Journal of Composites for Construction

This paper presents the results of an experimental study carried out to evaluate the structural behavior of precast concrete culverts reinforced with glass fiber–reinforced polymer (GFRP) bars. Five full-scale GFRP reinforced large culverts having a clear span of 1,530 and 960 mm high were tested under different combinations of lateral and vertical loads. The general behavior of the culverts including crack pattern, force-displacement behavior, ultimate capacity, and failure mode were evaluated and analyzed. The behavior of the culverts at the serviceability limit state were also monitored in terms of crack width and deflection. Punching shear failure at the top slab was found to be the typical mode of failure in all of the culverts tested. Failure was characterized by crushing of concrete with no rupturing of the longitudinal GFRP-reinforcement. The results indicated that GFRP-reinforced concrete culverts have an acceptable load-carrying performance with a small residual deflection and crack width. The presence of the lateral load, simulating the effect of soil, resulted in upward deflection (hogging) of the culverts and increased the load-carrying capacity of the culverts. Maximum deflections were observed when two walls of the culverts were unrestrained. The experimental study presented here indicated that serviceability limit state (deflection and crack width) rather than the strength governs the design of GFRP-reinforced concrete culverts. This study showed that GFRP can be a suitable alternative to steel for precast concrete culvert application, especially in aggressive environments where steel bars are vulnerable to corrosion.

The fire design of reinforced concrete (RC) members with glass fiber–reinforced polymer (GFRP) bars comprising lap splices and cold anchoring zones requires the explicit consideration of the GFRP–concrete bond degradation with temperature; however, few studies in the literature have addressed this issue. This paper presents numerical investigations in which three-dimensional finite-element models were developed to simulate fire resistance tests performed in GFRP-RC slab strips subjected to a fire load and current standards. The slabs comprised continuous and spliced reinforcements, as well as different concrete cover thicknesses and concrete strengths. In the models, the GFRP–concrete interaction was simulated by means of previously calibrated local bond stress–slip laws at different temperatures. This study provided new insights into the fire behavior of GFRP-RC flexural members, confirming that their fire resistance can be drastically reduced when lap splices, designed for ambient temperature conditions, are directly exposed to heat and that even adopting relatively low concrete cover, fire endurances above 120 min can be attained provided that the bars’ anchors remain sufficiently cold.

Abstract

This study presents a numerical model to evaluate the flexural behavior of concrete beams reinforced with hybrid fiber-reinforced polymer (FRP) and steel bars. The bond–slip action between the reinforcing bars and the surrounding concrete was considered. The cracking load, yielding load, ultimate flexural capacity, strain development, moment–curvature relationship, and midspan deflection were predicted using the proposed numerical model. The model was compared with the experimental results available in the literature and the theoretical results from the design codes. The equations from the design codes underestimated the cracking load by 7%–9%. The averages of numerical yielding moments without and with a bond were 0.96 and 0.97, respectively. The predicted yielding moment considering the bond behavior was approximate to that of neglecting bond. The predicted ultimate flexural capacity without a bond was 3% higher than the test result, whereas the predicted result with the bond was 1% lower than the experimental result. Both design codes underestimated the mid-span deflection under service loads for hybrid-RC beams. The postyielding deflection and deflection behaviors at the service load level were captured well by the proposed model. A parametric study investigated the effects of the reinforcement arrangement. Beams [with a glass FRP (GFRP) reinforcement ratio of 2.06%] with reinforcements placed in one layer presented the highest ultimate capacity, 19.6% and 14.0% higher than those of GFRP bars placed at the outer and inner layers, respectively. Beams with GFRP bars placed in the outer layer showed the highest deformability index when the GFRP reinforcement ratio was less than 1.75%.

Practical Applications

This study presents a reliable model to simulate the flexural behavior of concrete beams reinforced with hybrid fiber-reinforced polymer (FRP) and steel bars. The bond–slip action was considered in the model. ACI 318-19 and CAN/CSA A23.3-19 underestimated the cracking load by 7% and 9%, respectively. In addition to the tensile strength of the concrete and the geometry of the section, the layout of the reinforcement was considered in the proposed model, thus achieving a more accurate prediction of the cracking load. The model without bond stress overestimated the ultimate flexural capacity of compression-controlled members and underestimated the ultimate capacity of tension-controlled members. Both ACI 318-19 and ACI 440.1R-15 underestimated the midspan deflection under service loads for hybrid-RC beams. The strain in FRP bars was highly related to the effective reinforcement ratio based on the strength transform (Lau’s equation) for hybrid-RC beams. For a designed strain limit for the FRP bars, the required effective reinforcement ratio for beams can be obtained from Fig. 9(b). Beams with reinforcements placed in one layer exhibited the highest ultimate capacity.

Abstract

The structural performance of reinforced concrete (RC) beams strengthened in shear with embedded through-section (ETS) glass fiber-reinforced polymer (GFRP) bars is experimentally and analytically investigated. Three-point bending tests are performed. The investigated parameters include the number of existing steel stirrups (ρ_sw = 0.28%), concrete compressive strength ($f_c^{\mathrm{\prime }}$ = 27 and 43 MPa), shear span-to-effective depth ratio (a/d = 2.4, 3.6, and 4.8), anchorage presence (with and without anchorage), and anchorage properties (steel and GFRP anchorage systems, as well as the anchorage length). The results indicate that the shear capacity and stiffness of the beams are enhanced by applying ETS-GFRP, increasing concrete strength, and decreasing shear span-to-effective depth ratio. The ETS-GFRP-strengthened beams exhibit a more ductile failure mode than the unstrengthened beam owing to concrete crushing in loading areas. The beam stiffness depends significantly on the anchorage presence and properties, and the beam shear capacities differ considerably for different anchorage systems. Anchorage with four steel nuts or two GFRP nuts at the ETS bar ends provides the highest shear resistance and stiffness for the ETS-strengthened beams. The results of this study suggest that the details and configuration of the anchorage system should be carefully considered for the development of unanimous specifications. Additionally, previously proposed shear models can be used to conservatively analyze test results with sufficient accuracy. The newly developed model for estimation of the shear strengths of ETS-GFRP-strengthened beams and the effective strains in ETS-GFRP bars agrees well with the test data.

Practical Applications

The experimental results obtained from the present study demonstrate the potential of the embedded through-section (ETS) method for practical applications in the shear strengthening of the reinforced concrete (RC) beams. The predrilled holes through the beam height are made at the marked positions, which could be determined by a rebar detector. Next, the adhesive resin is fully injected into the holes prior embedding the fiber-reinforced polymer (FRP) bars. In the present study, the glass fiber-reinforced polymer (GFRP) bars are used. Then, the ends of each FRP bar are anchored with screwed nuts. Comparing with the unstrengthened beam, the ETS-strengthened beam offers a larger capacity, more ductility, and safer failure. The shear performance of the ETS-strengthened beams is proportional to the concrete compressive strength. The decrease of the shear span-to-effective depth ratio increases the shear resistance of the ETS-strengthened beams. The anchorage at two bar ends with two GFRP or four steel nuts is deemed to be most effective. Additionally, the proposed shear strength model can be used for the design of the beam with an ETS strengthening system.

The existing infilled reinforced concrete (RC) buildings’ poor energy performance is responsible for a significant part of the energy consumption in the European Union (EU). In addition, recent earthquakes showed the seismic vulnerability of the existing RC buildings that were not designed according to modern codes, where several casualties, collapses, and economic losses were reported. Around 40% of the EU buildings are located in seismic regions and designed with substandard safety requirements, of which 65% need both energy and seismic retrofit. New strategies are necessary to simultaneously improve the energy efficiency and seismic vulnerability of new constructions. Apart from the modern seismic and energy codes, new materials are being developed by the construction industry that can play a significant role in the next few decades. Based on this motivation, this paper aims to study the efficiency of using textile-reinforced mortar (TRM)-based solutions to improve the seismic behavior of masonry infill walls made of lightweight and energy-improved masonry blocks. This holistic strategy is designed for new constructions. For this, eight strengthened energy-improved infill walls were subjected to flexural strength tests to validate the TRM efficiency using a low-strength and a high-strength textile mesh and study the effect of using connectors. All the tests consisted of applying a monotonic out-of-plane tests were performed through a one-point load approach. The results will be presented in terms of out-of-plane force–displacement responses, flexural stress, and damage evolution. Lastly, a state-of-the-art discussion is carried out to analyze possible relationships between the textile mesh tensile strength and the flexural strength of the walls.

One typical application of textile-reinforced mortar (TRM) is as a confining material for concrete. The compressive behavior of TRM-confined concrete is often predicted by referring to the models of fiber-reinforced polymer (FRP)-confined concrete. Such reference may be inappropriate because TRM with apparent axial stiffness and nonlinear stress–strain behavior differs from linear elastic FRP. This paper first presents the experiments and analyses of the results to reveal the confinement mechanism of basalt TRM (BTRM) and then proposes an analysis-oriented stress–strain model for BTRM-confined concrete. Twelve compression tests were carried out on concrete columns with and without BTRM and with different textile layers (0–4 layers). Deformations of the BTRM shells and the concrete cores were measured in parallel to understand the mechanical behaviors of the shells/cores and their interactions during loading, i.e., confinement mechanism. The BTRM shell not only improved the compressive strength and the ultimate strain due to the confinement effect but also provided axial resistance through shear stresses at the core–shell interface. Both effects were quantified by a newly established model of which the key novel feature is the updating of the confinement pressure equations based on a careful description of core–shell interactions. The confinement pressure induced by the BTRM shell is separately evaluated in elastic and damaging stages differentiated by the cracking of the mortar matrix. The accuracy of the proposed model is confirmed through comparisons with new test data.

This paper investigates the performance of flax textile–reinforced mortars (FTRM) as a retrofitting solution for unreinforced masonry. Six medium-scale walls were subjected to in-plane cyclic shear tests. Four of the specimens were retrofitted on both sides with one or two layers of flax textiles embedded in lime-based mortar. One bare wall and one wall strengthened only with lime-based mortar were examined as reference samples. FTRM provided up to 118% higher shear load and ultimate drift and promoted the development of energy dissipation mechanisms, while ensuring structural integrity. Based on the experimental evidence, the contribution of individual shear resisting mechanisms was assessed and existing design models were found to overestimate the stress that can be developed in the flax textile when two layers were applied. A new design model that adopts a more rational limiting strain value and accounts for the contribution of the mortar and the unique mechanical performance of FTRM systems was proposed and validated against an experimental database, including natural and advanced textile-reinforced mortar systems.

An in-depth assessment is conducted to examine the analytical and experimental results that formed the basis of the net-section tensile rupture strength of single-bolt connections, stipulated in the ASCE Pre-Standard for Load and Resistance Factor Design (LRFD) for Pultruded Fiber-Reinforced Polymer (FRP) Structures. As a result of our findings, we propose that current ASCE net-tension tensile strength design criteria be consolidated and revised to a simple form attractive for routine uses by practicing engineers. The proposed simplified nominal resistance equation and the results from single-bolt double-lap connection experiments were used to determine the resistance factor ϕ with a target reliability index of 4.5.

Near-surface-mounted (NSM) carbon fiber–reinforced polymers (CFRPs) have emerged as a promising strengthening technique to improve the flexural performance of reinforced-concrete (RC) structures. Although these systems have been investigated extensively for flat soffit RC beams, their performance when applied to concavely curved soffit members requires investigation. This paper presents the results of an experimental program conducted to investigate the behavior of concavely curved soffit RC beams strengthened in flexure with NSM CFRP rods. Twenty RC beams were designed, fabricated, and statically tested, including 15 beams that contained curved soffits with varying degrees of curvature ranging between 5 to 20 mm/m. The remaining five beams were flat soffit and were used as control beams. The ultimate capacity, failure mode, flexural stiffness, ductility, and level of FRP strain prior to debonding of these beams are analyzed and discussed. This study identifies gaps in existing design guidelines and codes and presents recommendations for designers on NSM technology.

To better understand the effect of initial static loading on the dynamic shear performance of concrete deep beams reinforced with basalt fiber–reinforced polymer (BFRP) bars, a three-dimensional mesoscale numerical model was established considering the strain rate effect of each material and the interaction between concrete and BFRP bars. The effect of the initial static loading on the damage evolution and failure mechanism of the concrete deep beams (shear span ratio λ = 1.0) reinforced with BFRP bars (BFRP-RC deep beams) with different stirrup ratios was analyzed. The results prove that: (1) the shear capacity, failure mode, and deformation capacity of BFRP-RC deep beams have a strain rate effect, that is, the shear capacity, deformation capacity, and damage degree of beams increase with the increase of strain rate; (2) the increase of strain rate and stirrup ratio can improve the shear capacity and deformation capacity of beams, while the strain rate plays the leading role; and (3) the shear capacity, deformation capacity, and damage degree of BFRP-reinforced concrete deep beam decrease as the initial static loading increases under different strain rates. However, the increase in strain rate will weaken the effect of initial static loading on the dynamic performance of the beams.

In this study, a parallel-tendon and dispersed-tendon cable anchor system (CAS) for high-strength carbon-fiber-reinforced polymer (CFRP) cables were investigated based on a previously developed load transfer component (LTC). The static behaviors of three cables comprising 37 CFRP tendons with a 7-mm tendon diameter were experimentally evaluated and the failure mechanism of the cables was numerically revealed. The parallel-tendon cable exhibited an integral pull-out failure caused by a shear failure of the LTC, while the dispersed-tendon cables showed a mixed shear and compressive failure caused by an excessive axial tensile strain difference and wedge action of the LTC. From loading end to free end, the shear stress of the LTC first increased rapidly, and then increased slowly with fluctuations, and finally peaked the free end. The experimental and numerical results agreed well in the axial cable strains and shear stresses of the LTC. By optimizing parallel tendons into dispersed tendons in the anchor zone, the anchor efficiency of the cable was improved from 60% to 91%. Correspondingly, the cable force was improved from 2,684 to 4,070 kN. The increase in the anchor length and decrease in the conical angle can decrease the stress concentration of the dispersed-tendon CAS.

Various carbon fiber–reinforced polymer (CFRP) strengthening systems have been developed to increase the fatigue lifetime of existing aging steel structures. According to the literature, the results of fatigue tests on CFRP-strengthened steel plates showed a significant increase in the fatigue lifetime of the specimens, compared with the bare ones. In particular, the fatigue lifetime extension was more pronounced for short initial crack sizes (i.e., low initial damage level). In this study, the fatigue-crack growth curves in bonded CFRP-strengthened single edge notched tension (SENT) specimens were numerically investigated. The proposed numerical approach adopted a cyclic cohesive-zone model (CCZM), which enabled the simulation of crack growth in steel plates, through the definition of a scalar damage variable (k). The selected model contained some parameters that did not possess a precise physical meaning and therefore were not amenable to direct measurement. Therefore, a robust identification procedure was proposed to calibrate the model parameters that governed fatigue behavior, which was based on the response of unstrengthened specimens in the crack propagation curves. The successful identification was then validated by comparison with the measured response of the strengthened SENT specimens, which were modeled by adopting the same identified model parameters. The adhesive between the CFRP laminate and steel substrate was simulated by defining an elasto–brittle surface-to-surface contact model, whose properties were selected based on well known approaches that were proposed in the literature.

Concrete beams reinforced in shear and flexure with linear elastic and brittle glass fiber–reinforced polymer (GFRP) bars show differences in behavior when compared with the traditional steel-reinforced concrete beams. The flexural design of these beams follows similar principles as the design of steel-reinforced concrete members, except that the cross section is over-reinforced to compensate for the lack of reinforcement ductility. GFRP-reinforced beams are designed in shear using semiempirical modifications to the design equations for steel-reinforced concrete. The modified equations have not been well studied for beams with high shear span to depth (a/d) ratios. The presented research program is composed of three-point bending tests of ten GFRP-reinforced concrete beams, with a/d slenderness ratios from 4.5 to 10.5 with constant flexural reinforcement and varied shear reinforcing. The observed mode of failure transitioned from shear to flexure-controlled with increasing specimen slenderness and increased shear reinforcing. All failures were controlled by concrete behavior, either in tension for beams without shear reinforcement or compression for beams with shear reinforcement. The inclusion of GFRP stirrups in the beams prevented brittle failures by providing confinement to concrete. Comparisons with the current design rules showed good agreement with experimental results. However, the relative contribution of concrete and reinforcement to shear-carrying capacities differed in the code predictions from results derived from measured strains.

This study presents a numerical model to characterize the fracture process of a reinforced concrete (RC) beam strengthened with fiber-reinforced polymer (FRP) in detail. A numerical model based on the application of cohesive elements was developed. Mixed-mode constitutive models were proposed to characterize the mechanical behavior of the FRP–concrete interface, the concrete potential fracture surfaces, and the rebar–concrete interface. The normal separation of the interface and its coupling effect on the shear behavior were considered in the constitutive model. In addition, the friction effect was explicitly considered in the constitutive model. Three different typical cases of FRP-strengthened RC from other experimental research were selected to validate the numerical model developed in this paper. Finally, the influence of different constitutive models on the simulation accuracy was analyzed.

Currently, the effect of the concrete substrate on the load-bearing capacity of externally bonded carbon fiber-reinforced polymer (CFRP) strips is determined in the guidelines solely on the basis of the concrete strength. In addition to strength, surface preparations can improve the bond resistance by exposing the aggregates of the substrate. However, the interlocking also depends on the parameters that derive from the inner concrete structure such as the aggregate grain dimension and shape, as well as the air void distribution. Therefore, the influence of the concrete inner structure on the bond is investigated with double shear tests by comparing specimens with equivalent concrete strength and varying grain shape and dimension. Bond parameters are calculated using a novel procedure based on optical measurements. Furthermore, crack paths are analyzed by means of computed tomography (CT) scans, which prove to be an essential inspecting technique for characterizing the inner concrete structure. The fracture energy is approximately 30% higher for concrete with a maximum grain size of 8 mm compared to an equivalent mortar with 4 mm maximum grain size.

This paper provides an experimental study on the compressive behavior of steel fiber–reinforced polymer composite bars (SFCBs) confined in concrete columns. Thirty reduced-scale concrete columns, reinforced with different longitudinal SFCBs and fiber-reinforced polymer spirals, were tested under monotonic compression. The results showed that the maximum compressive peak stress of the SFCBs was approximately 50% of their tensile strength, and it was generally lower for those SFCBs that had a relatively high postyield stiffness ratio. The postyield stage of the compressive stress–strain curve of well-confined SFCBs did not develop with a stable postyield stiffness as in nonconfined monotonic compression, but first developed with a stiffness almost equal to zero and then increased rapidly until the compressive peak stress point was reached, which was potentially due to the forced transverse deformation effect. Because the actual compressive contribution of the SFCBs in concrete columns could be overestimated due to this effect, a tentative modification method was first proposed in this paper to calibrate the existing compressive stress–strain model of the SFCBs.

This study investigated the axial-impact resistance of unconfined and CFRP-confined UHPC. External confinement was provided by one to three plies of CFRP wraps with confinement ratios ranging from 0.126 to 0.378. A series of single- and multiple-impact tests was conducted using a Ø100 mm split Hopkinson pressure bar apparatus at mean strain rates ranging from 25 to 120 s⁻¹. The dynamic behaviors of the specimens were examined and compared with those under quasi-static loading. The results indicate that the confinement of CFRP can significantly improve the axial-impact resistance of UHPC, exhibiting a strong strain-rate dependency. However, this sensitivity decreases with an increase in the confinement ratio. The dynamic failure modes of the CFRP-confined UHPC are different from those in the static tests, and the CFRP confinement ratio and impact energy determine the impact failure mode. Unlike in unconfined UHPC, a history of multiple impacts results in considerably lower accumulative damage in the confined UHPC. A new model was proposed to estimate the dynamic compressive strength of the CFRP-confined UHPC by considering the coupling effects of the confinement ratio and core concrete lateral inertia.

The research addressed in the paper is aimed at calibrating a numerical model developed by using a free open-source finite-element code for the assessment of the structural performances of historical masonry buildings strengthened using the textile-reinforced mortar (TRM) technique. TRM is a near-surface-mounted system, which couples inorganic matrices with fiber-based textile or meshes. The main purpose is to develop a multiple-level numerical approach, starting with the detailed modeling of components and interfaces, followed by a computationally efficient intermediate level model, using layered elements, for the calibration of a lumped plasticity-based model suitable for the global analysis of structures. In this paper, the first research results are presented. In particular, a broad literature review concerning the mechanical characterization and analysis of TRM systems is collected. Then, the calibration of the numerical model, the validation through comparison with the results of experimental characterization tests available in the literature (tensile, shear bond, and in-plane shear tests) and a sensitivity analysis are reported. Nonlinear static analyses were performed, considering the nonlinearity of the composite material components and interfaces. The model was capable of accounting for the main parameters affecting the behavior of the composite material, such as the reinforcement ratio and orientation, the mortar characteristics and the wire–mortar interaction and proved to be a valid tool to investigate the optimization of TRM applicative details.

This paper investigates the effectiveness of carbon fiber–reinforced polymer strips ties (CST) as the transverse reinforcement for normal strength glass fiber–reinforced polymer reinforced concrete (GFRP-RC) square columns. The axial compressive behavior of GFRP-RC columns transversely reinforced with CST has been investigated. In particular, the effectiveness of CST configurations, confinement efficiency, and center-to-center spacing of the CST was investigated. A total of 13 specimens with 200 × 200 mm cross section and 800 mm height were tested until failure. One specimen was longitudinally reinforced with steel bars and transversely reinforced with square steel ties as a control specimen (S-RC). The remaining 12 specimens were longitudinally reinforced with GFRP bars and transversely reinforced by either square (S), or square overlapping square (SS), or square overlapping circular (SC) configurations of the CST. Test results showed that the specimens with SC configuration of CST achieved higher confinement efficiency and deformability than the specimens with S and SS configurations of the CST. In addition, the increases in the confinement efficiency and deformability for the reduction of the spacing of the CST are more pronounced for the specimens with SC configuration of the CST compared to the specimens with either S or SS configuration of the CST.

Replacing steel reinforcement with glass fiber-reinforced polymer (GFRP) reinforcement is an effective solution to avoid the corrosion problem in precast concrete tunnel-lining (PCTL) segments. In addition, using high-strength concrete (HSC) can improve the durability of concrete in the harsh environment of tunnels. This study pioneers in investigating the structural performance of GFRP-reinforced PCTL segments constructed with HSC by testing four full-scale specimens measuring 3,100 mm in length, 1,500 mm in width, and 250 mm in thickness under a three-point bending load. The investigated parameters included concrete compressive strength [normal-strength concrete (NSC) and HSC], reinforcement ratio (0.48% and 0.90%), and tie configuration (closed ties with U-shaped ties). The results are presented and discussed in terms of cracking behavior, failure mechanism, deflection behavior, strain in reinforcement and concrete, ductility, and deformability. An analytical investigation was carried out to evaluate and modify the existing design provisions (ACI 440.1R-15, CAN/CSA S806-12, CAN/CSA S6-19, and AASHTO 2018) for use in predicting the shear and flexural strength of GFRP-reinforced HSC PCTL segments. The results indicate that using HSC improves the flexural and shear strength of GFRP-reinforced PCTL segments, while it has a minimal effect on the postcracking stiffness and cracking behavior of the specimens. According to the analytical investigation, the procedure presented to modify ACI 440.1R-15 can be used to predict the flexural capacity of GFRP-reinforced HSC PCTL segments with high accuracy. In addition, CAN/CSA S806-12 predicts the shear capacity of HSC-GFRP-reinforced PCTL segments with an error of less than 7.0%.

Angle-ply (±55°) fiber-reinforced polymer (FRP) tubes are widely available and have been used in concrete-filled FRP tube (CFFT) members. Two observations have been reported regarding the behavior of these tubes in tension: a remarkably nonlinear stress–strain response and a significant increase in their tensile strength and stiffness when filled with concrete. To better understand these phenomena, a robust finite-element model is developed using LS DYNA software and validated against a diverse experimental database. It showed that the nonlinear behavior of the tube is mainly due to matrix cracking perpendicular to the fibers and to a lesser extent due to in-plane shear along diagonal bands. Concrete filling restrains the large radial and circumferential contraction of the hollow tube under longitudinal tension, thereby generating significant hoop tensile stresses and consequently a state of biaxial tensile stress. A failure envelope under such stress combination was developed and far exceeded uniaxial strength in either direction. A parametric study was performed on 68 new models with various properties. The longitudinal tensile strength (σ_max) of CFFT tubes with fiber angles (θ) relative to longitudinal axis of 35°, 45°, 55°, 65°, and 75° increased 2.9, 4.1, 3.3, 2.8, and 1.4 times, respectively, that of hollow counterparts. Design-oriented equations were developed to represent the enhanced longitudinal bilinear stress–strain curve when the tube is filled with concrete. It can be used for flexural strength calculations of CFFTs, which would otherwise be grossly underestimated if calculated using hollow tube properties reported by the manufacturer or established from longitudinal coupon tests or from classical lamination theory.

Glass fiber-reinforced polymer (GFRP) bars are used as internal reinforcement in many structural applications. The structural performance of GFRP-reinforced concrete elements is dependent on the physical and mechanical properties of GFRP reinforcement. There is a lack of experimental data on the flexural behavior of concrete beams reinforced with ribbed GFRP bars. This study evaluates the flexural strength and serviceability performance of concrete beams reinforced with ribbed GFRP bars. A total of 11 GFRP-reinforced concrete beams with dimensions of 4,350 × 400 × 200 mm (length × height × width) were constructed and tested under a four-point loading test setup. The main test parameters were the concrete cover, reinforcement ratio, bar spacing, and confinement due to the transverse reinforcement in the bending zone. The results uantify the effect of increasing the reinforcement ratio on the increase in the ultimate capacity and the reduction in deflection at the service and ultimate stages. In addition, the results showed that the increase in the confinement in the bending zone due to closely spaced stirrups resulted in a higher ductility index and ultimate capacity with no considerable effect on the postcracking stiffness of the beams. Moreover, based on the experimental results, the accuracy of deflection equations available in design codes and guidelines is evaluated and discussed.

Inconsistency and large scatter are widely observed in comparisons between experimentally obtained and analytically predicted shear capacity contributed by fiber-reinforced polymer (FRP) composites in FRP-strengthened reinforced concrete beams using existing codes and models. Shear crack configuration, overlooked by many design codes, guidelines, and analytical models, can possibly attribute to such a scatter and inconsistency. To that end, an innovative analysis approach was proposed, in combination with a conducted experimental study, to investigate the effect due to such a shear crack configuration. It was found that large axial rigidity of the FRP reinforcement and the shear span-to-effective depth ratio tended to create distributed shear cracks, which changed the shear behavior of strengthened beams by decreasing the bond length and the resultant FRP shear contribution. The strain of the shear reinforcement increased with the increase of the crack width, which reached the peak value after the peak load level. Since not all steel stirrups yielded, the shear contribution of the concrete itself was greatly underestimated. It is suggested to propose separate sets of design equations corresponding to different categories of shear crack to improve the precision and minimize such a scatter.

This paper presents an experimental investigation of the fatigue behavior of ultrahigh-performance concrete (UHPC) beams prestressed with external carbon fiber-reinforced polymer (CFRP) tendons. Seven T-shaped beams were tested, and the effects of the effective prestressing stress, partial prestressing ratio, and fatigue load level on the flexural behavior and stiffness were analyzed and presented. Overall, the CFRP tendon–anchor assembly exhibited excellent fatigue performance. All tested fully prestressed beams survived 2 million cycles in fatigue tests, and the variation in their flexural capacity was limited. The partially prestressed beam failed after approximately 97,200 cycles due to fatigue fracture of the internal reinforcement. After fracture of the tensile steel bars, the partially prestressed beam behaved similarly to the fully prestressed beam and sustained more than half of the flexural capacity after 2 million cycles. A higher effective prestressing stress was favorable for maintaining the stiffness of CFRP prestressed UHPC beams.

Use of fabric-reinforced cementitious matrices (FRCM) is a very efficient strengthening solution for improving the structural behavior of existing masonry elements. FRCM are capable of improving the load-bearing capacity of masonry panels, at the same time providing more ductile behavior. However, the mechanical performances of these materials could be significantly affected by environmental conditions, such as exposure to thermal variations. This aspect should be properly assessed by guidelines and standards devoted to the design of strengthening interventions. Within this framework, the objective of the present research was to evaluate the effect of a temperature increase on the tensile behavior of various FRCM systems, composed of steel, basalt, or aramid-glass fibers and lime-based or cement-based mortar matrices. Tensile tests were performed for each system under different thermal conditioning protocols, comprising different target temperatures, exposure periods, test conditions, and adopted heating sources. The test results showed that the effect of temperature is more evident in the first phases of the tensile tests, that is, during the uncracked phase and the mortar matrix cracking phase, whereas it is less significant in the final phase, which was more related to fiber behavior. Comparisons between the different thermal conditioning procedures are critically discussed within the paper and, in light of the results obtained, recommendations are included to optimize the testing procedures for future research and qualification procedures.