Search Results (927)

This study proposes a high-strength bottom-bar interlocking and anchorage precast beam–column joint (HSRU-PBCJ), which utilizes high-strength longitudinal reinforcement combined with U-shaped anchorage at the beam bottom. Low-cycle reversed loading tests were conducted on two precast specimens and one cast-in-place specimen to evaluate their seismic performance. Based on these results, parametric analyses were conducted through numerical simulations to investigate the effects of axial compression ratio, concrete strength, beam-end longitudinal reinforcement strength, and beam-end longitudinal reinforcement ratio on the seismic performance. The results indicate that the proposed joint exhibits stable and full hysteresis loops, cumulative energy dissipation comparable to that of the cast-in-place joint, and a 23.94–26.39% increase in equivalent viscous damping after yielding, achieving a displacement ductility coefficient of 4.14, which confirms its substantially improved seismic performance. The parametric study shows that maintaining a moderate axial compression ratio (≤0.6) enhances both load-bearing capacity and energy dissipation, whereas excessive values result in strength reduction. Increasing the beam-end longitudinal reinforcement strength significantly improves load-bearing capacity but may reduce energy dissipation. In addition, improving concrete strength and appropriately increasing the reinforcement ratio can further enhance both load-bearing capacity and energy dissipation, although a balance between seismic performance and economic considerations is recommended. Full article

The dynamic behaviour of a column excited at the base, e.g., under an earthquake load, has been extensively studied. However, the column may also experience impact at the tip like a heavy-duty truck braking on a bridge. The caused base shear of the pier is very important. In this work, the dynamic behaviour, particularly the impact load from the tip to the base, was studied on two different composites: double basalt- and double flax fibre-reinforced polymer tube (DBFRP and DFFRP)-confined coconut fibre-reinforced concrete (CFRC). For each composite, two columns with a height of 1 m, an inner diameter of the outer tube of 100 mm, and an inner tube of 30 mm were fabricated. The column was fully fixed at the base and struck at the top with an impulse hammer. The base shear was calculated through an equivalent mass method using the acceleration at the tip. The results show that both DBFRP-CFRC and DFFRP-CFRC can dissipate a portion of the impact force, resulting in a reduction in force at the base of the specimens. The base shear of DFFRP-CFRC columns is larger and dissipates energy faster than that of DBFRP-CFRC columns. Full article

Based on ongoing experimental research, the present manuscript presents the effect of the slippage of a steel reinforcing bar due to corrosion on the chord rotation and deformation of corroded Reinforced Concrete members. The experimental results recorded that the increase in the corrosion level of the steel led to bond strength loss and relative slip between the steel and concrete, which was increased from 1.5 mm in non-corroded conditions to 3.5 mm even at low corrosion levels, up to a 5% steel mass loss. This slippage of corroded reinforcing bars from the anchorage leads to a proportional increase in terms of chord rotation due to pull out resulting in an additional increase in the displacement of the column’s top. In conclusion, the present study highlights the great importance of the contribution of the resulting slippage of a steel reinforcing bar due to corrosion in the calculation of the limit chord rotation (column–beam), a term which is of major importance in the assessment of the structural integrity of old RC structures, which was introduced as an adequacy requirement by both Eurocode 8-3 and the Greek Code of Structural Interventions (KAN.EPE). Full article

In reinforced concrete structures, the quality of rebar sleeve connections directly impacts the structure’s safety reserve and durability. However, quality inspection is complicated by the periodic distribution of stirrups, concrete obstruction, and noise interference, presenting challenges for assessing sleeve connection integrity. This paper proposes a training-free, interpretable framework for automated rebar sleeve connection quality inspection, leveraging point cloud semantic filtering and geometric a priori segmentation. The method constructs a polar-cylindrical framework, employing hierarchical semantic filtering to eliminate stirrup layers. Geometric a priori instance segmentation techniques are then applied, integrating θ histograms, Kasa circle fitting, and axial bridging domain constraints to reconstruct each longitudinal rebar. Sleeve detection occurs within the rebar coordinate system via radial profile analysis of length, angular coverage, and stability tests, subsequently stratified into two layers and parameterised. Sleeve projections onto column axes calculate spacing and overlap area percentages. Experiments using 18 BIM-TLS paired datasets demonstrate that this method achieves zero residual error in stirrup detection, with sleeve parameter accuracy reaching 98.9% in TLS data and recall at 57.5%, alongside stable runtime transferability. All TLS datasets meet the quality requirements of rebar sleeve connection spacing ≥35d and percentage of overlap area ≤50%. This framework enhances on-site quality inspection efficiency and consistency, providing a viable pathway for digital verification of rebar sleeve connection quality. Full article

Existing studies have demonstrated that insufficient horizontal deformation capacity of columns under high axial compression ratios constitutes a key factor leading to seismic damage in ordinary concrete frame structures. This paper proposes a novel framed structure incorporating composite columns by combining ultra-high performance concrete (UHPC), which exhibits excellent mechanical properties, with normal concrete (NC). The design concept maintains the overall mechanical performance of the composite column frame structure while significantly reducing the lateral stiffness when the composite columns are configured in a “split-column form.” For instance, the lateral stiffness of ZH-5 in the “split-column form” is only one-tenth of that of ZT-1 in its initial state, leading to a substantial enhancement in horizontal deformation capacity. This design approach maintains the overall mechanical performance of the composite column frame structure while significantly enhancing its horizontal deformation capacity by reducing lateral stiffness through the “split-column” configuration. Using the ABAQUS finite element software 2021, a finite element model of a multi-story frame column structure was developed. Research findings indicate that the frame structure utilizing UHPC-NC composite columns exhibits reduced tensile damage, lower peak and plastic displacements, and a relatively smaller inter-story drift angle. Specifically, the plastic drift angle of the UHPC-NC composite column frame structure from the first to the fourth story is 5% to 31% smaller than that of the conventional reinforced concrete column frame structure. The novel UHPC-NC composite column frame structure demonstrates superior seismic performance. Full article

Concrete is widely used in the field of wind power generation. Under design conditions, concrete in wind turbine towers is often subjected to compressive cyclic fatigue loading. In this study, 10 specimens were experimentally investigated to clarify the high-cycle fatigue behavior of plain concrete (PC), steel-reinforced concrete (SRC), and concrete-filled double-skin steel tubular (CFDST) members. The specimens were designed based on a scaled-down model of the corner columns from an actual lattice tower structure, considering the most unfavorable fatigue load scenario. The fatigue life and failure modes of the different member types were analyzed. The results indicate that, in terms of fatigue life, CFDST members are superior to PC and SRC members. Experimentally, the mean fatigue lives were 31,008 cycles for PC members and 85,374 cycles for SRC members, whereas all CFDST specimens survived beyond 100,000 cycles without failure. The fatigue failure of these specimens is characterized by localized failure leading to global collapse. Under axial cyclic loading, the confinement effect provided by the double-skin steel tubes significantly enhances the fatigue life of the concrete core. Furthermore, the axial compressive capacity of the CFDST specimens with a low steel ratio still generally meets the requirements of relevant design codes. Finally, design recommendations for the corner columns of lattice wind turbine towers are proposed. Full article

The environmental impact of the construction sector underscores the urgent need for sustainable solutions to extend the service life of existing structures. This study explores High-Performance Fiber-Reinforced Concrete (HPFRC) for strengthening reinforced-concrete (RC) columns subjected to axial compression. Twelve RC columns were tested, each 1200 mm high and with varying cross-sectional shapes (circular, square, and rectangular). Strengthening was achieved using thin HPFRC jackets (less than 30 mm thick), applied without additional internal reinforcement and following simple surface preparation techniques such as sandblasting. Full-height jacketing significantly improved axial load capacity. Its effectiveness did not decrease with the shape of the cross-section, with square columns showing up to a 105% increase and rectangular ones up to 87%, compared to unstrengthened columns with the same concrete strength. The highest improvement was observed in the square column with full-height jacketing and the most significant geometric strengthening ratio (52.6%), which doubled its axial capacity. This ratio was directly related to performance gains. Although ductility gains were limited, the full-jacketed specimens did not fail explosively: their failure mode was progressive, providing a useful warning before collapse. HPFRC jacketing can be especially effective for non-circular columns, outperforming FRP jacketing and eliminating the need for additional protective layers against impact or fire. Full article

This study presents an experimental investigation into the seismic performance of seismically deficient reinforced concrete (RC) bridge columns retrofitted with passive and active confinement systems. Four single-cantilever RC columns, representing 1/3-scale bridge piers, were constructed with poor transverse reinforcement detailing to simulate seismic deficiency. One column was left un-strengthened for baseline comparison, while the remaining three were retrofitted using: (1) a CFRP jacket, (2) welded Fe-SMA plates, and (3) bolted Fe-SMA plates. All columns were subjected to quasi-static lateral cyclic push-only loading reaching extreme drift levels exceeding 16% and high loading rates up to 6 mm/s. The study specifically explores the confinement effectiveness of CFRP and thermally activated Fe-SMA plates, comparing their contributions to lateral strength, ductility, energy dissipation, failure mode, and damage suppression. The results show that while the as-built column failed at 3.65% drift due to brittle flexural-shear failure, all retrofitted columns demonstrated significantly enhanced ductility, drift capacity, and post-peak behaviour. The CFRP and Fe-SMA jackets effectively delayed damage initiation, minimized core degradation, and improved energy dissipation. The bolted Fe-SMA system exhibited the highest and full restoration of lateral strength, while the welded system achieved the greatest increase in cumulative energy dissipation of around 40%. This research highlights the practical advantages and seismic effectiveness of Fe-SMA and CFRP confinement systems under extreme drift levels. However, future work should explore full-scale column applications, refine anchorage techniques for improved composite interaction, and investigate long-term durability under cyclic environmental conditions. Full article

Accurately predicting the ultimate strain of fiber-reinforced polymer (FRP)-confined concrete columns is essential for the widespread application of FRP in strengthening reinforced concrete (RC) columns. This study comprehensively investigates the performance of ensemble machine learning (ML) models in estimating the ultimate strain of FRP-confined concrete (FRP-CC) columns. A dataset of 547 test results of the ultimate strain of FRP-CC columns was collected from the literature for training and testing ML models. The four best single ML models were used to develop ensemble models employing voting, stacking and bagging techniques. The performance of the ensemble models was compared with 10 single ML and 11 empirical strain models. The study results revealed that the single ML models yielded good agreement between the estimated ultimate strain and the test results, with the best single ML models being the K-Star, k-Nearest Neighbor (k-NN) and Decision Table (DT) models. The three best ensemble models, a stacking-based ensemble model comprising K-Star, k-NN and DT models; a stacking-based ensemble model comprising K-Star and k-NN models and a voting-based ensemble model comprising K-Star and k-NN models, achieved higher estimation accuracy than the best single ML model in estimating the strain capacity of FRP-CC columns. Full article

Research on the configuration and mechanical performance of arch-column-tie beam joints, which combine features of arch-tie beam joints and tubular joints, remains limited, particularly for long-span structures subjected to heavy loads at high building stories. This study focuses on a joint in an engineering structure comprising a circular arch beam, a square-section inclined column, and a tie beam, where both the arch and the inclined column are concrete-filled steel tube (CFST) members. A novel joint configuration was proposed, then a refined finite element model was established. The joint’s mechanical mechanism and failure mode under axial compression in the arch beam were investigated, considering two conditions: the presence of prestressed high-strength rods and the failure of the rods. Subsequently, a parametric study was conducted to investigate the influence of variations in the web thickness of the tie beam, the steel tube wall thickness of the arched beam, the steel tube wall thickness of the supporting inclined column, and the strength grades of steel and concrete on the bearing capacity behavior and failure modes. Numerical simulation results indicate that the joint remains elastic under the design load for both conditions, meeting the design requirements. The joint reaches its ultimate capacity when extensive yielding occurs in the tie beam along the junction region with the circular arch beam, as well as in the steel tube of the arch beam. At this stage, the steel plates and concrete within the joint zone remain elastic, ensuring reliable load transfer. The maximum computed load of the model with prestressed rods was 2.28 times the design load. The absence of prestressed rods could lead to a significant increase in the high-stress area within the web of the tie beam, decreasing the joint’s stiffness by 12.4% at yielding, but have a limited effect on its maximum bearing capacity. Gradually increasing the wall thickness of the arch beam’s steel tube shifts the failure mode from arch-beam-dominated yielding to tie-beam-dominated yielding along the junction region. Increasing the steel strength grade is more efficient in enhancing the bearing capacity than increasing the concrete strength grade. Finally, a design methodology for the joint zone was established based on three aspects: local stress transfer at the bottom of the arch beam, force equilibrium between the arch beam and the tie beam, and the biaxial compression state of the concrete in the joint zone. Furthermore, the construction process and mechanical analysis methods for various construction stages were proposed. Full article

This study proposes a field-calibrated, NDT-integrated BIM modeling framework to improve the reliability of post-earthquake assessment for reinforced concrete (RC) buildings. The approach combines destructive and nondestructive testing (NDT) data—including core drilling, Schmidt hammer, ultrasonic pulse velocity (UPV), and Windsor probe—through a site-specific WinSonReb regression model. The calibrated material properties (average compressive strength ≈ 18.6 MPa, CoV > 20%) were embedded into a Building Information Modeling (BIM) environment, producing an as-is, NDT-calibrated BIM model representing a Level-2 static digital twin of the structure. Nonlinear static pushover analyses performed in accordance with TBDY-2018 and ASCE 41-17 showed that the calibrated model exhibits a fundamental period of 0.85 s—approximately 18% longer than the uncalibrated BIM model. This elongation increased displacement demand and caused a shift in performance classification: while the uncalibrated model indicated Life Safety (LS), the calibrated model predicted behavior approaching Collapse Prevention (CP) in the Y direction. Furthermore, calibration reversed the predicted damage hierarchy, from ductile beam hinging to brittle column- and wall-controlled failure near elevator openings, consistent with post-event observations from the 2023 Kahramanmaraş earthquakes. These results demonstrate that integrating field-calibrated NDT data into BIM-based seismic models fundamentally alters both strength estimation and failure-mechanism prediction, reducing epistemic uncertainty and providing a more conservative basis for retrofit prioritization. Although demonstrated on a single case study, the proposed workflow offers a realistic and scalable pathway for NDT-supported seismic performance assessment of existing RC buildings. Full article

The supporting system of super-large cooling towers is crucial for the structural safety of nuclear power plants. The X-shaped reinforced concrete column has emerged as a promising solution due to its superior stability. However, the performance of the cast-in-place base joint, which is a key force-transfer component, requires thorough investigation. This study experimentally investigates the mechanical performance of the joints under ultimate vertical compressive and tensile loads. The loads represent gravity-dominated and extreme wind uplift scenarios, respectively. A comprehensive testing program monitored load–displacement responses, strain distributions, crack propagation, and failure modes. The compression specimen failed in a ductile flexural compression manner with plastic hinge formation above the column base. In contrast, the tension specimen exhibited a tension-controlled failure pattern. Crucially, the joint remained stable after column yielding in both loading scenarios. The result validates the “strong connection–weak member” design principle. The findings confirm that the proposed cast-in-place joint possesses excellent load-bearing capacity and ductility. Therefore, the study provides a reliable design basis for the supporting structures of super-large cooling towers. Full article

As the requirements for structural functionality increase, designers frequently opt for inclined columns instead of traditional vertical columns. This choice enhances the spatial dynamics, esthetic appeal, and lighting effects of the structure. However, the research on the failure mechanism and seismic performance of inclined columns under cyclic loading is not systematic. To promote the application of inclined columns in earthquake-prone areas, quasi-static tests were conducted on steel-reinforced concrete inclined columns (SRCIC). The study analyzed the elastic and elastic-plastic development trend, failure mechanism, second-order effect, deformation and energy dissipation of the inclined columns. Traditional vertical columns often experience bending or shear failure, while SRCIC exhibited a new failure pattern characterized by bending failure on one side and compression failure on the other. Based on the experimental design, the nonlinear finite element analysis model of SRCIC is established. The finite element model was validated for horizontal peak load, ductility coefficient, and damage area at various inclination angles, providing a foundation for further parameter analysis. In the numerical analysis section, the effects of inclination angle, steel ratio, reinforcement ratio, and stirrup ratio on the skeleton curve and ductility coefficient were studied in detail, leading to the application of SRCIC. Full article

This study investigates the cyclic behavior of reinforced concrete beam–column joints strengthened with hybrid GFRP–steel reinforcement using nonlinear finite element analysis. Six hybrid configurations—defined by varying the percentage of the total longitudinal steel reinforcement area, in the beam, replaced with GFRP bars (0%, 20%, 25%, 33%, 50%, and 100%)—were evaluated in terms of load–displacement hysteresis, stiffness degradation, dissipated energy, and crack development. A multi-criteria decision analysis (MCDA) was employed to quantitatively compare the six configurations. The findings demonstrate the potential of partial GFRP substitution to enhance the seismic performance of reinforced concrete beam–column joints. Full article

This review surveys the recent literature on the fire resistance of reinforced concrete (RC) columns based on a bibliometric analysis of publications to reveal research trends and focus areas. The collected studies are synthesized from the perspectives of materials, structural behaviors, parameter influences, and predictive modeling. From the material aspect, the review summarizes the degradation mechanisms of conventional concrete at elevated temperatures and highlights the improved performance of ultra-high-performance concrete (UHPC) and reactive powder concrete (RPC), where dense microstructures and fiber bridging effectively suppress spalling and help maintain residual capacity. In terms of structural behavior, experimental and numerical studies on RC columns under fire are reviewed to clarify the deformation, failure modes, and effects of axial load ratio, slenderness, cover thickness, reinforcement ratio, boundary restraint, and load eccentricity on fire endurance. Parametric analyses addressing the influence of these factors, as well as the heating–cooling history, on overall stability and post-fire performance is discussed. Recent advances in thermomechanical finite element analysis and the integration of data-driven approaches such as machine learning have been summarized for evaluating and predicting fire performance. Future directions are outlined, emphasizing the need for standardized parameters for fiber-reinforced systems, a combination of multi-scale numerical and machine-learning models, and further exploration of multi-hazard coupling, durability, and digital-twin-based monitoring to support next-generation performance-based fire design. Full article