Search Results (425)

This study investigates the shear damage mechanisms in reinforced concrete (RC) beams through non-linear numerical modeling. Using the Finite Element Method (FEM) in ABAQUS, a Concrete Damaged Plasticity (CDP) framework was validated against experimental results and subsequently utilized for a 36-model parametric investigation. The study isolated the influence of stirrup spacing, diameter, and yield strength to evaluate their roles in ultimate shear capacity. The results indicated that while increasing stirrup diameter yielded modest capacity enhancements of approximately 7%, the impact of increasing yield strength was negligible, as the failure modes were primarily governed by concrete web crushing before reinforcement yielding could occur. These physical limit states were compared against the linear Truss Analogy adopted by major design standards—including ACI 318-19, Eurocode 2, and TS 500—to quantify discrepancies in heavily reinforced sections. The findings reveal that, strictly within the investigated parameter space (a/d = 2.67, f’_c = 28.5 MPa), current linear equations can significantly overestimate the physical capacity gains provided by reinforcement modifications. These observations are configuration-specific and highlight the need for cautious application of linear models in heavily reinforced scenarios. Furthermore, the study suggests that utilizing 3D beam elements for transverse reinforcement provides a more nuanced representation of shear transfer mechanisms, such as dowel action, compared to standard truss models. Full article

Self-drilling hollow bar micropiles (HBMPs), which integrate drilling, grouting, and reinforcement into a single process, have broad application prospects in mountainous transmission lines and offshore wind power projects. However, existing research has focused mainly on friction piles in soil layers, and there is a lack of systematic understanding of the load-transfer mechanism and bearing capacity calculation method for rock-socketed HBMPs. Based on field static load tests of rock-socketed HBMPs, this study systematically investigates the vertical bearing behavior and capacity calculation method of single rock-socketed HBMPs through a combination of test data analysis, finite element numerical simulation, and theoretical analysis. The field test results show that the load-settlement curves of rock-socketed HBMPs are of a slowly varying type, exhibiting mixed friction-end-bearing characteristics. After data screening, the average Q-s curve of Pile No. 1 and Pile No. 5 was taken as the benchmark, and the representative ultimate bearing capacity of a single pile determined by the 40 mm settlement criterion is 5860 kN. The test data of Pile No. 3 and Pile No. 4 were retained as independent validation data. A three-dimensional finite element model considering the cohesive contact behavior at the pile–rock/soil interface was established using ABAQUS. After calibration with the test results, the error between the simulated and measured bearing capacity is −3.4%, demonstrating good model reliability. Parametric analysis indicates that the bearing capacity increases linearly with the grouting volume increase rate $V_{\mathrm{inc}}$, with the expansion effect being the main enhancement mechanism; the improvement amplitude under hard rock conditions is significantly smaller than that in cohesive soils. The effect of uniaxial compressive strength $q_u$ of hard rock on bearing capacity is negligible because the capacity is controlled by the pile–rock interface shear strength. The bearing capacity increases approximately linearly with the rock-socketed depth $L_r$, and a minimum rock-socketed depth of 1.0 m is recommended. Analysis of the load-transfer mechanism shows that rock-socketed HBMPs rely mainly on shaft resistance (accounting for 90.6%), and the axial force decays significantly along the pile length. Elastic compression of the pile accounts for 78% of the pile head settlement, and the limited displacement at the pile tip leads to insufficient mobilization of end bearing. A modified bearing capacity formula considering the grouting expansion effect is established with shaft resistance as the core. A hierarchical validation strategy is adopted to test its predictive ability: for the finite element cases not participating in parameter calibration, the prediction error is within ±2%; for the field test piles, the prediction error is +7.9%; and for Pile No. 3 and Pile No. 4, the errors are +1.7% and −2.1%, respectively. These values are significantly better than those of existing methods (errors ranging from −72.1% to +54.5%). The research results can provide a theoretical basis for the design of single HBMP bearing capacity under rock-socketed conditions. Full article

To investigate the static behavior of UT-type assembled semi-rigid joints and the effects of bolt pretension loss, two representative joint configurations, UT250 × 150 and UT400 × 200, were studied by combining full-scale tests with refined finite element analysis using ABAQUS. Pure bending, bending-shear, and constant-axial-force-coupled loading conditions were considered, with particular attention paid to the effects of single-bolt and multiple-bolt pretension loss on moment capacity, initial rotational stiffness (K_y), interface slip, and the failure mode of the joints. The results show that the UT-type joint mainly fails through concentrated plastic yielding in the joint zone, and its ultimate moment (M_u) is 12.3–18.7% higher than that of a conventional bolted-welded joint, satisfying the design principle of “strong joint and weak member”. Loss of pretension in a single bolt has only a limited influence on the yield moment (M_y) and ultimate moment (M_u), with a maximum reduction of 8.0% in the ultimate moment (M_u) under negative pure bending; however, it causes clear degradation in the initial rotational stiffness (K_y), and pretension loss in the upper bolt produces a greater stiffness reduction than loss in a single lower bolt, with a maximum reduction of 33.43%. Multiple-bolt pretension loss exhibits a pronounced coupling effect. Simultaneous loss in lower bolts on the same side is the most unfavorable case, leading to a maximum stiffness reduction of 67.78% (coupling coefficient of 1.17), whereas diagonal loss is relatively controllable and generally keeps the stiffness reduction within 7%. When the axial compression ratio does not exceed 0.3, the mechanical response of the joint remains relatively stable, and the adverse effect of pretension loss can be alleviated to a certain extent; further increases in the axial compression ratio accelerate the degradation of both stiffness and load-carrying capacity. The present study provides a useful reference for the design optimization, construction quality control, and in-service maintenance of UT-type semi-rigid joints. Full article

Four-point bending tests were conducted on precast ultra-high-performance concrete (UHPC) segmental beams reinforced with unbonded prestressing tendons. A nonlinear finite element model was established and rigorously validated against the experimental data to simulate their flexural behavior. The experimental results show that compared with monolithic beams, the segmental beams experience a slight reduction in flexural capacity of 9.22% and 12.44% for the double-joint and triple-joint configurations, respectively. Nevertheless, the segmental beams possess greater ductility reserves; specifically, their average peak displacements increased from 9.83 mm for the monolithic beams to 11.60 mm and 14.78 mm for the double-joint and triple-joint beams, respectively, demonstrating substantially improved ductility. Based on the validated finite element model, extensive parametric analyses were performed. The numerical results indicate that concrete strength and steel strand reinforcement ratio significantly enhance the load-carrying capacity. Furthermore, shifting the joint positions away from the loading points increases the beam’s bending capacity, though this enhancement aggressively flattens out beyond a critical distance threshold of 0.25 L (L is the effective span). Finally, segmental beams with shear-resistant keyed joints exhibit higher overall stiffness and ultimate load-carrying capacity compared to those with plain flat joints. Full article

The spatiotemporal evolution of seepage fields and the associated hydrodynamic risk of subsequent internal erosion pose a critical threat to the structural integrity of marine and hydraulic infrastructure. To quantify these complex fluid–solid interactions, this study develops a high-fidelity numerical model—coupling the Navier–Stokes equations with the Darcy–Forchheimer resistance model and the Volume of Fluid (VOF) method—to investigate transient hydrodynamics within porous foundations under complex geometric and geological boundary conditions. Parametric analyses reveal that spatial porosity distribution fundamentally dictates the system’s seepage capacity; notably, relocating a highly permeable stratum to the shallow sub-surface eliminates upper hydraulic bottlenecks and significantly escalates total volumetric discharge. Furthermore, the study systematically evaluates the hydrodynamic efficacy of multi-dimensional seepage control structures. Results demonstrate that while increasing the vertical depth of a cutoff wall is highly efficient in restricting bulk volumetric flux, it inadvertently induces intense localized streamline convergence and flow acceleration at the structural tip. Conversely, lateral expansion of the wall base, though yielding only a moderate reduction in total seepage, successfully diffuses this concentrated flow and substantially attenuates peak pore fluid velocities. Ultimately, a combined design paradigm is proposed for practical coastal engineering applications: prioritizing vertical penetration to optimize bulk seepage reduction, concurrently integrated with moderate lateral base expansion to redistribute concentrated hydrodynamic shear stresses, thereby minimizing the hydrodynamic potential for localized piping and ensuring long-term stability against seepage-induced degradation. Full article

In this study, we investigate the bearing capacity characteristics and controlling mechanisms of coastal beach sand in Quanzhou Bay, Fujian Province, China. The results provide support for coastal engineering construction and vehicle trafficability assessment in beach areas, while field sampling, laboratory static plate load tests, and data-based modeling were conducted to examine the effects of moisture content, particle size distribution, and relative density on the bearing behavior of beach sand. In total, 52 groups of static load tests were performed, with the results showing that relative density is the dominant controllable factor affecting the bearing capacity of coastal beach sand. When the relative density increased from 40% to 65%, the ultimate load increased by 80%, and the deformation modulus increased by 139.9%. The optimal relative density range was approximately 52–65%, and the improved particle size distribution enhanced bearing performance. The ultimate load of well-graded sand was 60% higher than that of poorly graded sand, and moisture content showed a threshold effect, with the best mechanical performance occurring at a moisture content of about 7%, whereas excessive moisture content significantly reduced the bearing capacity. Under natural conditions, the proportional limit load of medium-dense coastal beach sand in Quanzhou Bay was approximately 200 kPa, the ultimate load was 250 kPa, and the characteristic value of bearing capacity was 125 kPa, while the dominant failure mode was general shear failure. A semi-empirical bearing capacity model was also developed; its average relative error was 10.35%, indicating that it has both physical meaning and engineering applicability. The findings provide a reference for foundation design evaluation in Quanzhou Bay and similar coastal beach areas. Full article

Punching shear failure in reinforced concrete RC slabs is one of the most significant and detrimental failure modes due to its sudden nature and its dependence on a complex interaction between concrete strength, the reinforcement, and the loading conditions. In recent years, there has been increasing interest in utilizing sustainable cementitious materials and steel fibers as a way of enhancing structural performance and improving the durability of concrete. The study aims to assess the structural behavior of RC slabs utilizing a partial cement substitution with limestone powder (LP) and granulated blast-furnace slag (GBFS), with the addition of steel fibers. Twelve RC slabs were examined under uniform concentric loading to analyze cracking behavior, load–deflection relationship, stiffness variation, and ultimate punching shear strength. The results demonstrated that using limestone powder (LP) had a significant impact on the crack distribution pattern and resulted in a slight reduction in initial stiffness, with the load-bearing capacity decreasing to approximately 55.8% of the control mixture at high replacement ratios. Due to a slower hydraulic reaction than with other mixtures, increasing additional granulated blast-furnace slag resulted in a decrease in crack resistance and relative deformation. With a load-bearing capacity of approximately 92.9% of the control mixture, a tertiary mixture of limestone powder and granulated blast-furnace slag (GBFS) demonstrated a better balance in structural behavior, leading to improved crack control while maintaining a sufficient level of load-bearing capacity. The steel fibers also significantly contributed to enhanced post-cracking behavior by decreasing crack width and improving the stress redistribution mechanism within the RC slab. This led to increased punching shear resistance and enhanced energy absorption, with the ultimate load increased to 119 kN compared to the control mixture. Overall, the findings show that combining sustainable cementitious materials with steel fibers can effectively improve punching shear performance and enhance the efficiency and durability of reinforced concrete. Full article

The seismic design of spatial joints in long-span concrete-filled steel tube (CFST) arch bridges under complex stresses remains a critical challenge in high-intensity seismic zones. This study investigates the seismic performance and failure mechanisms of CFST spatial KT-type joints, using the Pingnan No. 3 Bridge as a case study. Based on similarity theory, four scaled test specimens were designed. The core variable was the axial compression ratio of the main pipe, while the load on the K-branch served as the parametric variable. Quasi-static tests were conducted under constant static loading on the main pipe and K-branches, coupled with low-cycle cyclic loading on the T-branch. Furthermore, nonlinear finite element analysis (FEA) was performed using Abaqus for cross-validation. The results indicate that the primary failure mode of this joint configuration is the shear-punching failure of the main pipe wall at the T-branch intersection. The load–displacement hysteresis curves exhibit a robust “bow-shaped” profile, indicating substantial plastic energy dissipation capacity. Comparative analysis confirms that hollow steel pipe T-branches offer superior ductility in long-span arch bridges compared to concrete-filled alternatives. By extracting shear stress distribution characteristics from the FEA model to precisely locate the neutral axis, this study proposes a theoretical correction to the ultimate load-carrying capacity calculation model. The derived theoretical values demonstrate good agreement with the experimental results. The relative errors between the calculated and experimental bearing capacities of KT783a, KT783, KT700, and KT607 were 1.99%, 0.23%, 2.26%, and 2.45%, respectively, referring to the T-branch out-of-plane bearing capacity predicted by the proposed formula. The proposed theoretical model provides a reliable quantitative basis for the seismic design and local strengthening of similar spatial joints in long-span CFST arch bridges. Full article

The deterioration of steel reinforcement through corrosion triggers cracking and loss of concrete cover, ultimately weakening the structure’s strength and ductility. In practical design and assessment, it is vital to precisely quantify the shear capacity of corroded reinforced concrete beams (CRCBs). In this paper, machine learning (ML) models are developed to predict the shear capacity of CRCBs, including kernel ridge regression (KRR), K-nearest neighbors (KNN), decision trees (DT), random forest (RF), gradient-boosted regression trees (GBRT), and extreme gradient boosting (XGBoost). A total of 408 data entries on the shear strength of CRCBs under different corrosion conditions were collected to establish an extensive database. The reliability of the proposed ML models is examined by contrasting their outputs with the experimental data. The XGBoost model demonstrated superior predictive capability, achieving an R² value of 0.994 and outperforming all other tested models, including RF, GBRT, and DT. The Shapley Additive Explanations (SHAP) algorithm is adopted to reveal the contribution of each input feature to the predicted shear capacity of CRCBs. The interpretive SHAP results show that the ultimate shear capacity of CRCBs is most influenced by beam depth (h), with the shear span-to-depth ratio (λ) and concrete compressive strength ($f_{cl,150}$) being the subsequent key contributors. A comparative assessment between the XGBoost model and traditional analytical models was carried out to estimate the shear strength of CRCBs. Results demonstrate that the XGBoost model delivers enhanced predictive accuracy and improved performance. A parametric investigation examined its robustness under variations in geometry and material properties, while a user-friendly interface was created to support its practical use. Full article

This study presents a mechanics based analytical framework for predicting the flexural–shear capacity of reinforced concrete (RC) beams strengthened with Engineered Cementitious Composites (ECCs) and a hybrid ECC–GFRP near surface mounted (NSM) system. Building upon previously reported experimental observations, the present work aims to establish rational prediction models capable of capturing the interaction between flexural and shear mechanisms in strengthened beams. The analytical approach integrates sectional analysis for flexural capacity with a modified truss analogy for shear resistance, explicitly incorporating the strain hardening tensile contribution of ECC and the tensile and confinement effects of GFRP reinforcement. An interaction based failure criterion is subsequently employed to identify the governing failure mode under combined flexural shear actions. The proposed model is validated against experimental results obtained from twenty seven beam specimens with varying flexural and shear reinforcement ratios and strengthening configurations. The predicted ultimate loads show good agreement with experimental values, with an average deviation within ±10%. The analytical framework accurately captures the transition between flexural dominated, combined flexural–shear, and diagonal tension failures observed experimentally. Results demonstrate that ECC significantly enhances ductility and shear crack control, while the hybrid ECC–GFRP system provides substantial strength enhancement with a controlled shift in failure mode. Overall, the developed analytical models offer a reliable and computationally efficient tool for predicting the flexural–shear capacity and failure behavior of ECC and hybrid ECC–GFRP-strengthened RC beams, supporting performance based design and practical strengthening applications. Full article

To investigate the shear performance of steel fiber-reinforced high-strength concrete (SFRHSC) corbels subjected to concentrated loading, an experimental program was executed on six specimens featuring welded anchorage for the upper longitudinal reinforcement. The control variables included shear span-to-depth ratios of 0.2 to 0.5 and steel fiber volume fractions of 0%, 0.75%, and 1.50%. During the testing phase, strain evolution within the steel reinforcement and concrete matrix was monitored to analyze the structural deformation sequence and ultimate failure modes. Anchored in the Mohr–Coulomb failure criterion and the foundational strut-and-tie model (STM) framework, a softened strut-and-tie calculation approach for corbel shear capacity was formulated; this method explicitly accounts for the softening effect of the steel fiber-reinforced concrete (SFRC) and incorporates a size effect correction. The established shear capacity calculation model, alongside STM-based provisions from ACI 318-19, EN 1992-1-1, and CSA A23.3-19, was deployed to forecast the shear capacities of the six fabricated specimens and 18 additional units sourced from existing literature. Ultimately, a rigorous comparative analysis was conducted between the theoretical predictions generated by each method and the empirical test data. The results indicate that the failure process of the SFRHSC corbels primarily involves three distinct stages: initial cracking, through cracking, and ultimate failure. The addition of steel fibers can alleviate stress concentration at cracks and limit crack growth, thereby improving the tensile performance of the cracked concrete. Test results indicate that the strain in the longitudinal tensile reinforcement increased with the shear span-to-depth ratio but decreased as the steel fiber volume fraction increased. At the point of specimen failure, all longitudinal tensile reinforcement had reached the yield strength, while the horizontal stirrups only partially yielded. The concrete strain distribution across the normal section of the corbel did not follow the plane section assumption. Furthermore, incorporating steel fibers increased both the cracking load and the ultimate load of the corbel normal sections. The mean value of the experimental-to-predicted ratios obtained from the STM provisions of various international codes was 1.453, with a variance of 0.029, indicating conservative calculation results. In contrast, the mean value of the experimental-to-predicted ratios for the calculation model developed in this study was 1.048, with a variance of 0.004, demonstrating closer agreement with the experimental results and less dispersion. Simultaneously, by explicitly considering the softening effect in SFRHSC and the size effect, it provides a better prediction for the shear capacity of corbels. Full article

This paper investigates the mechanical characteristics of rockbolt under combined tensile–shear loading conditions. By studying the stress and deformation throughout the elastic and plastic stages of rockbolt, a failure model for rockbolt under different tensile–shear combination loadings was established. Key parameters, including the maximum bending moment M_A and total plastic deformation λ, were identified and quantified as they evolve with changes in the displacement angle (combined tensile–shear state). The main novelty lies in formulating the key control parameters governing the elastic–plastic transition and failure process of rockbolts under combined tensile–shear loading and further incorporating them into FLAC^2D to improve the simulation of tensile–shear failure of rockbolts. Numerical simulations of rockbolts under combined tensile–shear loading were performed using FLAC^2D. The influence of a rock mass’ Young’s modulus and uniaxial compressive strength on the mechanical response of the rockbolt was investigated. The results indicate that the ultimate load-carrying capacity of the rockbolt remains essentially constant as the displacement angle increases, while the axial tensile force gradually decreases and the shear force gradually increases. The influence of a rock mass’ Young’s modulus on the stress–strain characteristics of the anchor exhibits a nonlinear positive correlation. When the uniaxial compressive strength of the rock mass is low, the rockbolt is prone to slippage during loading. Full article

This study comprised an experimental investigation of the in-plane performance of composite floor slabs under out-of-plane effects. Two composite floor slabs were subjected to pure in-plane loading, and in-plane and out-of-plane coupled loading, respectively. The study analyzed crack patterns, failure modes, and load–displacement curves, and evaluated how out-of-plane effects influenced in-plane performance. The test results indicated that both specimens exhibited a typical shear-tension failure mode, forming diagonal shear cracks. The specimen with out-of-plane loading exhibited a trend for lateral development of the shear cracks. The load–displacement curves of the two specimens showed obvious strength degradation, stiffness degradation, and a pinching effect. By comparing the two specimens, it could be observed that at a small out-of-plane displacement angle, the in-plane ultimate bearing capacity of a specimen was not significantly weakened; however, as the out-of-plane displacement continued to increase, the in-plane bearing capacity of the specimen decayed more rapidly. Full article

Seismic resilience assessment of high-rise buildings heavily relies on the deformation limits and fragility data of structural components, yet such data is still lacking for steel-reinforced concrete (SRC) columns, which are widely used in high-rise structures. To address this gap, this study establishes a test database consisting of 312 SRC column specimens, including 17 input parameters and three key experimental results, i.e., failure mode, yielding drift ratio θ_y, and ultimate drift ratio θ_u. Two machine learning (ML) frameworks are proposed and four ML models are trained and compared. It is found that the two-stage framework incorporating a failure mode classification shows only a slight improvement in the model performance. Thus, an end-to-end framework is recommended due to its simplicity and avoidance of error propagation, and RF and XGBoost models are adopted and tuned for θ_y and θ_u prediction for their optimal performance. Model interpretation is carried out using permutation importance (PI) and SHAP analyses to verify consistency with domain knowledge, with the key influencing factors identified as longitudinal reinforcement strength (f_yl) and axial load ratio (n_t) for deformation capacity, and shear-span ratio (λ) for failure mode classification. The performance of ML models is compared with conventional data-fitting approaches, and it is proven that ML models outperform conventional formulas, with the R² for predicting θ_y and θ_u improved by 26.5% and 32.9%, the RMSE reduced by 30.0% and 30.4%, and the MAPE reduced by 18.5% and 48.4%, respectively, thus providing a powerful data-driven tool for the seismic resilience assessment of SRC columns and expanding the fragility data of composite components. Full article

Inter-module connections are the critical load-transfer components in modular steel buildings (MSBs), whose mechanical behavior directly governs the overall safety and seismic performance of the entire structural system. To address the unresolved issue that the influence of complex loading conditions, especially the coupling effect of biaxial bending, on the load-transfer mechanism and degradation law of bayonet-type self-locking and unlockable connections remains poorly understood, two groups of full-scale quasi-static tests were conducted in this study. Specimen S1 (0°) was designed for the in-plane compression–bending–shear loading condition, while Specimen S2 (45°) was designed for the spatial compression–biaxial bending–shear loading condition. The test results demonstrate that both groups of specimens exhibit typical three-stage mechanical characteristics. The average initial stiffness of Specimen S1 (0°) is 5.47 kN/mm, while that of Specimen S2 (45°) is 6.08 kN/mm. The average ultimate load of S1 (0°) reaches 162.8 kN, and that of S2 (45°) is 164.85 kN. The average ductility coefficient of S1 (0°) and S2 (45°) is 2.79 and 2.14, respectively. Comparative analysis indicates that Specimen S1 (0°) presents superior energy dissipation capacity and ductility, while Specimen S2 (45°) has higher initial stiffness accompanied by faster stiffness degradation in the late loading stage. A high-fidelity refined FE model of the bayonet-type self-locking and unlockable connection was established. The FE analysis results are in good agreement with the test results, with the relative error of the positive flexural bearing capacity controlled within 5%. On this basis, parametric FE analysis was carried out to explore the influence of axial compression ratio on the mechanical performance of the connection. Furthermore, theoretical calculation formulas for the ultimate flexural bearing capacity of the connection under in-plane compression–bending–shear loading and spatial compression–biaxial bending–shear loading were proposed respectively. The calculated results are compared with the test data, with all relative errors within 5%, which verifies that the proposed formulas have favorable prediction accuracy for the ultimate flexural bearing capacity of the connection under both aforementioned complex loading conditions. Full article