Search Results (1,855)

Traditional structural strengthening methods involve high costs, increased self-weight of the structure, and complex construction procedures. In this context, there is a need for alternative materials that improve the mechanical performance of concrete without compromising its functionality. The objective of this study was to evaluate the effect of applying fiberglass layers to concrete with a design compressive strength of f’c = 20.59 MPa (210 kg/cm²). An applied research approach was used, with a quantitative methodology and a quasi-experimental design. Cylindrical concrete specimens measuring 12 cm × 6 cm were cured for 28 days and then coated with 1, 2, and 3 layers of fiberglass. The results showed that fiberglass has a chemical composition dominated by sodium (54.28%), silicon (25.64%), magnesium (9.98%), and aluminum (7.19%), which contributes to its stiffness and stability. Regarding compressive strength, the control specimens achieved an average strength of 20.69 MPa, while specimens coated with 1, 2, and 3 layers of fiberglass reached average strengths of 21.72 MPa, 23.49 MPa, and 25.71 MPa, respectively. These values represent increases of 4.98%, 13.53%, and 24.26% compared to conventional concrete. In terms of flexural strength, the control beams reached an average value of 3.50 MPa, whereas beams reinforced with 1, 2, and 3 fiberglass layers achieved average strengths of 3.66 MPa, 3.89 MPa, and 4.10 MPa, respectively. The results demonstrate that fiberglass improves both the compressive and flexural performance of concrete by providing external confinement, delaying crack propagation, and increasing the load-bearing capacity of the structural elements. It is concluded that fiberglass constitutes an effective and technically viable alternative for strengthening concrete structures. Full article

The seismic performance of reinforced concrete (RC) beam–column joints depends on both shear strength and failure mechanisms, the assessment of which remains challenging because of complex interactions among geometric, material, loading, and reinforcement parameters. This study presents a data-driven framework for assessing the shear strength and failure mechanisms of exterior RC beam–column joints. A database comprising 210 experimental specimens was systematically compiled from published studies. Seventeen input variables were selected based on structural mechanics, seismic design provisions, and previous experimental investigations. Machine learning models were developed for shear strength prediction and failure mode classification. SHAP was employed to interpret the trained models, while symbolic regression derived an interpretable design-oriented equation. On the independent test set, XGBoost achieved the highest shear strength prediction (R² = 0.973, RMSE = 40.09 kN), whereas the Support Vector Machine achieved 80.5% classification accuracy. The results indicate that the governing parameters for failure mechanisms differ from those controlling shear strength. Joint shear capacity was primarily influenced by geometric dimensions and longitudinal reinforcement ratios, whereas axial load ratio and joint transverse reinforcement had a greater influence on failure mechanisms. These findings highlight the importance of simultaneously assessing shear strength and failure mode in RC beam–column joints. Full article

This study investigates the shear behavior and failure mechanisms of innovative hybrid structural beams fabricated by filling pultruded glass fiber-reinforced polymer (GFRP) box sections with waste rubber-reinforced concrete (RuC). Environmentally friendly concrete was produced by replacing natural aggregate with recycled tire-rubber fibers at proportions of 0%, 5%, 10%, and 15%. Twelve hybrid beam specimens were tested to evaluate the synergistic effects of rubber content and stirrup spacings of 16, 20, and 27 cm on shear capacity, ductility, and crack propagation. The experimental results revealed that the reference specimen (S16-0%) exhibited the maximum shear capacity of 154.41 kN and a brittle failure mode, while an increase in rubber content to 15%, combined with wider stirrup spacing, significantly reduced this capacity to a minimum of 96.89 kN (S27-15%). However, the 5% rubber replacement ratio achieved an optimal performance balance by preserving sufficient load-carrying capacity while enhancing flexural deformation and ductility, particularly in specimens with 16 cm stirrup spacing. Damage analysis demonstrated that longitudinal splitting cracks initiated in the mid-span tension zone at the bottom of the pultruded profiles, with final localized damage concentrated at the geometric corners of the box section. Crucially, the outer pultruded GFRP profiles provided substantial structural confinement, effectively mitigating the strength loss associated with high rubber incorporation and controlling the progression of sudden brittle failure. These findings highlight that combining pultruded GFRP profiles and optimized RuC offers a structurally viable and sustainable solution for modern infrastructure applications. Full article

Double-column reinforced-concrete (RC) hollow bridge piers are often assessed using flexure-dominated models, although their thin walls can develop shear-related deterioration. This study reanalyzes seven previously reported cyclic tests on scaled square hollow-pier columns and extends the assessment to a full-scale double-column system in OpenSees. The tests varied the shear-span ratio and transverse and longitudinal reinforcement. A flexure-only fiber model and an axial–flexure–shear interaction membrane–beam–truss element model (AFSI-MBTEM) were evaluated using six response indicators before cyclic and nonlinear time-history analyses of the prototype system. Lower shear-span ratios increased resistance but intensified inclined cracking, stiffness loss, and post-peak deterioration; increasing L/D from 3.9 to 7.9 reduced peak strength from 320.5 to 145.9 kN. AFSI-MBTEM reduced the mean absolute errors in peak strength, yield displacement, and effective stiffness to 3.08%, 11.83%, and 12.86%, respectively, but did not improve residual-displacement or mean hysteretic-loop-energy predictions. At the system level, shear-span ratio most strongly affected cyclic stiffness and peak base shear; wall-thickness ratio, width-to-depth ratio, and longitudinal reinforcement were also influential. Under three near-fault records, AFSI-MBTEM predicted 5.31–10.32% lower peak base shear, while displacement changes remained record-dependent. Shear-sensitive modeling improves force and deformation assessment, but the system-level trends remain conditional on the adopted prototype, parameter ranges, and records. Full article

To enhance the seismic performance of existing reinforced concrete (RC) buildings during retrofitting, the study introduces a new type of joint connected by a T-shaped steel plate. Compared with previous similar strengthening methods, this novel structure incorporating a post-installed beam not only effectively improves the mechanical properties of RC columns, but the connectors also further enhance the integrity of the post-installed beam. Low-cycle reversed loading tests on one cast-in-place specimen (RC) and three T-shaped steel plate connection specimens (TRC1–TRC3) were conducted to evaluate failure modes, hysteresis and skeleton curves, and energy dissipation. Results show that the novel joint failure concentrates at beam-end–column steel jacket weld seams and column-side steel plate cracking, while the core-zone concrete remains intact. Compared with RC, the novel joints TRC1–TRC3 exhibit bearing capacity variations of −1.03%~+15.80% and significantly enhanced energy dissipation. The thickness of the beam’s wrapped steel improves the carrying capacity and energy dissipation, whereas the T-shaped connector thickness has limited influence on bearing capacity. ABAQUS parametric analysis indicates that bolt quantity, concrete strength, and connector thickness have limited influence and serve as secondary design factors. These findings provide a theoretical basis for retrofitting existing buildings. Full article

Fiber-reinforced concrete is increasingly used to improve the mechanical and structural performance of reinforced concrete elements. This study presents a comparative experimental investigation of reinforced concrete beams incorporating steel and polypropylene fibers. Seven beams were examined, including a reference concrete and fiber-reinforced concrete mixtures containing 1.0%, 1.5%, and 2.0% fiber volume fractions. The experimental program included compressive strength tests on 21 cube specimens, shrinkage measurements on 21 prism specimens, and bending tests on reinforced concrete beams. The properties studied included compressive strength, shrinkage strain, ultimate load capacity, load–deflection response, crack initiation, crack width, and post-cracking behavior. Polypropylene fibers provided the greatest crack-control benefit, reducing shrinkage strain and maximum crack width by up to 50% and 93%, respectively, compared with the reference concrete. Steel-fiber-reinforced beams achieved the highest ultimate load, with an increase of up to 22% relative to the reference beam, and showed higher calculated displacement ductility indices. The results indicate that, under the tested conditions, steel fibers were more effective in improving load-carrying capacity and displacement ductility, whereas polypropylene fibers were more effective in controlling shrinkage and crack development. These findings support fiber selection according to the required balance between load capacity, deformation response, crack control, and serviceability. Full article

To investigate the evolution of acoustic emission (AE) parameters during the flexural failure of reinforced concrete (RC) beams subjected to freeze–thaw and corrosion, four RC beams were fabricated and assigned to four conditioning regimes: no deterioration, freeze–thaw only (75 cycles), corrosion only (4.8% mass loss), and combined. Three-point bending tests were conducted, combining AE and digital image correlation (DIC) techniques. The damage process was divided into four stages: micro-crack initiation, stable crack propagation, unstable crack propagation, and failure. The evolution of AE parameters including ring count, energy, amplitude, peak count, and duration was analyzed. Each parameter is positively correlated with load level and rises as the damage stage advances. The slope of cumulative parameters reflects crack development more reliably than instantaneous values. The effect of corrosion on these parameters is significantly greater than that of freeze–thaw. For corroded beams, AE parameter levels are higher during the micro-crack initiation stage but lower during the stable crack propagation stage. The overall AE activity decreases with increasing deterioration degree. High-amplitude events increase with damage progression, but fewer high-amplitude events are observed at the failure stage of severely deteriorated beams. This study reveals the correspondence between AE parameters and damage stages, providing an experimental basis for damage assessment using AE techniques. Full article

Surface-breaking cracks in concrete structures can accelerate deterioration by facilitating the ingress of moisture, chlorides, and other aggressive agents. Reliable characterization of crack depth is therefore essential for structural health monitoring and maintenance of concrete infrastructure. This study presents an ultrasonic common midpoint (CMP)-based approach for crack-tip localization and crack-depth characterization in concrete. Ultrasonic measurements were acquired using a pitch-catch configuration in which the transmitter and receiver were positioned symmetrically on both sides of surface crack while maintaining a fixed midpoint. Measurements obtained at multiple transmitter–receiver separations were processed to extract the time-of-arrival (ToA) associated with crack-tip diffraction. The measured ToAs were subsequently used within a travel-time-based localization framework to generate crack-tip images and estimate crack-tip coordinates. The proposed methodology was evaluated on concrete slabs containing vertical and inclined surface-breaking cracks of varying depths. In addition, the approach was applied to a reinforced concrete beam specimen containing thin cracks caused by flexural loading. The localized crack-tip positions from ultrasonic imaging are in good agreement with the observed crack depths and geometries. The proposed method offers a non-destructive approach for crack-tip localization and crack-depth characterization in concrete and may support condition assessment of concrete infrastructure. Full article

Reinforced concrete (RC) structures are susceptible to crack initiation and propagation during service, making accurate numerical simulation of crack behavior essential for assessing structural durability and safety. Current numerical approaches for simulating concrete cracking include smeared/continuum approaches, extended finite element method (XFEM), phase-field methods, and meso-mechanical models. In particular, smeared/continuum approaches (e.g., smeared crack and plastic-damage models such as CDP) indirectly reflect cracking through diffusive damage fields without providing explicit geometric information on crack locations and propagation paths. The XFEM module in commercial software is further restricted to first-order elements and encounters difficulties in simulating multi-crack propagation. These limitations indicate that further development of complementary crack-simulation frameworks is warranted. To this end, this paper presents a cracking simulation framework for RC members within the theoretical framework of the Specified Stress Method, adopting an adaptive degree-of-freedom strategy to balance computational accuracy and efficiency. The method introduces inelastic strain as an additional unknown and establishes a variational principle and the corresponding virtual work equation. Concrete cracking is described by specifying the stress on the crack plane to zero, so that the crack-surface stress remains zero after cracking, thereby avoiding the issue of damage reversibility and improving computational convergence. The method requires neither a predefined crack path nor remeshing after cracking. Unlike smeared/continuum approaches that rely on diffusive damage fields, the crack propagation paths, distribution characteristics, and evolution of multiple cracks are characterized through the spatial distribution of cracked integration points within the finite element mesh. In the present implementation, crack initiation is governed by the maximum tensile stress criterion, and a linear elastic constitutive model is adopted for concrete as a deliberate simplification to establish and verify the core computational mechanism of the framework. The proposed method was examined through three numerical examples. First, comparison with theoretical solutions confirmed the algorithm’s correctness in simulating cracking in heterogeneous RC tension members. Second, comparison with experimental results demonstrated qualitatively consistent crack propagation trends and load–displacement responses for RC beams under mixed-mode cracking; the calculated ultimate load of the plain concrete beam is lower than the experimental value, which is attributable to the use of the maximum tensile stress criterion without fracture energy considerations, and certain crack morphology deviations are observed due to the neglect of reinforcement–concrete bond-slip. Third, a multi-crack simulation of an under-reinforced RC beam showed that, whereas the XFEM module in ABAQUS captures only a single dominant crack near the mid-span, the proposed algorithm predicts multiple distributed cracking zones on both sides of the mid-span, qualitatively consistent with the typical flexural cracking behavior of under-reinforced RC beams; the algorithm also supports second-order elements (e.g., C3D20R) unavailable in the ABAQUS XFEM implementation. While the method is still in an exploratory stage, these results confirm the feasibility and potential of the Specified Stress Method as a complementary framework for RC cracking simulation, providing a basis for further development. Full article

The connection between the space frame and its supporting columns is a critical aspect of structural design. The way these two elements are joined significantly influences the overall stability, load transfer, and behavior of the entire structure. This study investigates the seismic behavior of composite double-layer space frames with reinforced concrete (RC) slabs under three alternative support configurations: simple point supports, inverted-pyramid supports, and crosshead-beam supports. A detailed finite element (FE) model was developed in ABAQUS to conduct a nonlinear time-history analysis under recorded earthquake excitation. The selected record captures the temporal variation in ground motion and enables an accurate assessment of structural response under dynamic loading. The Concrete Damage Plasticity model was incorporated into the analysis of the concrete slab. The steel was modeled using an elastic–plastic material behavior to mimic the formation of plastic hinges. Maximum lateral displacements, base shear forces, and hysteretic behavior were studied to evaluate the comparative performance of the systems. The results show that the inverted-pyramid configuration reduced vertical (Y-direction) displacement by 33.6% compared to the simple point support. At the same time, the crosshead-beam system exhibited similar levels of vertical displacement. However, it exhibited significantly enhanced energy-dissipation capacity, with hysteretic force ranges up to 1250 kN, compared to approximately 922 kN and 860 kN for the simple point and inverted configurations, respectively. In the X-direction (lateral displacement), the simple support and inverted-pyramid cases showed comparable responses, whereas the crosshead-beam configuration exhibited greater displacement, indicating reduced lateral stiffness. Overall, the results of this study indicate that the inverted-pyramid system improves displacement control, and the crosshead-beam configuration provides superior hysteretic energy dissipation. These findings highlight the importance of selecting appropriate support configurations in the seismic design of composite space frame systems. Full article

In order to meet its need of functional improvement, the existing masonry structure generally adopts the method of replacing partial walls with concrete frame columns to expand the openings and reduce the number of the longitudinal walls. However, the partial removal of longitudinal masonry walls and the introduction of large openings may result in a nonuniform distribution of lateral stiffness in plan and consequently induce torsional response under horizontal seismic loading. In order to investigate the seismic performance of the existing masonry structure after replacement, a 1:4 scale four-story brick masonry–concrete structure model was designed and made. Based on the principle of stiffness equivalence, the partial walls on the side of the large openings of the model ground-level floor were replaced by frame columns and frame beams, and then the pseudo-static test was conducted on the model. Through the test, the failure patterns of each floor in the structure and the seismic performance indexes such as hysteresis curve, skeleton curve, displacement ductility, stiffness degradation, and energy dissipation capacity, were obtained. The results showed that the yield load of the ground-level floor with the equivalent frame columns is approximately 138% of that of the second and third floors, while its yield displacement is approximately 59% of that of them. That is, after the structure enters the yield stage, its ground-level floor has good bearing capacity and resistance to deformation. The ground-level floor of the structure consumes the least energy as compared to the second and third floors, while the second floor consumes the most energy and has stiffness mutation, and the damage to the walls in such layer is also the most serious. Hence, seismic strengthening of the second story should be considered to prevent the formation of a weak or soft story and the consequent risk of structural collapse. Although there is a significant difference in the material properties between reinforced concrete frames and masonry structures, it is feasible to use the replacement method based on the stiffness equivalence to solve the problem of structure torsion caused by the irregular plane arrangement. Full article

This study includes an interpretable machine learning (ML) framework for predicting the shear contribution of externally bonded fiber-reinforced polymer (FRP) composites in reinforced concrete beams. A database including total 313 experimental specimens was collected from previous experimental research. The data screening process has been conducted using the Isolation Forest algorithm, resulting in 268 cleaned specimens. The cleaned database was divided into a training subset containing 214 specimens and an independent test set containing 54 specimens. The trained subset was enlarged into 5204 synthetic data using two advanced generative models including Wasserstein generative adversarial network and conditional Variational autoencoder (CVAE). Separate constrained monotonic neural network (CMNN) models were then trained on both datasets and WGAN-based CMNN achieved $R^2=0.9524$ for the synthetic training dataset and $R^2=0.9120$ for the independent test set, whereas the CVAE-based CMNN achieved corresponding values of 0.9632 and 0.9011. To improve practical applicability, response functions were extracted from WGAN-based CMNN and fitted with analytical expressions to derive a closed-form prediction equation. The proposed equation was independently validated using separate unseen test specimens, which were not used in CMNN training and achieved R² $=$ 0.79, RMSE $=$ 24.98 kN, MAE $=$ 19.65 kN, MAPE $=$ 21.72%, VAF $=$ 79.35%, U95 $=$ ±54.94 kN, SI $=$ 3.04, and PI $=$ 0.11. Compared with ACI 440.2R-17, CSA-S806.12, CNR-DT200 R1.2013, TR-55, and JSCE, the proposed equation showed superior accuracy while maintaining a transparent and design-oriented format. Full article

Steel-reinforced concrete (SRC) frame-bent hybrid structures are widely used in conventional island buildings of nuclear power plants because of their favorable seismic performance and economic efficiency. However, the seismic fragility of these structures has not been adequately investigated. In this study, the main turbine building of the CAP1400 nuclear power plant in Rongcheng, Shandong Province, China, was selected as the prototype. A three-bay frame-bent substructure was extracted, and a 1/7-scale model was designed for pseudo-dynamic testing to investigate the evolution of seismic damage and the failure mechanisms of the structure. Based on the experimental results, a refined numerical model was developed in OpenSees. Incremental dynamic analysis (IDA) was subsequently conducted to evaluate the seismic fragility of the SRC frame-bent main turbine building under far-field and near-fault ground motions. The results indicate that the structural stiffness progressively decreases with increasing seismic demand because of concrete cracking and cumulative damage. Damage is primarily concentrated in the short columns, beam-column joints, and column bases. The fragility response also exhibits pronounced directional dependence. Because of the lower lateral stiffness in the X direction, the structure develops larger interstory drift demands and higher probabilities of exceeding the prescribed damage states in the X direction than in the Y direction. For the selected ground-motion suites, near-fault records generally produce slightly higher exceedance probabilities than far-field records at the same peak ground acceleration (PGA), with a maximum difference of 3.68%. However, the magnitude of this difference varies with the damage state, excitation direction, and ground-motion intensity. These findings indicate that pulse-like near-fault ground motions may have a measurable but moderate effect on the seismic fragility of SRC frame-bent main turbine buildings. This study establishes an experimentally validated framework for assessing the seismic fragility of SRC frame-bent structures in nuclear power plants and identifies their vulnerable components, dominant damage mechanisms, and fragility characteristics under different types of ground-motion input. Full article

The structural performance of reinforced concrete (RC) deep beams in both ultimate and serviceability limit states (ULSs/SLSs) is influenced by beam size effects and the adopted reinforcement ratios. In this study, the effects of cotton waste fibres (CWFs) and beam depth were studied using a four-point load test on five sets of 400 mm and 500 mm CWF high-strength RC deep beams with a 0.3% web reinforcement ratio. Control unnotched and notched, and notched specimens with 0–0.75% CWF content in each specimen set, were studied. The failure modes, stirrup and strut-and-tie zones’ strains, shear capacity, and load-deflection were analyzed. It was observed that the beam failure evolved from shear-compression in unnotched specimens to the web-splitting failure phenomenon in notched ones, coupled by 27.44% and 0.17% decline in ultimate shear capacity ($V_u$) in notched 400 mm and 500 mm beam sets, respectively. The notched RC deep beam specimens, mimicking the SLS shear performance parameters, showed a 34.28% and 14.71% $V_u$ increase in 400 mm and 500 mm depth beams, respectively. The crack opening load increased from 13.87 kN to 44.63 k and from 11.88 kN to 35.19 kN in these beam sets, respectively. In a similar analysis, 84.76% and 38.39% stiffness increase, and 49.15% and 39.95% shear ductility index increase in the outer-most stirrup, were observed in the respective specimen sets. The contribution factor of the shear reinforcement to $V_u$ improved from 0.31 to 0.94, and from 0.87 to 0.97 in 400 mm and 500 mm, with 0% and 0.75% CWF, respectively. These experimental results confirm the contribution of beam size effect and fibres to the shear performance properties of RC deep beams. The feasibility of using CWF in structural concrete is confirmed by its improvement of the SLS properties of the studied RC deep beam specimens with light shear reinforcement. Full article

The use of Glass Fiber-Reinforced Polymer (GFRP) bars to reinforce concrete beams can provide high resistance to corrosion, high performance, high sustainability, and reasonable strength but with low ductility. This study focused on the structural behavior and indirect evaluation of the ductility index of hollow and solid beam specimens reinforced with GFRP bars, steel bars, or both (hybrid). Eight simply supported beam specimens with dimensions of 1200 mm (length), 150 mm (height), and 100 mm (width) were made using self-compacted concrete (SCC) and tested using two-point repeated loading. The tests results showed that the ultimate load capacity of the tested solid and hollow beams reinforced with GFRP bars were 78% and 67% higher than that of the corresponding solid and hollow beam specimens with steel-bar reinforcement. The measured energy absorption is “instantaneous” energy absorption because the residual stress disappears after the load is removed at the end of the test and any cracks will close due to the semi-linear response of the beam specimens reinforced with GFRP bars. Regarding the solid beam specimens, those containing GFRP bars showed an increase in energy absorption of 64–127% compared with the corresponding reference beams. The hollow beam specimens containing GFRP bars showed an increase in energy absorption of 21–68% compared with the corresponding reference beam containing three steel bars. Full article