Search Results (838)

This study presents a detailed analysis of the influence of hole presence and size on the behavior of CFRP composite plates subjected to axial compression. The plates were manufactured by an autoclave method from eight-ply laminate in a symmetrical fiber arrangement [45°/−45°/90°/0°₂/90°/−45°/45°]. Four central hole plates of 0 mm (reference), 2 mm, 4 mm, and 8 mm in diameter were analyzed. Tests were conducted using a Cometech universal testing machine in combination with the ARAMIS digital image correlation (DIC) system, enabling the non-contact measurement of real-time displacements and local deformations in the region of interest. The novel feature of this work was its dual use of independent measurement methods—machine-based and DIC-based—allowing for the assessment of boundary condition effects and grip slippage on failure load accuracy. The experiments were carried out until complete structural failure, enabling a post-critical analysis of material behavior and failure modes for different geometric configurations. The study investigated load–deflection and load–shortening curves, failure mechanisms, and ultimate loads. The results showed that the presence of a hole leads to localized deformation, a change in the failure mode, and a nonlinear reduction in load-carrying capacity—by approximately 30% for the largest hole. These findings provide complementary data for the design of thin-walled composite components with technological openings and serve as a robust reference for numerical model validation. Full article

Ductile structures have demonstrated the ability to withstand increased seismic intensity levels. Additionally, these structures can be restored to their operational state promptly following the replacement of damaged components post-earthquake. This capability has been a subject of considerable interest and focus in recent years. The study presented in this paper introduces an innovative beam-column connection that incorporates V-shaped steel as the replaceable energy-dissipating component. It delineates the structural configuration and design principles of this joint. Furthermore, the paper conducts a detailed analysis of the joint’s failure mode, stress distribution, and strain patterns using ABAQUS 2022 finite element software, thereby elucidating the failure mechanisms, load transfer pathways, and energy dissipation characteristics of the joint. In addition, the study investigates the impact of critical design parameters, including the strength, thickness, and weakening dimensions of the dog-bone energy-dissipating section, as well as the strength and thickness of the V-shaped plate, on the seismic behavior of the beam-column joint. The outcomes demonstrate that the incorporation of V-shaped steel with a configurable replaceable energy-dissipating component into the traditional dog-bone replaceable joint significantly improves the out-of-plane stability. Concurrently, the V-shaped steel undergoes a process of gradual flattening under load, which allows for a larger degree of deformation. In conclusion, the innovative joint design exhibits superior ductility and load-bearing capacity when contrasted with the conventional replaceable dog-bone energy-dissipating section joint. The joint’s equivalent viscous damping coefficient, ranging between 0.252 and 0.331, demonstrates its robust energy dissipation properties. The parametric analysis results indicate that the LY160 and Q235 steel grades are recommended for the dog-bone connector and V-shaped steel connector, respectively. The optimal thickness ranges are 6–10 mm for the dog-bone connector and 2–4 mm for the V-shaped steel connector, while the weakened dimension should preferably be selected within 15–20 mm. Full article

This study investigates the behavior and performance of a newly proposed cone-top pile foundation designed to improve stability in layered, deformable, or strain-sensitive soils. Traditional shallow and uniform conical foundations often suffer from excessive settlement and reduced capacity when subjected to vertical loads and horizontal soil deformations. To address these limitations, a hybrid foundation was developed that integrates an inverted conical base with a central pile shaft and a rolling joint interface between the foundation and the superstructure. Laboratory model tests, full-scale field loading experiments, and axisymmetric numerical simulations using Plaxis 2D (Version 8.2) were conducted to evaluate the foundation’s bearing capacity, settlement behavior, and load transfer mechanisms. Results showed that the cone-top pile foundation exhibited lower settlements and higher load resistance than columnar foundations under similar loading conditions, particularly in the presence of horizontal tensile strains. The load was effectively distributed through the conical base and transferred into deeper soil layers via the pile shaft, while the rolling joint reduced stress transmission to the structure. The findings support the use of cone-top pile foundations in soft soils, seismic areas and areas affected by underground mining, where conventional designs may be inadequate. This study provides a validated and practical design alternative for challenging geotechnical environments. Full article

This paper outlines a structural qualification process to assess the use of newly developed high-modulus (HM) glass fiber-reinforced polymer (GFRP) bars with headed ends in the joint between concrete bridge barriers and decks. The main goals of the study are to evaluate the structural performance of GFRP-reinforced TL-5 barrier–deck systems under transverse loading and to determine the pullout capacity of GFRP anchorage systems for both new construction and retrofit applications. The research is divided into two phases. In the first phase, six full-scale Test-Level 5 (TL-5) barrier wall–deck specimens, divided into three systems, were constructed and tested up to failure. The first system used headed-end GFRP bars to connect the barrier wall to a non-deformable thick deck slab. The second system was similar to the first but had a deck slab overhang for improved anchorage. The third system utilized postinstalled GFRP bars in a non-deformable thick deck slab, bonded with a commercial epoxy adhesive as a solution for deteriorated barrier replacement. The second phase involves an experimental program to evaluate the pullout strength of the GFRP bar anchorage in normal-strength concrete. The experimental results from the tested specimens were then compared to the factored applied moments in existing literature based on traffic loads in the Canadian Highway Bridge Design Code. Experimental results confirmed that GFRP-reinforced TL-5 barrier–deck systems exceeded factored design moments, with capacity-to-demand ratios above 1.38 (above 1.17 with the inclusion of an environmental reduction factor of 0.85). A 195 mm embedment length proved sufficient for both pre- and postinstalled bars. Headed-end GFRP bars improved pullout strength compared to straight-end bars, especially when bonded. Failure modes occurred at high loads, demonstrating structural integrity. Postinstalled bars bonded with epoxy performed comparably to preinstalled bars. A design equation for the barrier resistance due to a diagonal concrete crack at the barrier–deck corner was developed and validated using experimental findings. This equation offers a conservative and safe design approach for evaluating barrier–deck anchorage. 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

The spray-applied pipe lining (SAPL) method, extensively employed in the trenchless rehabilitation of reinforced concrete pipes (RCPs) due to its operational versatility, remains constrained by an incomplete understanding of the failure behavior of rehabilitated pipelines, thereby impeding optimal design strategies. This study proposes an analytical approach to evaluate the structural performance of pipes with fiber-reinforced mortar lining, with a particular focus on interface failure and its consequences. Two RCPs with an inner diameter of 1000 mm, repaired with 34 mm and 45 mm centrifugally sprayed fiber-reinforced mortar liners, were subjected to three-edge-bearing (TEB) tests. The elastic limit loads of the two pipes were 57% and 39% of their pre-rehabilitation conditions, while the ultimate loads were 45% and 69%. A thicker liner exhibits a greater susceptibility to interface failure, leading to wider cracks around the elastic stage during loading. Once the interface failure occurs, load redistribution allows the liner to resist further cracking and sustain higher capacity, demonstrating enhanced bearing performance. Critical factors influencing the failure process were analyzed to inform design optimization, revealing that improving the interface takes precedence, followed by thickness design. Full article

The objective of this study is to examine the variations in the properties of cementitious materials subjected to bending loads in conjunction with dry and wet cycles of sulfate exposure. This investigation involved applying continuous bending loads at 0%, 20%, and 40% of the ultimate bending capacity to cementitious material specimens. Furthermore, three sets of mortars and concretes with differing water–cement ratios were formulated and analyzed using X-ray diffraction, scanning electron microscopy, and compressive strength tests. The findings indicated that while the flexural strength, compressive strength, and porosity of the specimens initially increased, they ultimately declined as the cementitious materials degraded over time within the sulfate solution. Additionally, it was observed that an increase in bending load corresponded with a decrease in flexural strength, alongside a rise in the internal sulfate ion concentration. By integrating an enhanced form of Fick’s second law with chemical reaction kinetics, a transport model for sulfate ions in cement-based materials was developed under the coupling effect of bending load and sulfate exposure, utilizing Comsol Multiphysics. The simulation results, which align well with the experimental observations, exhibit an error of approximately 5% at a depth of 5 mm. Full article

This study delves into the delamination-driven nonlinear buckling characteristics of metal–composite cylindrical shells with different interfacial strengths. Although surface treatments are known to affect bonding performance, their specific influences on the delamination buckling behavior of metal–composite cylindrical shells remain underexplored. Accordingly, sandblasting and polishing processes were employed to the fabrication of single-lap shear specimens. The topography of the treated surface was then characterized through scanning electron microscopy, optical profilometry, and contact angle measurements. For topography characterization and performance tests, sandblasted and polished metal–composite cylindrical shells were fabricated for hydrostatic tests. A cohesive zone model was used to analyze the influences of interfacial strength on the nonlinear buckling characteristics of metal–composite cylindrical shells, and the modeling results were validated by benchmarking them with experimental results. Subsequently, a detailed parametric study was conducted to investigate the effects of cohesive zone parameters and geometric imperfection on the load-bearing capacity of the shells. The new findings reveal that among the fabricated steel specimens, the specimens subjected to 80-mesh sandblasting exhibited the highest bond strength in single-lap shear tests, with the bond strength being 2.56 times higher than that of polished specimens. Moreover, sandblasted metal–composite cylindrical shells exhibited a 55.0% higher average collapse load than that of polished metal–composite cylindrical shells. Full article

In order to improve the efficiency of highway tunnel construction and ensure the construction quality, the design concept of a prefabricated inverted arch and partial cast-in-place lining of highway tunnels by a mining method is put forward. During the assembly of prefabricated tunnel invert arches, the longitudinal joints between adjacent invert sections were subjected to shear forces due to the combined effects of the invert’s self-weight and construction equipment loads. This study investigated the shear performance of these longitudinal joints under construction loads, with a particular focus on the influence of bolt-tightening torque. Three longitudinal joint specimens were designed and fabricated, varying the bolt-tightening torque as a key parameter, and subjected to shear tests. The failure modes, load–slip behavior, and shear capacity of the joints were analyzed in relation to the tightening torque of high-strength bolts. The results indicate that when the bolt-tightening torque was set to 50% and 70% of the standard torque, the upper bolts of the joint sheared off, while the threads of the lower bolts were damaged. When the torque reached the standard value, all bolts were sheared off. The ultimate shear capacity of the longitudinal joints increased with higher bolt-tightening torque, with the optimal torque range identified as 70% to 85% of the specified standard. Ultimately, a method of calculation for evaluating the shear-bearing capacity of inverted arch longitudinal joints was proposed, with computational outcomes demonstrating a conservative bias that aligns with structural safety requirements. Full article

In the case of strengthening building structures, the process usually involves elements that have a certain loading history and are typically subjected to loading during the strengthening process. In scientific research, on the other hand, strengthening is usually applied to elements that are not representative of real structures. This article presents a study of the effect of pre-damage on the behavior of eccentrically compressed concrete cylinders confined with PBO-FRCM (fabric-reinforced cementitious matrix with PBO fibers) composite. Concrete confinement introduces a favorable triaxial stress state, which leads to an increase in the compressive strength of concrete. FRCM systems are an alternative to FRP (fiber-reinforced polymer) composites. Replacing the polymer matrix with a mineral matrix primarily improves the fire resistance of the strengthening system. The elements were made of concrete with a compressive strength of about 40 MPa, which is typical for current reinforced concrete columns. Pre-damage was induced by loading the test elements to 80% of the average compressive strength and then fully unloading. The elements were then strengthened with three layers of PBO-FRCM composite and subjected to axial or eccentric compression with force applied at two different eccentricities. In addition to electric strain gauges, a digital image correlation system was used for measurements, to identify the initiation of PBO mesh overlap delamination. This study analyzed the elements in terms of load-bearing capacity, deformability, ductility, and failure mechanisms. In general, there was no negative effect of pre-damage on the behavior of the tested elements. Full article

In order to conduct an in-depth and exhaustive investigation into the mechanical properties of steel tubes filled with wood, a thin-walled steel–wood composite column was elaborately designed. The damage progression, failure mode, and mechanical performance of this column under eccentric compression were systematically investigated through both experimental research and finite element simulations. The impacts of different numbers of bolts on the mechanical properties of the composite column were minutely analyzed, and the test results of composite columns were compared with the pure steel pipe column under the same experimental conditions. It was clearly observed that the pure thin-walled steel pipe specimen was highly susceptible to elastic instability under eccentric compression, and the high-strength and high-ductility potential of structural steel was not fully developed. However, after filling with wood and applying bolt restraints, the greater the number of bolts in the specimen of thin-walled steel–wood composite column under the identical eccentricity condition, the higher the ultimate load-bearing capacity. Specifically, the ultimate load-bearing capacity of the columns filled with wood increased by 77.78–114% in comparison with that of the pure steel pipe column. Through a meticulous comparison between the test and finite element analysis results, the error was ascertained to be in the range of 4.9–11.1%. In addition, filling the thin-walled steel tube with wood and restraining it with bolts can effectively enhance the lateral deformation resistance of the specimens, and the reduction rate of lateral deflection exceeded 50%. Moreover, the greater the number of filling bolts, the smaller the strain of components subjected to the eccentric compression occurred, and the better the mechanical properties. Full article

This study explores the impact of thermal cycling and rubber particle content on the static and dynamic compressive properties of rubber–polyethylene fiber-reinforced engineered cementitious composites (RPECC). Through static and dynamic compression tests, supplemented by scanning electron microscopy and energy-dispersive X-ray spectroscopy, the mechanical behavior and microstructural evolution of RPECC under thermal cycling were analyzed. Results indicate that increasing rubber content from 10% to 30% enhances toughness and strain capacity but reduces the static compressive strength of ECC by up to 17.9% at 30%. Thermal cycling reduced strength: static and dynamic compressive strengths decreased by 18.0% and 41.2%, respectively, after 270 cycles. Dynamic tests demonstrated that RPECC is sensitive to strain rate. For example, C-20 specimens exhibited increases in dynamic strength of 6.9% and 9.9% as strain rate rose from 60.2 s⁻¹ to 77.4 s⁻¹ and 110.8 s⁻¹, respectively, and the dynamic increase factor correlated linearly with strain rate. By contrast, excessive rubber content (30%) diminishes dynamic strengthening, indicating that 20% rubber is optimal for enhancing strain rate sensitivity. Thermal cycling facilitates the formation of hydration products, such as calcium hydroxide, and creates interfacial defects, further deteriorating mechanical performance. These findings provide a reliable foundation for optimizing RPECC mix design and ductility in environments subject to temperature fluctuations and dynamic loading. Full article

Doors are considered vulnerable to failure in structures when subjected to extreme loads, such as blasts. Consequently, blast-resistant doors are designed to withstand blast pressure in important structures. This study developed a multi-layer Steel, Aluminum Foam, and Steel–Concrete–Steel composite door panel with Energy Absorption Connectors (SAFSCS-EACs) under near and far field blast loading using finite element analysis in LS-DYNA. Three dynamic response modes were observed based on the crushing strength of energy absorption connectors (EACs) for the SAFSCS-EAC composite door under both near and far field blasts. In addition, the membrane stretching phenomena was observed in the face steel plate. The AF shows a local densification in near field blasts and a global densification in far field blasts. For the SCS panel, a punching-like failure and a global flexural failure were observed in near and far field blasts, respectively. AF has a high energy absorption capacity as a first energy absorption layer, while the EAC also effectively dissipates blast energy through the rotation of the plastic hinges of curved steel plates, thereby reducing the damage to the SCS panel and increasing the door’s structural integrity. Moreover, to check the influence of the curved steel plate thickness of EACs and the core concrete thickness, a parametric study was carried out. The results showed that the blast resistance performance of the SAFSCS-EAC composite door could increase by appropriately designing the EAC curved steel plates’ thickness and ensuring that the compression displacement of the EAC under blast is close to its densification displacement. Additionally, increasing concrete thickness can reduce the degree of damage to the steel–concrete–steel composite panel during the blast, but it leads to a reduction in the energy dissipation of the EAC. Full article

Achieving the appropriate primary stability for immediate or early loading in areas with low-density bone, such as the posterior maxilla, is challenging. A three-dimensional (3D) stabilization implant design featuring a tapered body with continuous cutting flutes along the length of the external thread form, with a combination of curved and linear geometric surfaces on the thread’s crest, has the capacity to enhance early biomechanical and osseointegration outcomes compared to implants with traditional buttressed thread profiles. Commercially available implants with a buttress thread design (TP), and an experimental implant that incorporated the 3D stabilization trimmed-thread design (TP 3DS) were used in this study. Six osteotomies were surgically created in the ilium of adult sheep (N = 14). Osteotomy sites were randomized to receive either the TP or TP 3DS implant to reduce site bias. Subjects were allowed to heal for either 3 or 12 weeks (N = 7 sheep/time point), after which samples were collected en bloc (including the implants and surrounding bone) and implants were either subjected to bench-top biomechanical testing (e.g., lateral loading), histological/histomorphometric analysis, or nanoindentation testing. Both implant designs yielded high insertion torque (ITV ≥ 30 N⋅cm) and implant stability quotient (ISQ ≥ 70) values, indicative of high primary stability. Qualitative histomorphological analysis revealed that the TP 3DS group exhibited a continuous bone–implant interface along the threaded region, in contrast to the TP group at the early, 3-week, healing time point. Furthermore, TP 3DS’s cutting flutes along the entire length of the implant permitted the distribution of autologous bone chips within the healing chambers. Histological evaluation at 12 weeks revealed an increase in woven bone containing a greater presence of lacunae within the healing chambers in both groups, consistent with an intramembranous-like healing pattern and absence of bone dieback. The TP 3DS macrogeometry yielded a ~66% increase in average lateral load during pushout testing at baseline (T = 0 weeks, p = 0.036) and significantly higher bone-to-implant contact (BIC) values at 3 weeks post-implantation (p = 0.006), relative to the traditional TP implant. In a low-density (Type IV) bone model, the TP 3DS implant demonstrated improved performance compared to the conventional TP, as evidenced by an increase in baseline lateral loading capacity and increased BIC during the early stages of osseointegration. These findings indicate that the modified implant configuration of the TP 3DS facilitates more favorable biomechanical integration and may promote more rapid and stable bone anchorage under compromised bone quality conditions. Therefore, such improvements could have important clinical implications for the success and longevity of dental implants placed in regions with low bone density. Full article

Background/Objectives: This study aims to develop and evaluate neutrophil-membrane-coated nanoparticles (Siv@NMs) encapsulating sivelestat for the treatment of sepsis-induced endothelial injury. Leveraging the intrinsic chemotactic properties of neutrophil membranes, Siv@NMs are engineered to achieve site-specific delivery of sivelestat to damaged endothelia, thereby overcoming the limitations of conventional therapies in mitigating endothelial dysfunction and multiorgan failure associated with sepsis. Methods: Siv@NMs were synthesized through a combination of ultrasonication and extrusion techniques to encapsulate sivelestat within neutrophil-membrane-derived vesicles. Comprehensive physicochemical characterization included analysis of particle size distribution, zeta potential, and encapsulation efficiency. Stability profiles and controlled release kinetics were systematically evaluated under simulated conditions. In vitro investigations encompassed (1) endothelial cell biocompatibility assessment via cytotoxicity assays, (2) investigation of the targeting efficiency in suppressing endothelial neutrophil extracellular trap generation during inflammation, and (3) ROS-scavenging capacity quantification using flow cytometry with DCFH-DA fluorescent probes. In vivo therapeutic efficacy was validated using a cecal ligation and puncture (CLP) sepsis mouse model, with multiparametric monitoring of endothelial function, inflammatory markers, ROS levels, and survival outcomes. Results: The optimized Siv@NMs exhibited an average particle size of approximately 150 nm, and a zeta potential of −10 mV was achieved. Cellular studies revealed that (1) Siv@NMs selectively bound to inflammatory endothelial cells with minimal cytotoxicity, and (2) Siv@NMs significantly reduced ROS accumulation in endothelial cells subjected to septic stimuli. In vitro experiments demonstrated that Siv@NMs treatment markedly attenuated endothelial injury biomarkers’ expression (ICAM-1 and iNOS), suppressed formation of neutrophil extracellular traps, and improved survival rates compared to treatment with free sivelestat. Conclusions: The neutrophil-membrane-coated nanoparticles loaded with sivelestat present a breakthrough strategy for precision therapy of sepsis-associated endothelial injury. This bioengineered system synergistically combines targeted drug delivery with multimodal therapeutic effects, including ROS mitigation, anti-inflammatory action, and endothelial protection. These findings substantiate the clinical translation potential of Siv@NMs as a next-generation nanotherapeutic for sepsis management. Full article