Reliability Of FRP Strengthened Reinforced Concrete Simple Supported T-beam Bridges In Flexure

Strengthening of reinforced concrete structures with Fiber reinforced plastic (FRP) is quite widely applied for its advantages over classical structural materials in strengthening of structures. However, as a new composite structure composed of existing bridge, FRP and epoxy resin adhesive, the strengthened bridge’s performance is more difficult to be evaluated. Both the capacity and load effect of existing bridge and mechanical property of FRP fabrics/plates would influence performance of the strengthened bridge. Meanwhile, uncertainties exist in the evaluation because of limited cognitive ability and randomness in manufacturing and construction process of FRP. To take the uncertainties into account, reliability based method is needed to analyze the performance of strengthened bridges.To analyze the performance of existing bridges, a new vehicle load effect model was proposed. Based on the stationary binomial random process which is commonly used to model the vehicle load of highway bridge, an updating coefficient and a reduction coefficient were introduced into the vehicle load model to update the prior distribution specified in design code. Through the introduced coefficients, influence of actual traffic volume and expected service life of existing bridge on vehicle load effect could be considered. For the carrying capacity of existing bridges, a condition based evaluation method was adopted. Several coefficients of load-bearing capacity and a coefficient considering the uncertainty roots from the subjective inspection results were used. Through the analysis, the range of reliability of bridge in each condition state was obtained.As a quasi-brittle material, FRP’s strength would change with specimen size. In this study, the size effect was also considered in the determination of statistical characters of FRP strength. Based on the chain-of-bundles model for size effect analysis of fiber, a series-parallel model for FRP was proposed. The changing of mean, coefficient of variation, and distribution type of strength with size were analyzed. The result can be used in the calculation of the reliability of FRP strengthened structures.Strengthen requirement of the existing bridges and strengthen ability of the FRP materials were investigated. On the basis of the pre-mentioned models, a series of FRP strengthened bridges were designed considering different initial condition states of existing bridges. Reliability indexes of the strengthened bridges were calculated. In addition, sensitivity analysis was also conducted to determine the influence of each random variable on the reliability. Costs of the strengthening works were also analyzed and a probabilistic cost forecasting function, which might be useful for bridge managers, was proposed.