A fracture-based approach to understanding debonding in FRP bonded structural members

Abstract

(cont.) members. The experimental program for RC beams involves qualitative and quantitative observation of the changes in the debonding behavior and load capacity of the beams with various configurations of shear and/or flexural strengthening and anchorage conditions in four evolutionary experimental stages involving both monotonic and cyclic loading. A dramatic improvement in the debonding behavior and performance of the beams was observed with shear strengthening and with providing anchorage. An innovative design methodology involving a fracture mechanics approach was developed to describe the system failure by means of a global failure criterion. Modeling and evaluation studies confirm the potential of fracture mechanics approach for analysis and design of FRP-RC and FRP-steel systems against debonding failures.

At the dawn of a new century, the need for repair and strengthening of existing structural systems that have become substandard due to various reasons has become one of the most important challenges regarding the sustainability of existing infrastructures worldwide. A relatively new class of materials, called the fiber reinforced plastic (FRP) composites, are widely recognized for their potential use in infrastructure rehabilitation and renewal that may contribute to meeting this challenge. Prerequisite to wide range use of these materials, however, is a thorough understanding of the mechanical and failure behavior of FRP strengthened members and the development of related design codes and guidelines. From a structural mechanics point of view, an important concern regarding the effectiveness and safety of this method is the potential of brittle debonding failures. This thesis focuses on this important issue regarding applications to both reinforced concrete (RC) and steel members. The scope of the studies is limited to FRP-steel and FRP-concrete systems where debonding problems are most frequently encountered and play an important role in the member behavior and performance. The experimental program for steel members was focused on more fundamental aspects due to limited existing research and knowledge in this area. Notched steel specimens with different thicknesses were repaired with FRP patches of various sizes and were tested under tensile fatigue loading. Substantial increases in the remaining fatigue lives of specimens were measured as a function of the specimen thickness and FRP patch dimensions. A fatigue model based on linear elastic fracture mechanics approach was found suitable for modeling the fatigue life increase in repaired steel