Search Results (265)

In the marine environment, the suction caisson foundation (SCF) is often subjected to combined inclined and cyclic loading from wind and waves, which may significantly affect its ultimate bearing capacity. Under combined loading conditions, the evolution of ultimate bearing capacity is influenced by multiple factors, and the corresponding bearing capacity envelopes have become key issues that urgently need to be addressed. In this study, a series of model tests and numerical simulations were conducted considering the effects of load inclination angle, loading position, aspect ratio, soil undrained shear strength, and interface friction coefficient. The results show that under static loading conditions, as the loading depth increases, the load inclination angle corresponding to the maximum bearing capacity decreases from 45° to 0°. As the cyclic load ratio and static load ratio increase, cyclic loading significantly intensifies displacement accumulation and the degradation of ultimate bearing capacity. As the loading depth increases, the failure mechanism transitions from rotation-dominated to translation-dominated behavior. In addition, the ultimate bearing capacity increases monotonically with increasing aspect ratio, interface friction coefficient, and soil undrained shear strength. A normalized V–H bearing capacity envelope was established, which shows good agreement with the experimental and numerical results. By introducing a cyclic bearing capacity degradation coefficient, a modified envelope was proposed to describe the evolution of ultimate bearing capacity under cyclic loading conditions. The bearing capacity evolution patterns and envelope method proposed in this study provide a useful reference for the engineering design of SCF. Full article

To further improve the seismic behavior of high-strength foam concrete filled cold-formed checkered steel composite wall structures, it is crucial to investigate the bond–slip behavior between the cold-formed checkered steel (CFCS) and foam concrete (FC) within the wall. Hence, six CFCSFC specimens were designed and subjected to monotonic and cyclic loading tests to study the influence of anchorage lengths on failure modes, bond strength-slip displacement curves, and characteristic bond strength. Results indicated that with the anchorage length increases, the ultimate bond strength of the specimens continuously decreases, and the specimens exhibit more severe failure under cyclic loading than monotonic loading. Compared to the specimens with a 400 mm anchorage length, the ultimate bond strength decreased by 4.8–9.6% for those with a 500 mm length, and by 10.7–16.0% for those with a 600 mm length. Strain along the inner flange of the steel section generally decreased with increasing anchorage length, with loading end strain significantly exceeding free-end strain. Finite element simulations revealed that specimen failure primarily manifested as steel section yielding when anchorage lengths ranged from 1400 mm to 1800 mm. Furthermore, a calculation formula for characteristic bond strength as a function of anchorage length was proposed. Full article

Beam-to-column connections govern both seismic performance and post-earthquake repairability of steel moment-resisting frames. Yet direct, apples-to-apples comparisons among welded, bolted, and repair-oriented replaceable-fuse moment connections are still scarce, which hinders rational selection for resilient construction. This study conducts a unified finite-element comparison of three representative joint archetypes—W-RBS, Bolted, and Prefab-web-fuse—under monotonic and cyclic loading. Consistent moment-rotation definitions are adopted, and normalized indices are introduced to compare hysteresis shape, degradation, and energy dissipation across joint concepts with different strength scales. Component-wise plastic dissipation is also extracted to quantify damage localization and assess main-frame protection and replaceability. Results reveal clear trade-offs: W-RBS provides the highest strength and dissipation but degrades most in stiffness; the bolted joint shows pinching due to interface compliance; and the web-fuse concept concentrates inelastic demand in a replaceable segment, supporting repairability-oriented design. The proposed framework offers mechanism-based guidance for selecting steel moment connections toward resilient and repairable frames. Full article

This study examines the shear behavior of geopolymer (zero-cement) concrete (ZCC) beams under monotonic and cyclic loading, focusing on the effects of concrete compressive strength, reinforcement ratio, and shear span-to-depth ratio. A total of 48 simply supported beams were tested under two-point loading, with compressive strengths of 20 and 30 MPa, longitudinal reinforcement configurations of 2Ø10, 3Ø10, and 3Ø12, and shear span-to-depth ratios (a/d) of 2, 2.5, and 3. The results demonstrate that ZCC beams achieve shear capacity, ductility, and energy dissipation comparable to or exceeding those of conventional concrete beams, confirming their suitability for shear-critical structural applications and providing valuable experimental data to support future design and modeling of sustainable concrete systems. Results showed that under monotonic loading, increasing compressive strength and longitudinal reinforcement enhanced load capacity by up to 33%, improved energy absorption, and reduced deflection, while higher a/d ratios decreased load capacity by about 37% but increased deflection by nearly 48%. Similar trends were observed under cyclic loading, although beams exhibited additional vertical cracking and stiffness degradation; ZCC beams sustained 70–90% of their monotonic displacement capacity, with 30 MPa specimens demonstrating superior energy dissipation and ductility. Reinforcement strains were consistently lower in ZCC beams than in normal concrete beam, indicating improved bond performance. Failure was primarily governed by diagonal shear cracks at angles of 30–45°, similarly to NC beams but with more gradual crack development. The findings confirm that ZCC beams achieve shear performance comparable to beams made with conventional concrete while offering improved ductility and energy absorption, highlighting their potential as a sustainable alternative for shear-critical structural applications subjected to monotonic and cyclic loading. Full article

Duplex stainless steel (S22053) is increasingly favoured in construction and marine engineering due to its superior corrosion resistance, toughness, and high strength-to-weight ratio. This study presents a comprehensive investigation into the mechanical behaviour of duplex stainless steel under both monotonic and cyclic loading. First, monotonic behaviour is characterized, and the applicability of existing constitutive models is verified. Addressing the complexity of parameter identification for the cyclic constitutive model, a genetic algorithm (GA)-based calibration framework for the Chaboche model is proposed. This approach overcomes the subjectivity and inefficiency of traditional manual fitting. The proposed method is validated against experimental hysteresis curves, demonstrating high accuracy and providing a reliable basis for the seismic design of duplex stainless steel structures. Full article

Fiber-reinforced polymer (FRP) composites are increasingly used in civil, marine, offshore, and energy infrastructure, where components routinely experience temperatures above ambient conditions. While the design of these components is largely driven by fiber-dominated characteristics, the deterioration of shear properties can lead to premature weakening and even failure. Thus, the performance and reliability of these systems depend intrinsically on the response of interlaminar shear characteristics, in-plane shear characteristics, and flexure-based shear characteristics to thermal loads ranging from uniform and monotonically increasing to cyclic and spike exposures. This paper presents a critical review of current knowledge of shear response in the presence of thermal exposure, with emphasis on temperature regimes that are below T_g in the vicinity of T_g and approaching T_d. Results show that thermal exposures cause matrix softening and microcracking, interphase degradation, and thermally induced residual stress redistribution that significantly reduces shear-based performance. Cyclic and short-duration spike/flash exposures result in accelerated damage through thermal fatigue; steep thermal gradients, including through the thickness; and localized interfacial failure loading to the onset of delamination or interlayer separation. Aspects such as layup/ply orientation, fiber volume fraction, degree of cure, and the availability and permeation of oxygen through the thickness can have significant effects. The review identifies key contradictions and ambiguities, pinpoints and prioritizes areas of critically needed research, and emphasizes the need for the development of true mechanistic models capable of predicting changes in shear performance characteristics over a range of thermal loading regimes. Full article

Silicon nitride (Si₃N₄) ceramic bearings inevitably contain crack-like defects, yet their compressive capacity degradation and crack-driven failure mechanisms remain unclear. This study proposes a discrete element method (DEM) numerical framework within PFC2D to simulate a bearing containing a single prefabricated crack. First, a bearing DEM model was established and calibrated to reproduce the compressive mechanical response. Then, particle deletion introduced controllable central cracks in the ball and raceway with prescribed inclination angles. Finally, displacement-controlled compression-splitting simulations, serving as a surrogate for a quasi-static overload scenario relevant to quality screening, tracked crack initiation, propagation, and failure modes; under a fixed raceway-crack inclination, crack length was varied to quantify size effects. Results show that a single crack markedly reduces compressive strength. Failure progresses through elastic deformation, crack propagation, and final fracture, with cracks initiating at stress concentrators near crack tips. Crack inclination significantly regulates capacity: raceway cracks are most detrimental near 45°, while ball cracks exhibit an overall decrease in initiation and peak stresses with increasing inclination (with local non-monotonicity). Crack length has a stronger weakening effect than inclination, with accelerated capacity loss beyond 0.3 mm and a pronounced drop in initiation stress beyond 0.6 mm. The framework enables controllable defect parametrization and micro-scale failure interpretation for defect sensitivity assessment under compressive overload. Thus, this study focuses on simulating monotonic fracture events to elucidate fundamental defect–property relationships, which provides a foundation distinct from the prediction of rolling contact fatigue life under cyclic service conditions. Full article

In this study, the nonlinear and non-monotonic behavior of amperometric bienzyme biosensors employing an enzymatic trigger reaction is investigated analytically and computationally using a two-compartment model comprising an enzymatic layer and an outer diffusion layer. The trigger enzymatic reaction is coupled with a cyclic electrochemical–enzymatic conversion (CEC) process. The model is formulated as a system of reaction–diffusion equations incorporating nonlinear Michaelis–Menten kinetics and interlayer partitioning effects. Exact steady-state analytical solutions for substrate and product concentrations, as well as for the output current, are obtained for specific cases of first- and zero-order reaction kinetics. At the transition conditions, biosensor performance is further analyzed numerically using the finite difference method. The CEC biosensor exhibits the highest signal gain when the first enzyme has low activity and the second enzyme has high activity; however, under these conditions, the response time is the longest. When the first enzyme possesses a higher substrate affinity (lower Michaelis constant) than the second, the biosensor demonstrates severalfold higher current and gain compared to the reverse configuration under identical diffusion limitations. Furthermore, increasing external mass transport resistance or interfacial partitioning can enhance the apparent signal gain. Full article

This study investigates the flexural performance of geopolymer (zero-cement) concrete (ZCC) beams compared to normal concrete (NC) under monotonic and cyclic loading. Sixteen reinforced beams with compressive strengths of 20 and 30 Mpa and reinforcement configurations of 2Ø10 and 3Ø12 were tested to evaluate load–deflection behavior, ductility, energy absorption, and cracking characteristics. Under monotonic loading, ZCC beams achieved 9–17% higher ultimate strength and 5–30% greater mid-span deflection than NC beams, indicating superior ductility and energy dissipation. Under cyclic loading, ZCC beams demonstrated more stable hysteresis loops, slower stiffness degradation, and 8–32% higher cumulative energy absorption. ZCC specimens also sustained 8–12 cycles, corresponding to 70–90% of the monotonic displacement, whereas NC beams generally failed earlier at lower displacement levels. Increasing reinforcement ratio enhanced stiffness and load capacity but reduced deflection for both materials. Crack mapping showed finer and more uniformly distributed cracking in ZCC beams, confirming improved bond behavior between steel reinforcement and the geopolymer matrix. In addition, geopolymer concrete beams exhibited a significant enhancement in ductility, with the ductility coefficient increasing by nearly 50% compared to normal concrete under cyclic loading. Overall, the findings indicate that ZCC provides comparable or superior structural performance relative to NC, supporting its application as a sustainable, low-carbon material for flexure- and shear-critical members subjected to static and cyclic actions. Full article

This study thoroughly investigates the fatigue behavior and properties of additively manufactured (AM) 18Ni300 maraging steel, crucial for the design of load-carrying engineering components. Thin-walled flat specimens, produced via Selective Laser Melting (SLM), underwent a specific thermal process of annealing and aging. Extensive monotonic and cyclic tests (R = 0.1) were conducted to determine static and fatigue material properties. Optical microscopy revealed the thermal process’s effect on microstructure. Experimentally determined design S-N curves, covering low-cycle to engineering endurance limits, allowed estimation of fundamental elastoplastic properties. This work provides valuable new insights and experimentally verified data, addressing a significant literature gap and supporting advanced fatigue-based design for AM components. Full article

Steel girders with corrugated webs are increasingly used in bridge and building structures subjected to cyclic variable loads, where the geometry of the corrugation plays an important role in fatigue performance. This paper investigates the fatigue behaviour and failure mechanisms of full-scale steel girders with sinusoidal corrugated webs subjected to static and cyclic four-point bending. Five simply supported girders were tested: one reference beam under monotonic static loading, two beams under long-term cyclic loading with different load ranges ΔF and numbers of cycles N, and two beams subjected to cyclic loading followed by a static test to failure. The experimental programme focused on the influence of the load range ΔF and the number of cycles N on damage development, stiffness degradation and residual load-bearing capacity, as well as on the interaction between local web instability and global lateral–torsional buckling. The test results show that two main failure mechanisms may occur: (I) local buckling of the corrugated web combined with yielding of the flanges, and (II) a combined mechanism involving local web buckling and lateral–torsional buckling of the girder. For the investigated configurations and within the range of load ranges and numbers of cycles considered, the load range ΔF was found to be the dominant parameter governing fatigue damage, whereas the number of cycles had a secondary influence. The global stiffness of the girders in the elastic range remained almost unchanged until the late stages of loading, and even after pre-fatigue loading, the girders were able to carry a significant portion of their original ultimate load. The results provide experimental data and insight that are relevant for the fatigue assessment and design of steel girders with sinusoidal corrugated webs in bridge and building applications. Full article

This study introduces a comprehensive three-dimensional micromechanical framework to capture the nonlinear mechanical behavior of diverse composite materials, including coupled elastic degradation, inelastic strain evolution, and phenomenological failure in their constituents. The primary objective is to integrate a generalized elastic degradation–inelasticity (EDI) model into the parametric high-fidelity generalized method of cells (PHFGMC) micromechanical approach, enabling accurate prediction of nonlinear responses and failure mechanisms in multi-phase composites. To achieve this, a unified three-dimensional orthotropic EDI modeling formulation is developed and implemented in the PHFGMC. Grounded in continuum mechanics, the EDI employs scalar field variables to quantify material damage and defines an energy potential function. Thermodynamic forces are specified along three principal directions, decomposed into tensile and compressive components, with shear failure accounted for across the respective planes. Inelastic strain evolution is modeled using incremental anisotropic plasticity theory, coupling damage and inelasticity to maintain generality and flexibility for diverse phase behaviors. The proposed model offers a general, unified framework for modeling damage and inelasticity, which can be calibrated to operate in either coupled or decoupled modes. The PHFGMC micromechanics framework then derives the overall (macroscopic) nonlinear and damage responses of the multi-phase composite. A failure criterion can be applied for ultimate strength evaluation, and a crack-band type theory can be used for post-ultimate degradation. The method is applicable to different types of composites, including polymer matrix composites (PMCs) and ceramic matrix composites (CMCs). Applications demonstrate predictions of monotonic and cyclic loading responses for PMCs and CMCs, incorporating inelasticity and coupled damage mechanisms (such as crack closure and tension–compression asymmetry). The proposed framework is validated through comparisons with experimental and numerical results from the literature. Full article

This study investigates the shear behavior of horizontal joints in prefabricated monolithic short-limb shear walls under static and low-cycle reversed cyclic loading, supported by finite-element simulations. Four specimens were tested to evaluate the influence of the bundled shear reinforcement ratio, initial reinforcement stress level, and loading protocol on shear capacity. The results show that increasing the bundled shear reinforcement ratio significantly enhanced both the yield and peak loads, with increases observed in the yield, peak, and failure loads. Conversely, a higher initial stress level in the reinforcement weakened the shear-friction mechanism, leading to a reduction in the load-carrying capacity. Compared to monotonic loading, low-cycle reversed cyclic loading accelerated crack propagation and cumulative damage, leading to a significant reduction in load-carrying and deformation capacities. Finite-element simulations, using the Concrete Damaged Plasticity (CDP) model, were in good agreement with experimental results, although the simulations slightly overestimated the ultimate capacity, confirming the model’s validity. Parametric analysis indicated that increasing axial tension progressively reduced the yield and peak loads, with the reduction in peak load being more pronounced, while the cracking load remained unchanged. These findings provide a theoretical foundation for the shear design and seismic performance evaluation of horizontal joints in prefabricated shear walls, offering valuable insights for future design improvements and modeling strategies. Full article

The bending stiffness of flexible pipes is highly dependent on curvature, driven by the interaction between their structural layers—a behavior often misrepresented by traditional numerical models. To overcome this limitation, a finite-difference-based model was developed, integrating previously proposed formulations for monotonic bending and axisymmetric responses into a return-mapping algorithm to capture hysteretic behavior under cyclic loading. The model was calibrated against pure bending and pressurized tests, accounting for interlayer adhesion and friction, which govern stiffness variation, force levels, and energy dissipation. Results showed excellent agreement with experimental data across different load combinations, confirming the model’s predictive capability. Parametric analyses revealed that higher adhesion and friction coefficients increase imposed forces until a no-slip condition is achieved, while energy dissipation follows a nonlinear dependence on interlayer friction, peaking at intermediate values and vanishing under no-slip conditions. Cyclic bending tests performed on degraded samples demonstrated that, despite wire deterioration, the global bending response remains essentially unchanged, reinforcing the stability of riser behavior over time. However, fatigue resistance must still be reassessed through updated S–N curves to account for material degradation. These findings underscore the crucial role of interlayer mechanics in determining the overall performance of flexible pipes and offer a validated framework for assessing fatigue and integrity. Full article

A comprehensive numerical investigation of Fatigue Crack Growth (FCG) under negative stress ratios (R < 0) was conducted using the Finite Element Method (FEM) and the ANSYS Benchmark 19.2 SMART crack growth module on modified Compact Tension (CT) specimens. This study addresses the critical challenge posed by the compressive portion of cyclic loading, which traditional Linear Elastic Fracture Mechanics (LEFM) models often fail to capture accurately due to the complex interaction of crack closure and reversed plastic zones. The analysis focused on the evolution of the von Mises stress and maximum principal stress distributions at the crack tip across a range of stress ratios, including R = 0.1, −0.1, −0.2, −0.3, −0.4, −0.5, and −1.0. The results demonstrate a significant inverse correlation between fatigue life cycles and the magnitude of the negative stress ratio, consistent with the detrimental effect of increasing tensile stress. Crucially, the numerical simulation successfully captured the non-monotonic behavior of the crack tip stress field, revealing that the compressive load phase substantially alters the effective stress intensity factor range and the crack growth path, which was governed by the Maximum Tangential Stress (MTS) criterion. This research provides a validated computational methodology for accurately predicting FCG life in engineering components subjected to demanding, fully reversed, or compressive–dominant cyclic loading environments. Full article