Search Results (1,019)

The stability of shield tunnel segmental linings is highly sensitive to the lateral pressure coefficient, especially under weak, heterogeneous, and variable geological conditions. However, the mechanical behavior of steel plate-reinforced linings under such conditions remains insufficiently characterized. This study aims to investigate the effects of varying lateral pressures on the structural performance of reinforced tunnel linings. To achieve this, a custom-designed full-circumference loading and unloading self-balancing apparatus was developed for scaled-model testing of shield tunnels. The experimental methodology allowed for precise control of loading paths, enabling the simulation of realistic ground stress states and the assessment of internal force distribution, joint response, and load transfer mechanisms during the elastic stage of the structure. Results reveal that increased lateral pressure enhances the stiffness and bearing capacity of the reinforced lining. The presence and orientation of segment joints, as well as the bonding performance between epoxy resin and expansion bolts at the reinforcement interface, significantly influence stress redistribution in steel plate-reinforced zones. These findings not only deepen the understanding of tunnel behavior in complex geological environments but also offer practical guidance for optimizing reinforcement design and improving the durability and safety of shield tunnels. Full article

Reinforced concrete (RC) deep beams constructed with low-strength concrete are susceptible to sudden splitting failures in the strut region due to shear–compression stresses. To mitigate this vulnerability, various strengthening techniques, including steel plates, fiber-reinforced polymer sheets, and cementitious composites, have been explored to confine the strut area. This study investigates the structural performance of RC deep beams with low-strength concrete, strengthened externally using an Engineered Cementitious Composite (ECC) layer. To ensure effective confinement and uniform shear distribution, shear reinforcement was provided at equal intervals with configurations of zero, one, and two vertical shear reinforcements. Four-point bending tests revealed that the ECC layer significantly enhanced the shear capacity, increasing load-carrying capacity by 51.6%, 54.7%, and 46.7% for beams with zero, one, and two shear reinforcements, respectively. Failure analysis through non-linear finite element modeling corroborated experimental observations, confirming shear–compression failure characterized by damage in the concrete struts. The strut-and-tie method, modified to incorporate the tensile strength of ECC and shear reinforcement actual stress values taken from the FE analysis, was used to predict the shear capacity. The predicted values were within 10% of the experimental results, underscoring the reliability of the analytical approach. Overall, this study demonstrates the effectiveness of ECC in improving shear performance and mitigating strut failure in RC deep beams made with low-strength concrete. Full article

The superb dynamic performance of steel-plate composite (SC) structures under unexpected impact loading depends on the good design of the connection between the SC wall and foundation. This study investigated the flexural behavior and dynamic responses of SC wall-to-foundation connections subjected to low-velocity impact. Impact tests were performed on three SC connection specimens to evaluate failure mode, impact force, deflection, and strain responses. The effects of concrete strength grade and impact energy were analyzed in detail. All specimens exhibited flexural failure, with three distinct stages observed during impact. The experimental results demonstrated that compared to the specimen with C30 concrete, the specimen with C50 concrete significantly reduced wall damage, decreased deflections, and enhanced deflection recovery ability. It can be concluded that increasing the concrete strength grade effectively improves the impact resistance of SC wall-to-foundation connections. In addition, peak impact force, global deflection response, residual strains, and interface crack length were highly sensitive to changes in impact energy, whereas deflection recovery exhibited lower sensitivity. Furthermore, a finite element model was developed and validated against experimental results. Parametric studies explored the influence of key parameters with expanded ranges on the impact responses of SC wall-to-foundation connections. Full article

The performance of reinforced concrete (RC) frame structures will gradually decrease over time, posing a threat to the safety of buildings. Although the performance of some buildings may still meet the safety requirements, they cannot meet new usage requirements. Therefore, this paper proposes a new-type joint to promote the development of research on the reinforcement and renovation of RC frame structures in response to this situation. The RC beams and columns of the joints are connected by embedded horizontal steel plate (a single plate with dimension of 150 mm × 200 mm × 5 mm), and the beams and columns are individually wrapped in steel. Through conducting low cyclic loading tests, this paper analyzes the influence of carrying out wrapped steel treatment and the thickness of wrapped steel of the beam and connector on mechanical performance indicators such as hysteresis curve, skeleton curve, stiffness, ductility, and energy dissipation. The experimental results indicate that the reinforcement using steel plate can significantly improve the dynamic performance of the joint. The effect of changing the thickness of the connector on the dynamic performance of the specimen is not significant, while increasing the thickness of wrapped steel of beam can effectively improve the overall strength of joint. The research results of this paper will help promote the application of reinforcement and renovation technology for existing buildings, and improve the quality of human living. Full article

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

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

This study investigates two novel prefabricated frame joints: prestressed steel sleeve-connected prefabricated reinforced concrete joints (PSFRC) and non-prestressed steel sleeve-connected prefabricated reinforced concrete joints (SSFRC). A total of three PSFRC specimens, four SSFRC specimens, and one cast-in-place joint were designed and fabricated. Seismic performance tests were conducted using different end-plate thicknesses, grout strengths, stiffener configurations, and prestressing tendon configurations. The experimental results showed that all specimens experienced beam end failures, and three failure modes occurred: (1) failure of the end plate of the beam sleeve, (2) failure of the variable cross-section of the prefabricated beam, and (3) failure of prefabricated beams at the connection with the steel sleeves. The load-bearing capacity and initial stiffness of the structure are increased by 35.41% and 32.64%, respectively, by increasing the thickness of the end plate. Specimens utilizing C80 grout exhibited a 39.05% higher load capacity than those with lower-grade materials. Adding stiffening ribs improved the initial stiffness substantially. Specimen XF2 had 219.08% higher initial stiffness than XF1, confirming the efficacy of stiffeners in enhancing joint rigidity. The configuration of the prestressed tendons significantly influenced the load-bearing capacity. Specimen YL2 with symmetrical double tendon bundles demonstrated a 27.27% higher ultimate load capacity than specimen YL1 with single centrally placed tendon bundles. An analytical model to calculate the moment–rotation relationship was established following the evaluation criteria specified in Eurocode 3. The results demonstrated a good agreement, providing empirical references for practical engineering applications. Full article

Based on the engineering background of a new type of segmental-assembled steel temporary beam buttress, the fatigue strength evaluation method of the steel box girders with open longitudinal ribs was taken as the research objective. The fatigue stress calculation analysis and the full-scale fatigue loading test for the steel box girder local component were carried out. The accuracy of the finite-element model was verified by comparing it with the test results, and the rationality of the fatigue strength evaluation methods for welded joints was deeply explored. The results indicate that the maximum nominal stress occurs at the weld toe between the transverse diaphragm and the top plate at the edge of the loading area, which is the fatigue-vulnerable location for the steel box girder local components. The initial static-load stresses at each measuring point were in good agreement with the finite-element calculation results. However, the static-load stress at the measuring point in the fatigue-vulnerable position shows a certain decrease with the increase in the number of cyclic loads, while the stress at other measuring points remains basically unchanged. According to the finite-element model, the fatigue strengths obtained by the nominal stress method and the hot-spot stress method are 72.1 MPa and 93.8 MPa, respectively. It is reasonable to use the nominal stress S-N curve with a fatigue life of 2 million cycles at 70 MPa and the hot-spot stress S-N curve with a fatigue life of 2 million cycles at 90 MPa (FAT90) to evaluate the fatigue of the welded joints in steel box girders with open longitudinal ribs. According to the equivalent structural stress method, the fatigue strength corresponding to 2 million cycles is 94.1 MPa, which is slightly lower than the result corresponding to the main S-N curve but within the range of the standard deviation curve. The research results of this article can provide important guidance for the anti-fatigue design of welded joints in steel box girders with open longitudinal ribs. Full article

This paper investigates the shear performance of shear lugs commonly used in nuclear equipment foundations. A total of six groups of H-shaped steel shear lug specimens, six groups of angle steel shear lug specimens, and eight groups of steel plate shear lug specimens are designed and tested under horizontal shear loading. The failure modes, shear capacities, and deformation characteristics of the specimens are systematically examined. Furthermore, the influence of the embedment depth of the shear lug and the distance from the shear lug to the concrete edge on the shear performance of specimens is thoroughly analyzed. Based on the test results, equations for calculating the shear capacity of shear lugs are proposed. The result indicates that the failure modes of the three types of specimens under shear loading mainly show concrete shear breakout failure, and the changes in the embedment depth and concrete edge distance have a large effect on the shear capacity and ductility of the specimen. The proposed equations show good agreement with the test results, which can provide a theoretical foundation for the design of the shear lugs used in nuclear engineering. Full article

The tensile strength of loess, a key mechanical parameter for crack-related failures, has not received much attention in previous research, with the literature demonstrating a lack of systematic studies. Therefore, in this study, the variations in the tensile strength, crack distribution, crack number, and internal stress of an undisturbed loess were studied in detail by combining the unconfined penetration test (UPT) and a discrete element method (DEM)-based simulation. The tensile strengths of undisturbed loess samples with different height–diameter ratios (1, 1.5, and 2) were investigated by using the UPT with loading plates of different diameters (12.86 mm, 15.56 mm, and 19.02 mm). DEM simulation was then conducted based on the experimental results. The results showed that (1) the tensile strength of undisturbed loess decreased with increased height–diameter ratio, while it increased with an increase in the diameters of the loading plates; (2) the DEM simulation allowed us to study the tensile characteristics of the undisturbed loess, and the simulated tensile strengths obtained via DEM simulation agreed with those determined via the UPT; (3) the distribution of internal stress and crack number in the DEM model were significantly influenced by the height–diameter ratio and loading plate diameter; (4) the number of cracks in the DEM model increased with an increase in the diameter of the loading plate, while the number of cracks first increased and then decreased with an increase in the height–diameter ratio. This study helps us to understand the variation in the tensile strengths of undisturbed loess samples from both macroscopic and microscopic perspectives. It is expected to serve as a reference for design, construction, and maintenance in engineering projects hinging upon the Loess Plateau region in China. Full article

The intervertebral disc, an anatomical compartment interposed between vertebral bodies, plays a key role in spine flexibility and compression loading. It comprises three tissues: the nucleus pulposus, the annulus fibrosus, and the end plates. Degeneration-related changes in the extracellular matrix of the nucleus pulposus upon ageing or pathological conditions prompted the present investigation into the impact of proteoglycan reduction, the main constituent of the healthy nucleus pulposus, on its physicochemical properties and cellular phenotypical changes. To mimic the native extracellular matrix, three-dimensional NP-mimicking constructs were developed using a biomimetic hydrogel composed of collagen type I, collagen type II, and proteoglycans. This system was fabricated using a bottom-up approach, employing highly pure monomeric collagen types I and II, which were induced to form a reconstituted fibrillar structure closely resembling the natural NP microenvironment. A comprehensive physicochemical characterization was conducted at varying proteoglycan percentages using scanning electron microscopy (SEM), FTIR, rheological tests, and water retention property analysis. The effect of microenvironment changes on the phenotype of nucleus pulposus cells was studied by their encapsulation within the various collagen–proteoglycan hydrogels. The morphological and immunochemistry analysis of the cells was performed to study the cell–matrix adhesion pathways and the expression of the cellular regulator hypoxia-inducible factor 1 alpha. These were linked to the analysis of the synthesis of healthy or pathological extracellular matrix components. The findings reveal that the reduction in proteoglycan content in the nucleus pulposus tissue triggers a pathological pathway, impairing the rheological and water retention properties. Consequently, the cell phenotypes are altered, inducing the synthesis of collagen type I rather than securing the natural physiological remodelling process by the synthesis of collagen type II and proteoglycans. Identifying the proteoglycan content threshold that triggers these pathological phenotypical changes could provide new diagnostic markers and early therapeutic strategies for intervertebral disc degeneration. Full article

This study aimed to investigate the effect of the fatigue life enhancement of the rib-to-deck welded joints of orthotropic steel decks (OSDs) by extended peening treatment utilization. First, hammer peening was conducted around the weld bead of the test specimens of OSDs. It was found that the treatment on both the weld toes of the deck and the U-rib plates caused a deformation of the U-rib plate, i.e., peen forming. Then, fatigue tests were performed under R = 0.0, using an out-of-plane bending fatigue test machine by applying several magnitudes of pre-loadings, and the results showed that the specimens with peen forming had one JSSC class higher than the deck plate only. Finally, numerical simulations of peening treatment and peen forming were performed to reveal the reason for higher fatigue life enhancement by peen forming. Simulation results showed that peen forming would introduce about three times higher compressive residual stress at the weld root of the deck plate side than the peening treatment on the deck plate only, and induced compressive residual stresses around the weld root by peen forming were kept even after applying the pre-loadings. Therefore, it can be concluded that peen forming, as an extended peening treatment utilization, is highly effective in enhancing the fatigue life of OSDs. Full article

The purpose of this study was to estimate the peak stresses in a laser powder bed fusion (LPBF) additive-manufactured (AM) osteosynthesis plate during physiological loading and establish if the mechanical properties of LPBF titanium alloy were suitable for this use case. Finite element models of subject-specific osteosynthesis plates for a cohort of 28 patients were created and used to calculate the peak maximum principal stresses during physiological loading, which was estimated to be 166 MPa twelve weeks post-operatively. All specimens were LPBF additively manufactured in Ti-6Al-4V alloy. ISO compliant tests were performed for tensile and fatigue, respectively. Fatigue testing was performed for specimens that had been heat-treated only and those that had been heat-treated and polished. The Upper Yield Stress was 1012.5 ± 19.2 MPa. The fatigue limit was 227 MPa for heat-treated only specimens and increased to 286 MPa for heat-treated and polished specimens. The finite element predicted stresses were below the experimentally established limits of yield and fatigue. The tensile and fatigue properties of heat-treated LPBF Ti-6Al-4V are therefore sufficient to meet the mechanical requirements of osteosynthesis plates. Polishing is recommended to improve fatigue resistance. Full article

This study investigates the structural behavior of a sailing catamaran subjected to wind, wave, and self-weight loads, with the ultimate goal of improving the structural design through redrawing techniques. A digital model was developed using Creo software 6 and analyzed through Finite Element Analysis (FEA), complemented by experimental deformation tests conducted under dry conditions and controlled loading. These tests provided a reliable dataset for calibrating and validating the numerical model. The analysis focused on the structural responses of key components—such as bulkheads, hulls, and beam-to-hull connections—under both isolated as well as combined load scenarios. Most structural elements demonstrated low deformation, confirming the robustness of the design; however, stress concentrations were observed at the connecting plates, highlighting areas for improvement. The vessel’s overall stiffness, though advantageous for structural integrity, was identified as a constraint in weight redrawing efforts. Consequently, targeted structural modifications were proposed and implemented, resulting in reduced material usage, construction time, and overall costs. The study concludes by proposing the integration of advanced composite materials to further enhance performance and efficiency, thereby laying the groundwork for future integration with digital and structural health monitoring systems. Full article

The wide-spread application of carbon fiber-reinforced polymer (CFRP) composites in industrial fields has led to high demand for developing a rapid detection method for assessing the structural performance of CFRP composites in operation based on optical fiber sensing technology. Therefore, the effectiveness and reliability of evaluating the fatigue resistance of CFRP plates based on fiber Bragg grating (FBG) monitoring information were explored. The strain response of CFRP plates at key positions under constant amplitude fatigue load was monitored by bare FBGs in series and packaged quasi-distributed FBGs in series. The structural performance and fatigue resistance characteristics of CFRP plates were evaluated by statistical analysis and fatigue life prediction theory. The validity and accuracy of the test and analysis results were demonstrated by finite element modeling analysis. Compared with the traditional methods that evaluate the structural fatigue performance based on mass destructive experiments, this method significantly improves the detection efficiency and realizes the non-destructive and rapid online evaluation of structural service performance. Research shows that the designed FBG sensors can effectively monitor the strain response of CFRP plate under fatigue load, and the correlated fatigue algorithm can provide feasible and reliable technical approaches for online detection and evaluation on the structural performance of CFRP components. Full article