Journal of Composites for Construction

Corrosion of steel bars used in reinforced concrete bridge decks exposed to moisture and deicing salts is of concern. The chloride-induced corrosion of steel reinforcement increases the maintenance cost of the structure. The resistance of glass fiber reinforced polymer (GFRP) reinforcing bars to corrosion provides a viable alternative to steel reinforcement. Lightweight concrete allows structural members to have a reduced weight, which is advantageous for lifting and moving operations when precast concrete elements are used. This paper evaluates the one-way shear capacity of lightweight concrete panels reinforced with GFRP reinforcement. Three normal weight concrete and three lightweight concrete specimens reinforced with identical GFRP reinforcement details were tested to failure. The results of the tests are compared with the shear strength predictions of the American Concrete Institute (ACI) 440.1R-06 recommendations and a theoretical model based on the modified compression field theory.

In this paper, the effects of various environmental exposure conditions on concrete beams externally reinforced with carbon-fiber-reinforced polymer (CFRP) composites were studied. To evaluate the overall environmental effects on the durability of the interfacial bonding between concrete and CFRP, different commercial composite systems were investigated under various exposure conditions by using a new test method suggested previously. Results showed that the flexural strength of the beam specimens was reduced with environmental exposure. The commercial systems showed significant differences in the relative strength loss, although they were all intended for the same application, suggesting that durability is highly dependent on the epoxy system used in the composite. Under exposure to water and other fluids with different temperatures, CFRP systems employing wet lay-up composites showed high durability with the exception that one system revealed a considerable loss in strength with elevated temperature and time. A system using a precured laminate exhibited a large reduction in strength with exposure. Exposure to brackish water caused an increase in the flexural strength by virtue of buildup of barnacles, which protected the specimens from deterioration and increased the strength by acting as an additional reinforcement.

In this study, an analytical procedure for the evaluation of the expected performance of existing reinforced concrete (RC) beam-column joints before and after being retrofitted using fiber-reinforced polymer (FRP) composite materials is presented. Focus is given on the evaluation of the shear-strength versus deformation properties of the panel zone region either in the as-built or FRP-retrofitted configuration. Based on experimental and numerical evidence as well as on physical models representing the mechanics of the joint region, principal tensile stresses versus joint shear deformation relationships are adopted and preferred to more traditional nominal shear-strength rules, to evaluate, within a step-by-step iterative procedure, the combination of the joint shear contribution provided by the FRP composite material and that provided by the concrete core alone. The use of principal stresses allows one to directly account for the effects of variation of axial load, typically neglected in the assessment and retrofit of beam-column joints. The hierarchy of strength and sequence of events (damage mechanisms) expected within a beam-column subsystem are visualized via $M\mathrm{\text{-}}N$ interaction performance domains, used as a basis for a performance-based retrofit philosophy. Specific limit states or design objectives are targeted, with attention given to both strength and deformation limits. The proposed analytical procedure is validated on the results of a set of experimental tests available in the literature. With the intention to provide a simple design tool that can be easily implemented by practicing engineers, a worked example for the evaluation of the expected performance of an FRP retrofitted beam-column joint is provided and used as a basis for a parametric study to illustrate the effects of different strengthening schemes on the behavior of strengthened exterior joint panels under various axial load levels.

This study focuses on the development of a fracture-mechanics-based model that predicts the debonding behavior of RC beams strengthened with fiber-reinforced polymer (FRP). In this study, the existing debonding models based on fracture mechanics are reviewed. Since no approach exists that can exactly predict the failure mode, an extensive database that contains different beam debonding failure modes was prepared. This database includes 351 concrete prisms bonded with FRP plates tested in single and double shear. The existing fracture-mechanics-based models were applied to this database. The new proposed model was based on newly conducted carbon-fiber-reinforced polymer (CFRP)-to-concrete single shear tests and data were collected from two independent studies. A comparison between the experimental and the analytical results showed that the model predicts the bond strength accurately.

This paper presents test results of 16 reinforced concrete (RC) beams with web openings strengthened in shear with externally bonded carbon fiber reinforced polymer (CFRP) composite sheets. Test specimen was 2,600 mm long with a cross section of $85\mathrm{mm}\times 400\mathrm{mm}$ and a shear span to beam depth ratio of $a/h=2$ . All specimens had the same geometry and main longitudinal top and bottom reinforcement. No internal web reinforcement was provided in the test region to resemble the case of inclusion or enlargement of an opening in an existing beam which would typically result in cutting the internal web reinforcement around the opening. The test parameters were the width and depth of the opening and the amount of the CFRP sheets used for shear strengthening. Test results showed that the inclusion of web openings drastically reduced the beam shear capacity and stiffness. External strengthening with CFRP sheets around the opening was found to be very effective in improving the beam shear resistance and stiffness. Increasing the opening width or depth reduced the gain in the shear capacity caused by the CFRP. Doubling the amount of the vertical CFRP sheets from one to two layers increased the shear capacity but the additional shear capacity gain was not in proportion to the added amount of the CFRP. An analytical approach for prediction of the shear capacity of RC beams with openings strengthened in shear with CFRP was introduced on the basis of the American Concrete Institute (ACI) 440.2R-08 and other formulas published in the literature. The analytical approach showed good agreement with the test results.

This paper introduces an analytical method to calculate the interfacial shear and normal stresses in reinforced concrete (RC) beams strengthened by a fiber reinforced polymer (FRP) sheet or a steel plate (i.e., a soffit plate). The maximum interfacial shear and normal stresses are localized at the end of the soffit plate, and as a result, a debonding phenomenon develops at this position and may produce a sudden failure of the structure. The effects of the shear deformations are calculated in an RC beam, an adhesive layer, and a soffit plate. Thus, the composite RC beam is assumed to be a Timoshenko beam. Application of shear deformations to a Timoshenko beam results in a pair of simultaneous second-order and fourth-order ordinary differential equations. In the engineering literature, these equations are called coupled differential equations. These coupled equations are solved analytically considering all terms. The present paper illustrates the effects of interfacial stresses on the behavior of RC structures strengthened by FRP sheets or steel plates. Finally, the agreement of the results obtained from the analytical solution and the results available in the literature confirms the accuracy of the proposed approach in predicting both interfacial shear and normal stresses.

In this paper, the effectiveness of textile-reinforced mortars (TRMs), as a means of increasing the shear resistance of reinforced concrete beams, is experimentally and numerically investigated. Textiles comprise of fabric meshes made of long woven, knitted or even unwoven fiber rovings in at least two (typically orthogonal) directions. Mortars—serving as binders—may (or may not) contain polymeric additives usually used to have improved strength properties. These TRMs may be considered as an alternative to fiber-reinforced polymers (FRP), providing solutions to many of the problems associated with application of the latter without compromising much of the performance of strengthened members. In the present study, a new type of textile (basalt-based textile) was used as strengthening material. Two different mortar types’ viz. cementitious and polymer-modified cementitious mortars were used as binding material for the textile sheets. The studied parameters also included the number of textile layers as well as the orientation of the textile material. The experimental program comprises of testing two control beams which were intentionally designed to be deficient in shear, in addition to testing eight beams which were externally upgraded by TRM sheets for enhancing their shear capacity. On the basis of the experimental response of reinforced concrete members strengthened in shear, it is concluded that textile-mortar composite provides substantial gain in shear resistance; this gain is higher as the number of layers increases. With higher number of layers, textile with 45° orientation along with polymer-modified cementitious mortar provides the highest shear strength enhancement. Nonlinear finite-element (FE) analysis was also carried out on the tested beams using LS-DYNA, which is transient nonlinear dynamic analysis software. The numerical analysis carried out involved case studies for TRM modeled, with and without mortar. Good agreement was achieved between the experimental and numerical results especially for the ultimate load carrying capacity for the case of FE models incorporating mortar. The study was extended numerically to include additional cases of TRM-strengthened specimens with more number of TRM layers as well as a case of FRP-strengthened specimen.

The unique features of ultra-high-performance concrete (UHPC) in damage tolerance, energy absorption, and deformability were combined with the superior performance of concrete-filled fiber-reinforced polymer (FRP) tubes (CFFTs) to develop a novel hybrid system of FRP tube and UHPC, and the cyclic behavior of this system evaluated. Four specimens were tested. Two were steel-reinforced: one with conventional concrete (RC), and the other (RUHPC) with UHPC within twice the plastic hinge length and conventional concrete for the remainder of the column length. The other two had FRP tubes: one filled with conventional concrete (CFFT), and the other (UHPCFFT) filled with UHPC within twice the plastic hinge length and conventional concrete for the remainder of the column length. Each column was tested as a cantilever under a constant axial load and reverse cyclic lateral loads applied incrementally in displacement control. Each of the tubed specimens without any internal reinforcement achieved the same flexural strength and ductility as its steel-reinforced counterpart. Specimen UHPCFFT showed significantly higher flexural strength and initial stiffness, lower residual drift, and relatively similar energy dissipation as compared with Specimen RC. The proposed hybrid system can be optimized for strength and ductility as a viable alternative to the conventional RC column.

The compressive behavior of a steel-concrete composite column encased in a fiber reinforced polymer (FRP) tube is evaluated experimentally for columns with various slenderness ratios. The composite column consists of a FRP tube surrounding a steel I-section that is subsequently filled with concrete. A total of nine column specimens were tested ranging between 500 and 3,000 mm in height. Confinement and composite action resulted in enhanced compressive behavior of the composite columns. Maximum confinement occurred in the short column (slenderness ratio less than 0.2). Confinement action reduced with increased height of the column specimens. The column load- carrying capacity, ultimate axial strain, and compressive strength of the confined concrete core in the longest specimen (slenderness ratio of 0.9) were reduced to approximately 59, 14, and 51% of the short column values, respectively. A buckling strength curve of the composite columns was developed on the basis of the experimental results.

In this study, pultruded glass fiber reinforced polymer (GFRP) corrugated plates, connected together through pin-and-eye connections, were investigated as stay-in-place (SIP) forms for concrete decks. The SIP form completely replaced the bottom layer of reinforcement, whereas a top GFRP mesh was provided. Special attention was given in simulating the details of deck connection to supporting girders. Full-scale deck specimens, including a control deck with conventional steel reinforcement, were cast on concrete supports simulating a girder spacing of 1,780 mm. The 410-mm-wide supports had a rough surface finish along with protruding steel stirrups to simulate the flange of an AASHTO type III girder. An additional cantilevered specimen was tested to examine the feasibility of using SIP forms in deck overhangs at exterior girders. The study also investigated the effects of GFRP plate thickness and bond with concrete on performance. All specimens, except the cantilevered one that failed in flexure, had a punching shear failure while the GFRP pin-and-eye connections remained intact. The system demonstrated excellent performance, with safety factors ranging from 3.5 to 4.9, relative to the half-axle service load, including impact factor, of standard design trucks. Deflections at service were less than span/1,600. The system also displayed significant deformability associated with gradual loss of strength beyond punching shear, a major advantage over conventional decks. Adhesive bond improved stiffness but had little effect on strength. Constructability issues are also addressed along with the detailing particular to this system.