Search Results (79)

In this paper, a new type of combined column, square steel tube hybrid steel–basalt fiber reinforced concrete column (BSFCFST), is proposed for the first time, and a new hybrid machine learning model, NRBO-XGBoost, is proposed to predict the axial compressive load capacity of BSFCFST. Eleven specimens were designed and fabricated to investigate the axial mechanical properties of BSFCFST. The variables considered include basalt fiber volume content, steel fiber volume content, steel tube wall thickness and specimen length to slenderness ratio. The characteristics of damage modes, load-displacement curves and load-strain curves of the new combined columns were mainly investigated. The results showed that the hybrid fibers improved the ultimate load carrying capacity of the specimen, and the improvement of the ductility was obvious. On the basis of the experiments, a parametric expansion analysis of several structural parameters of the specimen was carried out by using ABAQUS finite element software, and a combined model NRBO-XGBoost, based on the Newton-Raphson optimization algorithm (NRBO), and the advanced machine learning model XGBoost was proposed for the prediction of the BSFCFST’s ultimate carrying capacity. The combined model NRBO-XGBoost was evaluated by comparing it with several prediction methods. The results show that the prediction accuracy of the NRBO-XGBoost model is significantly higher than that of other prediction methods, with R² = 0.988, which is a good alternative to existing empirical models. Full article

This study investigates the flexural performance of desert sand concrete-filled steel tube (DS-CFST) members through experimental validation and finite element modeling (FEM). An extensive database of square and circular CFST specimens subjected to pure bending was analyzed to validate an ABAQUS-based FEM. Parametric studies evaluated the influence of steel yield strength, steel ratio, stirrup confinement, and desert sand replacement ratio (r) on ultimate bending moment, stiffness, and failure modes. The results indicated that steel yield strength and section geometry significantly affected bending capacity, while desert sand substitution (r ≤ 1) had a negligible impact on capacity, reducing it by less than 3%. The FEM accurately predicted buckling patterns, moment-curvature relationships, and failure modes. New design formulas for predicting ultimate bending moment and flexural stiffness were proposed, demonstrating superior accuracy (mean error < 1%) compared to existing design codes (AIJ, AISC, GB). This study highlights that DS-CFST members, particularly circular sections, offer robust flexural performance, with enhanced ductility and uniform stress distribution. The findings underscore the potential of using desert sand as a sustainable material in concrete-filled steel tube structures without compromising structural integrity. Full article

In order to reduce the edge waves and defects of the strip in the forming process and obtain better properties of the strip, it is urgent to establish a better flexible cold forming process. In this paper, a finite element model of the production line was established to simulate the forming process, and the effective stress distribution at the corner of the strip was simulated. The effect of cold working hardening was basically consistent with that calculated by the analytical method and tensile test results. A mathematical model of the maximum normal strain along the tangent direction of the strip’s outer edge of each pass was established. With the constraint conditions that the maximum value of the normal strain value of each pass is less than the critical value and the upper and lower limit of the horizontal value of each test factor, and the maximum value of the normal strain of each pass as the goal, the number of cold forming passes, the bending angle of each pass and the working roll diameter of the roll have been determined. The optimized process parameters were used in the simulations. No edge wave at the strip edge and no “Bauschinger effect” in forming before high-frequency induction welding was found. The method proposed in this paper can optimize the key process parameters before the production line is put into operation, minimize the possible buckling of the strip edge during the forming process, and reduce the possible loss caused by design defects. Full article

Square steel tube (SST) columns are widely applied, and fire resistance is a critical issue in its design. Current research on the fire resistance of the SST column predominantly assumes that it is uniformly exposed to fire, ignoring the thermal insulation of the surrounding walls under actual fire conditions. The heat transfer and mechanical finite element model (FEM) for SST columns embedded in walls under an ISO 834 standard fire are established in this study, and the accuracy of the FEM is verified by existing experimental results. Subsequently, the wall effect on the temperature distribution and fire resistance of the SST columns exposed to fire is analyzed, the stress mechanisms of the SST column embedded in walls is investigated and further parametric analyses are performed. The results show that, for SST columns embedded in walls, the temperature rise rate of the wall-embedded region is significantly reduced, and the fire resistance is improved by 25.3% compared with the case of uniform exposure to fire. Under two fire conditions, the SST columns exhibit compressive bending failure, and when considering the wall effect, the uneven temperature distribution induces material strength eccentricity, causing the buckling direction to deviate toward the wall-thickness direction. Reducing the fire-resistive coating thickness of the wall-embedded region can mitigate the uneven stress distribution, thereby lowering construction costs while concurrently preserving fire resistance. Increasing the steel tube thickness can significantly improve the fire resistance, but the high steel strength and slenderness ratio result in the accelerated failure of the SST column when exposed to fire. Full article

To enhance the standardization and construction efficiency of prefabricated steel structures and to promote the application of cold-formed steel tubes with the advantages of high standardization, superior mechanical properties, and fast processing speeds, two types of composite beam to concrete-filled cold-formed high-strength square steel tubular column joints with different connection forms were designed in this study: the external diaphragm joint (ED joint) and the through diaphragm joint (TD joint). These joints were subjected to cyclic loading tests to evaluate the influence of the connection designs on key seismic performance parameters, such as failure modes, load-bearing capacities, the degradation of strength and stiffness, ductility, and energy dissipation capabilities. The results show that both the ED and TD joints experienced butt weld fractures at the bolted-welded connections on the beam, effectively transferring the plastic hinges from the joint zone to the beam and demonstrating good seismic performance. The ED joint specimen JD1 and the TD joint specimen JD2 exhibited similar load-bearing capacity, stiffness, strength degradation, and energy dissipation capacity. However, the TD joint showed lower ductility compared to the ED joint due to premature weld fractures. A nonlinear finite element model (FEM) was developed using MSC.MARC 2012, and the numerical simulation showed that the FEM could effectively simulate the hysteresis performance of the composite beam to concrete-filled, cold-formed, high-strength, square, steel tubular column joints with external and through diaphragms. Full article

This study aims to investigate the bending load-bearing capacity of precast hollow composite slabs composed of ultra-high-performance concrete (UHPC) and Normal Concrete (NC). Through finite element numerical analysis and verification, this study analyzes various key factors influencing the performance of the composite slab, including the wall thickness of the square steel tube, the diameter of transverse reinforcing bars, the thickness of the precast bottom slab, and the strength grade of the concrete. The results indicate that the use of UHPC significantly enhances the bending performance of the composite slab. As the wall thickness of the square steel tube and the strength of UHPC increase, both the yield load and ultimate load capacity of the composite slab show considerable improvement. By conducting an in-depth analysis, this study identifies different stages of the composite slab during the loading process, including the cracking stage, yielding stage, and ultimate stage, thereby providing important foundations for optimizing structural design. Furthermore, a set of bending load-bearing capacity calculation formulas applicable to UHPC-NC precast hollow composite slabs is proposed, offering practical tools and theoretical support for engineering design and analysis. The innovation of this study lies not only in providing a profound understanding of the application of composite materials in architectural design but also in offering feasible solutions to the energy efficiency and safety challenges faced by the construction industry in the future. This research demonstrates the tremendous potential of ultra-high-performance concrete and its combinations in modern architecture, contributing to the sustainable development of construction technology. Full article

High-strength concrete-filled steel tube (CFST) arches have been widely applied in underground engineering, among which there are special-shaped arches such as D-shaped sections. At present, most studies have concentrated on members with square or circular sections, while relatively few studies have been conducted on D-shaped section members. In this study, firstly, D-shaped sections were initially transformed into sections with a part square and part elliptical shape using an equivalent section method. The formulas for the axial compression and pure bending bearing capacities of the basic D-shaped CFST members were deduced using unified theory, and the bearing capacity of the D-shaped members was calculated in a given case. Secondly, numerical simulations of axial compression and pure bending of the basic CFST members with three section types (square, circular, and D-shaped) were carried out using ABAQUS software. To ensure the reliability of the numerical simulations, the concrete damage constitutive model and the elastic–plastic model were adopted to simulate the core concrete and the steel tube, respectively. In the results, the axial compression and pure bending bearing capacities of the D-shaped section obtained via theoretical calculation were 2339.6 kN and 84.8 kN·m, respectively, while the results obtained via numerical simulation were 2335.8 kN and 85.4 kN·m, respectively, which were relatively close. Among the three section types of members, the D-shaped members had the highest axial compression bearing capacity, which was 1.45% and 4.58% higher than those of the circular and square section members, respectively. However, their bending moment bearing capacity was relatively low. The stress distribution of the D-shaped members presented a characteristic where the circular part dominated, and the stress transfer effect of the members was favorable. In practical engineering, when the surrounding rock pressure is high and evenly distributed, D-shaped section arches can be selected, and increasing the proportion of the square area in D-shaped sections can enhance the overall flexural capacity of arches. Full article

The square steel tube–timber–concrete composite L-shaped columns are lighter in weight due to the inclusion of wood and exhibit superior seismic performance. This combination not only reduces transportation and labor costs but also enhances earthquake resistance. The wood contributes lightness and flexibility, the steel provides strength, and the concrete offers excellent compressive performance, thereby achieving an optimized design for performance. To investigate the axial compression performance of square steel tube–timber–concrete composite L-shaped short columns, axial compression tests were conducted on eight groups of L-shaped columns. The study examined ultimate load, failure modes, load–displacement relationships, initial stiffness, ductility, and bearing capacity improvement factors under different slenderness ratios, steel tube wall thicknesses, and wood content rates. The results show that the mechanical performance of the composite columns is excellent. Local buckling of the steel tube is the primary failure mode, with ‘bulging bands’ forming at the middle and ends. When the wood content reaches 25%, the synergy between the steel tube, concrete, and wood is optimal, significantly enhancing ductility and bearing capacity. The ductility of the specimen increased by 31.1%, and the bearing capacity increased by 4.14%. The bearing capacity increases with the steel tube wall thickness but decreases with increasing slenderness ratio. Additionally, based on the Mander principle and considering the partitioned constraint effects of concrete, a simplified calculation method for the axial compressive bearing capacity was proposed using the superposition principle. This method was validated to match well with the test results and can provide a reference for the design and application of these composite L-shaped columns. Full article

Welding residual stresses significantly influence the mechanical behavior of hollow section joints, especially in the pivotal connection zones of steel structures employed in construction. The research object of this study is the Q355 steel square tube–plate Y-joint welded using Gas Metal Arc Welding (GMAW) with CO₂ Shielding. The thermodynamic sequence coupling method was employed to simulate the temperature field, microstructure distribution, and welding residual stresses in square tube–plate Y-joints. Based on the monitored temperature field data and the cross-sectional dimensions of the weld pool, this study calibrated the finite element model. Subsequently, the calibrated finite element model was employed to analyze the influence of microstructural phase transformations and welding sequences on the welding residual stresses in square tube–plate Y-joints. The research findings indicate that the peak transverse welding residual stresses in the branch pipes of the four joint zones were lower when considering the phase transformation effect than when not accounting for it in the calculations. There was no significant difference in the transverse and longitudinal welding residual stresses on the surface of branch pipes under the three welding sequences. However, there were certain differences in the microstructural content of the weld zones under the three welding sequences, with the martensite content in the third welding sequence being significantly lower than that in the other two sequences. Full article

This paper deals with a numerical method of analysis of the performance of shear connectors in transferring load in high-strength concrete-filled steel tube square sections. The novelty of the model is that it considers all the important parameters that affect performance at once: bond strength, the transfer rate of each connector, and the stress distribution and deformation of each element. Four specimens fabricated using different types of connectors were validated using ABAQUS version 2017 software. The deformation of the connectors, concrete damage, and the local instability of the steel tube were extensively investigated. The main parameters considered were the ultimate bond strength and load transfer ratio. The shear connector arrangement consisting of four specimens, namely C1 with 16 studs, a circular rib (C2), a circular rib with 8 studs (C3), and a circular rib with 8 vertical ribs (C4), had a significant influence on the key parameters. Connectors C2, C3, and C4 transferred more than 80% of the total load. The circular rib was more effective in transferring the load and limiting slip than the vertical rib and the studs. The circular rib (C2) transferred the load mainly through the four corners. The deterioration of the concrete and local instability of the steel tube had complex deformations which were influenced by the geometry of the inserted connectors. Full article

To enhance the seismic resilience of building structures and refine the stability and longevity of buildings, it is essential to implement strategies that not only reinforce their structural integrity but also ensure their enduring functionality. The seismic performance test of corrugated steel plate–concrete–filled steel tube shear walls with transverse ribs was studied. Three specimens of shear walls featuring transversely ribbed corrugated steel plates filled with concrete were fabricated, namely, a C–shaped shear wall with four square steel tube concrete columns (specimen C40), a C–shaped shear wall with vertical loading beams (specimen C40X), and a C–shaped shear wall with two steel tube concrete columns (specimen C40LX). Each specimen was equipped with transverse–rib corrugated steel plates with the same parameters. The seismic performances of the specimens were tested by applying loads to different specimens through the displacement–controlled loading system. The tests show that the hysteretic curves of test piece C40 and test piece C40X are not full compared with that of test piece C40LX; the cracking load, yield load, peak load, and ultimate load of both are significantly lower than those of test piece C40LX; and the energy consumption levels of test piece C40 and test piece C40X are relatively weak. The test piece C40LX obviously has a high ductility coefficient, and the stiffness decrease under load is relatively small. During the loading process, the strain change law of the vertical reinforcement in the bottom section of the wall also maintains a reasonable state. It can be seen that the C–shaped transverse–rib corrugated steel plate–concrete–filled steel tube shear wall with two concrete–filled steel tube columns has a higher seismic performance. Full article

In the field of offshore engineering, the prediction of the crack propagation behavior of metals is crucial for assessing the residual strength of structures. In this study, fatigue experiments were conducted for large-scale T-pipe joints of Q235 steel using the automatic machine learning (AutoML) technique to predict crack propagation. T-pipe specimens without initial cracks were designed for the study, and fatigue experiments were conducted at a load ratio of 0.067. Data such as strain and crack size were monitored by strain gauges and Alternating Current Potential Drop (ACPD) to construct a dataset for AutoML. Using the AutoML technique, the crack propagation rate and size were predicted, and the root mean square error (RMSE) was calculated. The prediction accuracy of the AutoML ensemble learning approach and the machine learning foundation model were evaluated. It was found that when the strain decreases by more than 3% compared to the initial value, crack initiation may occur in the vicinity of the monitoring point, at which point targeted measurements are required. In addition, the AutoML model utilizes ensemble learning techniques to show higher accuracy than a single machine learning model in the identification of crack initiation points and the prediction of crack propagation behavior. In the crack size prediction in this paper, the ensemble learning approach achieves an accuracy improvement of 5.65% over the traditional machine learning model. This result significantly enhances the reliability of crack prediction and provides a new technical approach for the next step of fatigue crack monitoring of large-scale T-tube joint structures in corrosive environments. Full article

To address the issue of local buckling in thin-walled steel tube concrete columns, a form of helical stiffening ribs was proposed. Axial compression tests were conducted on five sections of square steel tube concrete column specimens. The research revealed that, compared to ordinary steel tube concrete columns, the axial compression bearing capacity and deformation capacity of steel tube concrete columns with helical rib constraints increased by 18.5% and 7.7%, respectively. The helical ribs effectively enhanced the buckling resistance of the thin-walled steel tube concrete components. The failure pattern of this new type of component was characterized by diagonal cracks in the encased concrete aligning with the direction of the helical ribs, and the buckling of the steel tube walls was concentrated between the helical stiffening ribs. Based on the experiments, an analysis of the buckling performance of thin-walled steel tubes with helical rib constraints was conducted, and this was incorporated into the bearing capacity calculation. The test, simulation, and theoretical calculations showed that the bearing capacity error of the composite columns for each specimen was within 10%. Ultimately, a formula for the critical buckling bearing capacity of the helical rib steel tubes was proposed. The research findings provide a foundation for the engineering application of this new type of component. Full article

In order to study the bending–shear performance of CFRP concrete-filled steel tubes, static tests were conducted on 15 circular concrete-filled CFRP steel tube bending–shear specimens. For all specimens, D_s was 120 mm, t_s was 2 mm, and m_l was 1. The shear displacement (V-Δ) curve of the specimen and the collaborative work between the steel tube and CFRP are discussed. ABAQUS was applied to simulate the V-Δ curve and failure mode of the specimen. We explored the effects of CFRP layers, material strength, the steel ratio, and the shear span ratio on the bending–shear performance of components. The experimental results show that a steel tube and CFRP can work together. As the shear span ratio increased, the bearing capacity and stiffness of the specimen decreased. An increase in the number of transverse CFRP layers could improve the bearing capacity of the specimen, but it had no significant effect on the stiffness. Calculating the elastic stage stiffness and bearing capacity of 15 short columns of test and FE curves revealed an average error of 6.71% and a mean square error of 0.83 for the elastic stage stiffness. The simulation results of the established finite element model are in good agreement with the experimental results. The average error of the bearing capacity was 3.88%, with a mean square error of 0.94. Based on experimental and finite element results, the moment shear correlation equation for concrete-filled CFRP steel tube bending–shear members is presented. Full article

Construction material management is crucial for promoting intelligent construction methods. At present, the manual inventory of materials is inefficient and expensive. Therefore, an intelligent counting method for steel materials was developed in this study using the object detection algorithm. First, a large-scale image dataset consisting of rebars, circular steel pipes, square steel tubes, and I-beams on construction sites was collected and constructed to promote the development of intelligent counting methods. A vision-based and accurate counting model for steel materials was subsequently established by improving the YOLOv4 detector in terms of its network structure, loss function, and training strategy. The proposed model provides a maximum average precision of 91.41% and a mean absolute error of 4.07 in counting square steel tubes. Finally, a mobile application and a WeChat mini-program were developed using the proposed model to allow users to accurately count materials in real time by taking photos and uploading them. Since being released, this application has attracted more than 28,000 registered users. Full article