Search Results (671)

Steel frame infilled with composite plate shear wall (SF-CPSW) is an effective structure for lateral-load resisting. In the structural design, the vertical loads are primarily carried by the boundary SF, while the horizontal loads are expected to be totally carried by CPSW. CPSW incorporates the steel web and the concrete encasements. For the CPSW bays, the boundary SF also inevitably withstands the lateral-loads due to the coordinated deformations between boundary SF and CPSW. The available researches, however, have not given a certain shear force assignment between the boundary SF and CPSW. Furthermore, their interactions under the cyclic lateral-loading are unclear. This paper conducted a study on the load-resisting mechanism of SF-CPSW by a structural model test and finite element analyses. The deformation pattern, failure mode, internal forces, and interactions of structural members were investigated. The effects of steel web and concrete thicknesses, cross-sections of boundary SF, and axial compression ratio on the lateral-load resistance of SF-CPSW were assessed. The results indicated that the interactions of CPSW and boundary SF caused significant normal stresses at the corners of CPSW, reducing the shear strength of steel web. However, the concrete encasements and boundary SF compensate it and mutually improved the stiffness and ductility. According to the analysis results, the formulas of the lateral stiffness and strengths of SF-CPSW were proposed for its seismic design. Full article

As part of this study, mechanical property tests were carried out at different stages with different curing temperatures to elucidate the effect of temperature on the mechanical properties of concrete. The curing temperatures were laboratory curing temperature (standard curing at 20 °C) and variable temperature curing (simulated site ambient temperature curing) according to the actual temperature of previous construction sites. The compressive strength, split tensile strength, axial tensile strength, and modulus of elasticity values were tested, and the growth rates were calculated. According to previous experiments, the maturity indexes under two kinds of maintenance conditions were calculated based on the N-S maturity formula, F-P equivalent age calculation formula, and D-L equivalent age calculation formula proposed by the maturity theory. Moreover, logarithmic function, exponential function, and hyperbolic function fitting were carried out using the fitting software to study the developmental relationship between strength and maturity. The physical phase analysis of low-heat cement was performed using XRD and simultaneous thermal analysis, and pore structure analysis was conducted using the mercuric pressure method (MIP). We also conducted an SEM analysis of hydration products and the micromorphology of low-heat cement with 25% fly ash. Energetic spectroscopy analyzed the elemental content. In this study, it was found that temperature has a significant effect on the mechanical properties of concrete, with temperature having the greatest effect on splitting tensile strength. The strength of low-heat silicate cement concrete increases with maturity. The highest correlation coefficient was based on the hyperbolic function fit in the F-P equivalent age. The improved development of concrete strength in the later stages of the two curing conditions in this test indicates that low-heat cement is suitable for use in hydraulic tunnels. The low-heat cement generates a large number of C-S-H gels via C₂S in the late stage, filling the internal pores, strengthening the concrete densification to make the structure more stable, guaranteeing the late development of concrete strength, and imparting a micro-expansive effect, which is effective for long-term crack resistance in hydraulic lining structures. Full article

This paper proposes a hybrid steel plate–bolt dry and wet jointing method, where the dry jointing part is a steel plate–bolt connector joint and the wet jointing part is a cast-in-place concrete. The novel precast concrete shear wall (PCW) combines the advantages of both dry and wet connections. A steel plate–bolt dry–wet hybrid connection shear wall model was developed using the finite element method, and a low circumferential reciprocating load was applied to the PCW. By analyzing the force and deformation characteristics of the wall, the results showed that the failure mode of novel PCWs was bending-shear failure. Compared to the concrete wall (CW), the yield load, peak load, and ductile displacement coefficient were 6.55%, 7.56%, and 21.49% higher, respectively, demonstrating excellent seismic performance. By extending the wall parameters, it was found that the increased strength of the novel PCW concrete slightly improved the load-bearing capacity, and the ductility coefficient was greatly reduced. As the axial compression ratio increased from 0.3 to 0.4, the wall ductility decreased by 22.85%. Increasing the reinforcement rate of edge-concealed columns resulted in a severe reduction in ultimate displacement and ductility. By extending the connector parameters, it was found that there was an increased number of steel joints, a severe reduction in ductility, enlarged distribution spacing, weld hole plugging and bolt yielding, reduced anchorage performance, and weakening of the steel plate section, which reduced the load-bearing capacity and initial stiffness of the wall, with little effect on ductility. Full article

This study aims to explore the mechanical behavior of Desert Sand Concrete (DSC) under freeze–thaw (F-T) cycles. By adjusting the number of F-T cycles, the research analyzed the impact of various desert sand replacement ratios on the frost resistance of concrete. The study focused on the dynamic changes in mass loss of concrete specimens, relative dynamic elastic modulus, cubic compressive strength, splitting tensile strength, and axial compressive strength. Scanning electron microscopy was employed to analyze the micro-morphology of specimens after F-T cycles. This analysis aimed to predict the service life of DSC and provide practical recommendations for the maximum compressive strength loss rate within the designed service life. The results indicated that although the frost resistance of DSC was similar to that of ordinary concrete before 50 F-T cycles, it subsequently exhibited a nonlinear degradation trend correlated with increasing desert and replacement ratios, with both frost resistance and compactness reaching optimal levels at a 40% replacement rate. Additionally, the F-T damage model proposed in this study demonstrated high applicability and fitting accuracy. This model provided effective theoretical support for understanding and predicting the mechanical behavior of DSC. Full article

In order to investigate the lateral working performance of large-scale steel casing-reinforced concrete pile composite members, this paper sets up large-scale steel casing-reinforced concrete pile composite members with different slenderness ratios λ, compressive axial force ratios N, and foundation strengths. It conducts quasi-static loading tests to investigate the effects of these factors on the hysteretic performance, bearing capacity, ductile performance, strength degradation, and stiffness degradation of the members. The results show that the hysteresis curves of the members all have a typical inverse S-shape, which is affected by slip and has a poor degree of fullness. The members with larger slenderness ratios exhibit better ductility performance, deformation performance, and energy dissipation performance, but their poorer bearing capacity and effect on stiffness degradation are limited. While members with smaller slenderness ratios exhibit better bearing capacity, their ductile performance is poor. As the compressive axial force ratio increases, the lateral bearing capacity and ductility of the members slightly improve. However, the bearing capacity rapidly decreases when the compressive axial force ratio reaches a critical value. As the strength of the foundation increased, the lateral bearing capacity of the structures continued to improve, but its improvement effect began to decay after reaching a certain value. This paper investigates the lateral working properties of large-scale steel casing-reinforced concrete pile composite members designed for overhead vertical wharves that are subjected to significant water level differences in inland rivers, aiming to provide a reference for their application in practical engineering. Full article

Three-dimensional printing is a highly promising manufacturing technology that enables easy production of complex shapes. Composite lattice structures are highly efficient, having the advantages of fiber-reinforced composites and the excellent structural performance of lattice configurations. Highly efficient structures can be developed by combining the benefits of 3D printing and composite lattice structures. This study examined the effect of printing path and axial angle in joint areas on the compressive strength of composite lattice unit cells fabricated via continuous fiber 3D printing. Compression tests were conducted to analyze deformation, failure modes, and causes of failure. A finite element model was used to analyze buckling behavior and establish design criteria. Results showed that the printing path significantly influenced failure mode and strength, while a fabrication method without a defect at the joint was important for improving structural performance. Finally, design criteria, in terms of the knockdown factor and in-plane bifurcation buckling behavior, were developed based on experimental and numerical results. Full article

Coal gangue, representing an industrial waste with the highest annual emissions and largest cumulative stocks worldwide, urgently requires resource utilization. This article uses mixed coal gangue aggregates (spontaneous-combustion coal gangue aggregate (SCGA) and rock coal gangue aggregate (RCGA)) as the research subject. The aim is to solve the technical problem of producing high-performance concrete with gangue instead of coarse aggregate. The research investigates the impact of various strength grades (C20, C30, C40, C50) and aggregate replacement ratios (0%, 20%, 40%, 60%, 80%, 100%) on the compressive strength of concrete. It explores the mechanical behaviors and properties of concrete mixed with coal gangue and develops a predictive model for its elastic modulus. The results show that (1) as the substitution rate of aggregates increases, the elastic modulus and compressive strength of the mixed coal gangue concrete significantly decrease. When the substitution rate is 100%, the elastic modulus and compressive strength of C30 concrete decrease by 3.5% and 11.3%, respectively, and the higher the grade, the more significant the reduction. For C50 concrete, the elastic modulus and compressive strength decrease by 10% and 35%, respectively. (2) A regression equation has been formulated to delineate the relationship between the compressive strength and axial compressive strength of mixed coal gangue concrete, taking into account the mix ratio of coal gangue and the compressive strength of standard concrete. This equation elucidates the correlation between the mechanical properties of concrete with varying coal gangue mix ratios and ordinary concrete across different strength grades. (3) Based on the correlation between elastic modulus and compressive strength, a prediction model for the elastic modulus of mixed gangue concrete was established, which effectively improved its prediction accuracy. Full article

This study evaluates four compression testing methods to determine the most reliable and reproducible technique for assessing the compression strength of murine lumbar vertebral bodies. Twenty female C57BL/6 mice (12 weeks old) were randomized into four groups: Group 1, compression of the complete lumbar vertebral body (LVB) with dorsal spinal processes; Group 2, compression at the vertebral body surface; Group 3, compression at the vertebral body surface after vertebral arch resection; Group 4, resection of the vertebral arch with straightening of the intervertebral joint surface. A mono-axial static testing machine applied compression, measuring load to failure, stiffness, yield load, and elasticity modulus. Method 1 resulted in significantly higher load-to-failure and yield-to-failure (25.9 N compared to 18.2 N, and twice 12 N for Methods 2–4), with the least variation in relative values. Method 3 had increased stiffness and a significantly higher Young’s modulus (232 N/mm, in contrast to 101, 130, and 145 N/mm for Methods 1, 2, and 4, respectively) but yielded inconsistent results. Method 4 showed the greatest variability across specimens. Method 2 yields suitable data quality as well, albeit with a slightly higher variation, and is the recommended procedure if the spinal processes have to be excluded from the measurement. Based on these findings, Method 1 produced the most consistent and reproducible data and is recommended for future studies evaluating vertebral biomechanics in mice. Full article

This study investigates the buckling performance of built-up cold-formed steel (CFS) columns, with a focus on how different thermal exposures and cooling strategies influence their susceptibility to various failure mechanisms. Addressing the gap in the literature on the fire behavior of mild steel (MS)-based CFS columns, the research aims to provide new insights. Compression tests were conducted on MS-based CFS column specimens after they were exposed to fire, to assess their post-fire buckling strength. The columns were subjected to controlled fire conditions following standardized protocols and then allowed to cool to room temperature. The study examined axial load-bearing capacity and deformation characteristics under elevated temperatures. To improve fire resistance, protective coatings—gypsum, perlite, and vermiculite—were applied to certain specimens before testing, and their performance was compared to that of uncoated specimens. A comprehensive finite element analysis (FEA) was also performed to model the structural response under different thermal and cooling scenarios, providing a detailed comparison of the coating effectiveness, which was validated against experimental results. The findings revealed significant variations in axial strength and failure mechanisms based on the type of fire-resistant coating used, as well as the heating and cooling durations. Among the coated specimens, those treated with perlite showed the best performance. For example, the air-cooled perlite-coated column (MBC2AC) retained a load capacity of 277.9 kN after 60 min of heating, a reduction of only 6.0% compared to the unheated reference section (MBREF). This performance was superior to that of the gypsum-coated (MBC1AC) and vermiculite-coated (MBC3AC) specimens, which showed reductions of 3.6% and 7.9% more, respectively. These results highlight the potential of perlite coatings to enhance the fire resistance of CFS columns, offering valuable insights for structural fire design. Full article

This study investigates the potential of cement-less recycled aggregate concrete (C.R.A.C.) as an eco-friendly alternative to traditional ordinary Portland cement (OPC) concrete, using industrial waste (fly ash) and construction and demolition waste (recycled coarse aggregates). This research explores the effects of mixes of varying sodium hydroxide (NH) molarities and percentage substitutions of natural coarse aggregates (N.C.As.) with recycled coarse aggregates (R.C.As.) on the mechanical properties of C.R.A.C. A total of eighteen ambient-cured C.R.A.C. mixes, using Thar Coal fly ash with varying NH molarities (12 M, 14 M, and 16 M), and percentage substitutions of N.C.As. with R.C.As. (0%, 20%, 40%, 60%, 80%, and 100%), were prepared and tested under axial compression and flexure. It was observed that the compressive strength increased by about 76% with an increasing NH molarity, whereas the compressive strength decreased by about 52.9% with an increasing percentage substitution of N.C.As. with R.C.As. The flexural strength increased by about 78.3% with an increasing NH molarity, whereas the flexural strength decreased by about 50.5% with an increasing percentage substitution of N.C.As. with R.C.As. The SEM analysis of the C.R.A.C. mixes highlighted the heterogeneous morphology of fly ash particles (e.g., irregular shape, rough surface texture, and porous regions), which negatively influenced the overall performance of the concrete matrix. The environmental assessment exhibited that the C.R.A.C. mixes exhibited about 45% lower CO₂ emissions than OPC concrete; however, the cost of the C.R.A.C. mixes was about 21% higher than that of OPC concrete mixes. Full article

Engineers commonly use the 28-day characteristic strength of concrete for project calculations, but this may not reflect the full-strength potential, especially in concretes with supplementary cementitious materials (SCMs). SCMs, known for their slow reactivity, often delay optimal strength beyond 28 days, requiring higher cement content to speed up early strength development, thus increasing production costs. This study examined the relationship between concrete age and mechanical strength across eight cement types, including tests for axial compression, water absorption, void index, and specific mass. The findings showed that pozzolan and slag cements gained significant long-term strength due to slow pozzolanic reactions. Conversely, limestone filler mixes had lower initial strength and slower progress, likely due to increased porosity from fine fillers. A correlation was found between higher pozzolan content and improved durability, including reduced water absorption and void index. Cost analysis indicated that optimizing cement mix designs for targeted strength levels could reduce production costs, especially for concretes with high SCM content. Using long-term characteristic strength rather than the traditional 28-day strength resulted in approximately 14% savings, particularly for slag- and pozzolan-based cements. The savings were less significant for other cement types, emphasizing the importance of adjusting mix designs based on both performance and financial considerations. Full article

Traditional monolithic precast and precast prestressed concrete joints often face challenges such as complex steel reinforcement details and low construction efficiency. Grouting sleeve connections may also suffer from quality issues. To address these problems, a new precast prestressed concrete frame beam-column exterior joint using ultra-high-performance concrete (UHPC) for connection (PPCFEJ-UHPC) is proposed. This innovative joint lessens the amount of stirrups in the core area, decreases the anchorage length of beam longitudinal reinforcement, and enables efficient lap splicing of column longitudinal reinforcement, thereby enhancing construction convenience. Cyclic loading tests were conducted on three new exterior joint specimens (PE1, PE2, PE3) and one cast-in-place joint specimen (RE1) to evaluate their seismic performance. The study concentrated on failure modes, energy dissipation capacity, displacement ductility, strength and stiffness degradation, shear stress, and deformation’s influence on the longitudinal reinforcement anchoring length and axial compression ratio. The results indicate that the new joint exhibits beam flexural failure with minimal damage to the core area, unlike the cast-in-place joint, which suffers severe core area damage. The novel joint exhibits at least 21.7% and 6.1% improvement in cumulative energy consumption and ductility coefficient, respectively, while matching the cast-in-place joint’s bearing capacity. These characteristics are further improved by 5.5% and 10.7% when the axial compression ratio is increased. The new joints’ seismic performance indices all satisfy the ACI 374.1-05 requirements. Additionally, UHPC significantly improves the anchoring performance of steel bars in the core area, allowing the anchorage length of beam longitudinal bars to be reduced from 16 times of the diameter of reinforcement to 12 times. Full article

A novel L-shaped concrete-filled steel tube (CFST) column is proposed in this study. A finite element model of the column is developed using ABAQUS software to analyze its load transfer mechanism and axial compressive behavior. The effects of factors such as the steel strength, steel tube thickness, support plate configuration, and perforation of the support plates on the compressive performance of the column are investigated. The simulation results reveal that the column exhibits robust axial compressive performance. Increasing the steel strength and incorporating support plates (SP) effectively enhance the column’s compressive bearing capacity and positively influence the bearing capacity coefficient (δ). However, increasing the steel tube thickness results in a reduction in δ, indicating that the rate of increase in the bearing capacity diminishes with increasing thickness. The failure mode is primarily characterized by local buckling in the midsection of the steel tube’s concave corner. Measures such as increasing the steel strength and tube thickness and the use of support plates help to mitigate buckling at the concave corner, improve concrete confinement, and enhance the overall compressive performance of the column. Full article

Gassy soil is prevalent in coastal regions, and the presence of gas bubbles can significantly alter the mechanical properties of soil, potentially leading to various marine engineering geological hazards. In this study, a series of triaxial tests were conducted on fine-grained gassy soils under different consolidation pressures (p_c’), stress paths, and initial pore water pressures (u_w0). These tests were also used to verify the applicability of a newly proposed constitutive model. According to the test results, the response to excess pore pressure and the stress–strain relationship of fine-grained gassy soils strongly depend on the initial pore water pressure (u_w0), with the degree of variation being influenced by the consolidation pressure (p_c’) and stress path. As u_w0 decreases, the undrained shear strength (c_u) of fine-grained gassy soils gradually increases, and this is lower under the reduced triaxial compression (RTC) path compared to the conventional triaxial compression (CTC) path, which can be attributed to the destruction of the pore structure due to an increase in gas volume. The newly proposed model accurately predicts the pore pressure and stress–strain relationship of fine-grained gassy soils at low consolidation pressures (p_c’), but it falls short in predicting the mechanical behavior during shear progression under high p_c’ or the RTC path. Although the model effectively predicts the excess pore pressure and deviator stress at the shear failure point (axial strain = 15%), further improvement is still required. Full article

Precast concrete is an advanced construction technique characterised by high precision, quality, optimisation and is increasingly used in commercial and residential buildings. However, connections between precast elements are often constructed using in-situ casting, which can delay projects and complicate disassembly at the end of a structure’s service life. Dry connections, aligned with the principles of manufacture-to-assemble (MTA), offer a practical and sustainable alternative but present significant challenges regarding seismic performance, particularly in earthquake-prone regions. This study addresses these challenges through a comprehensive parametric numerical investigation into the shear capacity of precast walls with dry connections. Using SeismoStruct 2024 software, more than 340 pushover simulations were conducted to evaluate the influence of various parameters, including concrete compressive strength, axial force percentage, wall section height, overall wall height, and connection characteristics such as bar diameter, quantity, and placement. This research provides critical insights into the combined effects of these parameters, identifying optimal configurations to maximise shear capacity, which is a vital factor for seismic performance. Key findings indicate that shear capacity is significantly enhanced by increasing section height, concrete strength, and axial load, with notable gains such as an 84% improvement in shear strength when section height increased from 2 m to 3 m under favourable conditions. Conversely, increasing overall wall height tended to reduce shear capacity, with a 58% decrease observed for walls extending from 1.5 m to 3.5 m. Adjustments in mechanical connections, including larger diameters, increased bar quantities, and optimised placements, further contributed to incremental improvements in shear strength, with increases ranging from 3% to 24%. Full article