Lifetime system reliability prediction for multiple structure types in a bridge network

Currently, the load rating is the method used by State Department of Transportations for evaluating the safety and serviceability of existing bridges in the United States. In general, load rating of a bridge is evaluated when a maintenance, improvement work, change in strength of members, or addition of dead load alters the condition or capacity of the structure. The AASHTO LRFD Specifications provide code provisions for prescribing an acceptable and uniform safety level for the design of bridge components. Once a bridge is designed and placed in service, the AASHTO Manual for Condition Evaluation of Bridges provides provisions for determination of the safety and serviceability of existing bridge components. Rating for the bridge system is taken as the minimum of the component ratings. If viewed from a broad perspective, methods used in the state-of-the-practice condition evaluation of bridges at discrete time intervals and in the state-of-the-art probability-based life prediction techniques share common goals and principles.; This thesis presents the results of a comprehensive study conducted on the system reliability-based lifetime evaluation of a number of existing bridges within a bridge network, including prestressed concrete, reinforced concrete, steel rolled beam, and steel welded plate girder bridges. Emphasis is placed on the interaction between rating and reliability results in order to relate the developed approach to current practice in bridge rating and evaluation.; In addition to establishment of a detailed database of existing bridges, the development of a network-level, time-variant, system reliability analysis program incorporating live load and resistance models, and applicable to multiple structure types located within a structure network is accomplished. Existing models for both resistance deterioration and live load increase in bridge members are investigated with the ultimate goal of customizing these models to de-icing and climatic conditions of the network bridges.; Rating factors and reliability indices for the network bridges are determined based on the resistance and load formulas prescribed by the code provisions. Every variation in structural behavior of different member types is considered. Limit state equations for steel girder bridges are developed to include variations in composite behavior, compactness, local buckling, and transverse versus longitudinal bracing. For serviceability of prestressed girders at service load stage, losses due to concrete shrinkage, elastic shortening, concrete creep, and relaxation of prestressing steel are considered.; Applicability of the methodology is demonstrated at a bridge network level and analysis results of the bridges within the existing bridge network are presented. The developed methodology, representing the accumulation of research in this field, is an essential analytical technique which can be extended to obtain the time-variant member and system reliability profiles for other structures in a civil engineering structure network.; Computational platforms incorporating sound analytical models for capturing the lifetime effects of mechanical and environmental processes and man-made actions (e.g., inspection, repair, replacement) on structural systems will provide strong analysis capabilities for the engineers in the future for optimal allocation of limited resources leading to improved management of the decaying civil infrastructure.