Reliability Evaluation Of Highway Prestressed Concrete Bridge

Following Unified Standard for Reliability Design of Engineering Structures (GB50153-92), two limit states, i.e., ultimate limit state and serviceability limit state must be carried in structural design. A great amount of important works, which are presented in various Unified Standards, have been contributed to reliability analysis of ultimate limit state. However, for serviceability limit state reliability analysis, comparably rare work can be found, and further research in this field is strongly required, which include the work in Unified Standard for Reliability Design of Highway Engineering Structures (GB/T 50283-1999), especially for the prestressed concrete bridge which appeared comparatively late. In this thesis, reliability of prestressed concrete bridge is investigated based on two editions of design code for highway bridges and culverts.First, the basic theory and several computation analysis methods of reliability are discussed, and the First Order Reliability Method (FORM) and Monte-Carlo method are emphasized.On the basis of previous studies, two basic sorts of variables, i.e., structural effect and resistance, are introduced, and corresponding random influence factors are discussed. Load including dead load and vehicle load is one of the major factors influencing bridges, and is considered to be random variables. According to the in-situ investigation data from home and abroad research, the stochastic models of dead load and vehicle load are introduced. It is assumed that the dead load follows normal distribution, and the vehicle load follows Type I extreme value type, which is devided into general traffic and dense traffic states. Statistical characteristics of variables about resistance are also given.The typical prestressed concrete beams with span of 25m to 40m specified in Chinese General Drawing Collection for Highway Bridges and Culverts (JT/GQS 024 - 83) are mainly considered. The ultimate limit state of bending and serviceability limit state of cracking and compressive stress resistance implied in the Chinese current code for design of highway concrete bridges and culverts (JTG D62 -2004) and its predecessor (JTJ 023 - 85) is adopted. The reliability indices of resistance are computed, and sensitivity analysis is carried. The results indicate that the reliability indices obtained from the two considered code can meet the requirement of the " unified standard ". The main influencing factors are also obtained.