Search Results (363)

Rectangular reinforced concrete (RC) hollow bridge piers may exhibit significant shear participation after flexural cracking and yielding, whereas their seismic responses are commonly evaluated using flexure-dominated numerical models. This study investigates the effects of axial–flexure–shear interactions on the cyclic response and seismic fragility of rectangular RC hollow bridge piers. Cyclic loading tests on seven one-eighth-scale specimens were analyzed to characterize the effects of the shear-span ratio and reinforcement configuration. The experimental results were then used to assess a conventional flexure model and an axial–flexure–shear interaction model, denoted as AFSI–MBTEM. Full-scale piers with heights of 16, 24, and 32 m were subsequently analyzed under cyclic loading and representative near-fault ground motions. Finally, 7200 nonlinear time-history analyses were conducted using 80 records divided into non-pulse and short-, medium-, and long-period pulse-like groups, while seismic fragility curves were developed using displacement ductility as the demand parameter. The tests indicated flexure-dominated but distinctly shear-sensitive behavior, particularly for specimens with low shear-span ratios. Compared with the flexure model, AFSI–MBTEM reproduced pinching, post-peak deterioration, and hysteretic energy more accurately, reducing the mean absolute error in hysteretic energy from 23.57% to 13.29%. For the full-scale piers, model differences generally decreased as the pier height and shear-span ratio increased together, although the effects on large-deformation stability and seismic response remained configuration- and ground-motion-dependent. AFSI–MBTEM predicted higher fragility in 46 of the 48 height–motion–damage-state comparisons. At the upper analyzed intensity of PGA = 1.5 g, it also produced higher DS4 exceedance probabilities in the examined critical cases. Within the investigated section configurations, axial-load ratios, and coupled height–shear-span cases, the results indicate that neglecting axial–flexure–shear interactions may lead to nonconservative fragility estimates, particularly for configurations with greater shear participation. Full article

Corrosion of steel reinforcement is a major cause of deterioration in reinforced concrete (RC) structures exposed to aggressive environments. Although fiber-reinforced polymer (FRP) reinforcement provides excellent corrosion resistance, its confinement effectiveness in RC columns has not been fully understood. This study experimentally investigated the axial compressive behavior of rectangular RC short columns reinforced with steel, carbon fiber-reinforced polymer (CFRP), and glass fiber-reinforced polymer (GFRP) bars. Ten specimens with different reinforcement types and stirrup configurations were tested under monotonic axial compression to evaluate compressive strength, axial strain response, deformation behavior, failure mechanisms, and confinement performance. The results indicated that the contribution of FRP reinforcement depended on the reinforcement configuration and confinement mechanism. Specimens reinforced with CFRP longitudinal bars exhibited higher axial capacity than the steel-reinforced control specimen within the tested configurations; however, the influence of the longitudinal reinforcement ratio should also be considered. GFRP stirrups exhibited confinement behavior comparable to CFRP stirrups, whereas CFRP stirrups experienced premature fracture at bent corner regions, which reduced their confinement effectiveness and deformation capacity. Reducing stirrup spacing from 150 mm to 75 mm provided limited improvement in compressive strength because of premature stirrup failure and insufficient development of confinement effects. Existing confinement models tended to overestimate the post-peak response of FRP-reinforced columns. These preliminary findings provide experimental insights into the confinement behavior of FRP-reinforced concrete columns and contribute to the development of improved analytical models. Full article

Mg-Gd-Y-Zr alloys, with strong age-hardening and thermal stability, are ideal for lightweight load-bearing components, yet forming large complex parts is limited by high sensitivity to hot deformation parameters. This work investigates the hot deformation behavior and microstructure evolution of a Mg-9Gd-4Y-0.5Zr (wt.%) alloy via hot compression at 400 to 510 °C and strain rates of 0.001 to 10 s⁻¹. An Arrhenius constitutive equation with an activation energy Q of 158.63 kJ/mol was established, and a hot processing map was constructed. EBSD characterization revealed the dynamic recrystallization, grain size evolution, and texture transition. The results show that flow stress depends strongly on temperature and strain rate. At strain rates of 0.001~1 s⁻¹, a dynamic balance between work hardening and dynamic softening is achieved, and the post-peak flow stress gradually stabilizes. At a high strain rate of 10 s⁻¹, the flow stress continues to decrease because the competition between softening from dynamic recrystallization and work hardening is disrupted by deformation-induced heating. Low strain rates (≤0.01 s⁻¹) and high temperatures (≥470 °C) promote dynamic recrystallization and significant grain refinement. Two optimal processing windows were determined: 400 to 430 °C at 0.001 to 0.01 s⁻¹, giving fully recrystallized fine equiaxed grains, and 440 to 460 °C at 0.01 to 0.1 s⁻¹ with a power dissipation efficiency η of 0.43 to 0.51, balancing processing efficiency and microstructural uniformity. This work provides systematic theoretical and data support for optimizing hot forming parameters of large Mg-Gd-Y-Zr load-bearing components and offers guidance for applying high-strength magnesium alloys in high-end equipment. Full article

Natural biological materials achieve synergistic strengthening and toughening through soft–stiff dual-phase architectures, inspiring artificial composites. Despite extensive studies on individual bio-inspired designs, systematic comparative investigations under fully unified experimental conditions remain limited. Here, five representative bio-inspired composite structures (brick–mud, cross-lamellar, interlock, overlap, and concentric) are fabricated via 3D printing and compared under quasi-static three-point bending. Key mechanical parameters—including flexural modulus, flexural strength, crack-initiation displacement, effective fracture displacement, total energy absorption, and post-peak energy dissipation ratio—are derived from force–displacement curves, complemented by high-resolution imaging of crack paths, crack front morphologies, and fracture surfaces. The concentric structure exhibits the highest flexural modulus and flexural strength, yet fails catastrophically with only a 9.95% post-peak energy dissipation ratio. The brick–mud and cross-lamellar structures achieve the highest post-peak energy dissipation ratios (27.69% and 27.42%, respectively), which may be attributed to crack deflection and interfacial debonding, yet at the cost of low flexural strength. The interlock structure, apparently lacking effective deflecting interfaces, shows straight-through propagation and brittle behavior. In contrast, the overlap structure appears to benefit from sustained crack deflection along inclined interfaces, thereby providing a balanced combination of high flexural strength, large deformability, and moderate energy absorption, demonstrating the best overall mechanical performance. Full article

Background/Objectives: Fetal Alcohol Spectrum Disorder (FASD) is a preventable neurodevelopmental condition associated with dysfunction of fronto-subcortical networks affecting attention, executive function, and behavioral regulation. Central auditory processing difficulties frequently persist despite preserved peripheral hearing, complicating clinical evaluation when behavioral testing is limited or unreliable, and objective markers that do not depend on behavioral cooperation are therefore needed. This exploratory observational case study investigated whether Frequency-Following Responses (FFRs) can capture measurable within-subject change in speech-evoked neural encoding in a pediatric patient with FASD. Methods: FFRs were recorded at two time points bracketing an eight-session period of non-invasive superficial neuromodulation (NESA^®) in an 8-year-old girl with FASD, using speech syllables (/da/, /ba/, /ga/) presented monaurally at 80 dB SPL. Two-tailed block-level Mann–Whitney U tests with rank-biserial correlations compared peak latencies, sustained pitch-tracking metrics (pitch strength, pitch error), onset stimulus–response correlation, and signal-to-noise ratio. Results: Sustained pitch-tracking metrics differed between time points, with increased pitch strength and reduced pitch error, whereas onset peak latencies, onset cross-correlation, and signal-to-noise ratio remained stable. Peak C, marking the transition to the sustained portion of the response, occurred earlier at the post-assessment in all six stimulus–ear combinations. The differences were therefore selective to sustained encoding rather than to onset timing or recording quality. Conclusions: FFR-derived pitch-encoding metrics detected measurable within-subject change, providing proof of concept for the feasibility of FFRs as a candidate objective tool for longitudinal monitoring of speech-evoked neural encoding in pediatric FASD. This single-case observation does not evaluate diagnostic accuracy, sensitivity, specificity, or discrimination from typically developing children, and therefore does not establish FFR as a validated diagnostic technique. The findings are hypothesis-generating and motivate controlled longitudinal studies. Full article

Reservoir landslides pose a persistent threat to the safe operation of hydropower projects, particularly where altered rock masses within water-level fluctuation zones undergo repeated wetting–drying and seepage-induced deterioration. This study investigates the mechanical behavior and long-term strength evolution of altered granite from the Guobu Slope near the Laxiwa Arch Dam in Qinghai, China. Rock masses with four alteration degrees, ranging from complete to slight alteration, were examined through an integrated experimental program involving torsional shear tests, hydro-mechanical coupled triaxial tests, large-scale direct shear and ring shear tests, Brazilian splitting tests, and long-term P-wave velocity monitoring. The results demonstrate that increasing water content progressively weakens the shear strength of altered granite, while elevated seepage pressure further reduces its strength and deformation resistance under hydro-mechanical coupling. Residual shear behavior also shows a clear dependence on water content, indicating that post-peak strength deterioration should be considered in slope stability assessment. Long-term P-wave monitoring further reveals that mechanical degradation is more pronounced during the early stage and gradually approaches a relatively stable state, suggesting a site-specific decelerating deterioration process rather than unlimited strength loss. Based on the experimental results, empirical relationships between shear-strength parameters and water content are established, and long-term lower-bound strength parameters are proposed for altered granite with different degrees of alteration. These findings provide experimental support for understanding the hydro-mechanical deterioration and long-term deformation behavior of reservoir-bank altered rock masses and offer a basis for parameter selection and stability assessment when combined with rock-mass reduction, field calibration, and sensitivity analysis. Full article

The recycling of construction and demolition waste and the reduction of carbon emissions are important issues in sustainable construction. Recycled aggregate concrete (RAC) is promising for structural use, but the weak old mortar and multiple interfacial transition zones in recycled coarse aggregate (RCA) may reduce the load-transfer capacity at the steel–concrete interface. To address this problem, this study developed carbonated recycled aggregate concrete-filled flat steel tube (FST-CRAC) members and investigated their interfacial bond–slip behavior through material strength tests and push-out tests on nine specimens. The effects of RCA replacement ratio, carbonation treatment, section aspect ratio, and width-to-thickness ratio were examined. RCA was carbonated at 0.5 MPa for 24 h. The 28-day compressive strength increased from 32.6 to 44.3 MPa in the uncarbonated P series and from 36.2 to 46.2 MPa in the carbonated T series. However, because the two series were developed through separate preliminary mix-design trials, these differences should be interpreted as being jointly associated with carbonation treatment and mix-proportion adjustments rather than as evidence of an isolated causal effect of carbonation. Push-out failure was governed by interfacial debonding, local crushing near the corners, and post-peak frictional slip, with damage consistently concentrated at the short sides and corners of the flat section. Carbonation treatment increased the peak bond load by 2.85–26.23%, with the largest benefit observed at a moderate replacement ratio, while increasing the RCA replacement ratio from 50% to 100% increased the peak load by 27.90% for uncarbonated specimens but only 4.21% for carbonated specimens, indicating that carbonation reduces the sensitivity of bond capacity to replacement ratio. A moderate increase in section aspect ratio increased the peak load by 22.30–25.86%, and reducing the width-to-thickness ratio increased the peak load by 5.95–40.92%. A four-linear bond–slip constitutive model was proposed to describe the full interfacial response, from initial bonding through peak degradation to residual friction. These findings provide experimental support for the use of carbonated recycled aggregates in steel tube-confined composite members and a basis for subsequent nonlinear analysis. Full article

To simulate the fracture behavior of members during structural collapse, this paper proposes a member fracture simulation algorithm that integrates the plastic hinge model with a ductile fracture damage model within the member discrete element method (MDEM) framework. The coupling is achieved by computing stresses at the four most unfavorable edge points of the contact section and using the minimum fracture strain as the section-level failure criterion. The algorithm is validated against a cantilever beam fracture example, yielding results in good agreement with reference data under two yield stress conditions. The fracture algorithm is then embedded as a self-contained module into an adaptively coupled DEM/FEM algorithm and applied to simulate the shaking table collapse test of a single-layer spherical reticulated shell. The simulation predicts structural collapse at a peak ground acceleration (PGA) of 2268 gal—consistent with the experimental value—with 126 members fractured at collapse onset, and reproduces the observed fracture sequence in which first-ring diagonal members near the supports fail progressively from the bottom upward. The proposed framework provides a computationally robust and practically deployable tool for collapse analysis of large-span reticulated structures, with direct implications for progressive-collapse prevention in seismic design and post-event structural forensic investigation of collapse mechanisms. Full article

Concrete structures are prone to cracking during service, and epoxy grouting is a widely adopted technique for structural intervention. However, the inherent brittleness and poor durability of neat epoxy under complex loading and environmental exposure remain critical challenges. This study systematically evaluates the mechanical performance of epoxy-grouted concrete interlayer systems modified by carbon fiber (CF), glass fiber (GF), and polyethylene microspheres (PE). A comprehensive experimental program was conducted, including compression, three-point bending, and Brazilian splitting tests at three loading angles, combined with digital image correlation for surface strain monitoring. The effects of grout thickness and wet–dry cycles were systematically investigated. Results demonstrate that reinforcement modification helps to improve the performance of grouted concrete, with optimal behavior highly dependent on loading mode. CF-reinforced specimens with strong interfacial bonding exhibit the highest compressive strength, which is 150% higher than the bearing capacity of intact concrete, but are prone to brittle fracture under loading involving tension-shear interaction. GF reinforced specimens with moderate interfacial bonding exhibit better load-bearing capacity under tensile-shear stress interaction, reaching a normalized splitting peak load of 0.95 at a grouting thickness of 5 mm. PE-reinforced specimens with weak interfacial bonding provide relatively extensive energy dissipation. A 3 mm grouting layer shows favorable performance among the tested thicknesses, balancing load transfer enhancement and defect control. A single wet–dry cycle temporarily improves performance, possibly due to epoxy post-curing and pore filling, whereas repeated cycling generates cumulative micro-damage. GF- and CF-reinforced systems demonstrate the most stable resistance to short-term wet–dry conditioning. These findings provide guidance for loading-mode-dependent reinforcement selection in epoxy grouting applications. Full article

Welded reinforcement cages (WRCs), which connect longitudinal reinforcement and stirrups through welding, have attracted increasing attention for industrialized construction of reinforced concrete (RC) structures. However, the welding process may introduce heat-affected zones, residual stresses, and local metallurgical changes in reinforcing bars, raising concerns regarding the potential influence of welded longitudinal-bar-to-stirrup connections on the seismic performance of RC bridge piers. This study experimentally investigates this issue through quasi-static cyclic tests on two large-scale RC bridge pier specimens with identical reinforcement layouts but different reinforcement connection methods. One specimen adopted conventional tied connections between longitudinal reinforcement and stirrups, whereas the other employed welded connections. The seismic responses of the specimens were evaluated in terms of failure mode, hysteretic behavior, skeleton curve, strength, ductility, stiffness degradation, energy dissipation, residual displacement, and strain development. The results showed that both specimens exhibited flexure-dominated failure with similar crack propagation and concrete-cover spalling characteristics. The differences in yield and peak strengths were within 5%, and the cumulative energy dissipation differed by only 2.1%, indicating comparable global seismic performance. The welded specimen exhibited a slightly larger ultimate displacement (12.8%) and ductility coefficient (9.4%), while the stiffness degradation characteristics remained nearly identical. Although several weld spots detached during the post-peak loading stage, no fracture or necking of the longitudinal reinforcement was observed, suggesting that the adopted welding procedure did not adversely affect the cyclic deformation behavior of the reinforcement. Within the scope of the tested specimens, the results demonstrate that welded longitudinal-bar-to-stirrup connections can maintain the seismic performance of RC bridge piers and provide experimental evidence for the potential application of WRCs in industrialized bridge construction. Further studies involving additional specimens and broader design parameters are required to validate the general applicability of these findings. Full article

To elucidate the structural evolution of fracture networks around gas drainage boreholes and their controlling mechanisms on grouting sealing performance, a coal seam in the Zhongmacun Mine (No. 2-1 coal seam) was selected as the engineering background. An integrated approach combining borehole camera observation, gray-level co-occurrence matrix (GLCM) texture analysis, and fractal theory was adopted to systematically characterize the development behavior, spatial heterogeneity, and fractal evolution of fracture networks under different stress zones surrounding the borehole. Furthermore, the quantitative relationship between fracture structure characteristics and grouting parameters was explored. Results indicate that three axial stress-related zones are formed, including a stress-relief zone (0–4 m), a post-peak stress concentration zone (4–20 m), and a pre-peak stress concentration zone (>20 m), with fracture development strongly dependent on stress state. Quantitative analysis based on GLCM parameters and their coefficients of variation reveals a progressive transition from highly complex and strongly heterogeneous fracture structures in the stress-relief zone to simpler and weakly heterogeneous characteristics in the pre-peak stress concentration zone. The fractal dimension (D) decreases from 1.847–1.907 to 1.676–1.713 across these zones, consistent with the evolution trends of GLCM metrics. Based on the relationship between fractal dimension and fracture connectivity, a prediction model for the equivalent permeability of fracture networks based on fractal dimension was established, and the quantitative relationship between grouting pressure and fractal dimension, slurry viscosity, and diffusion radius was derived, providing a theoretical method for analyzing the correlation between fracture structure characteristics and grouting parameters. On this basis, a zonal differentiated grouting sealing optimization scheme was proposed, and a theoretical calculation method for grouting pressure and sealing section length based on fractal parameters was established, providing theoretical references and technical support for precise sealing of gas drainage boreholes. Full article

Light pozzolanic soft clay has high compressibility and relatively poor structural stability, which limits its direct application in subgrade and foundation engineering. This study develops a sustainable combined stabilization–reinforcement system for lightweight volcanic ash soil using a steel slag–fly ash-based composite cementitious binder (GS) and recycled polyester fiber (RPF). Unconfined compressive strength tests, unconsolidated undrained triaxial tests, and microstructural characterization were conducted to evaluate the mechanical behavior and microstructural features of the treated soil. The results show that the GS binder markedly increased the soil strength, whereas RPF mainly improved specimen integrity and the post-peak response. Based on the single-additive and orthogonal test results, 24% GS, 0.6% RPF, and 9 mm fibers were identified as an appropriate mixture within the investigated factor levels for further mechanical evaluation. With the increase in confining pressure, the stress–strain response changes from strain softening to strain hardening. Scanning electron microscopy (SEM) observations showed fine particulate material at local particle-contact and fiber–matrix regions, while energy-dispersive X-ray spectroscopy (EDS) analysis identified a representative Ca-rich microregion containing Si and Al. The combined use of GS binder and RPF effectively improved the strength and deformation resistance of lightweight volcanic ash soft clay. Full article

Vertical joints are commonly required in precast concrete shear walls when large wall panels are divided for fabrication, transportation, and erection. To reduce on-site work and improve assembly efficiency, this study proposes and investigates a hybrid steel–grout vertical joint, namely a steel-anchor-ring grouted connection, which uses embedded threaded sleeves, steel anchor rings, an inserted vertical bar, and high-strength grout to transfer shear between adjacent wall panels. Monotonic direct shear tests, cyclic shear tests under normal tension and compression, and cyclic loading tests on precast shear wall specimens were conducted to investigate its mechanical behavior. The load–slip behavior, observed interface debonding, and final shank fracture in the direct shear tests suggested that grout–panel interface bond contributed substantially to the pre-peak response, whereas anchor-ring action became increasingly important after bond degradation. Comparison of the cyclic shear specimens suggested that normal tension promoted interface opening and bond degradation, leading to slip-dominated behavior, whereas normal compression enhanced interface contact and post-peak stability. For the specimens tested, the measured-to-calculated resistance ratios based on the code-based expression were 1.97–2.70 under direct shear and compression–shear conditions, but decreased to 1.20–1.31 under tension–shear loading. Wall-level demand analysis showed that the shear transferred across the vertical joint was significantly affected by both joint location and wall shear span ratio; larger shear span ratios increased the joint shear demand, whereas offset joint layouts reduced the demand. The wall specimens, designed relative to the code-based resistance, exhibited limited joint-related cracking and stable hysteretic behavior, and failed by wall-base flexural damage, indicating the shear-transfer effectiveness of the proposed joint under the tested configurations. Full article

This study investigates the repetitive overload turn-off behavior of a 1200 V/15 A trench field-stop IGBT using a clamped inductive load circuit. The DC-link voltage is set to 600, 800, and 1000 V, while the external circuit configuration and the 2 ms pulse interval remain unchanged. The displayed sequences at 600 and 800 V exhibit no destructive failure. Under the 1000 V condition, 24 of 30 devices fail, and the cycle-to-failure ranges from 6 to 27. Before failure, the peak V_CE, turn-off current, and E_off reach 1248.1 V, 80.2 A, and 12.87 mJ, respectively. During the final destructive event, V_CE first recovers to approximately 1.16 kV and then collapses toward zero, while I_C re-grows to approximately 106.8 A. A statically validated two-dimensional simulation model shows pulse-to-pulse temperature accumulation, mobility reduction, expansion of the high-field and impact-ionization regions, and persistence of an electron-rich transport path near the trench-gate active region. Post-failure SEM reveals a filament-like damage trace, emitter-side Al damage, damaged trench-gate structures, and contiguous multi-cell ablation. The combined evidence indicates that repetitive heating progressively strengthens the coupling among carrier transport, electric-field concentration, avalanche generation, current localization, and self-heating, which leads to delayed localized electrothermal instability. An auxiliary RC-IGBT comparison further confirms that the repetitive overload turn-off boundary depends on the device technology and operating conditions. Full article

Background/Objectives: Microvascular dysfunction is an early manifestation of vascular impairment in type 1 diabetes (T1D). Although physical activity may improve vascular health, the relationship between integrated 24 h physical behavior patterns and microvascular function remain unclear. This study evaluated the association between 24 h physical behavior patterns and cutaneous microvascular reactivity in adults living with T1D, and examined their relationship with endothelium-dependent microvascular function. Methods: This cross-sectional study included 92 adults with T1D. Physical activity and sedentary behavior were assessed through accelerometry and combined with self-reported sleep duration. Participants were classified into three clusters using partitioning around medoids. Cutaneous microvascular reactivity was assessed through laser speckle contrast imaging, with post-occlusive reactive hyperemia (PORH) peak and amplitude of cutaneous vascular conductance (CVC) as primary outcomes. Acetylcholine (ACh)-induced responses were evaluated as exploratory outcomes. Generalized linear models with progressive adjustment were used to examine the associations. Results: Three distinct behavioral patterns were identified. In the fully adjusted model, compared with Cluster 3, the estimates for PORH peak CVC were β = −0.02 (95% CI: −0.16 to 0.11) for Cluster 1 and β = 0.01 (95% CI: −0.13 to 0.16) for Cluster 2. Similar null findings were observed for PORH amplitude CVC and ACh-derived outcomes. Sensitivity analyses including microvascular burden did not alter the findings. Conclusions: In adults living with T1D, 24 h physical behavior patterns were not associated with microvascular reactivity or endothelium-dependent function. These findings suggest that daily behavior distribution may not be strongly related to microvascular responses, although subtle effects cannot be excluded. Longitudinal studies using fully device-based 24 h assessments are warranted. Full article