스피링계수를 고려한 응력보정에 따른 교량의 내하력 평가

Abstract

ABSTRACT

Load Carrying Capacity Assessment of Bridges with Stress Modification Considering Spring Stiffness

Jung Sung Yun Advisor : Prof. Park, Kil-Hyun, Ph. D. Department of Civil Engineering Graduate School of Chosun University

In safety diagnosis for determining the safety and load carrying capacity of bridges, the reliability of its results depends on field load test and structural analysis. Load tests for a bridge having a linear behavior characteristic should obtain responses of the same pattern regardless of load size but the similarity of pattern tends to be affected by the methods of gauge installation and connection, the measuring method, etc. Because there are not established rules on the position or condition of stress modification factor, the application of the factor is decided subjectively by the evaluator, and this often leads the evaluation of load carrying capacity to produce results with low objectivity. Moreover, analysis results may be different from actual behavior depending on the functionality of bridge bearing and structural analysis model. This study applied spring stiffness in order to evaluate load carrying capacity using measurement data obtained from load tests actively and utilizing various evaluation methods. In order to confirm the adequacy of structural analysis based on spring force and to improve the reliability of experiment results, we conducted a deflection test with flexural beams prepared as overhanging beams and, based on the results, performed precision safety diagnosis for real bridges under public service for improving the load carrying capacity evaluation method for bridges under public service. In the results of the bending test, compared to deflection calculated by the existing method, deflection obtained by applying spring stiffness was closer to the actually measured deflection. When load carrying capacity was evaluated by the grid analysis model, the deviation of load carrying capacity according to position was not large and the obtained load carrying capacity was similar to that obtained by the existing method. When load carrying capacity was evaluated by the shell analysis model, however, deviation from that obtained by the existing method was too large and the somewhat complicated process to obtain spring stiffness caused a difficulty in application. In the results of evaluating load carrying capacity for a simple support RC T beam bridge whose period of public use was 23years, the rating factor under public service based on spring stiffness was 1.47~2.36, which was smaller than 2.24~2.81, the rating factor evaluated by the existing method. In the results of evaluating load carrying capacity for a 3?]span continuous steel box girder bridge just after its completion, the rating factor under public service based on spring stiffness was 2.02~ 2.43, which was smaller than 2.48~2.88, the rating factor evaluated by the existing method. In the results of evaluating load carrying capacity for bridges different in terms of support type, used material, and superstructure type using the existing method and spring stiffness, load carrying capacity by spring stiffness was smaller by up to 39% than that by the existing method although in some cases the former exceeded the latter. The decrease of load carrying capacity was particularly larger in external girders than in internal girders. When the load carrying capacity of bridges is evaluated by the existing method the results vary among engineers due to lack of guidelines for evaluation such as the application of stress modification factor. This study was conducted as an effort to solve this problem through active research. There should be further studies on the methods of evaluating the load carrying capacity of bridges in order to produce data of broad diversity and high reliability and to improve the accuracy and efficiency of bridge safety diagnosis as well as bridge maintenance and management conducted with national budgets.