Abstract Prestressed concrete (PC) highway bridges often experience deterioration over time, necessitating structural strengthening to restore or increase capacity and maintain serviceability. One common external strengthening technique is the application of fiber-reinforced polymers (FRPs). However, limited research has addressed the deflection analysis of FRP-strengthened PC girders incorporating harped prestressing strands. This study presents a nonlinear sectional analysis, simplified through a trilinear moment–curvature response, to develop closed-form analytical expressions for the deflection of simply supported PC girders under various loading conditions. Using the trilinear moment–curvature response and moment-area theorem, the procedure derives closed-form deflection equations for uncracked, postcracked, and postyielded regions. The developed equation is used to compare the present analytical results with available experimental results, as well as the predictions of other deflection equations proposed in the literature, such as Branson and Bischoff's effective moment of inertia equations. The variables influencing the deflection of FRP-strengthened PC girders with harped strands, the current procedures in the literature to determine instantaneous deflection, and a proposed method for the effective moment of inertia after cracking of PC girders with harped strands are presented.
Abstract This paper evaluates the shear behavior of reinforced concrete beams incorporating a novel hybrid shear reinforcement system. The system combines internal steel stirrups for ductility with external basalt fiber–reinforced polymer (BFRP) stirrups for corrosion resistance, along with basalt macro fibers (BMFs) in the concrete matrix. This configuration optimizes material placement according to its mechanical and durability advantages and assesses the interaction between hybrid stirrups and BMFs to further enhance structural performance and long-term durability. Nine beams were fabricated and loaded in four-point bending tests to examine the effects of transverse reinforcement type (steel, BFRP, hybrid), BMF volume fraction (0%, 0.75%, 1.5%), and shear span-to-depth ratio ( a/d = 2.0, 2.8, 3.5) on failure mode, shear capacity, crack control, and deformation behavior. The results revealed that, at an equivalent shear reinforcement ratio, beams with hybrid stirrups exhibited superior stress redistribution and ductile failure mode, demonstrating enhanced shear strength by 4% and 19% compared with beams with only steel or FRP stirrups, respectively. The incorporation of steel in the hybrid system improved stiffness and increased ductility by 42% relative to beams with pure FRP stirrups. The BMF inclusion led to enhanced postcracking tensile resistance, narrower crack widths, and an increase in the ultimate load capacity up to 46%. Reducing the a/d ratio from 3.5 to 2.0 produced a 53% decrease in maximum mid-span deflection and a 34% increase in ultimate load. Strain data demonstrated effective collaboration, with internal steel stirrups reaching their yield point, while external FRP stirrups remained intact. Furthermore, the shear capacity of the hybrid stirrup–reinforced beams was evaluated using the provisions of available design codes, with the most accurate estimate among these codes having an average experimental-to-predicted shear capacity ratio ( V exp / V pre ) of 1.23.
Abstract Postfire retrofitting of reinforced concrete (RC) columns using fiber-reinforced polymer (FRP) confinement can restore axial capacity, yet the performance of discontinuous, hybrid, and prestressed systems under severe thermal damage remains insufficiently understood. This study investigates the axial compressive behavior of circular, square, and rectangular RC elements exposed to 700°C for 90 min and retrofitted using four strategies: (1) full wrapping with carbon fiber-reinforced polymer (CFRP), (2) CFRP partial strips, (3) a hybrid system consisting of a full glass fiber-reinforced polymer (GFRP) jacket with outer CFRP partial strips, and (4) prestressed CFRP partial strips applied via the strip constriction technique. Axial compression tests were conducted to evaluate strength recovery, stress–strain response, stiffness restoration, and confinement efficiency. Full CFRP wrapping achieved the highest strength recovery, in some cases exceeding original unheated capacity, while partial strip wraps provided greater deformability but limited stiffness restoration. Hybrid systems enhanced both strength and stiffness by mitigating stress concentrations in unwrapped zones. Prestressed confinement significantly increased initial stiffness and peak load by activating early confinement, albeit at the expense of reduced ultimate ductility. To generalize these findings, a unified strength model is proposed for FRP-confined heat-damaged concrete, incorporating (1) a thermal modification factor to account for fire-induced degradation, (2) a stiffness-dependent interaction formulation for hybrid confinement, and (3) a prestress enhancement factor for actively confined systems. Validation against an extensive experimental database demonstrates accurate and unbiased strength prediction across various cross sections and confinement configurations. The proposed framework provides a comprehensive basis for performance-based rehabilitation design of fire-damaged elements.
Interface shear reinforcement plays a critical role in ensuring load transfer across concrete cold joints. Although the increasing use of glass fiber-reinforced polymer (GFRP) bars in structural applications, their application as interface shear reinforcement remains not yet comprehensively addressed in current design provisions. This study investigates the performance of GFRP reinforcement in cold-jointed reinforced concrete (RC) through an experimental program comprising 18 push-off specimens, varying the interface condition (intentionally roughened, as-cast, and smooth), reinforcement ratio (0.48%-2.87%), reinforcement shape (closed stirrups, U-shaped bars, and straight bars), and embedment length from the interface plane. Results show that at low reinforcement ratios (<= 0.53%), concrete strength minimally affected the cracking load and the peak load but enhanced postpeak resistance. At higher reinforcement ratios, shear capacity gains were evident; for instance, increasing compressive strength from 35 to 59 MPa enhanced capacity by 27% at a 1.05% reinforcement ratio. Anchorage details significantly influenced postpeak behavior; closed stirrups and U-shaped bars maintained residual resistance, while straight bars with embedment lengths of 6-9 times the bar diameter failed abruptly at approximately 85% of the capacity of stirrup-RC specimens. Extending embedment to 12 times the bar diameter achieved a similar peak capacity but with reduced postpeak deformability. Interface roughening markedly increased load capacity and reduced slip and crack opening compared to smooth joints, whereas roughening from the as-cast condition primarily reduced slip and crack opening without substantially enhancing load capacity. A regression analysis further produced an improved predictive model for the interface shear resistance of GFRP-RC cold joints.
The ability to rapidly strengthen reinforced concrete structures is critical for military and disaster response applications, where conventional strengthening techniques may be impractical due to time, logistical, or technical constraints. This study evaluates the effectiveness of unbonded carbon fiber-reinforced polymer (CFRP) straps installed with mechanical anchors as a rapid strengthening technique for simply supported short-span reinforced concrete bridges. An experimental program was conducted on six 6-m-long reinforced concrete T-beams, including two control specimens and four strengthened beams, incorporating single or double layers of CFRP straps and variations of a custom-designed mechanical anchorage system. The introduction of tensioners improved load sharing by promoting a more uniform strain distribution among the CFRP straps. Experimental results demonstrated that unbonded CFRP strap systems can significantly enhance flexural capacity, achieving strength increases of up to 22% for beams strengthened with a two-layer CFRP configuration. Serviceability was also improved, with reduced deflections at high load levels and visibly delayed crack formation and propagation. Although no intentional prestressing was applied, posttest analysis indicated that beam elongation induced significant additional tensile forces in the CFRP straps during loading. A numerical model was developed to predict the load-deflection response of the strengthened beams and showed reasonable agreement with the experimental results. Overall, the study confirms that unbonded CFRP straps combined with mechanical anchorage provide a viable and practical solution for the rapid strengthening of short-span simply supported concrete T-beams, offering a promising alternative to bonded CFRP systems in time-sensitive applications.
Glass fiber-reinforced polymer (GFRP) headed-end bars were evaluated as shear friction reinforcement for interface shear transfer across concrete cold joints. Fourteen large-scale double L-shaped push-off specimens were constructed and tested under monotonic axial loading using two different concrete strengths (35 and 55 MPa) and five GFRP reinforcement ratios (0.33%-1.00%), together with steel-reinforced and unreinforced controls. It was observed that headed-end GFRP connectors enhanced postpeak stability through improved anchorage and sustained dowel action, whereas higher concrete strength increased peak resistance but promoted larger postpeak drops at low reinforcement ratios. Comparisons with current design provisions and models from the literature indicated that strength-based approaches that mobilize FRP tensile strength can overestimate capacity, whereas formulations using constant cohesion and/or overly conservative strain limits can substantially underestimate capacity. A strain-limited, concrete strength-dependent formulation was therefore proposed by adopting a GFRP strain of 0.003 and a cohesion expression as a function of concrete compressive strength. The proposed model provided improved capacity predictions and reduced scatter relative to the compared formulations for GFRP-reinforced concrete interface shear transfer.
Historic masonry bell towers are among the most vulnerable cultural assets in seismic regions, due to their slender geometries, heterogeneous construction (at different ages), and material decay. This study presents the seismic retrofit of San Domenico's church bell tower in southern Italy through the innovative combination of passive and active composite systems. A comprehensive diagnostic campaign, associated with a drone-aided photogrammetry survey of the geometry, was performed. Results revealed critical vulnerabilities associated with partial overturning and vault thrust, justifying a hybrid strengthening strategy. Passive composite-reinforced mortar systems were applied to vaults to improve shear capacity and limit crack propagation, while carbon fiber-reinforced polymer horizontal ties ensured boxlike behavior. In addition, active prestressed carbon cords introduced stabilizing compressive forces, significantly reducing the global overturning susceptibility. This study establishes a replicable model for combining seismic safety and conservation ethics, demonstrating that heritage structures can evolve into adaptive systems resilient to future seismic events.
In this study, the flexural and shear behavior of steel-reinforced concrete-filled fiber-reinforced polymer (FRP) tubes (CFFTs) with +/- 55 degrees fiber orientation is examined extensively through experimental and numerical approaches. A total of 18 CFFT beams, each 1,219.2 mm (4 ft) long and made of +/- 55 degrees glass FRP (GFRP) tubes with an inner diameter of 203.2 mm (8 in.), were tested under three-point bending. The test variables included GFRP tube thicknesses of 2.7, 4.7, and 6.7 mm, steel reinforcement ratios 1.85% and 3.70%, and shear span-to-depth ratios 0.5, 1.0, and 2.25. All specimens exhibited a pronounced nonlinear load-deflection response and failed in flexure due to GFRP rupture at the bottom tension zone. Despite the low shear span-to-depth ratio of 0.5, which typically promotes shear failure, no shear-governed failures were observed. Experimental results showed that the combination of +/- 55 degrees fiber orientation with internal steel reinforcement, along with reduced shear span-to-depth ratios, contributed to notable improvements in strength, stiffness, and load-carrying capacity. No significant interface slips were observed between GFRP tube-concrete core, and concrete core-steel, establishing strong composite action. Nonlinear finite-element models developed in LS-DYNA (version R10.0) accurately captured the flexural response and failure modes, showing good agreement with experimental results. Overall, the findings underscore the importance of accounting for the nonlinear behavior of +/- 55 degrees GFRP tubes in both experimental and numerical modeling of CFFT systems.
This paper presents experimental work that was conducted to investigate the feasibility of and set the limits for the reuse of fiber-reinforced polymer (FRP) jacketing after exposure to heat damage. In this study, a novel framework is proposed for addressing the suboptimal thermal performance of FRP materials in strengthening concrete. The experimental work outlined herein pursues two primary objectives: (1) to examine the compressive behavior of FRP-confined concrete cylinders under the effect of broad elevated temperature exposure, and (2) to study the feasibility of restoring the effectiveness of the heat-damaged carbon fiber-reinforced polymer (CFRP) jackets by postheating rehabilitation. The behavior and limits of the respective confinement scenarios are examined after exposure to elevated temperatures up to 650 degrees C. A total of 40 concrete cylinders were tested under various FRP wrapping scenarios and heated under a steady-state heating regime. The results indicated that the FRP jacketing effectiveness could be maintained up to 350 degrees C exposure (close to the matrix decomposition temperature). However, upon reaching and exceeding the matrix decomposition temperature, the whole system collapsed due to the complete loss of contact. In such cases, the carbon fabric was cleaned and reapplied with a new layer of epoxy, which improved the performance significantly, with an enhancement ratio of 1.82. In this work, the reuse concept was studied in detail to maximize/explore the sustainability potential of FRP jackets under heat/fire damage conditions. Furthermore, the results show that the success of such a jacket reapplication technique depends highly on the level of fabric oxidation. The results also established explicit limits for exposing FRP jacketing to elevated temperatures and the feasibility of reusing the heat-damaged fabric, along with the practicality of restoring the concrete's original strength. Finally, the findings were further implemented to construct a new framework for evaluating FRP jacketing serviceability and reuse limits.
This study investigates the structural performance of full-scale slender circular concrete columns reinforced with glass fiber-reinforced polymer (GFRP) bars and spirals under various eccentric loading scenarios. Seven full-scale specimens with a slenderness ratio of approximately 45 were tested under concentric loading and varying end moment conditions, including single and double curvature. The study aimed at evaluating the influence of end moment ratio and curvature type on strength, stiffness, and second-order effects. The results revealed that reinforced concrete (RC) columns with unequal end moments exhibited increased load-carrying capacity and lateral stiffness, primarily due to the reduction of second-order effects. In contrast, columns with equal end moments showed more pronounced lateral displacements and higher secondary-to-primary moment ratios, leading to stability-related failure. All specimens ultimately exhibited concrete crushing at the critical compression region; however, the eccentricity configuration influenced the governing member-level failure mechanism, with most specimens showing material-controlled response and a subset exhibiting stability-controlled behavior prior to crushing. The results highlighted that double-curvature columns exhibited improved stability and more controlled load-deformation responses, whereas single-curvature columns experienced intensified second-order effects and were more susceptible to instability-driven failure. A comparison between experimental results and analytical predictions based on American code and Canadian standards for fiber-reinforced polymer (FRP)-RC structures demonstrated the overly conservative prediction of axial capacity and flexural stiffness by current design provisions, primarily due to neglecting or underestimating the compressive contribution of GFRP bars. Flexural stiffness derived from experimental moment-curvature relationships exceeded code-based estimates for most specimens. Experimental peak strengths exceeded the corresponding code-based predictions by 20-30%, confirming the structural adequacy of GFRP reinforcement in slender columns within the investigated range of slenderness and eccentricity.
Compression-casting produces a densified concrete structure that lends itself to precast components operating in aggressive environments. In particular, compression-cast concrete (CC) reinforced with noncorrosive fiber-reinforced polymer (FRP) bars is an attractive combination for structures operating in marine environments. However, in such scenarios, FRP bars are susceptible to damage due to impingement of the coarse aggregate during compaction. This damage may affect durability. This paper presents the first experimental investigation on the effect of compression casting on the durability of glass FRP (GFRP) and basalt FRP (BFRP) bars embedded in concrete and exposed to seawater. Concrete prisms with embedded FRP bars were submerged for up to 360 days in substitute ocean water at a temperature of 40 degrees C. In addition, standalone GFRP and BFRP bars were conditioned in the same manner to study the influence of the concrete cover. The test matrix includes different CC and normal-cast concrete (NC) mixes. The objective was to study the influence of casting method, compressive strength, alkalinity, and use of seawater and sea sand in lieu of fresh water and conventional sand. The residual tensile strength of the FRP bars after conditioning served as a quantitative measure of degradation. Several test methods were employed to characterize pre-exposure surface damage from compression casting and to gain insight into the degradation mechanisms. For a given FRP material, the durability of bars embedded in CC was negligibly affected by surface damage. In fact, strength loss was comparable to that of companion FRP bars, either embedded in NC or standalone. Under all exposure conditions and durations, the BFRP bars underperformed the GFRP bars. Dissolution of the vinyl ester resin due to ester hydrolysis was preliminarily identified as the governing degradation mechanism for all FRP bars, both standalone and embedded in NC and CC, irrespective of mix design and exposure duration.
First-generation structural design standards for pultruded glass fiber-reinforced polymer (GFRP) materials are now available in North America and Europe. The orthotropic nature of pultruded GFRP (pGFRP) makes it susceptible to local buckling, and variation in available material properties adds uncertainty to the calculation of buckling limit states. Additionally, the method of analysis selected by the designer impacts the reliability of the final pGFRP design. In this paper, it is shown that depending on the combinations of these factors, pGFRP design may be very conservative, resulting in inefficient use of material, or may mask expected in situ structural behavior, resulting in undesirable design outcomes. A multiparameter study of cross-section-dominated stability-flange local buckling (FLB) and web local buckling (WLB)-of pultruded GFRP members is presented. In the context of North American and European design standards, two approaches to calculating the local buckling of cross sections assuming either no rotational restraint from adjacent plates (SS) or elastic rotational restraint from adjacent plates (WS) were carried out. Single-web W-, I,- and C-shapes and double-web box sections were considered, each having a significant range of individual plate slenderness. Additionally, the effects of varying material properties were captured by varying transverse (ET/EL) and shear (GLT/EL) modular ratios. It is shown that the ratio of FLB to WLB critical stress calculated using SS assumptions-already a minimum requirement for design-can be used to differentiate behavior and to assist in defining the means by which local buckling limit states can be mitigated. This paper highlights some of the shortcomings of the first versions of design standards for pGFRP. Pultruded GFRP behavior is very sensitive to cross-sectional shape, and reliability calculations-whether material resistance factors or partial factors-need to be reconsidered to include the effects of cross-sectional shape. The predictions of this parametric study were applied to a data set of experimentally obtained local buckling results to make an assessment of the reliability of extant design provisions.
Abstract Recent earthquakes in Türkiye have demonstrated the urgent need for practical strategies that can be scalable to the city level to reduce seismic risk in large substandard reinforced concrete (RC) building stocks. As fiber-reinforced polymer (FRP) jacketing is widely used as an effective technique for the enhancing ductility and shear capacity of substandard RC members, its applicability at the regional scale and its performance limits remain insufficiently quantified. This study proposes a rapid, performance-based evaluation and decision framework to identify buildings that can be effectively retrofitted using FRP jacketing, as well as those for which FRP interventions are inherently inadequate due to global strength or drift limitations. The framework integrates the PERA2019 rapid seismic assessment methodology with code-based provisions for FRP retrofitting and is applied to a large data set comprising approximately 25,000 existing RC buildings in Istanbul. A set of explicit selection criteria is introduced to exclude buildings unsuitable for FRP jacketing. For the remaining buildings, an incremental FRP jacketing scheme is employed to determine the minimum number of FRP plies required to achieve the maximum attainable seismic risk reduction. The results demonstrate that even a single layer of FRP jacketing can substantially reduce seismic risk for a significant portion of the building stock, while additional layers provide diminishing returns. Furthermore, the study quantifies the relationships among retrofit effectiveness, seismic demand, building capacity, and retrofit cost, highlighting the practical boundaries of FRP-based interventions. The proposed framework provides engineers and decision makers with a rational tool for large-scale prioritization and implementation of FRP jacketing in seismic risk mitigation campaigns.
Abstract In this study, eight hybrid glass fiber–reinforced polymer (GFRP)–steel-reinforced concrete (RC) columns were tested under a constant axial load and monotonic or cyclic lateral loads, followed by numerical analyses. These columns were divided into four groups based on the ratio of the GFRP area ( A f ) to the total reinforcement area ( A f + A s ), defined as ρ f/fs . The test results indicated that the 4%-drift cycles caused concrete crushing. The subsequent larger-amplitude cycles caused severe damage, degradation in stiffness and strength, and buckling of steel and/or GFRP bars. For columns with high ρ f/fs , the peak lateral load was reduced by up to 39.5% due to compression failure. An increase in ρ f/fs decreased stiffness and strength degradation while enhancing deformation capacity, recoverability, and postyield stiffness. As ρ f/fs increased from 0 to 1, the behavior transitioned from softening to hardening, and the absorbed energy decreased; however, the recovered energy increased. As ρ f/fs increased from 0 to 1, owing to the elastic behavior of GFRP bars, the ductility of GFRP–steel RC columns under monotonic loading increased from moderate to high. However, cyclic loading decreased the ductility by one level for columns with similar ρ f/fs and degraded stiffness by approximately 4% per cycle. The numerical analyses extended the findings to include different values of axial load ratio, concrete strength, steel strength, and ρ f/fs . The parametric study showed that, for the ultimate lateral load, ρ f/fs had a negative effect, while the axial load ratio, concrete strength, and steel strength had positive effects.
Glass fiber polymer-reinforced (GFRP) composite profiles offer advantages such as corrosion resistance and a favorable strength-to-weight ratio, but their limited ductility and poor fire resistance hinder broader structural use. This study examines the thermal and compressive behavior of carbon fiber-reinforced polymer (CFRP)-confined, geopolymer concrete-filled pultruded GFRP square tubes under elevated temperatures. A total of 90 specimens were prepared using geopolymer concrete with three different compressive strengths (average strengths of 59.8, 68.3, and 89.6 MPa), controlled by sodium hydroxide molarity: 4 M (geopolymer concrete with 4 M sodium hydroxide, denoted as GC4), 8 M (GC8), and 12 M (GC12). Specimens were externally wrapped with CFRP wraps and exposed to temperatures ranging from 25 degrees C to 350 degrees C. Results show that CFRP confinement significantly enhanced compressive capacity, particularly in lower-strength cores, with average strength gains of 87%, 63%, and 27% for GC4, GC8, and GC12 specimens, respectively. Interestingly, elevated temperatures improved strength further, with peak load increases of up to 25% at 350 degrees C. Average ductility indices decreased with increasing concrete strength, ranging from 1.42 (GC4) to 1.30 (GC12). One-way ANOVA revealed that temperature accounted for 82%, 79%, and 63% of variance in compressive capacity for GC4, GC8, and GC12 groups, respectively. These findings highlight the effectiveness of CFRP confinement and the potential of sustainable geopolymer-filled GFRP systems in fire-prone structural applications.
Fiber-reinforced polymer (FRP) anchors are known to enhance load transfer and prevent premature debonding in externally bonded fiber-reinforced polymer (EB-FRP) systems, yet experimental data and design guidelines for single- and multianchored EB-FRP systems under realistic field conditions remain limited. This study investigates the structural performance of anchored EB-FRP joints through a three-round experimental program consisting of 48 large-scale single-lap shear tests on reinforced concrete blocks (up to 1,520 & times; 450 & times; 150 mm). The program systematically varied anchor configurations, dowel diameters (7-25 mm), anchor spacing (305-1,215 mm), FRP strip thickness (0.5-6 mm), and concrete compressive strength (19.5-36.1 MPa). A 3D digital image correlation system was used to capture full-field strain and slip profiles, anchor engagement, and interfacial debonding. Anchoring substantially improved both load capacity and slip/deformation response. Sequential engagement was observed in multianchor configurations, and failure modes were governed by the capacity ratio between anchor rupture and strip fracture. An empirical simplified multilinear load-slip model was developed to describe debonding, anchor activation, and subsequent tension-cable action, in which the debonded FRP strips behave like a cable transferring load through the anchors. Model predictions showed strong agreement with test data (R2 = 0.86 for peak load and R2 = 0.81 for ultimate slip). Predictive expressions for anchor capacity and debonding strain were also validated. The results provide a validated framework for the performance-based design of anchored EB-FRP joints and offer guidance on anchorage detailing for structural strengthening applications.
Impressed current cathodic protection (ICCP) is an effective method for mitigating steel corrosion. Carbon fiber-reinforced polymer (CFRP) bars offer dual functionality in ICCP-integrated concrete structures, serving as both anodes and concrete reinforcement. This study investigates the behavior of CFRP bars subjected to anodic polarization in real concrete environments, rather than simplified solution-based conditions. Experimental evaluations were performed, including electrochemical monitoring to verify anodic performance, uniaxial tensile tests to assess residual mechanical properties, and microscopic characterizations to identify degradation mechanisms. Electrochemical measurements, including variations in feeding voltage and instant-off potential, confirmed the stability and reliability of CFRP bars as ICCP anodes. Tensile tests revealed a progressive reduction in residual strength with increasing current density and polarization duration, with negligible influence of concrete strength (30 and 60 MPa). Empirical models were developed to predict residual tensile strength, secant modulus, and ultimate strain based on electrochemical exposure parameters. As the current density or polarization time increased, the CFRP failure mode transitioned from longitudinal splitting fracture to lateral fracture, accompanied by a significant reduction in the fracture zone length. Acidification of the concrete adjacent to the CFRP-concrete interface was observed, with the concrete being powdery and porous. X-ray diffraction analyses revealed the depletion of alkaline hydration products and the formation of Friedel's salt near the anode. Scanning electron microscopy showed resin dissolution, fiber-resin interface delamination, and cracking formation within the resin matrix. Fourier transform infrared spectroscopy confirmed hydrolysis and oxidative degradation of the resin, accelerated by exposure to OH- and Cl- and by moisture ingress, leading to progressive internal damage of the CFRP bar from the exterior inward.
Many existing concrete structures are vulnerable to earthquake events, which could result in catastrophic consequences. Fabric-reinforced cementitious matrix (FRCM) systems offer unique advantages and are a viable alternative to other conventional materials for strengthening concrete structures. However, a comprehensive understanding of FRCM's impact on retrofitted reinforced concrete (RC) columns has yet to be explored. This study experimentally investigated the seismic behavior of RC columns retrofitted with carbon FRCM jackets. The 300-mm- diameter circular RC columns were 1,720 mm long and had a deficiency in their seismic reinforcement detailing in the plastic hinge region. The columns were retrofitted with either one or two FRCM layers installed in the plastic hinge region. The columns were subjected to quasi-static lateral cyclic loading, and the seismic performance was evaluated in terms of failure mode, load capacity, ductility, stiffness degradation, and energy dissipation. The test results revealed that the FRCM jacket with one layer delayed the buckling of the longitudinal rebars and enhanced the overall seismic response. The addition of a second FRCM layer allowed further improvement in the response as it prevented the buckling and resulted in a slower degradation rate. The comparison between the control unretrofitted column and the retrofitted columns showed that the FRCM jackets resulted in an average increase of 34% in lateral load capacity, 65% in ductility, and 30% in energy dissipation. This study highlighted the progressive failure of the FRCM system and how this is associated with the structural performance of the retrofitted columns.
This study investigates a novel stay-in-place permanent formwork system employing fiber-reinforced polymer (FRP)-reinforced ultrahigh-strength engineered cementitious composites (UHS-ECCs) to enhance the durability and structural performance of concrete structures. The flexural behavior and failure mechanisms of reinforced concrete beams incorporating a 3-mm FRP bar-reinforced, 20-mm-thick UHS-ECC formwork were evaluated through experimental testing, digital image correlation, and theoretical analysis. For comparison, ultrahigh-performance concrete (UHPC) was used as an alternative formwork material. To improve interfacial bonding, the precast formwork was fabricated with rectangular grooves spaced at 50 or 120 mm. The results indicated that the UHS-ECC formwork effectively mitigated early crack localization, resulting insuperior load-carrying capacity and postyield stiffness. In contrast, the UHPC formwork was more susceptible to localized cracking, which induced interfacial deformation incompatibility and consequently reduced structural ductility and load-bearing capacity. These findings demonstrate the potential of FRP-reinforced UHS-ECC permanent formwork as a viable solution for improving the mechanical performance and durability of concrete structures.
