LIFETIME RELIABILITY ANALYSIS OF ULTIMATE LIMIT STATES FOR EXISTING PRESTRESSED CONCRETE BRIDGE

摘要

Highway bridges are exposed structures that are continuously subjected to attack from the surrounding environment. In contrast with vehicular collision damage, environmental damage occurs gradually over time, and often goes undetected until significant damage has occurred. Such as sulfate attack, Alkali-silica reaction, Freeze-Thaw cycle attack, corrosion and so on. All of the environmental factors that can be harmful to reinforced concrete and reduction of structural reliability during their service life. In the present paper, the time-variant reliability of flexural capacity of prestressed concrete bridges under ultimate limit state is mainly concerned. A typical simply supported existing prestressed concrete T-beam bridge widely used in Chinese highway is discussed. The post-tensioned concrete girders of spans ranging from 20 to 40m are considered. The limit state function and random variables are separately derived from the code for design of highway reinforced concrete and prestressed concrete bridges and unified standard for reliability design of highway engineering structures. For all of the degradation in structural performance, chloride-induced reinforcement corrosion is emphasized. In addition, the loading model and probabilistic properties of corrosion models are developed. Through integrating first order reliability method (FORM) and time discretized approach, and varying the mean value and coefficient of variance of those variables, the lifetime reliability of ultimate limit states for existing prestressed concrete bridges are evaluated.