Until now, for evaluation of load-carrying-capacity for highway bridges, rating factor has been calculated first depending on the load-carrying-capacity, and then response modification factors have been reflected to take into consideration of an actual behavior of a bridge through load test. However, in the current evaluation method, the main response modification factors-response ratio and measured impact factor-are determined by the subjective judgment of an evaluator. For the reason, even in the bridges that have the same construction period or structure type, load-carrying capacity had large deviation, or the evaluation result was greatly different from condition rating often. In addition, because of field conditions that make it difficult to conduct load test of a bridge, it is impossible to evaluate load-carrying-capacity.
In order to improve the current evaluation method of load-carrying-capacity and propose a more objective and consistent evaluation method, this study statistically analyzed actually measured data of in-depth safety inspection and initial inspection reports about around 970 bridges.
According to the analysis, more than 50% of the bridges had rank C in which serviced time of a bridge is more than 15 years, and even bridges with rank D began to be found. In addition, among bridges with rank C and lower, some were found that their load-carrying-capacity fell short of their design based load-carrying-capacity.
As an improvement plan for load-carrying-capacity evaluation method, it was reasonable to take into account the effects of additional loads considered in the design step, including creep and shrinkage, in order to evaluate the load-carrying-capacity in the safety side in consideration of actual stress imposed on a bridge. According to analysis model, it was judged that by applying static load test results to improve actual behavior of a bridge sufficiently, it was possible to prevent load-carrying-capacity from being over-or under-evaluated. It was judged that it was reasonable to use measured values if measured impact factors exceeded designed impact factor because of stiffness reduction, and otherwise, to apply designed impact factor. In addition, it was judged that in order to analyze the change in load-carrying-capacity with a rise in served time, it was reasonable to correct weight of test vehicle on the basis of the recent diagnosis times in calculating response modification factors, and to apply designed impact factor to exclude diverse errors occurring in load test and obtain consistent evaluations results.
This study compared the existing rating factor with the rating factor in reliability-based load-carrying-capacity evaluation method which has the same basic concept as Korean Highway Bridge Code : limit state design code, and proposed a load-carrying-capacity evaluation method reflecting state rank in order to evaluate load-carrying-capacity of a bridge hard to apply to load test because of its field conditions. And this study applied the proposed method to sample bridges which already performed actual precision safety diagnosis, and conducted a comparison analysis with conventional load-carrying-capacity evaluation results.
It is judged that the improved evaluation method of load-carrying-capacity proposed in this study will be used to evaluate load-carrying-capacity of a bridge more objectively and to make preventive maintenance efficiently for bridge reinforcement cycle, determination of a priority, and estimation of reasonable served time.