Search Results (245)

Helical piles are widely used in geotechnical engineering, and their rapid installation and service reliability have attracted significant interest from the offshore wind industry. These piles are frequently subjected to cyclic loading in complex marine environments. Although the cyclic bearing behavior of helical piles has been studied, most research has focused on soil properties and loading conditions, with a limited systematic analysis of plate parameters. Moreover, the selection of plate parameters is not explicitly defined. As a crucial preliminary step in the capacity calculation, it is vital for the design of helical piles. To address this gap, the present study combines physical modeling tests and finite element simulations to systematically evaluate the influence of plate parameters on their cyclic bearing behavior. The parameters investigated include the plate depth, the plate diameter, plate spacing, and the number of plates. The results indicate that, under the same embedment conditions, cumulative displacement increases with the plate depth, with a critical embedment depth ratio of H_cr/D = 6 under cyclic loading conditions, but decreases with the number of plates. Axial stiffness increases with the plate depth, diameter, and number of plates, with an increase ranging from 0.5 to 3.0. However, the normalized axial stiffness decreases with these parameters, reaching a minimum value of 1.63. The plate spacing has a minimal influence on cyclic bearing behavior. Additionally, this study examines the evolution of displacement and stiffness parameters over repeated cycles in numerical simulations, as well as the post-cyclic pullout capacity of the helical pile foundation, which varies between −5% and +12%. Full article

The effectiveness of an innovative retrofit scheme using near-surface-mounted (NSM) X-shaped CFRP ropes for the strengthening of substandard RC beam–column joints was investigated experimentally. Three large-scale beam–column joint subassemblages were constructed with poor reinforcement details. One specimen was subjected to cyclic lateral loading, exhibited shear failure of the joint region and was used as the control specimen. The other specimens were retrofitted and subsequently subjected to the same history of incremental lateral displacement amplitudes with the control subassemblage. The retrofitting was characterized by low labor demands and included wrapping of NSM CFPR-ropes in the two diagonal directions on both lateral sides of the joint as shear reinforcement. Single or double wrapping of the joint was performed, while weights were suspended to prevent the loose placement of the ropes in the grooves. A significant improvement in the seismic performance of the retrofitted specimens was observed with respect to the control specimen, regarding strength and ductility. The proposed innovative scheme effectively prevented shear failure of the joint by shifting the damage in the beam, and the retrofitted specimens showed a more dissipating hysteresis behavior without significant loss of lateral strength and axial load-bearing capacity. The cumulative energy dissipation capacity of the strengthened specimens increased by 105.38% and 122.23% with respect to the control specimen. 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

This study proposes a novel hybrid connection method for precast concrete shear walls, where the edge walls are connected using grouting splice sleeves and the middle walls are connected using grouted corrugated metallic ducts. To investigate the effects of connection type and axial compression ratio on structural performance, five shear wall specimens were tested under low-cycle reversed loading, with detailed analysis of their failure modes and hysteretic behavior. Based on experimental results and theoretical derivation, a restoring force model incorporating connection type was developed. The results demonstrate that hybrid-connected specimens exhibit significantly improved load-bearing capacity, ductility, and seismic performance compared to those with only grouted corrugated metallic duct connections. A higher axial compression ratio enhances structural strength but also accelerates damage progression, particularly after peak loading. A three-line skeleton curve model was established to describe the load, displacement, and stiffness relationships at key characteristic points, and unloading stiffness expressions for different loading stages were proposed. The calculated skeleton and hysteresis curves align well with the experimental results, accurately capturing the cyclic behavior of the hybrid-connected precast shear walls. Full article

When deep-buried tunnels are excavated using the drill-and-blast method, the surrounding rock is subjected to combined cyclic blasting loads and excavation-induced stress unloading. Understanding the distribution characteristics of rock damage zones under these conditions is crucial for the design and safety of building-integrated underground structures. This study investigates the relationship between surrounding rock damage and in situ stress conditions through numerical simulation methods. A constitutive model suitable for simulating rock mass damage was developed and implemented in the LS-DYNA (version R12) code via a user-defined material model, with parameters determined using the Hoek–Brown failure criterion. A finite element model was established to analyze surrounding rock damage under cyclic blasting loads, and the model was validated using field data. Simulations were then carried out to explore the evolution of the damage zone under various stress conditions. The results show that with increasing hydrostatic pressure, the extent of the damage zone first decreases and then increases, with blasting-induced damage dominating under lower pressure and unloading-induced shear failure prevailing at higher pressure. When the hydrostatic pressure is less than 20 MPa, the surrounding rock stabilizes at a distance greater than 12.6 m from the tunnel face, whereas at hydrostatic pressures of 30 MPa and 40 MPa, this distance increases to 29.4 m. When the lateral pressure coefficient is low, tensile failure occurs mainly at the vault and floor, while shear failure dominates at the arch waist. As the lateral pressure coefficient increases, the failure mode at the vault shifts from tensile to shear. Additionally, when the horizontal stress perpendicular to the tunnel axis (σ_H) is less than the vertical stress (σ_v), variations in the axial horizontal stress (σ_h) have a significant effect on shear failure. Conversely, when σ_H exceeds σ_v, changes in σ_h have little impact on the extent of rock damage. Full article

As a part of the mining-induced stress redistribution process during coal mining, the repeated loading and unloading process with increasing peak stresses will cause more severe deformation and damage to mining roadways, which is different from the findings in other underground engineering practices. Consequently, cyclic triaxial compression tests with increasing amplitudes were carried out to investigate the mechanical behavior, acoustic emission (AE) characteristics, and damage evolution of coal materials. It is found that peak deviatoric stress and axial residual strain at the failure of coal specimens increase with increasing confining pressures, while the changes in circumferential strain are not obvious. Moreover, the failure patterns of coal specimens exhibit shear failure due to the constraint of confining pressures while some local tensile cracks occur near the shear bands at both ends of the specimens. After that, the damage evolution of coal specimens was analyzed against the regularity of AE counts and energies to develop a damage evolution model. It is concluded that the damage evolution model can not only quantify the deformation and failure process of the coal specimens under cyclic loads with increasing amplitudes but also takes into account both the initial damage due to natural defects and the induced damage by the cyclic loads in previous cycles. Full article

The pre-inserted method for precast shear walls involves casting concealed beams at floor slabs between upper and lower structures, with precast concrete supports spaced at intervals. Vertical rebars at the base of upper walls are pre-inserted and anchored in the beams before slab casting. It offers advantages such as convenient construction without the need for grouting, demonstrating broad application prospects and significant promotional value. To evaluate seismic performance, quasi-static cyclic loading tests were conducted on five specimens: three full-scale pre-inserted precast walls and two cast-in-place counterparts. Under increasing lateral displacement, low axial-load specimens failed via tensile fracture of the outermost rebars, while high axial-load specimens failed by concrete crushing in compression. The test results showed that under identical axial-load ratios, the precast walls exhibited comparable bearing capacity, stiffness degradation, and energy dissipation to cast-in-place walls, but superior deformation ductility. The ultimate drift ratios of pre-inserted walls exceeded those of cast-in-place walls by 16.7% (axial-load ratio 0.2) and 22.2% (axial-load ratio 0.4), demonstrating robust seismic performance. Full article

Fatigue endurance anisotropic behavior was evaluated for an API 5L X42 pipeline steel through axial force-controlled fatigue tests amongst Longitudinal, Diagonal, and Circumferential directions. This study shows that fatigue life anisotropy is mainly controlled by pearlite banding degree (A_i) and ferritic grain orientation (Ω₁₂). Also, it is foreseen that the observed behavior can be related to the dislocation arrays generated by the cyclic loading in relation to microstructure orientation, and the interactions of the fatigue crack tip with the microstructure during the crack propagation stage. 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

Three all-steel buckling-restrained brace (ABRB) specimens without unbonded materials were designed and manufactured. Through low-cycle reciprocating load tests, the seismic performance of these buckling-restrained braces was investigated, and the influence of the absence of an unbonded layer on failure modes, energy dissipation capacity, and low-cycle fatigue life was examined. The research findings suggest that in all-steel buckling-restrained braces lacking an unbonded layer, the excessive friction between the energy dissipation unit and the restraining unit can, to a certain degree, increase local compressive stress. This makes the braces more susceptible to local buckling at the ends. The frictional effect causes the axial force of the ABRB to follow a distribution pattern where it is greater at the ends and smaller in the middle. Correspondingly, the buckling wavelength of the energy dissipation unit shows a pattern of being shorter at the ends and longer in the middle, which also results in a significant cyclic hardening phenomenon in the ABRB. The fatigue performance of the ABRB is inversely related to the amplitude of local buckling in the energy dissipation unit. Full article

The process of rock damage and failure is accompanied by the dissipation of energy and an increase in plastic strain. This study attempts to determine the relationship between dissipated energy and plastic strain in sandstone during the damage and failure process. A conventional triaxial cyclic loading and unloading test was conducted on sandstone samples to analyze the energy evolution and plastic strain characteristics of rock during the mechanical performance degradation and deformation failure process. The analysis results indicate that the evolution law of rock energy dissipation and plastic growth during the whole stress–strain process is highly consistent. Before the peak stress, dissipated energy and plastic strain increased linearly with input energy and axial strain, respectively. In the residual stress stage, there is an approximate linear evolution relationship between dissipated energy and plastic strain. Based on the correlation characteristics of energy dissipation and plastic growth, a modified damage model was established by characterizing plastic deformation by damage. In addition, a numerical program was developed using the Finite Volume Method (FVM) based on the damage model. The rock damage model has been validated by experimental results and numerical test. The research findings may provide valuable insights into the correlation mechanism between energy dissipation and plastic growth. Full article

During deep mining engineering, coal bodies are subjected to complex geological stresses such as periodic roof pressure and blasting impacts, which may induce mechanical property deterioration and trigger severe rock burst accidents. This study systematically investigated the mechanical characteristics and failure mechanisms of coal under strain rates on two orders of magnitude through quasi-static cyclic loading–unloading experiments and split Hopkinson pressure bar (SHPB) tests, combined with acoustic emission (AE) localization and crack characteristic stress analysis. The research focused on the differential mechanical responses of coal-rock masses under distinct stress environments in deep mining. The results demonstrated that under quasi-static loading, the stress–strain curve exhibited four characteristic stages: compaction (I), linear elasticity (II), nonlinear crack propagation (III), and post-peak softening (IV). The peak strain displayed linear growth with increasing cycle, accompanied by a failure mode characterized by oblique shear failure that induced a transition from gradual to abrupt increases in the AE counts. In contrast, under the dynamic loading conditions, there was a bifurcated post-peak phase consisting of two unloading stages due to elastic rebound effects, with nonlinear growth of the peak strain and an interlaced failure pattern combining lateral tensile cracks and axial compressive fractures. The two loading conditions exhibited similar evolutionary trends in crack damage stress, though a slight reduction in stress occurred during the final dynamic loading phase due to accumulated damage. Notably, the crack closure stress under quasi-static loading followed a decrease–increase pattern with cycle progression, whereas the dynamic loading conditions presented the inverse increase–decrease tendency. These findings provide theoretical foundations for stability control in underground engineering and prevention of dynamic hazards. Full article

Background/Objectives: Biomineral adhesive bone adhesives composed of phosphoserine combined with magnesium oxides or phosphates exhibit exceptional adhesive properties. This study evaluates two experimental mineral–organic cementitious adhesives in a clinical test setup, investigating their potential for fracture reduction and simultaneous defect filling. Methods: The two experimental adhesives (Groups B and C) and a standard hydroxyapatite cement (Group A, reference) underwent compressive strength testing, shear strength testing, and screw pullout tests as part of a first biomechanical characterization. Furthermore, all materials were tested in a porcine tibial split depression fracture model, where they served both for fracture reduction and for filling the metaphyseal bone defect, supplementary to plate osteosynthesis. Fracture stability was assessed under cyclic loading in a materials testing machine. Results: The OPLS (O-phospho-L-serine) containing adhesive (Group B) demonstrated the highest compressive strength as well as the highest shear strength. All three materials showed comparable maximum pullout forces. Both experimental adhesives (Groups B and C) exhibited higher pullout stiffness compared to the standard cement (Group A). In the fracture model, no significant differences in displacement under cyclic loading were observed between groups. Conclusions: The biomineral adhesive bone adhesives (Groups B and C) demonstrated biomechanical advantages in axial compression, adhesive (shear) strength, and screw fixation compared to the standard hydroxyapatite cement (Group A). Furthermore, they achieved comparable stabilization of metaphyseal fractures under clinically relevant dynamic loading conditions. Full article

Steel structures subjected to earthquakes or extreme cyclic loadings may undergo extensive damage and fractures due to ultra-low-cycle fatigue (ULCF). Although assessments of damage initiation and evolution parameters have been carried out for some steels exposed to low-cycle fatigue, so far, these parameters for structural steels exposed to ULCF have neither been sufficiently studied nor quantified. Accordingly, this paper provides the results of finite element analysis (FEA) concerning the ULCF behaviors of S355 and S690 steel specimens. Calibration of the damage parameters is performed in SIMULIA Abaqus 6.11 FEA software using a direct cyclic algorithm and available experimental data. Kliman’s model for the hysteresis energy of cyclic loading is used to analytically verify the damage parameters. In addition, available experimental data were obtained from cyclic axial strain tests on S355 and S690 steel specimens according to the ASTM International standard E606/E606M-21. Finally, the non-linear Chaboche–Lemaitre (C–L) combined isotropic–kinematic hardening model is used for the characterization of the ULCF behavior of S355 steel in a simple cylindrical bar. It is found that the two damage initiation parameters are 5.0 and −0.8, the first damage initiation parameter is dominant when modeling the number of cycles to failure, and the second damage initiation parameter is a material constant. Full article

Steel frame infilled with composite plate shear wall (SF-CPSW) is an effective structure for lateral-load resisting. In the structural design, the vertical loads are primarily carried by the boundary SF, while the horizontal loads are expected to be totally carried by CPSW. CPSW incorporates the steel web and the concrete encasements. For the CPSW bays, the boundary SF also inevitably withstands the lateral-loads due to the coordinated deformations between boundary SF and CPSW. The available researches, however, have not given a certain shear force assignment between the boundary SF and CPSW. Furthermore, their interactions under the cyclic lateral-loading are unclear. This paper conducted a study on the load-resisting mechanism of SF-CPSW by a structural model test and finite element analyses. The deformation pattern, failure mode, internal forces, and interactions of structural members were investigated. The effects of steel web and concrete thicknesses, cross-sections of boundary SF, and axial compression ratio on the lateral-load resistance of SF-CPSW were assessed. The results indicated that the interactions of CPSW and boundary SF caused significant normal stresses at the corners of CPSW, reducing the shear strength of steel web. However, the concrete encasements and boundary SF compensate it and mutually improved the stiffness and ductility. According to the analysis results, the formulas of the lateral stiffness and strengths of SF-CPSW were proposed for its seismic design. Full article