Search Results (288)

This study presents the results of axial tension (uplift) and compression tests evaluating the capacity of helical piles installed in Shahriyar dense sand using the UTM apparatus. Thirteen pile load experiments involving single-, double-, or triple-helix piles with shaft diameters of 13 mm were performed, including six compression tests and seven tension tests with different pitches (D_h =13, 20, and 25 mm). The tested helical piles with a helix diameter of 51 mm were considered, and the interhelix spacing approximately ranged between two and four times the helix diameter. Through laboratory testing techniques, the Shahriyar dense sand properties were identified. Alongside theoretical analyses of helical piles, the tensile and compressive pile load tests outcomes in dense sand with a relative density of 70% are presented. It was found that the maximum capacities of the compressive and tensile helical piles were up to six and eleven times that of the shaft capacity, respectively. With an increasing number of helices, the settlement reduced, and the bearing capacity increased. Consequently, helical piles can be manufactured in smaller sizes compared to steel piles. Overall, the compressive capacities of helical piles were higher than the tensile capacities under similar conditions. Single-helices piles with a pitch of 20 mm and double-helices piles with a pitch of 13 mm were more effective than others. Therefore, placing helices at the shallower depths and using smaller pitches result in better performance. In this study, when compared to values from the L1–L2 method, the theoretical method slightly underestimates the ultimate compression capacity and both overestimates and underestimates the uplift capacity for single- and double-helical piles, respectively, due to the individual bearing mode and cylindrical shear mode. Full article

Coastal marine soft clays subjected to long-term storm wave loading often exhibit inclined initial principal stress orientation (α₀) and subsequent cyclic principal stress rotation (PSR). These stress states critically influence soil mechanical behavior and failure mechanisms, threatening offshore structural stability. This study employs hollow cylinder apparatus testing to investigate the undrained cyclic loading behavior of reconstituted soft clay under controlled α₀ and PSR conditions, simulating storm wave-induced stress paths. Results demonstrate that α₀ governs permanent pore pressure and vertical strain accumulation with distinct mechanisms, e.g., a tension-dominated response with gradual pore pressure rise at α₀ < 45° transitions to a compression-driven rapid strain accumulation at α₀ > 45°. Rotational loading with PSR significantly intensifies permanent strain accumulation and stiffness degradation rates, exacerbating soil’s anisotropic behavior. Furthermore, the stiffness degradation index tends to uniquely correlate with the permanent axial or shear strain, which can be quantified by an exponential relationship that is independent of α₀ and PSR, providing a unified framework for normalizing stiffness evolution across diverse loading paths. These findings advance the understanding of storm wave-induced degradation behavior of soft clay and establish predictive tools for optimizing marine foundation design under cyclic loading. 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

Under the impetus of achieving global sustainable development goals, the civil construction industry is accelerating its transition towards high-quality, green, and low-carbon practices. Prefabricated, modular building technology has become a key tool due to its advantages in energy conservation, emission reduction, and shortened construction periods. However, existing research on the seismic performance of prefabricated, modular, reinforced concrete column–beam (RCS) composite structures often focuses on the construction form of beam–column joints, paying less attention to the impact of floor slabs on the seismic performance of joints during earthquakes. This may make joints a weak link in structural systems’ seismic performance. To address this issue, this paper designs a prefabricated, modular RCS composite joint considering the effect of floor slabs and uses the finite element software ABAQUS 2023 to perform a quasi-static analysis of the joint. The reliability of the method is verified through comparisons with the experimental data. This study examines various aspects, including the joint design and the material’s constitutive relationship settings, focusing on the influence of parameters, such as the axial compression ratio and floor slab concrete strength, on the joint seismic performance. It concludes that the seismic performance of the prefabricated, modular RCS composite joints considering the effect of floor slabs is significantly improved. Considering the composite effect of the slabs, the yield loads in the positive and negative directions for node FJD-0 increased by 78.9% and 70.0%, respectively, compared to that of the slab-free node RCSJ3. The ultimate bearing capacities improved by 13.2% and 9.98%, respectively, and the energy dissipation capacity increased by 23%. Additionally, the variation in the axial load ratio has multiple effects on the seismic performance of the joints. Increasing the slab thickness significantly enhances the seismic performance of the joints under positive loading. The bolt pre-tensioning force has a crucial impact on improving the bearing capacity and overall stiffness of the joints. The reinforcement ratio of the slabs has a notable effect on the seismic performance of the joints under negative loading, while the concrete strength of the slabs has a relatively minor impact on the seismic performance of the joints. Therefore, the reasonable design of these parameters can optimize the seismic performance of joints, providing a theoretical basis and recommendations for engineering application and optimization. Full article

This preliminary study explores the feasibility of using the flat-jack test to assess residual prestress in post-tensioned concrete elements. Experimental testing was conducted on three concrete slabs under controlled laboratory conditions, with known stress states induced by axial loading. Two flat-jack sizes and two gage lengths were considered, and a tailored calibration procedure was implemented to reflect expected field conditions. The test produced acceptable stress estimations, with accuracy influenced by both the gage length and the jack size. The results are discussed within the broader context of prestress assessment, including a comparison between the flat-jack test’s performance in concrete and masonry and its positioning relative to alternative methods. The experimental design, result presentation, and theoretical analysis in this study are intentionally simple and not yet sufficiently mature to support practical application. Nevertheless, the findings offer promising initial insights and practical inspiration for practitioners and researchers exploring alternative methods for residual stress assessment in prestressed concrete structures, underscoring the need for further research to refine the methodology and validate its broader applicability. Full article

The human neck is highly vulnerable in motor vehicle crashes, and cervical spine response data are essential to improve injury prediction tools (e.g., crash test dummies, human body models). This feasibility study aimed to implement the use of pressure sensors in whole-body post-mortem human subject (PMHS) cervical spine intervertebral discs (IVDs) to confirm the feasibility and repeatability of cervical IVD pressure response to biomechanic research. Two fresh frozen whole-body PMHSs were instrumented with miniature pressure sensors (Model 060S, Precision Measurement Company, Ann Arbor, MI, USA) at three cervical IVD levels (C3/C4, C5/C6, and C7/T1) using minimally invasive surgical insertion techniques. Each PMHS underwent three quasistatic motion test trials, and each trial included multiple head/neck motions (i.e., gentle traction, flexion/extension, lateral bending, axial rotation, and forced tension/compression). Results showed marked pressure differences between both the cervical level assessed and the motion undertaken as well as successful intra-subject repeatability between the three motion trials. This study demonstrates that changes in cervical IVD pressure are associated with motion events of the cervical spine. Cervical IVD response data could be utilized to assess and supplement the characterization of the head/neck complex motion, and data could facilitate the continued improvement of injury prediction tools. Full article

Background and Objectives: This study compares the biomechanical performance of a new-generation implant designed for patella fracture fixation with the traditional tension band method. Its goal is to assess fracture fixation’s stability and the new implant’s potential advantages in reducing complications such as skin irritation, pain, and implant failure. Materials and Methods: In this experimental study, 20 calf patellae were divided into two groups. The first group was treated with the traditional tension band method, while the second group received the new-generation implant, designed using finite element analysis (FEA) for optimization. Both groups underwent biomechanical testing with axial forces at a 45° flexion angle to simulate real-life load conditions. The maximum forces at which mechanical insufficiency occurred were recorded. Data were analyzed using SPSS for statistical comparison. Results: Finite element analysis revealed that the new-generation implant provided better fracture line stability than the tension band method under applied forces. In the biomechanical tests, the maximum force at which mechanical insufficiency occurred was significantly higher in the new-generation implant group (1130 ± 222 N) compared to the tension band method group (680.5 ± 185.4 N), with a statistically significant difference (p = 0.008). The new implant demonstrated superior fixation, with better resistance to distraction forces. Conclusions: The new-generation implant offers enhanced biomechanical stability compared to the traditional tension band method, particularly regarding fixation strength under applied forces. This study supports the potential of the new implant to improve fixation stability and reduce common complications associated with patella fracture surgeries. Further testing in more extensive human cadaver studies is recommended to confirm these findings and assess long-term clinical outcomes. Full article

This paper examines the hysteretic behavior of the buckling restrained braces (BRBs) in the steel frame. Both experimental and finite element (FE) studies were conducted. The experimental results showed that the well-detailed buckling restrained braced frame (BRBF) withstood significant drift demands, while the BRB exhibited significant yield without severe damage. Although the BRB inside the steel frame was subjected to 2.69% strain of the CP under the axial compression demands, the local and global deformations were not observed. The FE model was developed and validated. The numerical investigations of hysteretic behavior of the BRBF in the literature are generally focused on the friction between the core plate (CP) and the casing member (CM). The results suggest that the behavior of the BRBF is significantly affected not only by the friction between CP and CM but also by the pretension load on the bolts and the friction between the contact surfaces of steel plates of slip-critical connections in the steel frame. The FE analysis showed that pretension loads of 35 kN and 75 kN gave accurate predictions for cyclic responses of BRBF under tension and compression demands, respectively. Moreover, the FE predictions were in good agreement with the test results when the friction coefficient is 0.05 between CP and CM and it is 0.20 between steel plates. Full article

Oxide dispersion-strengthened (ODS) steels are among the most promising candidate structural materials for fusion and Generation-IV (Gen-IV) fission reactors, but the ductility of ODS steels is inferior to its strength properties. Therefore, we investigate void nucleation, considered as the first step of ductile damage in metal, using molecular dynamics simulations. Given that the materials are subjected to extremely complex stress states within the reactor, we present the void nucleation process of 1–4 nm Y₂O₃ nanoclusters in bcc iron during uniaxial, biaxial, and triaxial tensile deformation. We find that the void nucleation process is divided into two stages depending on whether the dislocations are emitted. Void nucleation occurs at smaller strain in biaxial and triaxial tensile deformation in comparation to uniaxial tensile deformation. Increasing the size of clusters results in a smaller strain for void nucleation. The influence of 1 nm clusters on the process of void nucleation is slight, and the void nucleation process of 1 nm cluster cases is similar to that of pure iron. In addition, void nucleation is affected by both stress and strain concentration around the clusters, and the voids grow first in the areas of high stress triaxiality. Full article

Numerical simulations were conducted to investigate high-pressure water jets in air. The Eulerian multiphase model was employed as the computational framework. Through simulating a high-pressure water jet impinging on a flat plate, two turbulence treatment methodologies were initially examined, demonstrating that the mixture turbulence modeling approach exhibits superior predictive capability compared to the per-phase turbulence modeling approach. Subsequent analysis focused on evaluating turbulence model effects on the impact pressure distribution on the flat plate. The results obtained from the elliptic–blending turbulence model (the SST k-ω-φ-α model) and the other two industry-standard two-equation turbulence models (the realizable k-ε model and the SST k-ω model) were comparatively analyzed against experimental data. The analysis revealed that the SST k-ω-φ-α model demonstrates superior accuracy near the stagnation region. The effects of bubble diameter and surface tension were further examined. Quantitative analysis indicated that the impact pressure exhibits a decrease with decreasing bubble diameter until reaching a critical threshold, below which diameter variations exert negligible influence. Furthermore, surface tension effects were found to be insignificant for impact pressure predictions when the nozzle-to-plate distance was maintained below 100 nozzle diameters (100D). Simulations of free high-pressure water jets were performed to evaluate the model’s capability to predict long-distance jet dynamics. While the axial velocity profile showed satisfactory agreement with experimental measurements within 200D, discrepancies in water volume fraction prediction along the jet axis suggested limitations in phase interface modeling at extended propagation distances. Full article

The construction industry is a major contributor to the global climate crisis, prompting increasing interest in minimising the embodied carbon of structures, whether through material production regulations or the optimisation of structural elements. While a wide body of literature addresses the reduction of embodied carbon in superstructures, limited attention has been devoted to the optimisation of foundations, particularly piles. This research introduces a hybrid genetic algorithm optimisation tool designed to minimise the embodied carbon of tension piles in different soil conditions. Six different pile types are analysed: solid and hollow concrete piles, steel pipes, universal column (UC) sections, and timber piles in both square and circular forms. The optimal design parameters for each pile type on undrained clay and loose sand are presented and compared. The results demonstrate the potential for reducing the embodied carbon of tension piles when utilising optimised designs. Finally, a case study involving an 8-metre-high cross-road signpost is presented, illustrating the practical application of the proposed optimisation algorithm for reducing embodied carbon in future designs. Full article

Traditional concrete has low tensile strength, is prone to cracking, and has poor durability, which limits its scope of application. Basalt Fiber Textile–Reinforced Concrete (BTRC), a new type of fiber-reinforced cement material, offers advantages such as light weight, increased strength, improved crack resistance, and high durability. It effectively addresses the limitations of traditional concrete. However, the tensile properties of BTRC have not been fully studied, especially with fine aggregate concrete as the matrix, and there are few reports on this topic. Therefore, this study conducted uniaxial tensile tests of Basalt Textile–Reinforced Fine Aggregate Concrete (BTRFAC) and systematically investigated the effects of two mesh sizes (5 mm × 5 mm and 10 mm × 10 mm) and two to four layers of fiber mesh on the tensile strength, strain hardening behavior, crack propagation, and ductile tensile mechanical properties of BTRFAC thin slabs. The tests revealed that an increase in the number of fiber mesh layers significantly reinforced the material’s tensile strength and ductility. The tensile strength of the 5 mm mesh specimen (four-layer mesh) reached 2.96 MPa, which is 193% higher than plain concrete, and the ultimate tensile strain increased by 413%. The tensile strength of the 10 mm mesh specimen (four-layer mesh) was 2.12 MPa, which is 109% higher than plain concrete, and the ultimate tensile strain increased by 298%. The strength utilization rate of the 5 mm and 10 mm mesh fibers was 41% and 54% respectively, mainly due to the weakening effect caused by interface slippage between the fiber mesh and the matrix. An excessively small mesh size may lead to premature debonding from the matrix, but its denser fiber distribution and larger bonding area exhibit better strain hardening characteristics. More than three layers of fiber mesh can significantly improve the uniformity of crack distribution and delay propagation of the main crack. A calculation formula for the tensile bearing capacity of BTRFAC thin slabs is proposed, and the error between the theoretical value and the experimental value was very small. This research provides a theoretical basis and reference data for the design and application of basalt fiber mesh–reinforced concrete thin slabs. Full article

During long-span arch bridge construction, repeated adjustments of large cantilevered segments and nonuniform cable tensions can lead to deviations from the desired arch profile, reducing structural efficiency and increasing labor and material costs. To precisely control the process of cable-stayed buckle construction in long-span arch bridges and achieve an optimal arch formation state, a constrained optimization for the buckle and anchor cable forces under one-time tension is developed in this paper. First, by considering the coupling effect of the cable-stayed buckle system with the buckle tower and arch rib structure, the control equations between the node displacement and cable force after tensioning are derived based on the influence matrix method. Then, taking the cable force size, arch rib closure joint alignment, upstream and downstream side arch rib alignment deviation, tower deviation, and the arch formation alignment displacement after loosening the cable as the constraint conditions, the residual sum of squares between the arch rib alignment and the target alignment during the construction stage is regarded as the optimization objective function, to solve the cable force of the buckle and anchor cables that satisfy the requirements of the expected alignment. Applied to a 310 m asymmetric steel truss arch bridge, the calculation of arch formation alignment is consistent with the ideal arch alignment, with the largest vertical displacement difference below 5 mm; the maximum error between the measured and theoretical cable forces during construction is 4.81%, the maximum difference between the measured and theoretical arch rib alignments after tensioning is 3.4 cm, and the maximum axial deviation of the arch rib is 5 cm. The results showed the following: the proposed optimization method can effectively control fluctuations of arch rib alignment, tower deviation, and cable force during construction to maintain the optimal arch shape and calculate the buckle and anchor cable forces at the same time, avoiding iterative calculations and simplifying the analysis process. Full article

This study evaluates the feasibility of 3D-printed polymer composite external fixator (EF) rings as a cost-effective alternative to stainless steel fixators, focusing on hybrid fixators for complex tibial fractures. Mechanical performance was assessed in three stages: (1) evaluating the initial EF–tibia configuration under axial loading and wire pre-tension conditions; (2) analyzing the stiffness evolution and weight-bearing capacity during early healing with progressive callus formation; and (3) optimizing ring designs through numerical analysis to improve structural performance under increased pre-tension. The results showed that, for the metallic EF, the axial displacement under one-leg stance reached 8.41 mm without pre-tension, reducing to 6.83 mm at 500 N pre-tension, though transverse displacement remained significant, suggesting the need for higher wire tension. Callus formation enhanced the load-bearing capacity, as expected. However, excessive displacements persisted under the one-leg stance, indicating that full weight-bearing should be delayed beyond two weeks for a fracture gap of 3 mm. A ring design assessment showed that full-ring configurations with two wires per ring improved performance. The 3D-printed full-ring design made of carbon-fiber-reinforced polylactic acid (PLA-CF) reduced stress by 85% at 500 N pre-tension compared to the initial configuration, remaining within allowable limits. While confirming feasibility, the study highlights the need for geometric refinements to accommodate higher preloads and improve transverse stiffness. Full article

The excavation process for a deeply buried chamber in a high ground stress area is often dynamic. The design of reasonable excavation methods for differing geological conditions and surrounding pressure environments is of great engineering significance in order to improve the stability of surrounding rocks during construction. Based on the findings from conventional triaxial and cyclic loading laboratory tests on marble, this paper obtains a set of mesoscopic parameters that accurately represent the macro-mechanical characteristics of marble, uses the discrete element method (DEM) to establish a numerical model, and carries out numerical tests of triaxial and cyclic loading under varying circumferential pressures. The mechanical parameter evolution, crack propagation mechanism and mesoscopic force field distribution of marble under conventional triaxial stress and cyclic load-reversal conditions are compared and analyzed. The findings suggest that the peak strength, residual strength, peak axial strain, elastic modulus, and Poisson’s ratio of marble increase as the circumferential pressures rises for both stress paths. The peak strength and elastic modulus under cyclic loading at different circumferential pressures are lower than those observed under conventional triaxial conditions, while the Poisson’s ratio is higher compared to conventional triaxial conditions. The cumulative total number of microcracks in marble damage under cyclic loading is higher and the damage is more complete compared to conventional triaxial loading. The rock specimens in both stress paths are dominated by tension cracks. Nevertheless, a greater number of shear cracks are exhibited by the specimens subjected to cyclic loading conditions. The proportion of tension cracks in the rock specimens gradually decreases with increasing circumferential pressure, while the proportion of shear cracks gradually increases. For both stress paths, the angular distribution of microcracks following rock specimen failure is similar, and the force chain becomes progressively denser as the circumferential pressures increase. The force chain distribution within the rock specimens is more heterogeneous under cyclic loading conditions than under conventional triaxial conditions. Full article