Journal of Composites for Construction

The design of fiber-reinforced polymer reinforced concrete (FRP-RC) is typically governed by serviceability limit state requirements rather than ultimate limit state requirements as conventional reinforced concrete is. Thus, a method is needed that can predict the expected service load deflections of fiber-reinforced polymer (FRP) reinforced members with a reasonably high degree of accuracy. Nine methods of deflection calculation, including methods used in ACI 440.1R-03, and a proposed new formula in the next issue of this design guide, CSA S806-02 and ISIS M03-01, are compared to the experimental deflection of 197 beams and slabs tested by other investigators. These members are reinforced with aramid FRP, glass FRP, or carbon FRP bars, have different reinforcement ratios, geometric and material properties. All members were tested under monotonically applied load in four point bending configuration. The objective of the analysis in this paper is to determine a method of deflection calculation for FRP RC members, which is the most suitable for serviceability criteria. The analysis revealed that both the modulus of elasticity of FRP and the relative reinforcement ratio play an important role in the accuracy of the formulas.

This paper deals with an innovative technique for strengthening reinforced concrete (RC) structures using steel-reinforced polymer (SRP) materials. The results of an experimental campaign using RC beams strengthened in flexure with carbon fiber-reinforced polymer or SRP laminates are summarized, and the experimental outcomes are compared to the predictions provided by analytical models and code formulations in terms of flexural strength, curvature of the cross section, deflections, and crack widths. Under ultimate conditions, the ACI 440.2R-02 approach provided conservative flexural strength, and a modified expression for the bond coefficient $k_m$ was proposed. Under serviceability conditions, good agreement was obtained between experimental results and a theoretical model developed by the writers. Comparisons of code models in terms of both crack width and deflections highlighted the need for a calibration of code formulas to account for effects due to externally bonded reinforcement.

This paper presents a case study of prefabricated double-layer pultruded fiber-reinforced polymer (FRP) grids for bridge deck construction. These grids were used to reinforce a $39.6\mathrm{m}$ long by $13.7\mathrm{m}$ wide (130 by $45\mathrm{ft}$ ) bridge deck on US Highway 151 over the De Neveu Creek in Wisconsin. The Federal Highway Administration Innovative Bridge Research and Construction Program invested resources in this program to investigate new uses for off-the-shelf technologies in constructing highway bridges. The feasibility of modifying manufacturing techniques to create innovative double-layer, 3D pultruded, FRP grids measuring $12.9\mathrm{m}$ long by $2.4\mathrm{m}$ wide by $16.5\mathrm{cm}$ deep ( $42\mathrm{ft}$ $6\mathrm{in.}$ by $8\mathrm{ft}$ by 6 1/2 in.) was investigated. In addition, the feasibility of placing the grids rapidly and constructing a bridge deck was also demonstrated. The FRP grids were required to meet a prescriptive material specification and a structural performance specification. Shear connectors were designed by the manufacturer to join large top and bottom grids to form an integrated 3D reinforcing module. From a construction perspective, the reinforcement grids were designed to be moved in a single lift of a crane and placed on the bridge girders. The paper reports on the development of the FRP 3D grids and provides details on the construction aspects of the bridge project.

Earthquake damage to unreinforced masonry buildings has shown the vulnerability of perimeter walls to out-of-plane failure. This paper describes a study that was carried out to develop and test innovative fiber reinforced polymer (FRP) rehabilitation techniques that meet the stringent requirements for strengthening historical buildings and to be cost-effective alternatives applicable to other existing masonry structures. Unobtrusive FRP rehabilitation techniques that utilize flexible carbon fiber composite cables, mounted near the surface of the façade walls in epoxy-filled grooves in the bed and head joints, were developed. Ten full size walls were constructed of clay bricks and retrofitted using the developed FRP rehabilitation techniques. The test results demonstrated the high efficiency of the rehabilitation techniques under both monotonic and quasistatic cyclic loadings. Significant increases in ultimate capacities, energy absorption, and deformability were achieved for various reinforcing schemes compared to the behavior of the unreinforced walls.

Tuff buildings are a significant part of the Mediterranean area and are to be preserved from a structural viewpoint especially in seismic areas. Over the past few decades, the interest in strengthening of historical tuff masonry structures has led to developing specific and noninvasive architectural and engineering strategies. In the present paper, a comprehensive experimental program on tuff masonry panels is presented; the results are intended as a contribution to the knowledge of in-plane behavior of tuff masonry strengthened with composite materials. Particularly, a cement based matrix-coated alkali resistant glass grid system (CMG) was used to strengthen tuff masonry walls; different CMG layouts were selected, and overall performances were compared with those of as-built ones. The characterization of base materials was carried out first, followed by uniaxial tests of masonry and shear tests on triplets. Finally, tuff masonry panels were subjected to diagonal compression loading under displacement control in order to measure their in-plane deformation and strength properties, including the postpeak softening regime in view of seismic applications.

This paper investigates the structural retrofit of deteriorated reinforced concrete lighting poles using wet layup of fiber reinforced polymer (FRP) sheets. The study comprised of four full-scale Class B damaged poles and one full-scale Class C undamaged pole. Each pole was 14,000 mm long with a base diameter of 350 mm linearly tapered to a tip diameter of 165 mm. The damaged poles were reinforced with nine No. 10 steel bars each, whereas the undamaged pole had four prestressed steel strands of 3/8 in. (9.5 mm) diameter. Four different in situ applicable repair schemes, one for each damaged pole, involving the application of E-glass or carbon FRP lateral confining wraps only (unidirectional) or coupled with additional longitudinal flexure sheets (bidirectional) were investigated. The adequacy of the retrofit works was checked through full-scale bending test of the poles in accordance with specification of the Canadian Standard Association. All four repaired poles exceeded the CSA design transverse loading requirement for Class B poles. In addition, the bidirectional E-glass and carbon FRP repaired poles exceeded the benchmark performance of the undamaged Class C pole as a percentage of the required design load with the E-glass pole exhibiting the best performance.

Evaluation of environmental durability of concrete circular specimens strengthened using externally applied fiber-reinforced-polymer (FRP) composites for confinement reinforcement was studied. FRP-confined concrete cylinder tests were carried out for various environmental exposure conditions including interior, exterior, and freeze–thaw cycling in saltwater. Two types of resin matrix-based FRP composite systems, including epoxy and urethane resin, utilizing either carbon or glass fibers were used. In addition, continuous single and double layer wrapping schemes were applied for confinement for each of the four FRP composite systems. The overall stress–strain behavior of FRP-confined concrete does not change fundamentally but different levels of exposure significantly affect its absolute stress–strain curve. The radial strain and corresponding axial strain at the point of zero volumetric strain is significantly affected by different levels of environmental exposure. It is proposed that the relative FRP composite effectiveness must be used to calculate the ultimate radial strain of FRP-confined concrete. It was found that for the four FRP systems used in this study the ultimate radial strain is not significantly affected by the type of exposure. The writers believe that the results shown in this paper help engineers to understand the short and midterm effects of the environment on FRP confined concrete; long term effects are still under investigation.

Based on the test information available in the literature since 1990, a comprehensive database is assembled for an extensive survey of existing studies on the flexural behavior of reinforced concrete beams externally strengthened with fiber-reinforced polymer (FRP) composites. Beam dimensions, material properties (concrete, steel reinforcement, FRP composites, etc.), and corresponding flexural responses such as failure modes, moment capacities, and so on, are collected in this database. The purpose of this database is to verify the design formulas presented in ACI 440.2R-02, Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures. The performance of some other simple strength design models is investigated based on the same database and compared with that of the ACI model, which is found to have the least scattered prediction compared to others. Finally, a modified maximum strain FRP equation is recommended.

The use of adhesively bonded carbon fiber reinforced polymer (CFRP) laminates is increasingly being considered for the rehabilitation of metallic structures. The effective structural monitoring of steel/CFRP adhesive joints is of critical importance to assess the design service performance of the system, which ultimately depends on the bond damage tolerance at the load transfer regions. In the present study laboratory static and fatigue tests were conducted on steel/CFRP skin doubler and double strap joint specimens, which were monitored using the acoustic emission (AE) technique. The characteristics of the AE signals were correlated with the mechanical response of the samples, in order to understand the AE response associated with the accumulation of bond damage. One-dimensional source location was also performed to examine the initiation and the development of the disbond. The results show that AE parameter-based analysis is an effective nondestructive evaluation tool for bond damage detection and area location.

In this technical note, the importance of contact pressure ( $\mathrm{}$ 0.03 N/ ${\mathrm{mm}}^2$ ) during curing of adhesive between fiber reinforced polymer (FRP) and concrete is addressed. The shortcoming of fast-curing epoxy resin is pointed out. Different pressures and an ordinary epoxy resin were chosen to assess the effectiveness of contact pressure on FRP-to-concrete bond strength. The test results showed that the bond quality could be significantly improved by exerting a contact pressure $⩾$ 0.01 N/ ${\mathrm{mm}}^2$ . A simple and easy site-operation method for exerting contact pressure is also introduced.