Search Results (1,070)

Internal steel-core damage hidden within aluminum conductor steel-reinforced (ACSR) compression components may threaten the mechanical integrity of ultra-high-voltage transmission lines. This laboratory study evaluates metal magnetic memory testing (MMMT) responses to artificial discontinuities in seven-strand ACSR steel cores under four nominal lift-off distances, two nominal orthogonal specimen orientations, and a simplified aluminum-tube-covered condition. One intact specimen and five artificially damaged 1 m specimens were preloaded to 16 kN for 2 min, unloaded, and scanned using the normal magnetic-field component recorded by Channel 1 of a TSC-1M-4 detector. Quantitative descriptors included peak-to-peak amplitude, abnormal-field width, maximum gradient, and short-term within-specimen repeatability. At 5 mm lift-off, peak-to-peak amplitudes ranged from 18.7 to 91.4 A/m. Across three repeated repositioning scans, amplitude coefficients of variation ranged from 0.83% to 8.04%. Relative to 5 mm, the descriptive mean amplitude loss reached 66.3%, 81.9%, and 89.8% at 20, 30, and 40 mm, respectively. Orientation changed signal polarity and amplitude in a specimen-dependent manner. Anomalies remained visible under the aluminum-tube configuration, although covering and effective lift-off effects could not be separated. The results provide preliminary laboratory evidence for further evaluation of MMMT as a screening approach; the reported feature values are not field detection thresholds. Full article

The FRP–concrete–steel double-skin tubular column (DSTC) is a novel composite column designed to meet the structural demands for high strength, exceptional durability, and lightweight characteristics. To investigate the axial compression performance of DSTCs, this study conducted axial compression tests on 16 circular DSTCs and three circular fully filled columns (FCSCs). This research focused on analyzing the effects of steel tube wall thickness, void ratio, rubber content, steel fiber content, and GFRP tube wall thickness on stub columns’ failure modes, load–displacement curves, load–strain curves, and stress–strain relationships of concrete. The results demonstrated that GFRP tube wall thickness is the most critical parameter influencing the bearing capacity and deformation capacity of the column. The ultimate bearing capacity of all specimens ranged from 1606.9 to 3447.9 kN; the peak displacement of the specimens ranged from 7.49 to 17.77 mm. Increased void ratios decrease bearing capacity but enhance ductility, whereas steel tube wall thickness and steel fiber content have relatively minor effects. Based on the experimental results, models for the ultimate bearing capacity, ultimate strain, and stress–strain relationship of short columns were proposed, taking into account rubber content. The average predicted-to-experimental capacities ratio is 0.97 and the predicted load–displacement curves match well with the experimental curves, indicating the very high accuracy of the proposed models. Full article

316L stainless-steel capillary tubes are important in medical devices, precision fluid transport and micro heat exchangers, but their slender geometry and dense passivation film make inner-surface finishing inefficient. This study proposes a stepwise chemical-assisted magnetorheological finishing (CMRF) process for 316L capillaries. The inner surface was first pretreated with hydrogen peroxide/oxalic acid to form a removable reaction layer, and then finished by magnetorheological abrasives. The effects of the two reagents on material removal and surface integrity were evaluated, and the optimal pretreatment was determined to be 2.25 wt.% oxalic acid and 1.5 wt.% H₂O₂. Compared with conventional magnetorheological finishing, CMRF increased the material removal rate by approximately 54% and reduced the final inner-surface roughness Sa to 0.116 μm. Characterization results show that hydrogen peroxide and oxalic acid generate a dynamic oxidation–complexation–dissolution–reoxidation cycle, converting the dense passive film into an oxygen-rich, porous, low-crystallinity reaction layer and reducing surface hardness by about 30%. This softened layer promotes preferential abrasive removal instead of direct cutting of the metallic substrate, thereby improving finishing efficiency and surface quality. Full article

Concrete-filled steel tube (CFST) structures are widely used in modern infrastructure due to their superior strength, ductility, and composite action. However, long-term corrosion of the steel tube, particularly under aggressive environmental conditions, poses significant challenges to their durability and structural performance. This study presents a comprehensive review of corrosion mechanisms and mitigation strategies for CFST structures. The primary corrosion processes, including general corrosion, localized (pitting) corrosion, and circumferential corrosion, are critically examined with emphasis on the influence of chloride ingress, carbonation, marine exposure, and combined environmental actions such as freeze–thaw cycles and sustained loading. The effects of corrosion on structural behavior are analyzed in terms of load-carrying capacity, ductility, buckling resistance, and failure modes. A systematic evaluation of existing mitigation strategies is conducted, encompassing material-based approaches, protective coatings, cathodic protection systems, and structural strengthening techniques such as fiber-reinforced polymer (FRP), fabric-reinforced cementitious matrix (FRCM), and steel jacketing. The comparative performance of these methods is assessed based on effectiveness, cost–benefit considerations, service life extension, and practical implement ability. The review highlights that no single mitigation strategy is universally optimal; instead, integrated approaches combining multiple techniques provide the most effective long-term protection. Key research gaps are identified in the areas of long-term performance monitoring, internal corrosion detection, and durability modeling under combined environmental actions. The findings of this study provide valuable insights for the design, maintenance, and rehabilitation of CFST structures, contributing to the development of more durable and sustainable infrastructure systems. Full article

Bio-inspired auxetic–conventional hybrid tubular metamaterials were investigated for lightweight energy absorption. The tubes combined 6063 aluminium alloy inner tubes with 304 stainless-steel outer tubes containing oval, circular, rotating-square, or re-entrant perforations. Experiments showed that the outer tube altered the collapse mode of the inner tube and produced topology-dependent responses. The Circle-Hybrid tube achieved the highest mean specific energy absorption (SEA) of 6.95 ± 0.04 kJ/kg; the Oval-Hybrid tube was 17.1% lower at 5.76 ± 0.25 kJ/kg but had a 24.1% lower maximum force and a CFE 6.68 percentage points higher. Its SEA was approximately 159.5% higher than that of the Oval-Single tube. A validated finite element model was used to examine oval-hole aspect ratio and inner-tube wall thickness. At fixed porosity, decreasing the aspect ratio promoted progressive folding and increased load-bearing capacity and energy absorption, while an intermediate ratio maximised CFE. Increasing the inner-tube wall thickness enhanced load-bearing capacity and energy absorption but produced more localised or asymmetric buckling. These findings demonstrate that perforation topology can tailor collapse mode, peak-force demand, crushing efficiency, and energy absorption in hybrid tubes. Full article

The use of recycled aggregate concrete (RAC) enables the valorization of construction waste and supports carbon-reduction strategies. However, long-term service-induced deterioration means that recycled aggregates and their interfacial transition zones inevitably contain defects, which severely restrict the safe application of RAC in load-bearing structures. Notably, although RAC reduces embodied carbon by recycling construction waste, steel tube manufacturing introduces an additional carbon footprint; such carbon trade-offs can be well compensated by the improved structural efficiency and extended service life of steel-confined concrete, achieving superior whole-life carbon benefits. In the present study, a steel-tube-confined recycled aggregate concrete (STCRC) composite system is proposed. Through designed external confinement, the stress state of the internal concrete is altered from uniaxial compression to triaxial compression, thereby enhancing its axial load-bearing capacity. Axial compression tests were performed on 36 short column specimens of steel-tube-confined concrete (STCC) composed of C30 aggregate concrete and Q235 steel tubes with three wall thicknesses (4.5 mm, 6 mm, 8 mm). Further parametric finite element analyses with 16 calculation cases were conducted to quantify the effects of higher concrete strength grades (C40 and C50) and of steel tube strength grades. The evolutionary characteristics of the load-displacement response, the axial stress–lateral strain relation, and the lateral strain–longitudinal strain were systematically investigated across various parameters. Test outcomes indicate that steel tube confinement significantly restrains lateral dilation of RAC and enhances its ductility and ultimate bearing capacity, with higher confinement efficiency observed for RAC than for natural aggregate concrete (NAC). Numerical results further identify the differing sensitivities of NAC and RAC to variations in tube wall thickness, steel yield strength, and concrete strength grade. Using combined experimental and numerical datasets, a peak stress modification factor is proposed, and a tailored stress–strain constitutive model for STCRC is developed and validated. The research findings provide theoretical guidance for the design of axially compressed short columns made of prefabricated recycled concrete. Full article

Concrete-filled steel tube (CFT) columns have been widely used in high-rise buildings and bridge structures due to their excellent composite performance. In practical applications, CFT columns inevitably experience eccentric loading due to structural imperfections, asymmetric load distributions, and seismic actions, particularly in corner columns of seismic-resistant structures where biaxial eccentric compression may occur. However, despite extensive studies on the local buckling behavior of CFT columns under axial compression and uniaxial eccentric compression, the behavior under biaxial eccentric compression remains insufficiently understood. In this paper, a theoretical study on the local buckling behavior of rectangular CFT columns subjected to biaxial eccentric compression is presented. Based on classical elastic stability theory and the energy variation method, an analytical model is developed by assuming that both the loaded and unloaded edges of the steel tube are elastically restrained against rotation and selecting an appropriate deflection function satisfying the boundary conditions and compatibility requirements. The relationship of local buckling strength of rectangular CFT columns subjected to biaxial eccentric compression and width-to-thickness ratios under different stress gradient coefficients is obtained. The results indicate that the local buckling strength σ_cr of steel tubes decreases significantly with the increasing width-to-thickness ratios b/t when the stress gradient coefficient α₀₁ and α₀₂ remain unchanged, and the local buckling strength of the broad face is much lower than that of the narrow face. As the stress gradient coefficient increases, the local buckling strength σ_cr of steel tubes increases. When the stress gradient equals 0, the steel tube is subjected to axial compression and the minimum of the local buckling coefficient can be obtained. When the stress gradient equals 2, the steel tube is subjected to pure bending and the maximum of the local buckling coefficient can be obtained. The proposed model provides a rational prediction of local buckling strength under different biaxial eccentric compression conditions. Finally, recommended width-to-thickness ratio limits for steel tube plates with different steel grades and stress gradient coefficients are proposed, which can provide practical guidance for preventing premature local buckling and improving the material utilization efficiency of rectangular concrete-filled steel tube columns. Full article

Predicting the mechanical properties of bolted connection nodes in prefabricated Concrete-Filled Steel Tube (CFST) column–steel beam assemblies remains challenging due to complex nonlinear relationships, high degrees of parameter coupling, and limited generalization capabilities of traditional empirical formulas. This study proposes a data-driven prediction model integrating an Improved Particle Swarm Optimization (IPSO) algorithm with a Deep Neural Network (DNN). Drawing upon 196 sets of experimental data on CFST column–steel beam nodes with Extended Hollo-Bolt (EHB) connections from the published literature, the model employs bolt diameter, steel tube wall thickness, concrete compressive strength, beam–column cross-sectional parameters, and connection configuration parameters as input variables, while designating ultimate moment capacity, initial stiffness, and joint ductility coefficient as prediction targets. A multi-layer DNN is constructed to capture the highly nonlinear mapping between structural parameters and mechanical responses. The IPSO algorithm, enhanced with adaptive inertia weight and Lévy flight perturbation, performs global optimization of the network weights and hyperparameters to improve convergence speed and prediction stability. Five-fold cross-validation is embedded within the IPSO fitness evaluation loop to guide hyperparameter selection, while dropout regularization and early stopping are applied during final training to mitigate overfitting; prediction performance is ultimately verified on an independent hold-out test set. Experimental results demonstrate that the proposed IPSO-DNN model outperforms a tuned shallow neural network (SNN), Support Vector Regression (SVR), and Random Forest (RF) models across the coefficient of determination ($R^2$), root mean square error (RMSE), and mean absolute error (MAE), effectively capturing the nonlinear mechanical characteristics of CFST nodes under complex loading conditions. Full article

The decarbonization of industrial heating systems is one of the major challenges of the current energy transition. Gas-fired radiant tubes dominate industrial heating in large-span, high-bay buildings due to their high efficiency and low operating costs; however, the absence of equivalent electric solutions capable of replacing them represents a significant technological and scientific gap. This paper presents the design, construction, and experimental characterization of an innovative electric radiant tube prototype developed within the INFRAEL research project. The prototype consists of a 100 mm diameter steel tube housing nickel–chromium resistive elements in various configurations, powered from a 230 V AC supply. Thermal measurements were performed using Type K thermocouples distributed along the tube, a non-contact infrared thermometer, and thermovision imaging, complemented by MATLAB R2025bTrial-based interpolation for mapping the thermal field on a receiving plane placed 2 m below the tube. Experimental results show that at a total power of ~1.2 kW (two resistors in parallel), the tube surface reaches temperatures exceeding 250 °C, corresponding to medium-wave infrared emission (~4 μm). A single 630 W resistor yields surface temperatures of approximately 136–160 °C. The temperature distribution on the receiving plane is relatively uniform. The study identifies key optimization directions—resistor geometry, thermal insulation, and integration with photovoltaic sources—with the goal of developing a competitive, zero-carbon alternative to gas-fired radiant heating systems in industrial environments. Full article

The presence of ferrite in 316 austenitic stainless steel affects its magnetic permeability, and the secondary precipitates formed by ferrite decomposition can further degrade the corrosion resistance, limiting its application in industries such as nuclear power and medical devices. In previous studies, the characteristics of ferrite and precipitates in several 316 stainless steel continuous-casting billet samples with different Ni contents were analyzed. In this work, remelting experiments were further conducted on several 316L stainless steels with different Ni contents using a tube furnace; according to the Ni content, they are designated as L-316, M-316, and H-316 stainless steels. Metallographic analysis and electron back-scattered diffraction (EBSD) characterization were employed. The effects of Ni content and cooling rate on the microstructure of 316 stainless steel were systematically investigated. The results show that for the L-316 stainless steel, the ferrite morphologies in water-cooled, oil-cooled, air-cooled, and furnace-cooled samples change successively as follows: skeletal and lath-like, clustered network, lath-like and clustered network, and short rod-like. For the M-316 stainless steel remelted samples, the ferrite morphologies are network and skeletal, network and short rod-like, semi-network and short rod-like, and semi-network, respectively. The solidification modes of the L-316, M-316, and H-316 stainless steel remelted samples are FA, FA, and AF modes, respectively. Increasing Ni content reduces the ferrite content under all cooling conditions. When the Ni content increases from 10% to 12.17%, the ferrite content decreases significantly, with a greater reduction at higher cooling rates; when the Ni content further increases to 14.25%, the decrease in ferrite content slows down, indicating that after Ni content reaches a certain level, its inhibiting effect on ferrite formation weakens. The effect of cooling rate on ferrite content depends on the solidification mode: in the FA mode, slow cooling promotes diffusional transformation of ferrite to austenite, so the ferrite content decreases with decreasing cooling rate—for L-316 stainless steel, the ferrite content drops from 22.44% in the water-cooled sample to 2.71% in the furnace-cooled sample. In the AF mode, slow cooling favors the enrichment of elements at grain boundaries and promotes ferrite nucleation and growth; the overall trend of ferrite content increases as the cooling rate decreases. For the H-316 stainless steel specimens, the ferrite content is similar between water-cooled specimens (0.36%) and oil-cooled specimens (0.26%); for air-cooled specimens, the ferrite content increases significantly to 1.49%; and finally, it reaches 1.94% for the furnace-cooled specimen. Regarding secondary precipitates, the phase constituents of the L-316 stainless steel specimens after water cooling, oil cooling, and air cooling consist of an austenite matrix and ferrite, with a secondary precipitated Chi phase forming only under furnace cooling conditions. For the M-316 stainless steel, the Sigma phase and Chi phase begin to form under oil cooling conditions, and the Sigma phase also precipitates in the oil-cooled specimens of the H-316 stainless steel. In the air-cooled and furnace-cooled specimens of both M-316 and H-316 stainless steels, the secondary precipitated phase is the Sigma phase. All three types of water-cooled stainless steel specimens exhibited no secondary precipitate phase; increasing the cooling rate suppresses atomic diffusion, thereby reducing the precipitation of Chi phase and Sigma phase; however, a higher Ni content shifts the solidification mode toward the AF mode, making secondary precipitates more prone to form. Full article

Global decarbonization represents one of the defining challenges of the 21st century. Geothermal energy offers a robust alternative for reducing fossil fuel dependency for both residential and industrial heating and cooling. While shallow geothermal systems are versatile and high-performing, comprehensive Life Cycle Assessments (LCA) remain scarce in the literature. This study evaluates the environmental impact of the manufacturing and installation processes of next-generation coaxial probes featuring a galvanized steel outer tube and an internal polyethylene pipe. The LCA identifies material composition as the primary environmental driver: steel production accounts for 41% of the total impact, while the hot-dip galvanization process contributes 30%, significantly affecting the “climate change” and the “resource use” categories. A comparative LCA with conventional double U-tube installations shows similar overall environmental impacts. A sensitivity analysis on the coaxial probes was conducted to explore potential mitigation strategies aimed at reducing the associated environmental impacts, providing indications for sustainable eco-design. The LCA results demonstrate that optimizing the design, specifically by reducing the steel quantity in the coaxial outer tube and avoiding the zinc coating process, results in a 34% reduction in total environmental impact, confirming that LCA is a fundamental tool for supporting the environmental sustainability of developing technologies. Full article

The width-to-thickness ratio (B/t) is a pivotal design parameter for square concrete-filled steel tubular (CFST) columns, governing the suppression of local buckling and directly influencing the load-bearing capacity and ductility of members. To establish differentiated B/t limits for cold-formed (CFCFST) and tailor-welded (CFTWST) square CFST columns, this study critically reviews and compares five representative design formulas from international codes and the literature. Their applicability, theoretical rationality, and inherent limitations are systematically assessed. Particular attention is paid to the distinct mechanical characteristics induced by cold forming (strain hardening) and welding (residual stresses), based on which the suitability of each formula for CFCFST and CFTWST columns is separately evaluated. Through parametric analyses using a rigorously validated finite element (FE) model—verified against 14 in-house experiments and 210 literature specimens—and grounded in the steel–concrete compatibility mechanism, targeted B/t limits are proposed for each tube type. Full article

Long-span transmission towers in the Yangtze River basin are exposed to coupled low-temperature, high-humidity and strong-wind conditions, which promote nonuniform ice accretion on steel members and increase structural loads and ice-shedding risks. Although superhydrophobic coatings are promising passive anti-icing materials for civil infrastructure, most existing evaluations use idealized flat or cylindrical specimens and do not capture the geometry, substrate condition and coating uniformity of in-service tower members. Here, a multifactor coupled icing simulation system was developed, and comparative icing tests were conducted on three representative steel members (aged plain circular steel tube, new galvanized circular steel tube and new galvanized angle steel) under controlled temperature, wind speed, spray rate and icing duration. For uncoated members, ice mass increased with supercooling degree and spray rate, first increased and then decreased with wind speed, and exhibited a decelerating growth pattern within 24 h. The superhydrophobic coating reduced ice mass, ice thickness and circumferential nonuniformity under all tested conditions, but its effectiveness depended strongly on environmental loading and member geometry. Under reference conditions, the ice-reduction rates reached 41%, 45% and 38% for the three members, respectively, and remained 27–32% after 24 h of icing. Smooth circular substrates showed the best coating response, whereas angle steel was less effective because edge-induced flow distortion and poor coating uniformity promoted local wetting failure. Performance degradation under harsh conditions was associated with accelerated freezing, water-film formation and localized wetting failure. These findings define the applicability and durability limits of superhydrophobic coatings for passive anti-icing protection of long-span transmission tower steel members. Full article

To address the performance degradation of reinforced concrete (RC) columns, this study experimentally investigated the axial compressive performance of RC columns strengthened with self-compacting expansive concrete (SCEC)-filled steel tubes. A realistic loading protocol was adopted in which only the RC column was directly compressed, compelling the steel tube and SCEC layer to serve exclusively as confinement. A total of 16 specimens were tested, considering seven key parameters, including the height and cross-sectional shape of the RC columns, the strengthening method, the steel tube thickness, the infilling concrete type, the interface treatment method, and the compressive loading region. The results demonstrated that the external steel tube changed the brittle failure mode of un-strengthened RC columns into a ductile one, with the ultimate axial capacity increasing by up to 184%. Steel tube thickness was identified as the most influential parameter, with an increase from 2 mm to 6 mm improving the capacity by 58.5%. Interface roughening was found to be essential for preventing premature debonding. Based on the Mander model and superposition theory, a simplified analytical formula was proposed, yielding a conservative mean calculated-to-experimental ratio of 0.823. The proposed system offers a reliable high-performance solution for rehabilitating bridge piers and similar RC structures. Full article

This study presents the results of investigations into a new low-alloyed steel grade CT80 designed for coiled tubing (CT) with increased cold resistance requirements. Based on data concerning the structural-phase transformations of overcooled austenite, various thermomechanical treatment modes were defined and tested on a reversing hot rolling mill DUO-500 combined with an accelerated cooling system. Controlled rolling and accelerated cooling regimes were established, ensuring the formation of the most favorable microstructure for achieving a high level of ductile-plastic properties at the specified strength level of CT80-class steel. Full article