Showing papers by "Antonio Nanni published in 1998"

Contribution of Externally Bonded FRP to Shear Capacity of RC Flexural Members

Abstract: Fiber reinforced polymer (FRP) materials are continuing to show great promise for use in strengthening reinforced concrete (RC) structures. These materials are an excellent option for use as external reinforcing because of their light weight, resistance to corrosion, and high strength. Externally bonded FRP sheets have been used to increase moment capacity of flexural members and to improve confinement in compression members. Investigations into the use of externally bonded FRP sheets for use in shear strengthening have also been conducted and have shown this to be a viable strengthening method. The objective of this study is to review the current research on shear strengthening with FRP and propose design algorithms to compute the contribution of FRP to the shear capacity of RC flexural members. Methods for computing the shear capacity based on the stress level to cause tensile fracture of the FRP sheet (which may be less than ultimate due to stress concentrations) and based on delamination of the sheet from the concrete surface are presented. Areas which have the potential for further development are also discussed.

Effect of Cyclic Loading on Bond Behavior of GFRP Rods Embedded in Concrete Beams

Abstract: Three types of glass fiber-reinforced plastic (GFRP) rods with different surface configurations were embedded in concrete beams to determine their bond behavior under cyclic loading. Load amplitudes and numbers of cycles were chosen based on the GFRP rod type and its bond behavior in virgin beams loaded monotonically to failure. After completion of cyclic loading, all beams were tested quasi-statically to failure to determine the residual bond strength. Results were presented as load-slip curves, load-midspan displacement curves, and slip versus number of cycles curves. In all types of GFRP rod evaluated, cumulative slip increased as the number of cycles and/ or loading amplitude increased. The bond strength in cyclically loaded beams increased relative to the bond strength in virgin beams.

Proposed procedure for the design of rc flexural members strengthened with frp sheets

Abstract: As the development of new materials (particularly FRP) spawns innovation in the field of structural engineering, an accepted procedure for the design of the strengthened system must be created. The goal of this paper is to present a design protocol and suggest alterations/additions to the language of the current ACI-318 code for the use of FRP materials as strengthening reinforcement externally bonded to the concrete. The focus of the discussion is the design of RC members subjected to flexure. Thus, the design for shear strengthening or concrete confinement under compression is not addressed. The paper presents the design at ultimate state using the classical failure mode of steel yielding followed by concrete crushing or FRP rupture. In addition, the topic of required ductility is addressed. For the service state, acceptable stress levels in all materials at working loads and deflection are also considered, taking into account residual stresses. The proposed methodology can be a useful tool for professional engineers.

Strength assessment of external frp reinforcement

Abstract: Strengthening reinforced concrete and prestressed concrete structures becomes necessary when there is an increase in load requirements, a change in use, a degradation problem, or design and/or construction defects. Externally bonded fiber reinforced plastic (FRP) composites offer a potential solution to structural repair. Rapid in situ load testing has been used in other countries by threshold engineers to check structural performance compliance. This testing technology can be successfully adopted in the case of strengthening projects involving the use of externally bonded FRP. The primary objective of the rapid load test is to verify that the strengthening method is performing as designed. Furthermore, since an situ load test provides easy-to-understand physical results, it provides reassurance and confidence in the structure to clients and owners.

Environmental degradation of repaired concrete structure

Abstract: Externally bonded fiber reinforced plastic (FRP) reinforcement is the basis of a new repair technology for deteriorated constructed facilities. The fibers are adhered to a concrete surface after minimum surface preparation by means of polymeric resin. This study is being conducted to determine whether the FRP or the steel reinforcement would degrade as a result of inadvertent galvanic coupling. In the literature, it has been shown that FRP blisters/delaminates when galvanically coupled to less noble materials. Also, it is known that the degradation of the reinforcement steel accelerates due to unfavorable electrochemical difference between the fibers and the steel. In this research, galvanic behavior of the reinforcing steel and the externally bonded FRP materials were investigated. Immersion tests of the couple in artificial seawater environment were conducted to monitor blister formation on the composite material. During these tests, electrochemical impedance spectroscopy tests were conducted to examine the interactions between FRP and the steel.