Reliability-based design and life-cycle management of FRP-strengthened RC structures

Abstract

Ageing transportation infrastructure imposes a huge risk to the well-being of society. The grand challenge brought by the ageing infrastructure is not only embodied in the large repository of deficient structures, but also arises from the ever diminishing availability of resources for maintenance actions. The current state of ageing infrastructure requires that maintenance actions be effective and sustainable; they should also be applied on critical structures/structural members at the most appropriate times during their service life. Reinforced concrete (RC) structures, an important constituent of transportation infrastructure, may undergo severe deterioration during their service life. In tackling the ageing problem of RC structures, fiber reinforced polymer (FRP) composites provide a viable solution for effective and sustainable structural strengthening, while life-cycle management can be used to decide the optimal strengthening plan. As great amounts of uncertainties are involved in both structural design and life-cycle management, probability-based methods that are capable of handling uncertainties should be used for rational planning of FRP-strengthening of RC structures. The present PhD research project was undertaken to provide an innovative maintenance solution to deteriorating RC structures, i.e. using FRP composites for structural maintenance and adopting life-cycle management for maintenance planning. To this end, three aspects of FRP strengthening were studied in detail: (a) the reliability evaluation of FRP-strengthened RC structures; (b) the development of deterioration models for RC and FRP-strengthened RC structures; and (c) the development of life-cycle management tools for FRP-strengthened RC structures. In order to handle the uncertainties involved, epistemic uncertainties of various design models for FRP-strengthened RC beams were quantified by virtue of two comprehensive test databases collected from the literature. Structural safety of FRP-strengthened RC beams was assessed by using time-independent reliability analysis, based on which revisions to existing design rules were proposed to achieve more reliable designs. For life-cycle assessment, time-dependent reliability was employed. To tackle the high computational cost, a novel cross-entropy-based importance sampling method was proposed for the efficient evaluation of time-dependent reliability of deteriorating structures. Regarding deterioration modeling, deterioration of both RC and FRP-strengthened RC structures were considered. For the former, a dynamic Bayesian network (DBN) model for chloride-induced corrosion was proposed for deterioration prediction and Bayesian updating. For the latter, moisture-induced deterioration was modeled for FRP composites and FRP-to-concrete bonded interfaces, respectively. Based on the time-dependent reliability analysis and deterioration models, life-cycle management can be performed by using both the threshold-based approach and multi-objective optimization. A risk-based bridge ranking method was developed to link up all preceding studies for a holistic life-cycle management framework for the FRP-strengthening of RC structures.