Title: Strength, Durability and Health Monitoring of Composites Overlays on Civil Engineering Structures
1 Strength, durability and health monitoring aspects of composite overlays on civil engineering structures are discussed. The perspective and benefits of the repair, upgrade, retrofit, and rehabilitation of US civil infrastructure using composite overlays is briefly reviewed. Bond strength, durability, and in-service health monitoring are identified as critical issues blocking the wide acceptance of these novel structural systems in the construction engineering community. A theoretical and experimental research program, set up at the University of South Carolina, is briefly presented. Test methods development, modeling efforts, and proposed outcomes are discussed. The wider perspective of developing national standards and engineering guidelines for the design and utilization of composite overlays on civil infrastructures is also addressed. INTRODUCTION According to the US Department of Transportation and the Federal Highway Administration, there are about 576,000 bridges in the national bridge inventory, and 23% of these are structurally deficient and in need of repair. Several States have demonstrated that advanced fiber reinforced polymers (FRP) can be used to improve the load capacity of concrete bridges. FRP repair technology offers a practical way to rehabilitate aging concrete bridges without disrupting traffic flow. Masonry buildings also form an important component of US civil engineering structures with historical value. Repairs, rehabilitation and upgrades of masonry are required to meet new strength and seismic requirements. The use of FRP composite overlay on masonry has many potential benefits. A major obstacle in the widespread use of these new engineering solutions is the lack of standards and practices for assessing the quality of the repairs and the durability of the composite-to-concrete bond. Figure Error! Not a valid link. presents a few examples of
NEW RESULTS IN THE APPLICATION OF E/M IMPEDANCE METHOD TO MACHINERY HEALTH MONITORING AND FAILURE PREVENTION
The electro-mechanical (E/M) impedance method for structural health monitoring, damage detection and failure prevention is a new technology utilizing the emitter-detector properties of active material sensors and the structural drive point mechanical impedance. In previous work, the authors showed that changes in the drive point mechanical impedance of a structure or machinery can be sensed in the form of changes in the apparent E/M impedance of the active material sensor. Subsequently, a number of situations have been considered for the use of E/M impedance method in conjunction with active material sensors to important health monitoring and failure prevention applications. The paper starts with a brief review of the electro-mechanical (E/M) impedance method for structural health monitoring and non-destructive evaluation. Experimental results from tests conducted on various pieces of structures and machinery are presented. The experimental set-up consisted of an HP 4194A impedance analyzer, Pentium computer, National Instruments data acquisition hardware and software, and an array of PZT active sensors. These proof-ofconcept demonstration experiments proved the suitability of the electromechanical (E/M) impedance method to a number of industrial applications. This paper brings together, in a unified format, a large body of knowledge that has been accumulated regarding the electro-mechanical (E/M) impedance method and indicates its suitability to failure prevention monitoring in complex machinery. The theoretical and practical issues posed by its further development and wide industrial applications are also addressed.
Guidelines for flexural design of prestressed composite beams
Prestressed steel has only recently been considered in the design of structures, despite a long, successful history of prestressed concrete structures. Prestressing the steel in a composite steel-concrete beam increases the load at which the steel beam yields, and also increases the ultimate strength of the composite section. At the same time, precompressing the tension flange reduces the effective stress-range cycle and improves the fatigue strength. Prestressed composite beams can be used in new structures as well as for the strengthening of existing structures. Several analytical studies of single-span prestressed composite beams are reported in the literature, but no comprehensive design methodologies are given. This paper presents guidelines and equations for the design of prestressed composite beams in positive- and negative-moment regions. In the positive-moment region, a steel beam is prestressed first and then compositely connected to concrete deck. In the negative-moment region, a steel beam is prestressed and then compositely connected to a precast, prestressed concrete deck panel. The guidelines and equations are given for working-stress and load-factor design methods and are presented in a manner suitable for easy use by bridge-design engineers. A design example is also given to demonstrate the benefits of prestressing for strengthening existing bridges.