Search Results (1,020)

The modification of cementitious binders using active mineral additives and nano-components represents a crucial pathway for developing high-performance, sustainable concrete composites. Nevertheless, unilateral modification of the matrix with highly reactive siliceous materials often leads to an undesirable increase in composite brittleness. This study investigates the synergistic effect of the concurrent application of nano-silica (NS), silica fume (SF), and Class F fly ash (FA) in ternary and quaternary binders, aimed at optimizing both load-bearing capacity and fracture toughness. The experimental program was conducted on seven concrete series, evaluating their mechanical parameters and non-linear fracture properties using the two-parameter fracture model (TPFM) on notched beams subjected to three-point bending. Additionally, a high-resolution energy partitioning framework was applied, decomposing the total fracture energy into four distinct components—fracture initiation energy in the elastic range (G_ini), pre-peak microcracking energy (G_pre), main material softening energy (G_soft), and residual tail energy dissipated at large crack openings (G_tail)—along with the determination of the characteristic length (l_ch). The results demonstrated that while purely siliceous systems (modified with NS and SF) generate high strength increments, they simultaneously trigger a “brittleness trap,” manifested by a 13.65% decrease in the l_ch parameter. The introduction of FA effectively mitigates this hazard, transforming the failure mode into a quasi-ductile behavior. The concrete series modified with the NS+FA hybrid (Mix-5) exhibited a spectacular 107% increase in G_f and an increase in l_ch of nearly 50%, while maintaining high fracture toughness. Energy decomposition analysis in quaternary concretes confirmed a desirable reduction in the initiation energy share in favor of the softening and tail phases (G_tail reaching a record 13.1% for Mix-7), suggesting the probable activation of macroscopic crack-bridging mechanisms driven by the delayed hydration of FA particles. The research indicates that precise design of multi-component binders allows for achieving an optimal technological equilibrium point—the “sweet spot”—combining high structural capacity with safe material ductility. Full article

Natural gas pressure-reduction stations dissipate a significant portion of the gas pressure energy during conventional throttling. The recovery of this energy at small-capacity stations remains challenging due to low gas flow rates and variable operating conditions. This study investigates the application of a volumetric expander–generator regulator based on a vane-type positive-displacement expander as a combined pressure control and energy recovery device for small natural gas pressure-reduction stations. A mathematical model of gas-dynamic processes in the expander–generator regulator was developed and verified using experimental data obtained from a laboratory-scale compressed-air test facility. Experimental investigations were carried out within four pressure-drop ranges of 25–65, 45–105, 75–175, and 125–285 kPa under both rotor-speed stabilization and outlet-pressure stabilization modes. Based on the experimental results, second-order regression models were developed to describe the dependence of rotor speed on operating pressures and were subsequently used to estimate annual energy recovery. The results indicate that outlet-pressure stabilization provides higher energy recovery than rotor-speed stabilization across the investigated operating ranges. Depending on operating conditions, the estimated annual recovered energy ranged from 83 to 2265 kWh, which is sufficient to cover the auxiliary power demand of cabinet-type pressure-reduction stations and cathodic protection systems. The experimental validation presented in this study was performed using compressed air as the working medium. Therefore, the obtained quantitative results should be regarded as a laboratory-scale assessment of the feasibility of the proposed approach rather than a direct validation of a natural-gas expander–generator system. The results suggest the potential applicability of volumetric expander–generator regulators for energy recovery at small-scale gas pressure-reduction stations operating under variable flow conditions. Full article

This study investigates the dynamic response and local stability of gravity-anchored foundations constructed in layered argillaceous sandstone under the coupled effects of wet–dry cycling degradation and cyclic vehicle loads. Based on in situ direct shear tests and FLAC3D 7.0 numerical simulations, a concrete–rock interface model, a rock mass direct shear model, and a three-dimensional dynamic model of the anchored foundation were developed. The parameters of the interface model were validated using the results of the direct shear tests. Wet–dry cycling degradation was subsequently incorporated to analyze the cyclic shear response of the interface and rock mass under different numbers of cycles. Cyclic vehicle loads were modeled as increments in main cable tension with an equivalent sinusoidal waveform. The results indicate that as the number of wet–dry cycles increases, the cyclic shear hysteresis loops shift overall toward lower shear stress levels. Peak shear stress decreases by approximately 49.26–51.64% compared to the natural state, and the hysteresis loop area decreases significantly. This indicates that wet–dry cyclic degradation weakens the cyclic shear resistance and energy dissipation capacity of the contact surface and rock structural planes. Dynamic analysis results for the anchor foundation indicate that wet–dry cycling degradation significantly increases the displacement response levels of the rock mass near the front toe and rear heel. Specifically, under the n = 20 condition, the displacement at the last peak increased by approximately 109.3–123.9% compared to the undisturbed state; simultaneously, the local plastic zones in the rock mass surrounding the anchorages gradually expanded, and the local safety factors of the rock mass near the toe and heel decreased overall. This study elucidates the degradation mechanisms and dynamic behavior of gravity anchors under the combined action of environmental and operational loads, providing a basis for the design and safety assessment of foundations for long-span suspension bridges. Full article

Timber is a natural and renewable construction material, so it is environmentally friendly. However, timber has natural defects and also deteriorates over time. These problems require structural reinforcement. The present study aims to systematically explore the compression performance of natural Larch circular columns reinforced with Carbon Fiber-Reinforced Polymer (CFRP) and Basalt Fiber-Reinforced Polymer (BFRP). Thirty specimens were tested in pure axial compression to investigate the influence of the number of wrapping layers (0–3 layers), the specimen height (150, 200 and 300 mm) and the type of FRP material. The strengthening mechanism primarily relies on the passive hoop confinement provided by the FRP, which restricts the transverse expansion of the timber under axial load. Because CFRP possesses a higher tensile strength and elastic modulus than BFRP, it activates confining stresses more rapidly and provides a stronger restraint, leading to distinct improvements in load-bearing performance. The experimental results show that the failure mode of the short columns changes from inherent brittle splitting to a more ductile failure pattern, characterized by FRP ruptures and crushing of the timber as a result of external FRP wrapping. The axial compressive performance of the timber columns has been improved with both FRP materials. Given the same conditions, the CFRP caused increases in load-bearing capacity and stiffness, as a result of its higher tensile strength and elastic modulus, which gave rise to peak loads that were 4.9% to 7.8% greater than the BFRP-strengthened groups. There was a tendency for the reinforcement efficiency to increase with the number of layers of CFRP wrapping, and 2–3 layers of CFRP was found to be the optimal number of layers based on the aspect of material efficiency. In addition, FRP confinement was able to prevent premature failure and improve the ultimate transverse strain by as much as 2.1 times, significantly increasing ductility and energy dissipation. Finally, a theoretical ultimate strength prediction model was developed based on the passive confinement theory with the introduction of a height correction factor to consider the slenderness effects. The proposed model showed an overall coefficient of determination R² of 0.8027, which was good for reference for designing the reinforcement and evaluation of the performance of sustainable timber structure. Full article

Conventional masonry infill walls can significantly alter the seismic response of framed buildings and often produce damage patterns incompatible with resilience-based seismic design. Dry-jointed sliding masonry wall systems have therefore emerged as deformation-tolerant alternatives that accommodate drift through controlled interface motion rather than damage accumulation. This study investigates the sequential in-plane (IP) and out-of-plane (OOP) behavior of such systems considering wall thickness, openings, and boundary detailing. Six full-scale specimens were tested, including thick- and thin-wall reference specimens, thick-wall specimens with window openings, and thin-wall specimens with door openings. IP performance was evaluated using global hysteretic and energy-based response parameters, whereas OOP behavior was assessed through load–displacement response, an equivalent acceleration index, and selected image-based displacement fields. The results show that IP drift was mainly accommodated through distributed sliding along horizontal interfaces and local block rotation, without diagonal compression strut formation or brittle cracking, even at drift ratios up to approximately 3.5%. Wall thickness improved IP strength, stiffness, shear resistance, and cumulative energy dissipation, while openings mainly affected deformation compatibility and load-transfer continuity. Under OOP loading, wall thickness and boundary continuity increased stiffness and capacity while enabling resistance mobilization at smaller displacement levels. As inertia-based comparison indicators, boundary-enhanced thick- and thin-wall specimens reached equivalent acceleration capacities of 3.41 g and 1.64 g, respectively. Overall, the system reduced IP damage accumulation, but adequate OOP stability requires appropriate wall thickness, unit geometry, and boundary detailing. Full article

Seismic retrofitting is widely used to enhance the dynamic performance of steel structures. This study experimentally investigates the effect of seismic damper retrofitting on a scaled steel frame using ambient vibration testing. Both as-built and retrofitted configurations were evaluated under low-amplitude excitations generated on a shake table. Modal parameters, including natural frequencies, mode shapes, and damping ratios, were identified using output-only Operational Modal Analysis (OMA) based on the Enhanced Frequency Domain Decomposition (EFDD) method. The results show a significant increase in damping ratios, with more than a 23-fold improvement in the first mode, along with mode-dependent frequency variations ranging from 17.63% to 142.74%. Mode shape comparison confirms strong consistency between configurations. The findings indicate that the integration of the damping devices enhanced the overall energy dissipation capacity of the scaled steel frame by increasing its global damping ratios and modifying the modal responses. The results suggest that output-only OMA can provide valuable insights into damper effectiveness, offering a practical alternative when controlled input excitation is not available. Full article

In this paper, an innovative T-stub connection with square-neck one-side bolts (TS-SNUBC) is developed to improve the bearing capacity and construction reliability of the box column-H beam joint. Twelve T-stub specimens, considering variations in bolt type, flange thickness, and bolt hole orientation, were designed and tested under uniaxial tension. The failure modes, load–displacement responses, ultimate load-bearing capacities, and key quantitative mechanical indicators (initial stiffness, ductility index and cumulative energy dissipation) of the specimens were evaluated. The results indicate that all specimens failed due to the yielding of the thin flange. Specimens with conventional bolts demonstrated the highest load-bearing capacity, followed by those with TS-SNUBC and then slotted one-side bolts. Increasing the thin flange thickness significantly improved the ultimate bearing capacity of the TS-SNUBC specimens. Notably, TS-SNUBC specimens with thin flange thicknesses below 10 mm experienced tear-out failure. Furthermore, specimens with horizontally oriented bolt holes exhibited higher load-bearing capacity than those with vertically oriented holes. A thin flange thickness above 10 mm ensures high initial stiffness, and TF12H has a stiffness of 32.00 kN/mm. Ductility gradually reduces with the growth of thin flange thickness. Energy dissipation decreases sharply when the thin flange is thicker than 10 mm. The joint with 16 mm thick flange, 8 mm thin flange and horizontally arranged square-neck one-side bolts presents the best comprehensive performance. The proposed TS-SNUBC shows favorable bearing performance and initial stiffness, offering a promising solution for reliable and efficiently constructed connections between box columns and steel beams. Full article

Fractures are widely developed in deep coal-mine surrounding rocks. They weaken the load-bearing capacity and energy-storage capacity of rock specimens, which may induce surrounding-rock deformation, roof collapse, and other hazards. Current studies on fractured rock masses mainly focus on a single parameter, such as fracture number or fracture dip angle. However, their coupled effects remain unclear. Integrated analyses of mechanical behavior, crack propagation, and energy evolution are also limited. In this study, uniaxial compression simulations of intact sandstone, single-fracture sandstone, and double-fracture sandstone were conducted using PFC^2D. The effects of fracture number and fracture dip angle on mechanical properties and failure characteristics were investigated. The results show that fractures reduced the peak stress and modulus of elasticity. A stronger weakening effect was observed with increasing fracture number. With increasing fracture dip angle, both peak stress and modulus of elasticity showed a V-shaped trend. The minimum peak stress occurred at 15°, while the minimum modulus of elasticity occurred at 45°. Sandstone failure was mainly dominated by tensile cracks. At 15°, the total crack number was the lowest, with 932 and 818 cracks for single-fracture and double-fracture specimens, respectively. Energy analysis showed that increasing fracture number reduced elastic strain energy and promoted dissipated energy. The weakest energy-storage capacity was observed at 30°. Overall, fracture number and fracture dip angle jointly controlled strength degradation, crack propagation, and energy evolution. This study provides a reference for fracture–damage assessment and disaster prevention in deep coal-bearing sandstone. Full article

Enhancing the ampacity of existing overhead transmission conductors through surface heat-dissipation regulation is important for grid capacity expansion. Herein, a superhydrophobic radiative heat-dissipating conductor was fabricated by combining phosphoric acid anodization with low-surface-energy modification. Porous anodic aluminum oxide (AAO) layers were in situ constructed on ACSR conductors under different anodizing current densities and oxidation times, followed by modification with hexadecyltrimethoxysilane or 1H,1H,2H,2H-perfluorodecyltrimethoxysilane to obtain H-AAO and F-AAO conductors, respectively. The surface morphology, optical properties, wettability, electrical resistance, current-induced temperature rise, and aging stability were systematically evaluated. The porous AAO layer enhanced the broadband infrared emissivity of the conductor surface while maintaining relatively high solar-band reflectance. The F-AAO conductor exhibited a water contact angle of 164.9° and a sliding angle of 1.8°, confirming excellent super-hydrophobicity. At 450 A, the steady-state temperature of the F-AAO conductor decreased from 106.85 °C for the Bare conductor to 75.34 °C. Under a 70 °C temperature limit, the allowable current increased from 343.58 to 431.57 A, corresponding to a 25.6% enhancement. Moreover, the F-AAO conductor retained stable heat-dissipation performance after 28 days of thermal aging. These findings demonstrate that anodization-assisted surface engineering is a feasible strategy for improving radiative heat dissipation, environmental adaptability, and current-carrying performance of overhead transmission conductors. Full article

In modern multistory buildings, integrating beam web openings adjacent to beam–column connections (BCCs) is frequently required to accommodate utility ducts and piping. While this optimizes clear story height, it drastically alters the stress distribution within the BCCs under seismic loading. Consequently, this study evaluates the seismic performance of twenty-one exterior BCCs, with particular emphasis on the coupled effects of opening configuration (size and location) and concrete type: normal strength concrete (NSC, f_c′ = 25 MPa), high-strength concrete (HSC, f_c′ = 80 MPa), and ultra-high-strength concrete (UHPC, f_c′ = 120 MPa). For BCC specimens without openings, upgrading from NSC to HSC and UHPC increased the failure load (P_f) by about 66.67% and 111.11%, and the ultimate capacity (P_u) by 61.54% and 100.0%, respectively. Conversely, web openings reduced the (P_u) of HSC specimens by 14–34%, and UHPC specimens by 12–31%, respectively, when compared to the reference specimens without openings. Furthermore, the presence of web openings compromised cumulative energy dissipation capacity by 16–36% for (NSC), 13–31% for (HSC), and 12–28% for (UHPC), compared with the corresponding reference specimens without openings. Although HSC and UHPC provided superior absolute energy performance, they did not eliminate the structural deficiencies associated with openings positioned adjacent to the joint core. Consequently, a critical threshold value of S/D ≥ 0.5 (where S represents the distance from the column face to the edge of the opening, and D denotes the beam depth), is recommended for HSC and UHPC. In contrast, conventional NSC strictly requires a more conservative limit of S/D ≥ 1.0 to prevent severe cyclic shear degradation near the high-stress region. Full article

Currently, the development of civil engineering industry is gradually slowing down, with the focus gradually shifting toward the reinforcement and renovation of existing buildings. Among these existing structures, reinforced concrete (RC) structure is a kind of structure with high proportion. Therefore, this paper conducts research on the seismic properties of RC buildings after adding new beams to existing columns. This paper first introduces the design situation of the specimen, followed by an experimental investigation of its mechanical properties using pseudo-static tests. Based on the failure patterns and hysteresis curves, the differences between the new-type specimen and RC specimen are analyzed. The findings indicate that, while ensuring load-bearing capacity, the new-type joints exhibit better seismic performance: the bearing capacity and maximum displacement are increased by at most 9.2% and 14.9% respectively, and the fuller hysteresis curve shows that the new-type specimen has better energy dissipation capacity. Finally, this paper extends the analysis of the design parameters of the specimens using finite element components. The modeling results reveal that the bearing capacity varies by less than 1% with different parameters such as connector thickness, concrete strength grade, and bolts quantity and strength, indicating that these parameters have a relatively small impact on the bearing capacity. While for the specimen dimensions and thickness and strength of wrapped steel of beam, the maximum increase in bearing capacity is 32.3% and 6.0%, respectively. Indicating that their impact is quite significant. The findings of this paper provide a reference for structural design and contribute to advancing the work of reinforcement and renovation of existing concrete structures. Full article

In the context of the new power system, modular multilevel converter high-voltage direct current (MMC-HVDC) has become a key technical solution for the large-scale grid integration of wind power. However, when a fault occurs in the AC grid at the system receiving end, the high-voltage direct current (HVDC) system faces challenges such as wind power redundancy, DC overvoltage, and equipment overcurrent. To address this, this paper proposes an energy storage-coordinated fault ride-through (FRT) control strategy suitable for different fault scenarios. The strategy optimizes the allocation of energy storage capacity according to the state of charge (SOC) of the energy storage units (ESUs), preventing individual ESUs from prematurely shutting down and reducing energy dissipation. Finally, a comparison with a conventional DC dissipation resistor scheme on the PSCAD/EMTDC platform demonstrates that the proposed strategy provides smoother power regulation characteristics and smaller DC voltage fluctuations, thereby enhancing the economic efficiency and reliability of system operation. Full article

Light irradiance and spectral quality are key environmental factors that influence the growth, photosynthetic performance, and metabolic responses of cyanobacteria. In this study, the effects of increasing white and PAR-red light irradiances on Anabaena variabilis were evaluated in repeated-batch cultures, focusing on photosynthetic efficiency, biomass productivity, and the modulation of antioxidant systems, while cultures maintained under constant irradiance were used as control. Results showed that A. variabilis can maintain photosynthetic efficiency, as indicated by F_V/F_M values, within the optimal range for healthy cultures despite variations in light conditions. PAR-red light, in particular, enhanced biomass productivity and induced stronger photoacclimation responses compared to white light. Moreover, analysis of chlorophyll fluorescence (JIP parameters) revealed that photosynthetic machinery adapts to increased irradiance by modulating energy fluxes. Dissipated energy (DI₀/RC) increases by 4.5-fold under increasing PAR-red light with respect to control cultures, which suggests that PAR-red light promotes thermal dissipation of excess absorbed energy at the phycobilisome level, independently of and complementarily to, the increase in light-harvesting antenna pigments (chlorophylls and phycobiliproteins), thereby reducing the net oxidative pressure in the electron transport chain. The increase in photosynthetic pigments reflects an adaptive adjustment to optimize light harvesting under red light, with a phycocyanin content of 123 mg·g⁻¹ biomass, 30% higher than that obtained in control culture. Overall, A. variabilis demonstrated a robust capacity to acclimate increasing light irradiance and varying light quality through coordinated photoacclimation and antioxidant responses, in repeated-batch cultures. These findings highlight its physiological flexibility, which can be properly driven to maximize the production of valuable bioactive compounds, particularly phycobiliproteins such as phycocyanin, with applications in biotechnology. Full article

Reinforced concrete (RC) infilled frames are widely used structural systems; however, seismic design provisions often idealize masonry infill as non-structural, leading to uncertainty in performance assessment. This study experimentally and numerically investigates the role of unreinforced masonry infill in RC frames, focusing on load-transfer mechanisms, strain evolution, and energy redistribution. Two 2/3-scale single-bay, single-storey RC frames (bare and fully infilled) were tested under constant axial load and quasi-static reversed cyclic lateral loading. Reinforcement strain gauges were used to capture local deformation demands, and a nonlinear macro-model was developed and validated against experimental results. Results show that the presence of masonry infill significantly increases ultimate strength, initial stiffness, and energy dissipation capacity, in comparatively more brittle post-peak cyclic behavior and accelerated stiffness degradation that leads to more abrupt post-peak degradation. Strain measurements provide clear evidence of a staged interaction mechanism: at low drift levels, the infill governs lateral resistance through diagonal compression strut action, limiting reinforcement demand in the frame; with increasing drift, progressive cracking and crushing of the infill promote a gradual transfer of forces to the RC frame, reflected by increasing reinforcement strains and stiffness degradation. At higher drift levels, the system transitions to frame-dominated behavior with localized strain concentration and shear failure at column bases or joints. These findings demonstrate that infill significantly modifies structural response and highlight the importance of incorporating strain-based mechanisms in the seismic assessment of infilled RC frames. Full article

This study presents an experimental characterization and numerical assessment of Cu–Al–Be (CAB) shape memory alloys (SMAs) for potential applications in U-shaped flexural plate (UFP) seismic dampers. Six alloy compositions were evaluated through monotonic tensile tests, ASTM F2516 superelastic protocols, and increasing-amplitude cyclic loading to identify the material exhibiting stable superelastic behavior at room temperature. Among the tested materials, alloy CAB4.76-A showed the most favorable response, with high transformation stress, stable pseudoelastic behavior, and strain recovery exceeding 95% for strains up to 2.5%. A phenomenological finite element model based on the Auricchio constitutive formulation was calibrated using experimental data within the validated strain range (ε ≤ 0.025), showing good agreement in stiffness and stress prediction. The calibrated model was subsequently applied to simulate the response of a UFP device under orthogonal cyclic loading. The results indicate a strong dependence on loading orientation due to coupled bending–torsion effects, with the 90° direction exhibiting significantly higher strength and energy dissipation capacity. Comparison with analytical formulations originally developed for steel UFPs showed that these expressions provide approximate estimates when applied to SMA-based devices. The results suggest that Cu–Al–Be alloys are a promising alternative for UFP applications, while highlighting the importance of loading orientation and the need for future experimental validation at a device scale. Full article