Search Results (2,709)

This work experimentally examines the seismic performance of steel frames with masonry infill walls produced with geopolymer and traditional mortars under both rigid and flexible joint configurations. Four single-span specimens were evaluated on a uniaxial shake table utilizing eleven scaled earthquake records that represent both in-plane and out-of-plane excitations. Flexible joints markedly diminished acceleration requirements and enhanced deformation capacity in comparison to stiff systems. Rigid frames attained maximum accelerations of 1.82 ± 0.21 g, whilst flexible-joint specimens measured 1.15 ± 0.18 g; the associated lateral displacements were 6.8 ± 0.9 mm and 10.5 ± 1.1 mm, respectively. Geopolymer mortar improved interface adhesion and rigidity, elevating dominant frequencies in rigid systems by around 40% and fostering more ductile behavior in flexible structures. Frequency-domain analysis indicated that decreases in dominant frequency correlated with stiffness deterioration. Geopolymer–flexible systems yielded the minimal acceleration responses and displayed only negligible cracking, indicating enhanced seismic performance. Full article

Strengthening square reinforced concrete (RC) columns with full ultra-high-performance fiber-reinforced concrete (UHPFRC) jacketing is highly effective, but such complete wrapping is often impractical due to architectural or geometric constraints. Previous studies have not systematically examined the performance of partial-coverage UHPFRC patterns for these sections. This study numerically investigates the axial performance of square RC columns strengthened with strategically arranged UHPFRC elements—including horizontal shortcuts, vertical strips, and hybrid configurations—using finite element analysis in ABAQUS. Key parameters include jacket thickness, element dimensions, column height, and reinforcement details. Results show that a 10 mm full UHPFRC jacket more than doubles axial capacity (+105.9% for 800 mm columns), with significant gains in stiffness. Vertical strips enhance strength but reduce ductility; horizontal shortcuts improve post-peak stability; and hybrids offer a balanced response. With full jacketing, internal steel details have minimal impact on peak capacity, while column height chiefly influences energy dissipation. This work establishes that optimized partial UHPFRC layouts—specifically strips, shortcuts, and their combinations—can achieve tailored performance improvements, introducing a novel, practical, and material-efficient design strategy for strengthening square columns where full wrapping is not feasible. Full article

Flexible concrete blankets (FCBs) are emerging as a promising material for slope protection and surface stabilization, offering advantages of light weight, ease of installation, and environmental adaptability. This study investigates the mechanical properties, freeze–thaw resistance, and microstructural evolution of FCBs fabricated with varying cement–sand ratios and high alumina cement dosages. A series of mechanical tests, including compressive, flexural, and tensile strength evaluations, were conducted alongside freeze–thaw cycling tests (up to 125 cycles) to assess mass loss and strength retention. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were employed to elucidate the hydration mechanisms and damage evolution at the microstructural level. The results demonstrate that FCBs exhibit ductile failure behavior, with peak tensile strengths ranging from 3.1 to 4.5 MPa and tensile strain capacities ranging from 5 to 16%. The optimal mix achieved a compressive strength of 51.2 MPa after 28 days of curing. Freeze–thaw cycling induced a two-stage degradation pattern, with damage initiation occurring at approximately 50 cycles and significant deterioration beyond 75 cycles. After 125 cycles, mass loss ranged from 4.39% to 4.99%, and compressive strength retention varied between 78% and 83%, depending on the mix composition. Mixtures with balanced cement–sand ratios (1:1) and moderate Portland cement content demonstrated superior frost resistance, whereas high alumina cement-rich mixtures exhibited pronounced structural loosening due to phase transformations of unstable hydration products. These findings provide a theoretical and experimental basis for optimizing the composition of FCBs to achieve enhanced mechanical performance and durability in cold-region engineering applications. Full article

Precast bridge columns offer efficiency and environmental benefits, yet complex mountainous terrain and limited workspace severely restrict the transportation of large segments. To address this challenge and the limited ductility of traditional connections, this study proposes a multi-segment precast bridge column with hybrid connections (PSC-GSPT) utilizing grouted sleeves and unbonded prestressing tendons. Quasi-static tests and OpenSees simulations compared a three-segment PSC-GSPT specimen with a cast-in-place (CIP) column. Results demonstrate that the hybrid system shifts the plastic hinge above the sleeves due to their high stiffness, ensuring controlled damage. Compared to the CIP specimen, the PSC-GSPT increased peak load by 30.2% and ductility by 20.7%, while exhibiting excellent self-centering capability and 27% higher cumulative energy dissipation. Numerical parametric analysis indicates that a central tendon configuration delays yielding, boosting ductility by over 15% versus perimeter layouts, and an initial prestress level of 30% is recommended to optimize both self-centering and ductility. This study provides a theoretical basis for applying high-performance precast piers in transportation-restricted environments. Full article

U-shaped steel−concrete composite beams (USCCBs) have been widely used in civil engineering due to their numerous advantages, including high load-bearing capacity, high rigidity, good ductility, short construction periods, and compatibility with the development of prefabricated buildings. In particular, USCCBs have been increasingly applied to super high-rise buildings and extra-large span bridges. Over the past decade or so, many new types of shear connectors and structural forms for USCCBs have been developed. Meanwhile, significant progress has been achieved in research on the flexural, shear, torsional, and fire-resistance performance of USCCBs, the seismic behavior of beam−column joints, and the strengthening of concrete beams with U-shaped steel casings. Nevertheless, challenges and limitations remain in both experimental research and practical applications. This paper presents a systematic review of recent research advances in USCCBs. Existing problems, development prospects, and future research priorities are comprehensively summarized and discussed, with the aim of further promoting the development and engineering application of USCCBs. Full article

This study investigates the axial–flexural behavior of steel fiber–reinforced concrete (SFRC) columns under combined constant axial load and monotonic lateral loading. Nine column specimens with different axial load ratios (0.0, 0.10, and 0.20) and steel fiber contents (0.0%, 0.5%, and 1.0%) were tested under monotonic loading to evaluate their failure modes, load–deflection behavior, ductility, and energy absorption capacity. In addition, a sectional P–M interaction analysis was performed to examine the influence of steel fiber inclusion on flexural strength under different axial compression levels. The interaction diagrams indicated that steel fibers expanded the flexural strength envelope, with a more pronounced enhancement in the low-axial-load region. The test results revealed that increasing the axial load ratio enhanced the specimens’ peak load capacity but reduced their ductility, leading to a brittle failure mode. Conversely, the incorporation of steel fiber improved the crack distribution, delayed crack propagation, and enhanced both ductility and energy absorption, particularly under moderate axial load conditions. The failure modes were characterized generally by flexural cracking and localized crushing in the compression zone, with the specimens that contained steel fiber exhibiting a more gradual post-peak load response than the specimens without steel fiber. The energy absorption capacity, quantified as the area under the load–deflection curve, was maximized when the axial load ratio of 0.10 was used in tandem with steel fiber reinforcement, indicating an optimal balance between strength and ductility. Overall, steel fiber inclusion improved deformation capacity and energy absorption under monotonic loading, particularly at low-to-moderate axial load ratios. Full article

Conventional Fiber-Reinforced Polymer (FRP) materials may exhibit certain performance uncertainties in harsh environments, limiting their reliability for structural strengthening. To address this, Basalt Fiber-Reinforced Polymer (BFRP) plates fabricated with silicate-modified epoxy resin are proposed for the flexural strengthening of reinforced concrete (RC) beams. The research aims to evaluate their short-term strengthening performance and establish a reliable calculation method for flexural capacity. Four-point bending tests were conducted to investigate the effects of BFRP plate thickness and end anchorage configuration on failure modes, flexural capacity, and ductility. Finite element simulations incorporating interfacial bond–slip behavior reproduced typical debonding failures, followed by a comprehensive parametric analysis. Based on the experimental and numerical results, a modified BFRP plate strain formula at debonding was proposed to establish a calculation method for the flexural capacity of BFRP-strengthened beams governed by debonding failure. The results indicate that beams without end anchorage were prone to interfacial debonding, where increasing the plate thickness from 0.5 mm to 2 mm raised the flexural capacity gain from 4.5% to 15% but intensified the ductility reduction from 42.9% to 64.9%. Conversely, applying mechanical anchorage improved the ductility index by over 20% compared to unanchored counterparts. The adopted FRP–concrete bond–slip constitutive model accurately characterizes interfacial debonding behavior, and the proposed flexural capacity model demonstrates high accuracy with overall deviations within 5%. It can be concluded that the novel BFRP plates exhibit strengthening behavior comparable to existing FRP systems. Effective end anchorage further enhances flexural capacity and prevents brittle failure. The proposed debonding strain formula for the novel BFRP system offers a reliable basis for capturing the critical onset of interfacial failure. Building upon this, the developed flexural capacity model provides a reliable theoretical basis for the design and assessment of RC beams strengthened with the novel BFRP plates. Full article

A Ti6Al4V alloy fabrication via laser powder bed fusion (L-PBF) leads to the formation of coarse columnar β grains that give rise to anisotropic mechanical properties and inadequate strength. Incorporating the rare-earth oxide, yttrium oxide (Y₂O₃), has proven an effective strategy in enhancing the mechanical performance of Ti6Al4V alloys. Nevertheless, the critical Y₂O₃ content required to achieve an optimal strength–ductility balance in L-PBF Ti6Al4V has not been systematically determined. To address these critical gaps, this study, for the first time, systematically investigates the effect of various Y₂O₃ contents on the microstructural evolution and mechanical properties of Ti6Al4V alloys fabricated via L-PBF. The results demonstrate that a Y₂O₃ addition of 0.2 wt.% produces β grains and α phases with average sizes of 61.6 and 7.6 μm, respectively. Transmission electron microscopy observations reveal that Y₂O₃ nanoparticles, together with elemental Y nanoparticles formed by reduction, are distributed both within the α-Ti matrix and along phase boundaries. This distribution effectively reinforces grain boundaries and promotes heterogeneous nucleation, thereby refining the microstructure. Mechanical property tests indicate that the alloy strength significantly improves as the Y₂O₃ content increases. Specifically, the alloy with 0.2 wt.%Y₂O₃ exhibits a tensile strength of 1106 MPa, a yield strength of 1074 MPa, and an elongation of 10.7%. This study proposes an innovative rare-earth strengthening method for refining the microstructure of L-PBF-fabricated titanium alloys and comprehensively enhancing their mechanical properties. Full article

Grout filling completeness (GFC) is the primary factor affecting the mechanical properties of grouted sleeve connections. To investigate the influences of vertical top void defects on semigrouted sleeve connections, two groups of samples with different rebar diameters (14/16 mm) were designed, incorporating five levels of grouting fullness gradients (GFGs): 60%, 70%, 80%, 90%, and 100%. A total of 60 semigrouted sleeve connection samples were prepared and subjected to uniaxial tensile tests and high-stress cyclic loading tests. The changes in the failure modes and mechanical responses under varying loads were systematically analyzed. The results indicated the following: (1) GFC Threshold Effect: When the GFC was less than 90%, both groups of connections failed to maintain reliable performance, with failure modes transitioning from rebar tensile fracture to interfacial bond-slip failure. Under cyclic loading, interfacial bond-slip failure occurred six times more frequently in the 16 mm-diameter samples than in the 14 mm-diameter samples, indicating significantly reduced reliability for larger diameters. (2) Uniaxial Tensile Behavior: The strength metrics of both joint groups exhibited consistent correlations with the GFC. The yield limits were weakly correlated, whereas the ultimate tensile strengths were significantly strongly correlated. The residual deformation and grout damage depth were not uniformly correlated with the GFC. As the GFC decreased, the yield phase elongation and elongation in the experimental curves generally increased. (3) High-Stress Cyclic Loading Behavior: The mechanical parameters of the 14 mm-diameter samples were not significantly correlated with the GFC. Conversely, the 16 mm-diameter samples exhibited dual dependencies on strength and deformation, with the ultimate tensile strength and grout damage depth showing strong correlations. Under cyclic loading, yield phase elongation and overall elongation decreased inversely with decreasing GFC—a trend opposite to that under uniaxial tensile loading. This phenomenon provided critical theoretical support for the ductility design of prefabricated structural joints under seismic conditions. Full article

This research explored the performance of steel fiber concrete-filled stainless-steel tube columns stiffened with embedded carbon steel T-sections with various steel fiber ratios under biaxial bending conditions. A numerical parametric analysis was adopted, using finite element modeling with Abaqus CAE/2021 to evaluate the effects of the fiber ratio (ranging from 0% to 1.5%) on the load-bearing capacity and deflection behavior of columns. In addition, the compressive strength of concrete ranged between 45 and 65 MPa. An increase in the fiber ratio led to a substantial improvement in the ultimate load-bearing capacity (up to 24%), a reduction in deflection (of approximately 49%), and an improvement in column ductility, which were obtained at 1.25% fiber content. The addition of steel fibers enhanced column performance, and energy absorption improved by up to 27% compared to specimens without steel fibers. Experimental validation demonstrated improved accuracy in terms of behavior and predicted models. The conclusions of this work provide valuable design insights enabling the adaptation of the overall column system under complex loading scenarios. Full article

While steel sheets are an effective strengthening technique for existing structures, experimental evidence on galvanised steel sheets is limited, necessitating their evaluation as a durable and cost-effective solution for the flexural strengthening of reinforced concrete (RC) beams. This study analyses the influence of external reinforcement using galvanised steel sheets applied to RC beams. The structural behaviour of the specimens was assessed through flexural tests, with monotonic loading applied at one-third and two-thirds of the effective span, in accordance with ASTM C78 guidelines. In addition, an analytical model was formulated to capture the non-linear behaviour of concrete, reinforcing steel, and galvanised steel sheets. The results indicate that beams strengthened with external reinforcement exhibit an increase in load-bearing capacity of up to 69% in the elastic range, together with significant improvements in ductility of up to 22%. Moreover, the use of vertical U-wrap sheets and anchor bolts enhances the bond between the sheets and the concrete, thereby reducing the risk of premature debonding. Overall, the findings confirm that the use of galvanised steel sheets is an effective and practical strengthening technique for improving the flexural performance of RC beams. Full article

Selective laser melting (SLM), a pivotal additive manufacturing (AM) technology for titanium alloys, enables near-net-shape forming of complex structures with relative densities of up to 99.9%, making it indispensable in aerospace, biomedical, and marine engineering. This review comprehensively updates the state of the art on SLM-fabricated TC4 (Ti-6Al-4V) alloy, addressing critical gaps in previous studies by integrating novel research progress, in-depth mechanistic analyses, and multi-dimensional comparisons. The core focus is on the unique thermal cycle (10⁶–10⁸ °C/s heating/cooling rates) of SLM, which induces a predominant needle-like martensitic α′ phase (99.7%) and minimal β phase (0.3%), leading to intrinsic anisotropy and low ductility. Room-temperature tensile strength reaches 1315.32 MPa with 9.6% elongation, and high-cycle fatigue limits the range from 417 to 829 MPa, strongly dependent on process parameters and post-treatment. Corrosion anisotropy is systematically analyzed: the XY plane (parallel to scanning direction) exhibits superior corrosion resistance in 1 M HCl (fewer pits and lower corrosion current density) and 3.5% NaCl (more stable passive film) compared to the XZ plane (deposition direction). Novel insights include: (1) synergistic effects of SLM process parameters (laser power–scanning speed–hatch spacing) on defect evolution and microstructure uniformity; (2) atomistic mechanisms of α′→α + β phase transformation during post-heat treatment; and (3) corrosion–mechanical coupling behavior in harsh environments (e.g., marine and biomedical). Post-treatment strategies are refined: annealing at 800 °C for 2 h achieves 1099 MPa tensile strength and 17.4% elongation, while hot isostatic pressing (HIP) reduces porosity from 0.08% to 0.01% and weakens fatigue anisotropy. This review also identifies unresolved challenges (e.g., in situ defect monitoring and multi-field regulated performance) and proposes future directions (e.g., AI-driven process optimization and functional gradient structures). Full article

In this study, Inconel 600 alloy with reductions of 20%, 50%, and 80% was obtained through cold rolling, and the effects of plastic deformation on its mechanical properties and corrosion behavior in a hydrofluoric acid (HF) solution were systematically investigated. The results show that cold rolling induces pronounced work hardening, with both hardness and strength increasing continuously with increasing reduction, while the ductility decreases accordingly. The alloy with 80% reduction exhibits the highest strength, with an ultimate tensile strength of 1270 MPa and a yield strength of 1210 MPa. In contrast, the macroscopic corrosion resistance of the alloy in HF solution remains essentially unchanged with increasing deformation, although a slight intensification of pitting corrosion is observed. The combined effects of deformation-induced pitting and passivation enhancement resulted in retention of corrosion resistance. These findings demonstrate that appropriate control of cold rolling enables effective mechanical strengthening of Inconel 600 without significantly sacrificing its corrosion performance in aggressive fluorine containing environments. Full article

Polymer blends are an essential category of materials formed by physically combining two or more polymers. The plasticizing process is advantageous for brittle or rigid polymer systems that need improved flexibility or ductility. The increasing demand for environmentally friendly and high-performance polymeric materials has spurred research into alternative plasticization methods. The use of ionic liquids as non-volatile plasticizers in polymer blends is owing to their outstanding properties. In this short review, several ionic liquids employed in polymer blends and some polymers used in blends with ionic liquids are listed. Additionally, the plasticizing effects of ionic liquids on the properties of polymer blends are concisely elucidated. This review also provides a brief overview of the potential applications of polymer blends plasticized with ionic liquids. In summary, many studies reveal that ionic liquid-based plasticization impacts the structural, thermal, conductive, and mechanical properties of polymer blends. The potential applications of polymer blends plasticized with ionic liquids cover various fields, including energy systems, packaging, electronics, and soft robotics. Full article

The strengthening of reinforced concrete (RC) beams requires repair systems that can enhance strength, stiffness, and energy dissipation without significantly increasing self-weight or compromising durability. This study explores the structural response of RC beams strengthened using an integrated shear–flexure system combining near-surface-mounted carbon fiber-reinforced polymer (NSM-CFRP) ropes and steel-reinforced geopolymer overlays in the compression zone. Monotonic three-point bending tests were performed on two RC beam specimens, one unstrengthened control and one strengthened beam, to obtain preliminary observations of load–deflection behavior, stiffness, ductility, and energy absorption. The strengthened specimen exhibited increases in ultimate load (28.6%), stiffness (13.6%), and energy absorption (7.65%) relative to the control beam, suggesting the potential for effective composite action between the CFRP ropes and geopolymer material. A three-dimensional nonlinear finite element model was developed using ATENA to support interpretation of the experimental response, incorporating detailed constitutive models for concrete, steel reinforcement, and CFRP ropes. The numerical predictions showed reasonable agreement with the experimental results. Within the limitations of the test matrix, the results indicate that the proposed dual strengthening system may offer a viable and sustainable approach for enhancing the shear–flexural performance of RC beams. Full article