Journal of Composites for Construction

Engineers have proposed the idea that there may be some arching action present in bridge deck cantilever overhangs stiffened along their longitudinal free edge through a traffic barrier, subjected to a wheel load. This paper includes the details of a full-scale corrosion-free bridge deck with cantilever overhangs stiffened along their longitudinal free edge by a traffic barrier wall that has been constructed and tested under static and fatigue wheel loads at the University of Manitoba. It also reviews experimental test results and postulates various discussions that suggest the presence of arching action in cantilever slab overhangs. The test results indicated static ultimate load capacities significantly greater than the ultimate capacity if the mode of failure and behavior of the cantilever overhang was completely flexural. These early results confirm and indicate the presence of arching action resulting in a significant breakthrough in cantilever behavior when subjected to a wheel load. The theory to account for this arching action is not yet developed, and further research should be conducted.

Fiber-reinforced polymer (FRP) strengthening systems for infill-masonry walls are typically designed to resist flexural stresses caused by out-of-plane pressure. Previous research has shown that there are potential premature failure mechanisms caused by shear sliding of the infill, which could reduce the effectiveness of the strengthening system. Current design guidelines for strengthening of masonry walls with FRP do not include guidelines for infill-masonry. This paper presents a rational approach for the design and analysis of FRP-strengthened infill-masonry walls subjected to out-of-plane loading, including the effect of using FRP end anchorage. The approach is based on consideration of four potential mechanisms: arching, shear sliding, debonding of the FRP in the overlap region, and failure of the FRP end-anchorage system. The predictions based on the proposed rational approach agree well with the measured values from two experimental programs.

The repair and retrofit/rehabilitation of existing concrete and masonry structures have traditionally been accomplished with externally bonded fiber-reinforced polymer (FRP) systems, steel plates, reinforced concrete (RC) overlays, and posttensioning, just to name some of the many techniques presently available. Fabric-reinforced cementitious-matrix (FRCM) composites have recently emerged as an additional strengthening technology. FRCM is a composite material consisting of a sequence of one or more layers of cement-based matrix reinforced with dry-fiber fabric. This paper has three objectives: (1) to review existing guidelines for tensile testing and calculation of FRCM material properties to be used in analysis; (2) to report on some of the results of an experimental program intended to characterize the tensile behavior of FRCM coupons; and (3) to discuss the performance and analysis of concrete RC slab-type elements strengthened with FRCM. The laboratory results demonstrate the technical viability of this new composite material system for strengthening flexural RC members.

Many studies performed on reinforced concrete (RC) members strengthened in flexure with externally bonded (EB) fiber-reinforced polymers (FRPs) have indicated quite low strengthening efficiency caused by debonding of the FRP from the concrete surface prior to the capacity of the FRP material being achieved. It should be emphasized that although flexural strengthening with FPR increases the load-bearing capacity of RC members, it has little effect on the serviceability limit state (i.e., cracking moment and deflections). Prestressing the EB FRP has been proposed as a method of increasing utilization of the FRP tensile strength and of improving the efficiency of strengthening in terms of serviceability limit states. An experimental research program consisting of three series of RC slabs with variations in the longitudinal steel reinforcement ratio, concrete strength, preloading level before strengthening, and adhesion between the CFRP laminates and the concrete is described. A practical and unique aspect of the program focuses on an analysis of the effect of preloading on the strengthening efficiency of RC slabs strengthened with prestressed carbon fiber-reinforced polymer (CFRP) laminates. Although the preloading is one of the most important parameters to be accounted for in the design of strengthening existing RC structures, this aspect has been investigated only rarely. Two levels of slabs preloading were considered: the slab self-weight acting alone and the self-weight plus an additional external load. The self-weight preloading level corresponded to 25 and 14% of the yield strength of nonstrengthened slabs in Series I and III, respectively. The higher preloading level, equal to 76% of the yield strength of the nonstrengthened slab, was chosen to approach the elastic limit of the slab behavior. Experimental tests yielded promising results for the ultimate and serviceability limit states of the strengthened slabs. The strengthening ratio, defined as the ratio of the difference between the ultimate load of the strengthened and nonstrengthened slabs to the ultimate load of the nonstrengthened slab, reached values in the range of 0.64–1.19. The influence of the tensile steel reinforcement ratio, adhesion between the prestressed CFRP laminate and concrete, and preloading level on the ultimate load carrying capacity following strengthening is discussed.

Carbon fiber reinforced polymer (CFRP) has great potential in strengthening steel structures and the bond between CFRP and steel is a critical issue in the strengthening technique. State-of-the-art reviews have been reported in the literature on the bond behavior between CFRP and steel under static loading at ambient temperature. However, steel structures are often subjected to dynamic loading and harsh environment conditions, and the bond between CFRP and steel may be affected by these conditions. This paper presents a state-of-the-art review on the effects of dynamic loading (e.g., fatigue, impact, and earthquake) and environmental conditions (e.g., subzero temperatures, elevated temperatures, sea water, and ultraviolet light) on the bond between CFRP and steel. The combined effect of applied loading and environmental conditions is also included. Directions for future research are indicated and a comprehensive reference list is provided.

This paper presents the results of an experimental study on fiber-reinforced polymer (FRP) to timber bonded interfaces. A series of tests on 86 single shear FRP-to-timber joints is reported, of which the test parameters are (1) adhesive type, (2) FRP plate type, and (3) timber species. The results include descriptions of the behaviors of the specimens in addition to categorization of failure modes. Joint strengths, strain and bond stress distributions, and bond stress-slip relationships are also presented. Finally, a test-based $J$-integral method is briefly introduced, which can predict the bond stress-slip behaviors of bonded joints. The results presented in this paper are expected to aid design engineers in selecting suitable adhesives and FRP plate types with which to strengthen different species of timber. The results may also be used to inform the design of future experimental studies on the topic.

A fundamental understanding of the mechanical properties and the failure mechanism of hybrid fiber-reinforced polymers (FRP) is required for the effective application of FRP in construction. This paper presents a new methodology for predicting the tensile behavior of hybrid FRP tendons by considering the interfacial stress transfer between the resin and the fibers in hybrid FRP. Subsequently, the authors utilize the fundamental concepts of fracture mechanics to derive a model capable of predicting the mechanical properties of hybrid FRPs. For this paper, the authors conducted an experimental study on the tensile properties of hybrid basalt/carbon FRP tendons and hybrid glass/carbon FRP tendons. They identified the effects of resin type, fiber fraction, and fiber arrangement over the cross section. The results show that the stress-strain relationship of hybrid FRP can be modified from the linear behavior of FRP to a ductile behavior with a steady pseudoyielding plateau and a high ultimate failure strain. Meanwhile, the load drop in hybrid FRP, which is attributable to the fracture of the fibers with low elongation capacity, can be controlled effectively by the proper design of the hybrid fiber proportions, resin type, and volume fraction. The proposed hybridization results in improving the deformation ability of fibers with low elongation capacity. Moreover, the proposed model for the description of failure progression and prediction of mechanical properties is verified by good agreement with the experimental results of this paper and those from prior studies by others.

Numerical simulations using the nonlinear finite-element method (FEM) have been successfully used to predict the full nonlinear response of reinforced concrete (RC) members strengthened with fiber-reinforced polymers (FRPs). Calibrated numerical models have the potential to reduce the number of experimental tests through the use of parametric studies that can provide further data on the influence of key parameters. A relatively new area of research is the use of FRP anchorage systems to improve the efficiency of FRP-strengthened members by preventing the various modes of deboning failure. Although FRP anchorage systems have shown exceptional potential for widespread use, further experimental and numerical data are required before establishing theoretical models and design guidelines. The focus of the present work is to develop and validate an FE modeling approach to expand the available data on FRP-to-concrete joints anchored using unidirectional and bidirectional fiber patch anchorages. The critical bond properties among multiple layers of FRP sheet, laminate, and concrete are simulated using interface elements and a calibrated interface bond law. The proposed modeling approach and calibration techniques have resulted in replication of prepeak and postpeak response with a reasonable level of accuracy. Numerical parametric studies have also been conducted to expand the experimental data to encompass variations in concrete strength and the overall effect on anchorage effectiveness.

This paper presents an experimental study on the shear behavior of RC members fully wrapped with polyethylene terephthalate (PET) fiber-reinforced polymer (FRP) composites, which are a new type of FRP material characterized by a much larger rupture strain (LRS) compared with conventional FRPs (i.e., made of carbon, glass, and aramid fibers). A total of 10 PET fully-wrapped RC beams, which were designed to fail in shear and with different shear-span to effective-depth ratios, transverse reinforcement ratios and shear strengthening ratios, were tested under 4-point bending loads. The overall load-deflection responses and the shear deformation of the beams as well as the strain development of the transverse steel reinforcement and the FRP jackets were carefully observed. Based upon the extensive strain measurements, the shear contributions by concrete, FRPs, and transverse reinforcement are differentiated. It was found that the use of PET FRP composites as the jacket material of RC members could shift the mode of shear failure from a brittle one to an ideal ductile one whereas the ultimate state of the members is no longer caused by FRP fracture. In order to efficiently predict the shear strength of RC members wrapped by LRS FRPs, the effective strain in LRS FRPs and the degradation of concrete at the peak member shear strength should be appropriately considered.

The fatigue performance of concrete bridge decks with glass fiber–reinforced polymer (GFRP) stay-in-place structural forms replacing the bottom layer of rebar is studied. The forms were either flat plate with T-up ribs joined using lap splices or corrugated forms joined through pin-and-eye connections. The decks were supported by simulated precast girders, AASHTO Type III, spaced at 1,775 mm. Two surface preparations were examined for each GFRP form, either using adhesive coating that bonds to freshly cast concrete, or just cleaning the surface before casting. For the bonded deck with flat-ribbed forms, adhesive bond and mechanical fasteners were used at the lap splice, whereas lap splice of the unbonded deck had no adhesive or mechanical fasteners. All decks survived 3 million cycles at 123 kN service load of the CL625 design truck of the Canadian standard. The bonded flat-ribbed-form deck further survived additional 2 million cycles at a higher load simulating a larger girder spacing of 2,365 mm. Stiffness degradations were 9–33% with more reduction in unbonded specimens. Nonetheless, live load deflections of all specimens remained below $\mathrm{span}/\mathrm{1,600}$. The residual ultimate strengths after fatigue were reduced by 5% and 27% for the flat-ribbed and corrugated forms, respectively. However, these strengths remain 7 and 3 times higher than service load, respectively. Both the lap-splice and pin-and-eye connection survived fatigue. Concrete crack width at the top surface over the girders remained below the AASHTO limit of 0.3 mm.

The development of fiber-reinforced inorganic polymer (FRIP) composites for strengthening reinforced concrete (RC) structures has become an active field of research in recent years. Compared with fiber-reinforced polymer (FRP) strengthening systems, a FRIP strengthening system possesses improved fire resistance but its performance depends largely on appropriate inorganic paste selection. This paper presents a comparative study of four typical inorganic pastes, made from the following: (1) magnesium phosphate cement (MPC), (2) magnesium oxychloride cement (MOC), (3) geopolymer (GP) cement (i.e., alkali-activated slag cement), and (4) polymer-modified mortar (PMM). The aim was to investigate their performance both as a matrix and bonding adhesive for FRIP strengthening systems. The evaluated performance included the workability and mechanical properties of inorganic pastes, the bonding strength of these pastes with both a concrete substrate and dry fiber sheets, the tensile properties of the formed FRIP composites, and the flexural strength of FRIP-strengthened concrete beams. The microstructures of the four types of inorganic matrix and the fiber-to-matrix interface were also examined. The MPC-based and MOC-based inorganic pastes exhibit similar structural performance as commercially available PMM and are well-suited for the development of FRIP strengthening technology. Geopolymer seems to be the most brittle among the four studied inorganic pastes.

Providing additional confinement by external fiber-reinforced polymer (FRP) wrapping is one of the most common and effective techniques for the retrofit of existing reinforced concrete columns. Over the past 2 decades, researchers have made much progress on the development of constitutive models to describe the behavior of FRP-confined circular concrete sections in compression. However, only recently have a few models been published representing the first attempts to develop a constitutive model for circular concrete columns in compression confined by both external FRP wraps and internal transverse steel. A critical review and evaluation of existing FRP-and-steel-confined concrete constitutive models highlights the need for a more robust model. This paper presents the development of a new FRP-and-steel-confined concrete in compression constitutive model for circular sections based on the passive-confinement approach. A new lateral-to-axial strain relationship and failure surface function are developed. Through a comparison with published experimental data, the accuracy of the proposed model is demonstrated.

Collisions between overheight vehicles and bridges are becoming more commonplace. Generally, collision damage is far from catastrophic, although sound repair techniques are critical if additional damage (typically related to corrosion) is to be mitigated. Although the decision to repair or replace a collision-damaged prestressed concrete structure must ultimately be made on a case-by-case basis, basic criteria for making this decision may be established. This paper describes parameters affecting the efficacy of external carbon fiber-reinforced polymer (CFRP) composite repair methods for restoring the flexural capacity of damaged prestressed concrete bridge girders. The study focuses on impact damage requiring structural repair (rather than simply aesthetic measures). The physical limitations of each CFRP repair method are described to define an initial design space, followed by a parametric study using two prestressed girder shapes (box and I-girder) and three CFRP repair techniques (externally bonded, prestressed, and near-surface mounted) in which the goal was to identify the design space of each technique. The effective design space for each method is then described by the spectra of damage to which the method may be effectively applied. The spectra of damage may be envisioned as having two thresholds: the no repair—repair threshold and the repair—replace threshold.

Five 609.5-mm deep fiber-reinforced polymer (FRP) beams with a span-to-depth ratio of $4:1$ were tested in three-point bending with the beam ends constrained to prevent global failure. A concentrated load was applied at midspan either directly to the top flange or through a 101.6 mm wide by 12.7-mm thick FRP bearing plate resting on the top flange. VIC-3D Digital Image Correlation Measurement Software from Correlated Solutions captured out-of-plane displacement of the webs, and Southwell plots were generated to determine buckling loads. Each specimen experienced a stability failure of the web before undergoing material failure in the upper web-flange junction. On average, web buckling occurred at 90% of the ultimate load. The introduction of a bearing plate did not significantly affect the buckling load or ultimate capacity of the specimens. One specimen was tested into the postbuckling range, unloaded, and reloaded to material failure and experienced no loss of strength or stiffness. Another specimen with significant damage to the unloaded web-flange junction was tested and compared with a virgin sample. The damaged sample experienced no significant loss of strength or stiffness. Comparisons of experimental data with three theoretical equations for web-buckling capacity of FRP beams are provided.

The paper presents a technique for strengthening of reinforced concrete infilled frames with textile-reinforced mortar (TRM) jacketing. The key objective of the study is to examine different methods of masonry infill-concrete connection by developing and testing textile-based anchors at the interface between masonry wallettes and concrete. The parameters examined include mainly the type of boundary conditions at the masonry-concrete interface, the geometry and fiber volume of anchors and the type and number of layers of the textile. It is shown that the anchors developed in this study enable the transfer of substantial tensile forces between masonry and concrete and that their magnitude may be estimated on the basis of anchor properties.

The present study addresses the applicability of reinforced concrete shear walls totally reinforced with glass fiber–reinforced polymer (GFRP) bars to attain reasonable strength and drift requirements as specified in different codes. Four large-scale shear walls—one reinforced with steel bars (as reference specimen) and three totally reinforced with GFRP bars—were constructed and tested to failure under quasistatic reversed cyclic lateral loading. The GFRP-reinforced walls have different aspect ratios covering the range of medium-rise walls. The reported test results clearly show that properly designed and detailed GFRP-reinforced walls could reach their flexural capacities with no strength degradation and that shear, sliding shear, and anchorage failures were not major problems and can be effectively controlled. The results also show recoverable and self-centering behavior up to allowable drift limits before moderate damage occurs and achieving a maximum drift meeting the limitation of most building codes. Acceptable levels of energy dissipation accompanied by relatively small residual forces, compared to the steel-reinforced wall, were observed. The promising results can provide impetus for constructing shear walls reinforced with GFRP and constitute a step toward using GFRP reinforcement in such lateral-resisting systems.

The flexural behavior of fatigued reinforced concrete (RC) beams strengthened using prestressed near surface mounted (NSM) carbon fiber–reinforced polymer (CFRP) strips was investigated. Five RC beams were tested; one beam served as a control unstrengthened beam, while the other beams were prestressed to strain values corresponding to 0, 21, 40, and 60% of the CFRP ultimate tensile strain. The beams were subjected to fatigue load conditions for 3 million cycles. Thereafter, the postfatigue monotonic flexural behavior of the beams was compared with identical unfatigued beams. Test results showed that the fatigue loading had a minor effect on the bond performance at the concrete-epoxy interface of the RC beams. In general, fatigue loading did not affect significantly the postfatigue monotonic performance of the tested beams in terms of yield and ultimate loads and deflections, as compared with identical unfatigued beams tested in static conditions. The ductility of the tested beams was also evaluated and compared with similar unfatigued beams using several ductility models found in the literature. No fatigue effect on ductility (NFED) prestress strain was introduced and proposed as a mean to define the prestress strain at which the fatigue loading has no effect on the ductility of the RC strengthened beams. The NFED prestress strain for the particular specimens that were considered in this research ranges from 62 to 82% of the CFRP ultimate tensile strain, which indicates that the ductility of the fatigued beams is higher than that of the unfatigued beams for most of the practical prestress values.

This paper is concerned with the development of an accurate bond strength model for carbon-fiber-reinforced polymer (CFRP) strips near-surface mounted (NSM) to concrete where debonding occurs as a result of cohesion failure in the adjacent concrete. Based on an existing analytical solution and the fracture energy equation recently developed by the authors, a bond strength equation is first proposed for NSM CFRP strip-to-concrete bonded joints with a sufficient bond length (i.e., the bond length exceeds a threshold value referred to as the effective bond length). The influence of an insufficient bond length on the bond strength is next examined through a parametric study conducted using a beam-spring numerical model in which a bond-slip model recently proposed by the authors is incorporated. Based on the numerical results, expressions are formulated for the effective bond length and the bond-strength reduction factor for insufficient bond lengths. The combination of these equations leads to a new bond strength model for NSM CFRP strip-to-concrete bonded joints. The predictions of the proposed bond strength model are compared with the results of 51 test specimens collected from seven existing studies and the predictions of the only existing bond strength model for such joints. These comparisons indicate that the proposed model is accurate and superior to the existing bond strength model, particularly for joints with insufficient bond lengths. The proposed bond strength model, because of its accuracy and simplicity, can be readily incorporated in design codes and guidelines.