Abstract Seismic retrofitting of existing reinforced concrete (RC) columns with fiber-reinforced polymer (FRP) jackets typically requires removing plaster to ensure direct bonding. Although widely practiced, plaster removal increases labor, cost, and environmental impact and can damage the weak concrete surfaces common in substandard buildings. Previous experimental studies have mostly examined FRP confinement applied directly to concrete; however, the axial behavior of columns strengthened without plaster removal remains largely unexplored. In particular, the combined effects of plaster thickness, plaster strength, and FRP jacket configuration have not been systematically evaluated for square columns with retained plaster. This study addresses this gap by experimentally investigating the monotonic axial behavior of plastered concrete columns retrofitted with carbon FRP (CFRP) jackets. Twenty unreinforced square columns (275 × 275 × 550 mm), cast with low-strength concrete (approximately 10 MPa), were tested under axial compression. The parameters varied were plaster thickness (12.5, 25.0, and 37.5 mm), plaster compressive strength (approximately 4.5 and 9.0 MPa), and CFRP jacket configuration (one or two layers). Test results show that, within the engineering-relevant axial strain range (≤1.5%), CFRP jacketing over plastered surfaces effectively maintains the axial load-carrying capacity regardless of plaster properties, demonstrating adequate confinement. These findings confirm the feasibility of CFRP retrofitting without plaster removal and provide a practical framework for strengthening RC members constructed with low-strength concrete. A new constitutive model was developed to represent the axial stress–strain response of plastered CFRP-jacketed concrete, explicitly incorporating plaster thickness, plaster strength, and CFRP jacket configuration. The proposed model captures the experimental behavior with high accuracy and offers a reliable tool for the design and assessment of plaster-interlayered CFRP-strengthened columns.
Abstract Reinforced concrete (RC) infrastructure exposed to marine environments and deicing salts suffers from premature deterioration due to chloride-induced corrosion, while existing strengthening systems often provide limited protection once cracking develops. This study investigates chloride transport in an innovative thin strengthening system based on an ultrahigh-performance fabric-reinforced cementitious matrix (UHP-FRCM), incorporating polyparaphenylene benzo-bisthiazole and carbon meshes embedded in a UHP matrix, under coupled mechanical loading and aggressive exposure conditions. Concrete disks and prisms were tested using rapid the chloride migration test, including tests under sustained flexural loading. Digital image correlation was used to quantify crack development and relate crack width to chloride transport. UHP-FRCM systems significantly improved durability compared to commercial systems, reducing apparent diffusion coefficients by up to 90% in uncracked conditions and limiting chloride ingress by up to 80% under loading, with penetration depths reduced to approximately 35 mm. Hybrid matrices combining steel and ultrahigh-molecular-weight polyethylene fibers provided the best performance by controlling crack width and disrupting transport pathways. A clear exponential relationship between crack width and chloride diffusion was observed. Service-life analysis based on apparent diffusion coefficients from accelerated tests indicates that UHP-FRCM systems can increase the predicted time to corrosion initiation at a 50-mm concrete cover depth by approximately 2.5–3.0 times compared with commercial FRCM systems, depending on the applied loading level. The findings demonstrate the potential of UHP-FRCM systems for crack-controlled durability design in chloride-exposed reinforced concrete structures.
Abstract Textile-reinforced ultra-high-performance concrete (TRUHPC) has emerged as a promising solution for strengthening reinforced concrete (RC) beams; however, its structural efficacy is often compromised by premature interfacial debonding. To address this challenge, this paper proposes a novel hybrid strengthening method that integrates end self-locking anchorages with surface grooving. Four-point bending tests were conducted to evaluate the efficacy of the proposed method. The results show that the proposed strengthening method effectively prevented end debonding and significantly impeded the development of intermediate debonding. The end anchorage system efficiently mitigates stress concentrations by transferring peeling forces from the TRUHPC end into the deep beam core. Concurrently, the grooves expand the effective bond area and reduce peak shear stress at the interface, resulting in a 43.1% increase in debonding load. To complement the experimental findings, finite-element simulations were performed and verified, showing good agreement with test results. The verified model was subsequently extended to perform parametric analysis, investigating the impacts of different strengthening schemes and groove configurations. Finally, an analytical model was proposed to predict the full-range load–deflection response of RC beams utilizing the proposed hybrid strengthening system.
Abstract Floor slabs are among the most material-intensive structural elements in buildings and therefore offer significant potential for reducing concrete consumption and associated CO 2 emissions. At the same time, the realization of material-efficient slab geometries remains limited by labor-intensive construction methods and challenges related to automation. To address these issues, this paper presents a modular ceiling system that combines historical principles of material efficiency, as pioneered by Pier Luigi Nervi, with digital fabrication technologies. Individual ceiling modules are fabricated using a multimodal production process that integrates extrusion-based three-dimensional concrete printing (3DCP), robotic casting, and automated placement of carbon fiber-reinforced polymer (CFRP) reinforcement. By combining prefabricated modules through dry-joint connections and post-tensioning, the system enables efficient on-site assembly while achieving significant reductions in concrete consumption and allowing for potential reuse of components. This paper discusses reinforcement integration challenges in the 3D printing process and the development of a digital production workflow. A full-scale prototype demonstrates the feasibility of the approach, while ongoing research explores robotic milling of early-age concrete to improve joint precision and advance automation.
Abstract Substandard reinforced concrete (RC) building stocks continue to pose a major seismic risk in earthquake-prone regions. While fiber-reinforced polymer (FRP) jacketing has been widely demonstrated as an effective retrofitting technique at the member level, its rational application at a large scale requires rapid yet reliable decision-making tools. In this study, the accuracy and applicability of a rapid FRP retrofitting framework integrated into the PERA2019 performance-based seismic assessment methodology are evaluated through a detailed investigation of five actual representative existing RC buildings. For each building, seismic performance before and after FRP retrofitting was evaluated using both the PERA2019 procedure and detailed nonlinear pushover analyses, which served as benchmark solutions. In addition, the framework was validated against the results of a full-scale experimental study reported in the literature. The results indicate that PERA2019 provides seismic safety ratio estimates that are in satisfactory agreement with detailed analysis outcomes. Buildings classified as A class by PERA2019 were consistently shown to satisfy the corresponding controlled damage performance target in detailed analyses, whereas buildings failing to reach A class did not meet this target. A comparison with the experimental results further demonstrated that the framework accurately captured the relative performance improvement achieved through FRP retrofitting and remained on the safe side of the observed structural response. Overall, the findings confirm that the proposed methodology can reliably distinguish buildings that can be effectively upgraded using FRP jacketing from those requiring alternative interventions. The framework provides a computationally efficient and practically applicable tool for large-scale seismic risk mitigation and prioritization of FRP retrofitting strategies.
