Consideration of Time-Dependent Degradation in the Development of Probabilistic Based Design of FRP Strengthening

摘要

Current guidelines for the application of FRP to strengthen existing reinforced concrete structures follow a deterministic approach that is in direct contrast to the probabilistic based methods that are the current trend in civil design, typically implemented through Load and Resistance Factor Design (LRFD). In order to develop a probabilistic code for design of FRP strengthening, extensive knowledge of FRP properties and their variation as manufactured in the field is required. Given the wide variety of composite materials this constitutes a significant challenge. The susceptibility of FRP to environmental degradation also requires explicit consideration of the variation of material properties with time. Current approaches often account for degradation through the use of a reduction factor to lower the design strength of the composite. However, these reduction factors are not based on the time the composite is expected to be in service, and in some cases the exposure environment is neglected as well. Without explicitly considering the conditions likely to be faced by the composite, it is impossible to accurately predict the required strength reduction, resulting in factors that are either too conservative or not conservative enough, depending on the design situation. A probabilistic design format is ideal for handling the uncertainty that exists in composite degradation. This paper addresses the development of a reliability based design code for FRP strengthening employing time and exposure condition dependant composite material reduction factors. Considerable effort is given to making the design procedure apply to as many different composites as possible. It is acknowledged that much of the data required for this endeavor is unavailable or in the preliminary stages of collection, thus the recommended approach also allows for the easy incorporation of new findings.