Journal of Composites for Construction

Past test data show that the bond stress distribution of bond anchorages is nonuniform along the bonded length and that the point of the peak bond strength shifts from the entry of the tendon to an inside point of the anchorage as the applied load increases. Based on these results, this paper analyzes the working mechanism of bond anchorages for fiber-reinforced polymer (FRP) tendons and presents a conceptual model to calculate the bond stress at the tendon-grout interface and the tensile capacity of bond anchorages for FRP tendons. Experimental and analytical results show that the geometry of FRP tendon and steel sleeve and the mechanical properties of filling grout are the relevant parameters in the development of tendon-grout interface stresses. The characteristic bond strength depends mainly on the properties of the bonding agent-cement grout, the geometry and surface conditions of the tendon, and the radial stiffness of the confining medium. A comparison of the calculated and experimental results showed good agreement.

A composite bridge deck system assembled from glass/polyester pultruded components has been developed. This system utilizes square tubes running transverse to the traffic direction, mechanically fastened and bonded together, and flat cover plates bonded to the tubes with an epoxy adhesive and through-anchored to the deck support structure using mechanical connectors. A 4.27 × 1.22 m section of the deck system integrally connected to the superstructure at a 1.2 m girder spacing was tested to failure under a single patch loading. The results indicate a factor of safety of 4 on strength and a deflection-to-span ratio of about L/300. Another section of the deck was fatigued to 3,000,000 cycles under service loading at a load ratio of R = 0.1 and a nominal frequency of 3 Hz. Results from these tests indicate no loss in stiffness up to 3,000,000 cycles. Following the fatigue testing, this section was also tested to failure; no loss in strength was observed. In addition, a finite-element model of the laboratory tests was developed. The results from the model showed good correlation to deflections and longitudinal strains measured during the tests.

The rehabilitation of RC columns jacketed with carbon fiber-reinforced plastic (FRP) composites for improving shear strength, confinement, and ductility has received considerable attention. However, research for improving the shear capacity of beam-column T-joints using FRP composite materials is still in the early stages. The present paper describes the experimental results of 14 1/3-scale tests of concrete beam-column joints. The variables considered were the composite system, the fiber orientation, and the surface preparation. The tests have demonstrated the viability of carbon FRP composites for their use in improving the shear capacity of the joints as evidenced by the experimental results. Based on these experimental results, a design aid was developed for T-joints with inadequate confinement and shear reinforcement.

A closed-form high-order analytical solution for the analysis of concrete beams strengthened with externally bonded fiber-reinforced plastic (FRP) strips is presented. The model is based on equilibrium and deformations compatibility requirements in and between all parts of the strengthened beam, i.e., the concrete beam, the FRP strip, and the adhesive layer. The governing equations representing the behavior of the strengthened beam, along with the appropriate boundary and the continuity conditions, are derived and solved with closed-form analytical solutions. Comparison of the closed-form high-order model with other simplified approaches, based on one- and two-parameter elastic foundation concepts, is included. It is shown that the current high-order model can be reduced, by omitting the appropriate terms, to the simplified theories. A numerical example of a typical RC beam strengthened with an externally bonded FRP strip is discussed with emphasis on the shear and peeling stress distributions at the edge of the FRP strip. Stress analysis results concerning the edge stresses determined by the high-order model are compared with those determined by the elastic foundation models and finite elements. Finally, a parametric study that characterizes the main parameters governing the magnitude and intensity of the edge stresses is performed. The paper is concluded with a summary and recommendations for the design of the strengthened beam.

Despite many studies on beams and slabs strengthened using fiber-reinforced plastic (FRP) plates, no study has been reported on the strengthening of RC cantilever slabs (e.g., canopies and balconies) using FRP materials. This paper presents the results of an experimental study of the feasibility of strengthening deficient RC cantilever slabs by bonding glass FRP (GFRP) strips/sheets on the top surface (the tension side). As the key to the success of this strengthening method is a proper way of anchoring the GFRP strips into the supporting wall and the slab, the effectiveness of different anchorage systems was the focus of the experiments. Based on the test results, a simple and effective method is identified in which the GFRP strips are anchored into the walls through horizontal slots and onto the slab using fiber anchors.

A detailed experimental investigation of local and global deformations of tensile-loaded, cracked, rectangular, concrete prisms reinforced with externally bonded carbon fiber reinforced polymer (CFRP) sheets was carried out. High and low modulus sheets were applied using three different thicknesses of epoxy interlayer between the sheet and concrete. It was found that the stiffness of the CFRP sheet had a dominant effect on global tension stiffening, whereas interlayer thickness had a dominant effect on local load transfer and damage formation. Thicker interlayers transferred load into through-cracked concrete over longer transfer zones, thereby increasing the spacing of subsequent cracks in the concrete. The combined effect on global stiffness of changes in transfer zones and crack spacing due to interlayer thickness was negligible. Increasing the stiffness of the CFRP sheet resulted in considerably increased global tension stiffening. Full field strain measurements by moiré interferometry revealed detailed information about local load transfer in the CFRP sheet, epoxy interlayer, and concrete in the vicinity of cracks.

In this technical note, fiber-reinforced plastics (FRP) strengthening efficiency for reinforced-concrete columns will be examined from a micromechanical point of view by accounting for direct mechanical interaction between FRP sheet and concrete. Concrete compressive failure is initiated by wing-crack propagation. The mechanical interaction dictates the compressive behavior of FRP-wrapped concrete from the first bent-over point to the peak load in the load/displacement curve. A possible detailed interaction under compression is described.