp Systems

Advances in the fields of polymers and composites have resulted in a major development of high strength fibre reinforced polymers (FRP). These materials offer great potential for cost-effective retrofitting of concrete structures. In response to the growing need for concrete repair and rehabilitation, an experimental program was conducted at the University of Manitoba in Winnipeg, Manitoba, Canada, to investigate the feasibility of using different strengthening techniques as well as different types of FRP in strengthening posttensioned bridge slabs. Half-scale models of a reinforced concrete bridge were constructed and tested to failure. The model, with dimensions of 8.5 x 1.2 x 0.4 meters, consisted of one simple span and two overhanging cantilevers. Each specimen was tested at three different locations. The first and second tests were perfonned on the two cantilevers with the load applied at the edge of each cantilever, while the third test was conducted on the mid-span. Three different strengthening techniques were investigated including embedded CFRP bars, strips and surface mounted reinforcement. Ultimate capacity, failure mechanism and cost analysis of various strengthening techniques for concrete bridges are presented. INTRODUCTION In an aggressive environment, concrete may be vulnerable to chemical actions such as carbonation and chloride contamination which breaks doWn the alkaline barrier in the cement matrix. Consequently, the steel reinforcement in concrete structures becomes susceptible to rusting and corrosion. Such a phenomena leads to further cracking and spalling of the concrete and even delamination of the concrete at the reinforcement level under more severe conditions. In the United States, nearly one third of the nation's 581,000 bridges were graded structurally deficient or functionally obsolete by the FHWA [Us DOT,1997]. A large number of these deficient bridges are reinforced or prestressed concrete structures, and are in urgent need of repair and strengthening. In the United Kingdom, over 10,000 concrete bridges need structural attention. In Europe, it is estimated that the repair of structures due to corrosion of rebars in reinforced concrete structures costs over $600 million annually [Tann and Delpark, 1999]. A possible solution to combat reinforcement corrosion is the use of non-corrosive materials to replace conventional steel bars. High tensile strength, lightweight, adequate ductility and corrosion resistance characteristics make FRP ideal for such applications. FRP also provides cost effectiveness and a practical technique for the repair and strengthening of structures and bridges using externally bonded sheets or prefabricated laminates. The City of Winnipeg, Manitoba, Canada is considering upgrading a concrete bridge constructed thirty years ago using embedded FRP reinforcement. The analysis conducted using current codes indicated that the flexural strength of the bridge deck is not sufficient to withstand modem truck loads. To accommodate the HSS30 AASHTO truck design load, the analysis indicates a need of approximately