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
Parametric Study of Beams with Externally Bonded FRP Reinforcement
FRP reinforcement may be externally bonded to the soffit of existing flexural members in order to increase their strength and rigidity. A parametric analysis is conducted to investigate the effects of FRP reinforcement on serviceability, strength, and failure mechanisms of repaired RC beams. FRP reinforcement parameters considered in the analysis are: stiffness, bonded length, thickness, and the adhesive stiffness. The choice of the repair material parameters is important in the design phase in order to obtain the desired results of strengthening or stiffening without other unforeseen effects. In this paper, three typical RC beam cross sections are considered with height-to-width ratios of 0.5, 1, and 4. Two characteristic compressive strength levels (20 and 30 MPa), and two shear span-to-reinforcement depth ratios (4.5 and 7) are considered. All other parameters related to material and geometry of the beams are maintained constant. The results of the analysis are shown in terms of repaired-to-un-repaired strength and deflection ratios. They indicate that brittle failure mechanisms can develop at loads much lower than expected when considering only flexural performance controlled by concrete crushing and FRP tensile rupture. The analytical model used for the parametrization accounts for brittle failure mechanisms induced by debonding of the FRP reinforcement or shear-tension failure in concrete in the plane of the main longitudinal steel reinforcing bars. Even when considering the limitation of the RC member due to its un-modifiable shear resistance, it is shown that the application of FRP reinforcement can considerably increase load resistance capacity and limit deflection at service.
Bonded steel plating for strengthening concrete structures
Abstract Research into the technique of bonding steel reinforcement externally to hardened concrete is described. Laboratory work consisted of testing 4.9 m and 3.5 m beams, with steel plates bonded to their tension flanges, in 4-point bending. Results showed that a full composite action was provided by the adhesive and that significant improvements in performance could be achieved in terms of ultimate load, crack control, and stiffness. Exposure tests are being carried out on 0.5 m unreinforced concrete beams with steel plates bonded to one face. Results to data have shown that significant amounts of corrosion of the steel plate may take place during natural exposure. The resin and concrete consist of a labyrinth of very fine interconnected cracks through which corrosive salts can migrate. The corrosion may cause slight reductions in strength.