INFLUENCE OF CHANGE OF VEHICLE LOADS ON FATIGUE RELIABILITY OF STEEL HIGHWAY BRIDGES

1994年2月修订的新版《日本公路桥规范》中，根据交通车辆标准的修订，将设计车辆荷载由20Tf改为25Tf。设计车辆荷载的变化被认为与旧版规范设计的既有公路桥梁疲劳可靠度的降低有关。本文首先通过对典型钢梁桥的疲劳可靠度分析，对其影响进行了评估。采用概率断裂力学模型和蒙特卡罗模拟技术，对连接中央横梁和主梁腹板的竖向加劲肋进行了分析。其次，研究了Highaway桥梁维修加固的规划方法。在此基础上，对公路桥梁刚构钢桥墩在地震作用下的可靠性进行了评估。主要研究结果如下：(1)交通车辆设计荷载的变化对新旧规范设计桥梁的疲劳可靠度有较大影响。提出了一种最大化期望总成本效益的优化方法。对混凝土桥梁进行了疲劳可靠性分析，但没有得到特别提到的结果。(4)评估了按许用应力设计法(ASDM)设计的既有公路桥梁钢管的可靠度水平，并详细分析了地震荷载效应对桥墩结构可靠度的影响。指出了ASDM的一些不足之处。

In the new version of Japanese Highway Bridge Specifications revised in February, 1994, the design vehicle load is changed from 20 tf to 25 tf according to revision of the standard of the traffic vehicles. The change of design vehicle load is considered to be concerned with the reduction of fatigue reliability of existing highway bridges designed by the old version of the specifications. In this study, first, the influence is estimated by the fatigue reliability analysis of typical types of steel girder bridges. The analysis is performed for the vertical stiffeners connecting the central transverse girder to the web of the main girders by the use of a probabilistic fracture mechanics model and Monte-Carlo simulation technique. Second, a planning method of repair and reinforcement for highaway bridges is investigated. Furthemore, the reliability evaluation of rigid-frame steel pires of highway bridges subjected to earthquake load is done. The main results obtained in this study are as follows :(1) The change of traffic vehicle design load give a large influence on the fatigue reliability of bridges designed by the new version of the specification as well as the old one. The investigations for maintenance such as reinforcement and repair are required.(2) A optimization method which maximize the expected total cost benefit is introduced. The optimal method is introduced to determine the total number of repair, type of repair, and the time required for repair.(3) The studies on the fatigue reliability analyzes are performed for concret bridges, however, the results mentioned specially are not obtained.(4) The reliability levels for steel pires of existing highway bridges designed by the allowable stress design method (ASDM) are evaluated, and then the influence of load effect due to earthquake on reliability of pier structures is examined in detail. Some shortcomings of the ASDM are pointed out.