Search Results (114)

This study investigates how different longitudinal steel rebars influence the flexural performance and cracking mechanisms of reinforced ultra-high-performance concrete (UHPC) beams, combining axial tensile tests using acoustic emission monitoring with standard four-point bending tests. A series of experimental assessments on the flexural behavior of UHPC beams reinforced with various types of longitudinal reinforcement was conducted. The types of longitudinal reinforcement mainly encompassed HRB 400, HRB 600, and NPR steel rebars. The test results revealed that the UHPC beams reinforced with the three types of longitudinal steel rebar exhibited distinctly different failure modes. Compared to the single dominant crack failure typical of UHPC beams reinforced with HRB 400 steel rebars, the beams using HRB 600 rebars exhibited a tendency under balanced failure conditions to develop fewer main cracks (typically two or three). Conversely, the UHPC beams incorporating NPR steel rebars exhibited significantly more cracking within the pure bending zone, characterized by six to eight uniformly distributed main cracks. Meanwhile, the HRB 600 and NPR steel rebars effectively upgraded the flexural load-bearing capacity and deformation ability compared to the HRB 400 steel rebars. By integrating the findings from the direct tensile tests on reinforced UHPC, aided by acoustic emission source location, this research specifically highlights the damage mechanisms associated with each rebar type. Full article

Rapid connectors for shield tunnels represent a critical advancement in underground engineering construction. This study proposes a novel auto-lock connector, detailing its structure and working principle. The flexural behavior of the auto-lock joint is investigated through theoretical analysis and numerical simulation, with a comprehensive evaluation of influencing factors. The results indicate that joint opening increases with reduced axial force, peaking at 24.1 mm under negative bending under a 100 kN axial load. The ultimate bending moment demonstrates a nonlinear variation with axial force. At low axial forces, increasing material strength or dimensions enhances joint flexural capacity, with more pronounced improvements under lower loads. This research establishes a theoretical foundation for the practical application of auto-lock connectors. Full article

Conventional bolts frequently fail under large deformations due to stress concentration in soft rock tunnels. In contrast, yielding bolts incorporate energy-absorbing mechanisms to sustain controlled plastic deformation. This study employed FLAC3D to numerically investigate the pull-out, shear, and bending behaviors of yielding bolts, evaluating their support effectiveness in soft rock tunnels. Three-dimensional finite difference models incorporating nonlinear coupling springs and the Mohr–Coulomb criterion were developed to simulate bolt–rock interactions under multifactorial loading. Validation against experimental pull-out tests and field measurements confirmed the model accuracy. Under pull-out loading, the axial forces in yielding bolts decreased more rapidly along the bolt length, reducing stress concentration at the head. The central position of the maximum load-bearing capacity in conventional bolts fractured under tension, resulting in an hourglass-shaped axial force distribution. Conversely, the yielding bolts maintained yield strength for an extended period after reaching it, exhibiting a spindle-shaped axial force distribution. Parametric analyses reveal that bolt spacing exerts a greater influence on support effectiveness than length. This study bridges critical gaps in understanding yielding bolt behavior under combined loading and provides a validated framework for optimizing energy-absorbing support systems in soft rock tunnels. Full article

This paper investigates the axial deformation characteristics and crashworthiness of thin-walled metal tubes (TWT) reinforced with Polyetherketoneketone (PEKK) honeycomb lattice structures consisting of bio-inspired hierarchical cellular topological features. Experimentally validated numerical results revealed that the specific energy absorption capacity (SEA) of these composite structures increased with filler volume corresponding to a specific cellular topology. This includes the bio-inspired hierarchical sparse (BHS) topology, which registered a remarkable improvement in SEA over the hollow tube of 202%. In contrast, the central (BHC) topology deformed in an unstable hex-dominated pattern and triggered catastrophic failure of the composite in global bending mode. Furthermore, rigid cells were shown to drastically increase the initial peak force (IPF), while cells with low stiffness were beneficial for maintaining a low level of IPF and moderately improving SEA. Moreover, the rib and wall thickness of the BHS honeycomb cells were suitably tailored to increase the SEA by 2.1%, while simultaneously reducing the IPF by 3.7%. These findings suggest that multi-functional mechanical attributes of PEKK hierarchical honeycomb lattice fillers can mutually benefit thin-walled tubes with superior energy absorption capability and lightweight features over conventional lattice-filled tubes or a hollow tube. Full article

Composite reinforcement concrete square piles exhibit excellent bending resistance and deformation capacity, along with construction advantages such as ease of transportation. In recent years, they have been widely adopted in building pile foundation applications. However, their seismic behavior, particularly under multi-directional excitation, remains inadequately explored. This study employs large-scale shaking table tests to evaluate the seismic response of a single composite reinforcement square pile embedded in a soft clay foundation under different horizontal excitations (0° and 45°) and two distinct ground motions (Wenchuan Songpan and Chi-Chi) to assess directional anisotropy and resonance effects, with explicit consideration of soil–structure interaction (SSI). The key findings include the following: the dynamic earth pressure along the pile exhibits a distribution pattern of “large at the top, small at the middle and bottom”. And SSI reduced pile–soil compression by 20–30% under 45° excitation compared to 0°. The dynamic strain in outer longitudinal reinforcement in pile corners increased by 30–60% under 45° excitation compared to 0°. Under seismic excitation considering SSI, the bending moment along the pile exhibited an “upper-middle maximum” pattern, peaking at depths of 3–5 times the pile diameter. Axial forces peaked at the pile head and decreased with depth. While bending moment responses were consistent between 0° and 45° excitations, axial forces under 45° loading were marginally greater than those under 0°. The Chi-Chi motion induced a bending moment about four times greater than the Songpan motion, highlighting the resonance risks when the ground motion frequencies align with the pile–soil system’s fundamental frequency. Full article

As a key load-bearing component in building structures, the effective strengthening of reinforced concrete (RC) columns is critical to enhancing their structural reliability and service life. To tackle the issue of excessive self-weight from the increasing section strengthening method and further optimize the seismic performance of encased steel strengthening, this paper presents a novel composite strengthening method for RC columns, which is characterized by using Lightweight Alkali-Activated Slag Concrete (LAASC) as the strengthening layer and an X-type encased steel structure. By conducting axial compression tests on six columns and utilizing in-depth research on small eccentric compression and hysteresis performance through numerical simulation, the specific effects of different strengthening materials and encased steel forms on the mechanical properties of the columns are systematically explored. Experimental results indicate that compared to ordinary concrete strengthening layers, LAASC can reduce the self-weight of the strengthening layer by 25%, boost the bearing capacity of the strengthened components by 37%, and enhance the vertical deformation capacity by 100%. Numerical simulation also confirms that X-type encased steel composite strengthening can effectively control bending deformation under small eccentric compression, reducing lateral deflection by 30–35% compared to un-strengthened columns. Under horizontal reciprocating loading, the cumulative energy dissipation of X-type encased steel composite-strengthened columns is 15–30% higher than that of traditional steel encased composite-strengthened columns, reflecting the diagonal bracing effect of the X-type batten plates. Full article

In recent years, there has been a growing use of cold-formed steel (CFS) structures in the field of civil engineering. The objective of this study is to utilize gene expression programming (GEP) in order to forecast the ultimate bearing capacity of cold-formed steel columns. The buckling resistance of built-up back-to-back cold-formed (BCF) thin-walled tube columns under axial compression, and of cold-formed thick-walled steel columns under combined axial compression and bending, is examined in this paper. The data were collected from various studies to develop and verify the proposed model, with training and testing sets of 160 and 14, and 2000 and 500, respectively. The performance of the genetically developed GEP models was evaluated and compared with that of the mechanical models specified in American and Chinese specifications. The GEP models demonstrated significantly better performance compared with that of the code-specified models. The results generated by the GEP models demonstrate stronger alignment with both experimental data and analytical predictions. This study also demonstrates the capability of the GEP models to calculate the ultimate bearing capacity, with the proposed mechanical models being used as a reference for calculations. Full article

While the longitudinal pre-embedded holes in a reinforced concrete column have a variety of beneficial functions during the whole life of the building, they have certain negative influences on the mechanical properties of the column. To investigate the influences of longitudinally pre-embedded holes on the mechanical properties of reinforced concrete (RC) columns, numerical simulations were conducted using the finite element software ABAQUS 2021 to analyze the effects of various parameters, including hole diameter, concrete strength, stirrup ratio, and slenderness ratio, on the mechanical behavior of RC columns under axial pressure. The results show that the presence of longitudinally pre-embedded holes reduces the load-bearing capacity of the columns. Furthermore, when the hole diameter exceeds 75 mm and the concrete strength is over C35, the failure mode of the columns shifts from axial compression failure to shear failure at the bending section of the pre-embedded hole. Increasing the stirrup ratio effectively enhances the ductility and load-bearing capacity and avoids brittle failure, whereas the influence of slenderness ratio variations on the column’s bearing capacity is negligible. These results provide a theoretical basis for the safe design of longitudinally pre-embedded hole columns in green buildings, effectively balancing the requirements between structural lightweight design and load-bearing performance. Full article

Machine learning methods are widely used to predict the bearing capacity of concrete-filled steel tubular (CFST) columns. However, in addition to this task, the engineer often faces the inverse problem: to determine what cross-section dimensions of the CFST column are required for given loads. This paper is devoted to the development of machine learning models for predicting the geometric parameters of a circular cross-section for concrete-filled steel tubular (CFST) columns under the combined action of bending moments and compressive axial forces. This problem has not been solved by machine learning methods before. The main focus is on automating the design process of CFST columns using the CatBoost algorithm and artificial neural networks. Three machine learning models were developed to solve the problem. The first and second models are based on the CatBoost algorithm. They predict the column diameter at minimum and maximum wall thicknesses, respectively. The third model is an artificial neural network, which is designed to determine the wall thickness of a CFST column. The models were trained on synthetic data generated in accordance with Russian design codes. The first and second models demonstrated high accuracy in predicting the column diameter (RMSE = 3.86 mm and 4.12 mm, respectively). The third model showed high efficiency over the entire range of wall thicknesses (correlation coefficient R = 0.99974). Feature importance analysis using SHAP values confirmed the key role of bending moment and axial force in predicting geometric parameters. Full article

Traditional design and shaping methods of helical gears may have difficulties in meeting the requirements of multiple performance indicators simultaneously, such as tooth surface accuracy, load-carrying capacity, and transmission efficiency. This study attempts to overcome these limitations through a multi-objective optimization method and achieve the comprehensive optimization of multiple performance indicators. This paper aims to boost gear system power transmission and cut vibration and noise. It assesses gear shaping impacts via normal load per unit length of the helical gear surface and gear vibration amplitude. Traditional gear shaping schemes were first determined using classic theories and formulas. Then, an improved genetic algorithm was applied to seek optimal helical gear shaping parameters. An eight-degree-of-freedom lumped mass model of the helical gear transmission system, considering bending–torsion–axial coupling, was developed based on Newton’s second law and solved via the fourth-order Runge–Kutta method. Comparisons showed that the traditional shaping scheme reduced the maximum normal load per unit length by 20.6% and the system’s vibration amplitude by 18.3%. In contrast, the improved genetic algorithm achieved greater reductions of 26.34% and 27.2%, respectively. Both methods effectively decreased the maximum normal load per unit length and system vibration amplitude, with the improved genetic algorithm yielding superior results. This work offers a key theoretical basis and reference for enhancing load transmission, reducing costs, and mitigating vibration and noise in gear transmission systems. Full article

This paper proposes a hybrid steel plate–bolt dry and wet jointing method, where the dry jointing part is a steel plate–bolt connector joint and the wet jointing part is a cast-in-place concrete. The novel precast concrete shear wall (PCW) combines the advantages of both dry and wet connections. A steel plate–bolt dry–wet hybrid connection shear wall model was developed using the finite element method, and a low circumferential reciprocating load was applied to the PCW. By analyzing the force and deformation characteristics of the wall, the results showed that the failure mode of novel PCWs was bending-shear failure. Compared to the concrete wall (CW), the yield load, peak load, and ductile displacement coefficient were 6.55%, 7.56%, and 21.49% higher, respectively, demonstrating excellent seismic performance. By extending the wall parameters, it was found that the increased strength of the novel PCW concrete slightly improved the load-bearing capacity, and the ductility coefficient was greatly reduced. As the axial compression ratio increased from 0.3 to 0.4, the wall ductility decreased by 22.85%. Increasing the reinforcement rate of edge-concealed columns resulted in a severe reduction in ultimate displacement and ductility. By extending the connector parameters, it was found that there was an increased number of steel joints, a severe reduction in ductility, enlarged distribution spacing, weld hole plugging and bolt yielding, reduced anchorage performance, and weakening of the steel plate section, which reduced the load-bearing capacity and initial stiffness of the wall, with little effect on ductility. Full article

This study investigates the dynamic behavior of a jacket-supported offshore wind turbine (JOWT) by developing its substructure and controller tailored for the IEA 15 MW reference wind turbine. A fully coupled numerical model integrating the turbine, jacket, and pile is established to analyze the natural frequencies and dynamic responses of the system under wind–wave–current loading and seismic excitations. Validation studies confirm that the proposed 15 MW JOWT configuration complies with international standards regarding natural frequency constraints, bearing capacity requirements, and serviceability limit state criteria. Notably, the fixed-base assumption leads to overestimations of natural frequencies by 32.4% and 13.9% in the fore-aft third- and fourth-order modes, respectively, highlighting the necessity of soil–structure interaction (SSI) modeling. During both operational and extreme wind–wave conditions, structural responses are governed by first-mode vibrations, with the pile-head axial forces constituting the primary resistance against jacket overturning moments. In contrast, seismic excitations conversely trigger significantly higher-mode activation in the support structure, where SSI effects substantially influence response magnitudes. Comparative analysis demonstrates that neglecting SSI underestimates peak seismic responses under the BCR (Bonds Corner Record of 1979 Imperial Valley Earthquake) ground motion by 29% (nacelle acceleration), 21% (yaw-bearing bending moment), 42% (yaw-bearing shear force), and 17% (tower-base bending moment). Full article

Despite the widespread use of precast concrete segmental bridges (PCSBs), concerns persist regarding their structural reliability, particularly due to the interruption of longitudinal reinforcement at joints. To address this, a novel approach based on the Grid Shear Reinforcement Theory is proposed, featuring precast segmental beams with continuous longitudinal reinforcements across joints. Experimental tests were conducted on one monolithic beam and two segmental beams under combined bending and shear with joint types as the primary variable. Key performance metrics included crack propagation, reinforcement strain, failure modes, stiffness, and load-bearing capacity. Results show that continuous longitudinal reinforcement effectively resists axial tension from shear forces, contributing to shear resistance comparable to stirrups. It also restrains diagonal crack propagation and limits main crack widths, significantly improving shear stiffness. Reinforced joints adhered to the plane section assumption and exhibited monolithic beam behavior throughout loading. These findings highlight the critical role of continuous longitudinal reinforcement in segmental beam joints. The study further compares shear reinforcement design approaches in European Codes, ACI, AASHTO, GB, JTC, and the Grid Shear Reinforcement Theory. Practical construction methods for implementing continuous longitudinal reinforcements are also proposed, offering valuable insights for engineering applications. Full article

The pier-type repair equipment for bridges is a crucial branch of bridge emergency repair. However, the existing bridge pier repair equipment predominantly utilizes rod systems, which require substantial assembly work, hindering the rapid restoration of damaged bridges. Modular steel structure buildings, as a highly integrated form of prefabricated construction, can play a significant role in emergency rescue operations. Based on the modular architectural design concept, this paper proposes a new type of modular steel structure emergency repair pier joint that facilitates rapid assembly and connection between modular units. Using ABAQUS 2022 software to establish a finite element model of the joint, the bending performance under lateral displacement loads perpendicular to the joint opening direction (X-direction in the model coordinate system) and parallel to the joint opening direction (Z-direction in the model coordinate system) is analyzed. The influence of the width-to-thickness ratio of the upper corner piece base plate D/t₁ (where D is the width of the upper corner piece base plate and t₁ is the thickness of the upper corner plate), the height-to-thickness ratio of the lower corner piece top plate h/t₂ (where h is the height of the protrusion of the lower corner piece and t₂ is the thickness of the lower corner piece top plate), the height of the protrusion of the lower corner piece (h), and the bolt diameter (d) on the bending performance of the joint is investigated. Recommendations for the design values of the joint are provided. Then, the flexural behavior of the joint under 0.1, 0.2, and 0.3 axial compression ratios is studied, respectively. The results show that with the increase of axial compression ratio, the yield rotation angle and ultimate rotation angle of the joint decrease, and the bearing capacity decreases faster after the joint reaches the ultimate bearing capacity. When the joint is subjected to the X-direction horizontal lateral displacement load, the initial flexural stiffness and flexural capacity of the joint increase with an increase in the axial compression ratio. When subjected to the horizontal lateral displacement load in the Z-direction, the initial bending stiffness of the joint increases with an increase in the axial compression ratio, and the bending capacity does not change much. In addition, the joint is classified; from the perspective of load-bearing capacity, it is a partially resistant joint, and from the perspective of stiffness, it is a semi-rigid joint. Finally, a simplified calculation model for the joint is proposed based on the component method. Full article

Prefabricated insulation grid shear walls are a new type of wall which integrates structure, insulation and formwork. A grid-like reinforced concrete shear wall with vertical and transverse limbs is formed by casting concrete into the reserved vertical and transverse hollow cavities in the prefabrication of cement polystyrene granular concrete wall formworks. In this paper, based on an earthquake engineering simulation open system (OpenSees), a new modeling approach for grid shear walls is proposed, and nonlinear analysis of two grid walls with different grid sizes under cyclic load is carried out. The accuracy and effectiveness of the grid shear wall model are verified by comparison of the predicted hysteretic response and experimental results. On this basis, the seismic performance of grid shear walls with different parameters (axial load ratio, vertical reinforcement ratio, transverse reinforcement ratio and transverse limb height) is analyzed. The results show that both axial load ratio and vertical reinforcement ratio can significantly improve the load capacity of grid shear walls. However, with an increase in the axial load ratio, the ductility of the grid shear walls decreases. The influence of transverse reinforcement ratio and transverse limb height on the load capacity of shear wall with large shear span ratio is relatively small, mainly because the failure mode of shear wall with large shear span ratio is bending failure. Based on parameter influence analysis, design suggestions for reinforcement ratio in vertical and horizontal limbs and the height of the transverse limb of grid shear walls are put forward. The research in this paper provides a reference for the application of grid shear walls in engineering. Full article