Search Results (340)

This study investigates the residual web crippling behavior of pultruded glass fiber-reinforced polymer (P-GFRP) hollow sections after exposure to elevated temperatures. The primary objective is to evaluate the combined influence of temperature and loading configuration on web crippling capacity, failure mechanisms, and structural performance, and to develop practical prediction models for engineering applications. A total of twenty pultruded GFRP hollow section specimens were exposed to temperatures of 24 °C, 200 °C, 250 °C, 300 °C, and 350 °C and tested under four loading configurations: End Ground (EG), Interior Ground (IG), End Two Flange (ETF), and Interior Two Flange (ITF). In addition to web crippling tests, tensile, SEM-EDS, TGA-DSC, DMA, and FT-IR analyses were conducted to investigate the mechanical, thermal, and microstructural degradation mechanisms. The results showed that elevated temperatures significantly reduced the web crippling capacity, with strength losses reaching up to 80% at 350 °C due to matrix degradation, fiber–matrix debonding, and loss of structural integrity. Among the investigated loading configurations, IG exhibited the highest load-carrying performance, whereas ETF experienced the greatest capacity reduction. A temperature-dependent reduction factor and unified empirical prediction equations were developed and demonstrated good agreement with the experimental results, with experimental-to-predicted ratios ranging from 0.97 to 1.15. The findings provide valuable insight into the post-fire behavior of pultruded GFRP hollow sections and offer practical guidance for the design, assessment, and fire safety evaluation of GFRP structural members exposed to elevated-temperature environments. Full article

Large-diameter rescue shafts serve as critical infrastructure for emergency response in mining disaster scenarios, and their structural deformation directly affects the safe passage of rescue capsules. In this paper, we investigate three-dimensional (3D) reconstruction techniques for large-diameter rescue shaft environments and develop a Neural Radiance Fields (NeRF)-based reconstruction and deformation assessment scheme. The proposed workflow integrates no reference signal-to-noise-ratio (NR-SNR), image-quality filtering, SfM-based camera-pose estimation, Nerfacto reconstruction, point-cloud export, and circular-section fitting. The NR-SNR retention-ratio experiment shows that retaining approximately 35% high-quality images provides a practical efficiency–quality trade-off for the present dataset, reducing the computational burden of SfM pose estimation while preserving sufficient geometric information for subsequent reconstruction. The reconstructed radiance field is further exported as a dense point cloud and evaluated using relative radius error, circle-fitting residuals, and image-level rendering metrics. Experiments on a simulated large-diameter rescue shaft platform show that the proposed NeRF-based scheme provides favorable geometric measurement applicability and visual reconstruction quality under weak-texture and low-illumination conditions. Compared with conventional MVS and the tested 3DGS baseline, the proposed scheme produces a point-cloud output that is more suitable for subsequent circular-section fitting and deformation-related assessment. In addition, comparison with a representative SDF-based baseline indicates that direct implicit surface recovery remains challenging for the tested hollow cylindrical shaft-wall scene. The results demonstrate the potential of the proposed NeRF-based workflow for rescue-shaft inner-wall reconstruction and engineering-oriented deformation evaluation. Full article

A hollow steel structure with a hat cross-section was axially compressed under impact or quasistatic conditions. The hat height and hat width were 40 mm. The thickness was 0.6, 0.8, and 1.0 mm. The effect of the reinforcing member attached to the main structure on the collapse behavior was experimentally investigated. The formation of buckling lobes was observed, and the energy absorption performance was evaluated. The addition of the internal reinforcing member achieved increased compressive force, exhibiting a stepped force variation. This step became more pronounced as the wall thickness increased, and it was larger under impact conditions. When the height of the reinforcing member was 20 mm, or the hollow shape is square, a higher crush strength was achieved, with a very regular collapse pattern. To explain the increase in compressive force by using the reinforcing member, the deformation energy was calculated by considering the deformed shapes and the mechanical properties of the material. The calculated increase ratio of 3.18 was comparable with the experimental result of 3.54. The strain measurement at the hat top of the structure during the initial compression revealed that the damage, where the strain level is greater than 0.003, was successfully delayed at the reinforced section in the partially reinforced structure. Full article

Prestressed centrifugal concrete hollow square piles often require on-site splicing, and the structural reliability of the pile connection largely governs the performance of the assembled pile. To address the limitations of conventional welded and mechanical joints, a section steel plug-in composite joint combining central grouted steel tube anchorage and peripheral end-plate welding was developed and experimentally evaluated. Flexural and shear tests were conducted on 12 full-scale specimens, including pile shaft specimens and joint specimens with cross-sectional side lengths of 400, 500, and 600 mm. The flexural and shear behavior of the jointed specimens was assessed in terms of bearing capacity, load–deflection response, crack development, and failure mode by comparison with the corresponding pile shafts. Under flexural loading, the pile shaft specimens mainly failed by fracture of prestressing steel bars at midspan, whereas the joint specimens failed near the loading point by prestressing steel fracture, indicating that the critical failure region shifted away from the joint core. The flexural capacities of the joint specimens reached about 92–97% of those of the corresponding pile shafts. Under shear loading, both pile shaft and joint specimens mainly exhibited diagonal compression failure in the flexural–shear region, while no obvious damage was observed in the joint core region. The shear capacities of the joint specimens were about 103–130% of those of the corresponding pile shafts. These results indicate that the proposed section steel plug-in composite joint can effectively maintain flexural resistance while enhancing shear performance. The central steel tube, hardened grout, anchorage reinforcement, and peripheral welds jointly contributed to the integrity and force transfer capacity of the connection, showing favorable potential for engineering application in prestressed centrifugal concrete hollow square pile splicing. Full article

High-performance fiber-reinforced cementitious composite (HPFRCC) has shown considerable potential as a strengthening material for improving the crack resistance, integrity, and deformation capacity of masonry structures. In aging concrete hollow block masonry walls subjected to long-term eccentric compression, material degradation may lead to premature cracking, local crushing, stiffness deterioration, and reduced safety margins, thereby adversely affecting structural reliability and service performance. However, studies on the eccentric compression behavior of HPFRCC-strengthened concrete hollow block masonry walls with simulated material degradation remain limited. In this study, experimental, finite element, and theoretical analyses were conducted on three HPFRCC-strengthened specimens with an eccentricity ratio of 0.5y, namely a 30 mm double-sided strengthened specimen, a 45 mm double-sided strengthened specimen, and a 30 mm single-sided strengthened specimen. The failure modes, load–displacement responses, lateral deformation, strain development, and DIC strain distribution characteristics were investigated. The results showed that, under the test conditions considered in this study, the double-sided strengthened specimens exhibited higher load-bearing capacity, greater stiffness, and better structural integrity than the single-sided strengthened specimen. Among them, the 45 mm double-sided strengthened specimen reached the highest peak load of 1643 kN, whereas the 30 mm double-sided strengthened specimen exhibited a gentler post-peak response, more dispersed crack development, and better deformation compatibility. The finite element results were generally consistent with the experimental results; the ratios of the experimental to numerical peak loads ranged from 0.96 to 1.01, while the corresponding peak displacement ratios ranged from 1.02 to 1.09. Within the parameter range considered in the numerical analysis, increasing the strengthening thickness was generally beneficial to the eccentric compression capacity. The proposed preliminary sectional bearing capacity model showed acceptable agreement with the test results for the specimens considered in this study; however, its broader applicability requires further validation using additional specimens. Full article

Limit state analysis provides building designers with a better understanding of fundamental structural resistance and deformation requirements, resulting in an overall material economy and offering clear safety boundary conditions for intelligent structural design. Cold-formed high-strength steel has extensive application prospects in structural engineering due to its excellent mechanical properties and flexible cross-sectional options. However, most existing research focuses on its ultimate strength-related behavior, lacking sufficient investigation into deformation properties. This study aims to comprehensively reveal the continuous variation laws of structural resistance and ductility of cold-formed high-strength CHSs (circular hollow sections) with different cross-sectional selections under axial load. Through reliable finite element analysis, the effects of yield strength (f_sy) of cold-formed CHSs, diameter-to-thickness ratio (D/t), and cross-sectional slenderness (λ) on compressive performance in the limit state, including failure mode, axial load-end shortening curve, ultimate-to-yield strength ratio (N_u/N_y), and ductility indicators (displacement ductility coefficient (μ) corresponding to the ascending stage and post-buckling ductility degradation coefficient (R_0.85)), were systematically investigated. The results indicate that the dominant failure mode of high-strength CHSs exhibits outward deformation. With an increase of f_sy and D/t, the value of N_u/N_y decreases, and the development of multiple compression performance exhibits significant nonlinearity, which indicates that blindly improving material strength may not necessarily be conducive to developing structural compressive performance or achieving efficient and economical design solutions. To better serve the ductile limit design of high-strength CHSs, combined with available experimental data and simulation results, the upper limit of λ is proposed to be 0.22, and the predictive models of μ and R_0.85 are established, respectively. Full article

Welding is one of the key joining routes for expanding the engineering applications of dissimilar magnesium alloys. However, after experiencing rapid non-equilibrium heating and cooling cycles, the heat-affected zone (HAZ) of a welded joint tends to undergo grain coarsening as well as dissolution or agglomeration of precipitates, and therefore becomes the region most susceptible to failure. In this study, 3 mm thick sheets machined from AZ61A and AZ80A magnesium alloy hollow sections were joined by metal inert gas welding (MIG). Different ranges of welding heat input were obtained by combining multiple sets of welding parameters, in order to further tailor the HAZ of dissimilar magnesium alloy joints and achieve sound weld quality. The results showed that the joint exhibited the best overall mechanical performance at 523 J·mm⁻¹, with an ultimate tensile strength, yield strength, and elongation of 292 MPa, 172 MPa, and 5.4%, respectively. All fractures occurred in the HAZ on the AZ61A side. Under this condition, the second phases in the HAZ were more finely and uniformly dispersed, with a volume fraction of 3.19%, an average size of 2.51 μm, and a minimum average grain size of 23.65 μm. Full article

Concrete building systems require decisions at both the member and the building level, because locally efficient cross sections do not necessarily lead to a favorable whole-building response. This study presents a two-level comparative framework comprising (i) a member-level parametric assessment of nine reinforced-concrete and composite cross-section families across six concrete grades (54 scenarios) and (ii) a building-level ETABS assessment of seven structural configurations (Models A–G) derived from a residential reinforced-concrete frame benchmark. At the member level, the alternatives were evaluated based on axial resistance, along with simplified screening-level CO₂ and cost proxies. At the member level, axial resistance increased with concrete grade, although the marginal benefit diminished at higher grades for steel-dominant layouts. Balanced composite sections showed the most favorable normalized strength-to-material-proxy trends, whereas steel-heavy alternatives provided high absolute resistance but lower overall efficiency. The comparison between the member-level hybrid-section screening and the building-level composite configuration further showed that promising local section behavior does not automatically translate into superior whole-building performance. At the building level, the compared configurations were assessed through vertical base reactions, modal properties, and top-level lateral displacement response. Replacing solid beams and columns with hollow members of identical outer dimensions reduced the self-weight-related base reaction from 9591 to 8832 kN (7.9%) but slightly increased the top-level displacement response, indicating a mass–stiffness trade-off. Larger improvements were obtained when the global lateral-force-resisting mechanism was modified directly: the braced configuration produced the shortest fundamental period ($T_1=0.433$ s) and the lowest displacement response, while the core-wall configuration also reduced both period and displacement substantially. By contrast, the height-extended configuration produced the most flexible response among Models A–F. An additional exploratory variant with semi-rigid beam-to-column connections (Model G) confirmed that connection-level flexibility produces a measurable but moderate increase in period and displacement relative to the reference frame, without altering the global load-resisting mechanism. Overall, the results confirm that member-level and building-level assessments should be treated as complementary decision levels in early-stage structural design. Full article

In this work, the focus is laid on the mean stress effect on the fatigue strength of thin-walled rectangular hollow section T-joints made of high-strength steel S960 M x-treme. The specimens are cyclically tested at a stress ratio of R = −1 and R = 0.1 in both as-welded and ground (weld-profiled) conditions. In the context of nominal stress evaluations, the ground specimens demonstrate a distinct advantage in contrast to the as-welded condition, exhibiting an increase of +33% at R = 0.1 and +16% at R = −1. Based on the experimental results, a corresponding Haigh diagram is evaluated, revealing a notable difference in the mean stress sensitivity, with M₁ = 0.58 for the as-welded condition and M₁ = 0.39 for the ground condition. Finally, mean stress factors are presented, enabling feasible application in the fatigue design of welded and post-treated structures. The resulting factors are compared with values from the literature for steel applications, showing an increased mean stress influence using high-strength steel as the base material. Full article

This study proposes a novel parameterized hollow spiral lattice (HSL) structure designed for additive manufacturing (AM). The structure is composed of two right-handed and two left-handed spiral members. Its unit cell is formed by sweeping a circular ring cross-section along a cylindrical helical path, creating a porous topology that integrates continuous flow channels with structural load-bearing capability. An analytical model correlating key design parameters, including spiral radius, helix angle, and tube inner/outer diameters, with the structural relative density is established. Considering the manufacturability constraints of Laser Powder Bed Fusion (LPBF), an adaptive parametric design framework is developed to simultaneously optimize the geometry, relative density, and process feasibility. Ti6Al4V HSL samples were fabricated using LPBF. Their thermo–mechanical performance was systematically characterized through Computational Fluid Dynamics (CFD) simulations, Finite Element Analysis (FEA), and quasi-static compression experiments. Thermal analysis under internal and internal–external flow conditions reveals that the centrifugal force induced by the spiral geometry generates Dean vortices. This enhances momentum exchange between the central mainstream and near-wall fluid, significantly improving radial mixing, promoting temperature uniformity, and effectively suppressing local hot spots. Mechanically, the HSL exhibits significantly superior specific strength and stiffness compared to traditional body-centered cubic (BCC) and diamond lattices, approaching the performance of cubic topology, thus demonstrating outstanding lightweight load-bearing potential. The developed HSL structure presents a promising innovative design strategy for next-generation applications requiring integrated thermal management and structural load-bearing functions. Full article

Periodic lattice materials exhibit tunable mechanical properties, yet the impact of non-cylindrical, non-circular strut cross-sections on crashworthiness remains largely unexplored. This study extends the concept of shape transformers—dimensionless ratios representing the area and second moment of area of a strut cross-section relative to its enclosing envelope—to two canonical lattice topologies: the octet and rhombic dodecahedron topologies (stretching-dominated and bending-dominated, respectively). Eleven distinct cross-sectional shapes (solid and hollow circular, diamond, and square) were systematically varied under constant area and constant envelope conditions to isolate microscale geometric effects on macroscopic impact response. Results demonstrate that adjusting Ψ_i alone can enhance specific energy absorption by up to 62% in bending-dominated lattices (compared to 18% in stretching-dominated lattices). Furthermore, the influence of geometric efficiency (λ = Ψ_i/Ψ_a) on plateau stress and energy absorption trends across topologies has been quantified. These findings establish shape transformers as significant design parameters for crashworthy lattice materials, and design charts are presented to facilitate the development of additive-manufactured cellular structures aimed at optimized energy absorption performance. Full article

The stability of retained roadways in closely spaced coal seams beneath a goaf is strongly affected by complex stress redistribution and the deterioration of roof structures under downward mining conditions. To address this issue, a combined approach involving theoretical analysis, numerical simulation, and field monitoring was adopted to investigate the deformation characteristics and stability control of gob-side retained roadways in short-distance coal seam groups. The movement characteristics of the roof and the deformation law of surrounding rock of the retained roadway under downward mining were revealed. An embedded short-arm beam structural model for a roof cutting retained roadway was established, and a calculation method for determining the required support resistance of the retained roadway was proposed. Based on this model, design criteria for the passive support system of the retained roadway were developed. A surrounding rock control technology with hollow grouting anchor cable support and low-disturbance directional roof cutting as the core was proposed, and the support resistance of a one-beam–four-column support system was determined to effectively limit roof subsidence. Field application results show that the surrounding rock displacement was controlled within 350 mm, and the roadway section shrinkage rate was maintained at 16.4%, indicating good stability of the retained roadway and satisfying the requirements of ventilation and transportation. This study provides a mechanical basis and practical guidance for stability control and support design of roof cutting retained roadways in closely spaced coal seams beneath goaf. Full article

To investigate the mechanical behavior and load-carrying capacity calculation methods of square concrete-filled steel tube (SCFST) members under biaxial eccentric tension, an experimental program was designed and conducted involving three square hollow steel tube members and six SCFST members subjected to biaxial eccentric tensile loading. The key parameters considered in this study include concrete strength, eccentricity, and eccentric angle. The failure processes and modes of the members were carefully observed and documented. Based on the experimental measurements, the load–displacement curves, load–strain curves, and moment–rotation curves were obtained for all tested members. The test results demonstrated that SCFST members exhibited superior mechanical performance under biaxial eccentric tension. Although the concrete in the tensile zone did not directly bear external loads after cracking, the interaction between concrete and steel tube significantly enhanced both the load-carrying capacity and stiffness of the members. The eccentricity had a pronounced influence on the ultimate tensile strength of the members, with increasing eccentricity leading to reduced bearing capacity. The concrete strength showed limited effect on the ultimate eccentric tensile strength. Based on experimental data and theoretical analysis, this study proposed a method for calculating the ultimate load-carrying capacity of SCFST members under biaxial eccentric tension. Using the stress equilibrium approach, the cross-sectional stress distribution was simplified as a biaxial rectangular pattern, and a calculation formula for the eccentric bearing capacity of the members was established. Comparison between calculated and experimental values demonstrated that the proposed method could predict the ultimate bearing capacity of the members with reasonable accuracy. Full article

The twin-blade planetary mixer is critical for processing highly viscous materials in the chemical and polymer industries, yet optimizing its mixing characteristics alongside energy efficiency remains challenging. This study investigates the twin-blade planetary mixer, using computational fluid dynamics simulation methods to analyze the operating parameters and multi-objective optimization of performance in viscous systems. First, the multi-axis stirring process was simulated numerically based on the Planetary Motion Method, revealing the working process at the cross-section and of the blades, thereby unveiling a mixing mechanism driven by cyclic transitions between local shear-intensive kneading and global convective circulation. Then, through orthogonal experiments and ANOVA, the dominant role of the hollow blade’s self-rotation speed on performance was clarified. Furthermore, based on Kriging and NSGA-II, with LINMAP employed for decision making, an optimal parameter combination, specifically a hollow blade self-rotation speed of 94.86 rpm, a speed ratio of 0.063, and a blade-to-bottom height of 2.79 mm, successfully achieved an 8.15% reduction in power consumption, a 20.03% increase in global axial flow, and a 5.01% enhancement in maximum kneading pressure. Full article

This study investigates the seismic behavior of reinforced concrete (RC) columns with hollow rectangular cross-sections through experimental testing and analytical evaluation. A series of hollow-sectioned column specimens with different shear span ratios and failure modes were tested under cyclic lateral loading to examine their flexural and shear performance. The results demonstrated that flexure-dominated columns exhibited stable load-deformation responses and sustained seismic performance, even with the reduced shear span ratio. The experimental results also showed that the presence of the hollow cross-section had minimal influence on flexural strength and bar strain distribution. The shear strength of RC columns with hollow cross-sections tended to be underestimated by the conventional equation; however, improved accuracy was achieved by applying an equivalent cross-sectional area in the calculation. A nonlinear finite element analysis successfully reproduced the flexural load-deformation response of the specimens. While some discrepancies were observed in the shear-dominated cases, the analytical model provided conservative estimates under positive loading. These findings provide new insights into the seismic design of RC columns with hollow cross-sections, highlighting their potential applicability in building structures when flexural and shear behaviors are properly considered. Full article