Search Results (1,966)

To achieve efficient design and ensure the safety of concrete structures, the use of high-strength concrete, reinforcing steel, and prestressing tendons has been steadily increasing. In this study, for flexural design of prestressed concrete (PSC) structures employing high-strength strands with tensile strengths of 2160 MPa and 2360 MPa, the applicability of the current design-code equation for predicting the strand stress at flexural failure (f _ps )—which was originally proposed based on studies of conventional strands with tensile strengths of 1860 MPa or lower—was evaluated. Furthermore, an improved prediction equation was proposed. Section analyses based on stress–strain curves obtained from numerous tensile tests of high-strength strands were conducted, and the results were compared with the existing prediction equations specified in ACI 318 and the Korean KDS code. The comparison revealed that, for high-strength strands, the strand stress tends to be underestimated in the tension-controlled region and overestimated in the compression-controlled region. To address these issues, a new prediction equation was proposed that retains the form of the existing equation but incorporates correction factors reflecting the characteristics of high-strength strands. The performance of the proposed equation was evaluated not only for rectangular sections but also for T- and I-shaped sections, and its predictive accuracy was verified by comparing the predicted strand stresses and nominal flexural strengths with those obtained from section analyses. As a result, the proposed prediction equation demonstrated improved accuracy compared with the existing one, while maintaining an appropriate level of conservatism. Therefore, it is expected to enhance design efficiency for PSC structures employing high-strength strands. Full article

3D concrete printing (3DCP) is an emerging intelligent construction technology that enables the direct transformation of digital models into physical components, thereby facilitating the precise fabrication of complex geometries. This study investigates the anisotropic mechanical properties and construction applicability of low-carbon 3D printed concrete for reusable formwork systems. Axial compression, flexural, and splitting tensile tests were conducted to examine mechanical anisotropy, and the effects of steel slag and iron tailings replacement levels on mechanical performance were evaluated. Carbon emission analysis was also performed. Using the coefficient-of-variation TOPSIS method, an optimal printable low-carbon mixture was identified, comprising 30% steel slag, 40% iron tailings sand, and 0.3% fibre content, balancing both mechanical performance and environmental benefits. To address the challenges associated with printing large monolithic formwork units, such as excessive weight and demoulding difficulties, three connection strategies for curved wall modular reusable formwork were designed. Finite element analyses were conducted to assess the strength and stiffness of each strategy, and an optimized connection configuration was proposed. The findings demonstrate the feasibility of accurately fabricating complex architectural components using low-carbon 3D printed concrete, providing theoretical and practical support for the industrialized production of large-scale, geometrically complex structures. Full article

This article aims to describe a novel workflow designed for generating a new family of minimal surface-based lattice structures with improved performance in terms of material budget compared to the well-known cells like Gyroid and Schwartz. The implemented method is based on the iterative resolution of a dynamic model, where proper forces are applied to generate minimal surface lattices, considering the boundary conditions and the constraint configurations. The novelty of the approach is given by the ability to create a minimal surface without resolving the partial differential equation and without knowing the exact minimal surface generative function. The starting geometry used for the lattice generation is the hypercube, parametrized to create different lattice configurations. Creating five different starting geometries and two constraint configurations, ten different lattice cells were created. For the comparison, a representative parameter of the material budget has been introduced and used to define the two best cells. The material budget is crucial for particle accelerator components, sensors, and detectors. These cells have been compared with Gyroid and Schwartz of the same thickness and bounding box, highlighting improvements of a factor of 2.3 and 1.7, respectively, in terms of material budget. The same cells have also been 3D-printed and tested under compression, and the obtained force–displacement curves were compared with those from a finite element analysis, demonstrating good agreement in the elastic region. Full article

Considering the complexity and diversity of water-rich soft soil strata, indoor triaxial shear tests and creep tests were conducted on soft soil to explore its deformation law and creep characteristics. To address the nonlinear characteristics of soft soil creep, a nonlinear pot element was proposed and substituted for the two linear pot elements in the Burgers model, thus establishing an unsteady parametric Burgers model. The one-dimensional creep equation of the unsteady Burgers model was derived, theoretically determining that the unsteady model can describe three stages of creep. Based on this, the creep equation of the unsteady Burgers model was extended to a three-dimensional stress state, and the triaxial compression creep test curves of Ningbo soft soil were fitted and parameters identified. The above model was derived from a three-dimensional finite difference scheme suitable for numerical solution in FLAC3D. A custom constitutive creep model was developed in FLAC3D, and the non-accelerated creep stage and accelerated creep stage of the improved model were analyzed to verify the accuracy and reliability of the constitutive model. The results show that the numerical simulation results and the indoor creep test results are in good agreement in terms of strain increment and the creep change curve, which confirms the effectiveness and applicability of the proposed unsteady Burgers creep constitutive model and its secondary development application. Full article

During mining, rock failure and water infiltration induce variations in deformation, energy release, electrical conductivity, and water content. Their response laws underpin water-preserving mining optimization, environmental impact mitigation, and mining area sustainability, while facilitating the prediction of stratum instability and water migration. In this study, uniaxial compression experiments were conducted on sandstone with different water saturations, during which the responses of strain, acoustic emission energy, and electrical resistivity were monitored. The temporal characteristics of the rock’s multi-parameter responses were analyzed, and the influence of water content on precursor information of rock failure was revealed. Multi-parameter response equations for rocks under loading, incorporating the effect of water saturation, were established. A segmented variable-weight-integrated damage constitutive model for water-bearing rocks was developed based on the multi-parameter responses. The findings showed that the temporal characteristics of multi-parameter coupling responses can reflect the damage evolution and pore water migration during the instability and failure process of water-bearing rocks. As water saturation increased from 0% to 100%, the rock exhibited the following variations: peak stress decreased by 38.49%, strain at peak stress increased by 8.79%, elastic modulus decreased by 41.58%, cumulative acoustic emission energy drops by 93.23%, and initial electrical resistivity plummets by 98.02%. Compared with the theoretical stress–strain curves based on strain damage variables, cumulative acoustic emission energy damage variables, and electrical resistivity damage variables, the theoretical stress–strain curve based on the integrated damage variable shows better agreement with the measured curve, with the coefficient of determination exceeding 0.98. The research findings offer valuable insights into rock mass instability and groundwater migration, supporting water-preserving mining and sustainable mining area development. Full article

Lattice structures, inspired by the crystal lattice, are periodically arranged structures composed of rods and nodes, featuring buffering, energy absorption, and excellent thermal insulation properties. Five types of unit cell structures were tested and the diamond lattice structure exhibited relatively smoother stress–strain curve, and its compression failure process was more stable. The diamond lattice structure was then subjected to the quasi-static compression test at temperatures of −40 °C, 25 °C, 100 °C, and 170 °C. It was found that there is a significant plateau stress during compression, and the magnitude of this plateau stress can be adjusted by changing the rod diameter. Subsequently, its thermal insulation performance was tested, and it was found that as the rod diameter increases, the plateau stress increases, but the thermal insulation performance decreases. Therefore, when designing shock absorber filler materials, the relationship between plateau stress and thermal insulation performance should be balanced, and the parameters with the best comprehensive performance should be selected. Full article

The determination of compressive strength of hemp–lime composite (HLC) is currently based on diverse and non-unified approaches, which complicates the direct comparison of results obtained in different studies. This study compares commonly used strength-determination methods using a dedicated experimental dataset and proposes a new, more universal approach, defining compressive strength as the stress corresponding to 1% permanent strain. Cubic specimens (150 × 150 × 150 mm) were produced at three compaction levels (150%, 170%, 190%) and tested under uniaxial compression. Increasing compaction increased density and resulted in compressive strengths of 219, 316, and 349 kPa, respectively. Methods based on fixed strain levels (5% and 10%) showed good repeatability but primarily reflected serviceability limits, whereas those based on loss of linearity or stiffness reduction were less reliable and highly sensitive to curve interpretation. The proposed 1% permanent-strain method accurately captured the onset of irreversible deformation and aligned with the real behavior of hemp–lime infill in frame structures, supporting its use for standardizing compressive-strength testing of hemp–lime composites. Full article

Pre-tensioned T-beams with polygonal tendons offer high load-bearing capacity and suitability for large spans, demonstrating broad application potential in bridge engineering. The cracking state of a prestressed beam is a crucial indicator for assessing its service state, while the ultimate bearing capacity is a key metric for structural safety. In this study, we designed a novel 30 m pre-tensioned T-beam with polygonal tendons and investigated its shear cracking performance and ultimate bearing capacity under a shear-span ratio of 2.5 through a full-scale test. A graded loading protocol was employed. The results indicate that during the initial loading stage, the shear cracking load of the inclined section was 1766 kN. A distinct inflection point appeared on the load–displacement curve, accompanied by a significant reduction in stiffness. Cracks initially developed at the junctions between the web and the top flange, as well as the diaphragm, and subsequently propagated towards the shear–flexural region, exhibiting typical shear–compression failure characteristics. During the secondary loading to the ultimate state, the beam demonstrated good ductility and stress redistribution capability. The ultimate shear capacity reached 3868 kN. Failure occurred by crushing of the concrete in the compression zone after the critical inclined crack penetrated the web, with the member ultimately reaching its ultimate capacity through a plastic hinge mechanism. Strain analysis revealed that the polygonal tendons effectively restrained the premature development of inclined cracks, thereby enhancing the overall shear performance and deformation capacity. This study verifies the mechanical performance of the new T-beam under a shear span-to-depth ratio of 2.5 through calculations based on different codes and finite element numerical analysis, providing experimental evidence and theoretical references for its engineering application. Full article

As the requirements for structural functionality increase, designers frequently opt for inclined columns instead of traditional vertical columns. This choice enhances the spatial dynamics, esthetic appeal, and lighting effects of the structure. However, the research on the failure mechanism and seismic performance of inclined columns under cyclic loading is not systematic. To promote the application of inclined columns in earthquake-prone areas, quasi-static tests were conducted on steel-reinforced concrete inclined columns (SRCIC). The study analyzed the elastic and elastic-plastic development trend, failure mechanism, second-order effect, deformation and energy dissipation of the inclined columns. Traditional vertical columns often experience bending or shear failure, while SRCIC exhibited a new failure pattern characterized by bending failure on one side and compression failure on the other. Based on the experimental design, the nonlinear finite element analysis model of SRCIC is established. The finite element model was validated for horizontal peak load, ductility coefficient, and damage area at various inclination angles, providing a foundation for further parameter analysis. In the numerical analysis section, the effects of inclination angle, steel ratio, reinforcement ratio, and stirrup ratio on the skeleton curve and ductility coefficient were studied in detail, leading to the application of SRCIC. Full article

To understand the hot deformation behavior of 7085 aluminum alloy, compression tests were performed under varied conditions (593–743 K/0.001–1 s⁻¹). While the true stress–strain curves predominantly display the features of dynamic recovery, the softening mechanism shifts towards dynamic recrystallization when deforming at higher temperatures and lower strain rates. The validity of the constructed strain-compensated Zener–Hollomon model is confirmed by its exceptional precision in forecasting the flow stress, achieving an R² value of 0.992. The instability areas are concentrated in the high-strain-rate regions, and the optimal deformation processing for 7085 aluminum alloy is 693–743 K/0.01–0.001 s⁻¹. The alloy’s softening mechanism undergoes a transition from solely dynamic recovery to a progressively more significant coordinated role of dynamic recovery and dynamic recrystallization as the temperature rises and the strain rate drops. Full article

The increasing demand for sustainable construction materials has motivated the optimization of mortar mix designs to reduce cement consumption and its environmental impact while maintaining adequate mechanical performance. This study develops a machine learning (ML) model for optimizing mortar mixtures used in concrete roofing tiles by integrating aggregate particle packing techniques with non-linear regression algorithms, using an industry-grade dataset generated in the Central Laboratory of Wienerberger Ltd. Unlike most previous studies, which mainly focus on compressive strength, this research targets the transverse strength of industrial roof tile mortar. The proposed approach combines Tarantula Curve gradation limits, experimentally derived packing density ($\eta$), and ML regression within a unified and application-oriented workflow, representing a research direction rarely explored in the literature for optimizing concrete mix transverse strength. Fine concrete aggregates were characterized through a sand sieve analysis and subsequently adjusted according to the Tarantula Curve method to optimize packing density and minimize void content. Physical properties of cements and fine aggregates were assessed, and granulometric mixtures were evaluated using computational methods to calculate fineness modulus summation (FMS) and packing density. Mortar samples were tested for transverse strength at 1, 7, and 28 days using a three-point bending test, generating a robust dataset for modeling training. Three ML models—Random Forest Regressor (RFR), XG-Boost Regressor (XGBR), and Support Vector Regressor (SVR)—were evaluated, confirming their ability to capture nonlinear relationships between mix parameters and transverse strength. The analysis of input variables, which consistently ranked as the highest contributors according to impurity-based and permutation-based importance metrics, revealed that the duration of curing, density, and the summation of the fineness modulus significantly influenced the estimated transverse strength derived from the models. The integration of particle size distribution optimization and ML demonstrates a viable pathway for reducing cement content, lowering costs, and achieving sustainable mortar mix designs in the tile manufacturing industry. Full article

This study experimentally evaluates the structural performance of Concrete-Filled Double-Skin (CFDS) hybrid connections that are intended as key components of large-scale floating offshore wind substructures. The innovative aspect of this work lies in the direct experimental comparison of five representative connection details—Headed Stud (HS), Perfobond (PB), L-beam-joint (LJ), L-beam-spacing (LS), and Angle (AN)—with respect to multiple performance indices that are critical under harsh offshore environments. First, full-scale CFDS specimens were fabricated with identical global dimensions while varying only the connection details. The hybrid behavior of the CFDS system arises from the complementary actions of the outer steel tube, which primarily resists tensile forces, and the infilled concrete, which provides dominant compressive resistance and confinement. This composite interaction enhances the stiffness, ductility, and energy absorption capacity of the member under flexural demands, which are essential for floating offshore structures operating under complex marine loading. Second, monotonic bending tests were conducted using a 2000 kN actuator under a cantilever-type configuration, and load–displacement responses were recorded at three locations. Third, the stiffness, ductility, and energy absorption capacity (toughness) were quantified from the measured curves to clarify the deformation and failure characteristics of each connection type. The results show that the PB connection achieved the highest maximum load and exhibited stable ductile behavior with plastic energy dominating the total toughness. The LJ connection provided well-balanced stiffness and deformation capacity with low sensitivity to measurement locations, indicating high reliability for design applications. In contrast, the HS and LS connections experienced localized slip and position-dependent stiffness, while the AN connection showed the lowest load-carrying efficiency. Overall, the findings highlight that connection-level detailing has a decisive influence on the global performance of CFDS hybrid members and provide fundamental data for developing design guidelines for floating offshore structures operating under complex marine loading conditions. Full article

To clarify the effect of sand ratio on the freeze–thaw performance of full solid waste geopolymer concrete (FSWGC) and establish a constitutive model for its post-freeze–thaw mechanical behavior, FSWGC was prepared via alkali activation—using fly ash, slag, silica fume as cementitious materials, and cold-bonded geopolymer lightweight aggregates (CBGLAs) and recycled sand as aggregates. With sand ratios (0.45, 0.55, 0.65) as the core variable, rapid freeze–thaw tests were conducted to measure mass loss, relative dynamic elastic modulus, mechanical properties, and axial compressive stress–strain characteristics of FSWGC. Results show that higher sand ratios significantly aggravate freeze–thaw damage: after 100 cycles, the 0.65 sand ratio specimen has a mass loss rate of 4.61% and a relative dynamic elastic modulus retaining only 34.4% of its initial value, with accelerated strength degradation. This is due to yjr weakened wrapping of recycled sand by cementitious materials, forming a weak interfacial transition zone. The modified Guo constitutive model for FSWGC, and the further established model considering freeze–thaw cycles, accurately describe the stress–strain curve of FSWGC before and after freeze–thaw. This study provides theoretical and experimental support for FSWGC mix optimization, durability design, and mechanical response calculation in cold regions. Full article

Hydrogen energy is vital for a clean, low-carbon society, and proton exchange membrane fuel cells (PEMFCs) represent a core technology for the conversion of hydrogen chemical energy into electrical energy. When PEMFC single cells are stacked under assembly force for high power output, their porous electrodes (gas diffusion layers, GDLs; catalyst layers, CLs) undergo compressive deformation, altering internal transport processes and affecting cell performance. However, existing microscale studies on PEMFC porous electrodes insufficiently consider compression (especially in CLs) and have limitations in obtaining compressed microstructures. This study proposes a combined framework from a microstructure perspective. It integrates the finite element method (FEM) with computational fluid dynamics (CFD). It reconstructs microstructures of GDL, CL, and GDL-bipolar plate (BP) interface. FEM simulates elastic compressive deformation, and CFD calculates transport properties (solid zone: heat/charge conduction via Laplace equation; fluid zone: gas diffusion/liquid permeation via Fick’s/Darcy’s law). Validation shows simulated stress–strain curves and transport coefficients match experimental data. Under 2.5 MPa, GDL’s gas diffusivity drops 16.5%, permeability 58.8%, while conductivity rises 2.9-fold; CL compaction increases gas resistance but facilitates electron/proton conduction. This framework effectively investigates compression-induced transport property changes in PEMFC porous electrodes. Full article

The high penetration rate of renewable energy poses significant challenges to the planning and operation of power systems in regions with scarce data. In these regions, it is impossible to accurately simulate the complex nonlinear dependencies among hydro–wind–solar energy resources, which leads to huge operational risks and investment uncertainties. To bridge this gap, this study proposes a new data-driven framework that embeds the natural climate cycle (24 solar terms) into a physically consistent scenario generation process, surpassing the traditional linear approach. This framework introduces the Comprehensive Similarity Distance (CSD) indicator to quantify the curve similarity of power amplitude, pattern trend, and fluctuation position, thereby improving the K-means clustering. Compared with the K-means algorithm based on the standard Euclidean distance, the accuracy of the improved clustering pattern extraction is increased by 3.8%. By embedding the natural climate cycle and employing a two-stage dimensionality reduction architecture: time compression via improved clustering and feature fusion via Kernel PCA, the framework effectively captures cross-source dependencies and preserves climatic periodicity. Finally, combined with the simplified Vine Copula model, high-fidelity joint scenarios with a normalized root mean square error (NRMSE) of less than 3% can be generated. This study provides a reliable and computationally feasible tool for stochastic optimization and reliability analysis in the planning and operation of future power systems with high renewable energy grid integration. Full article