Search Results (8)

E36 steel, widely used in shipbuilding and offshore structures, offers moderate strength and excellent low-temperature toughness. However, its welded joints are highly susceptible to fatigue failure. Cracks typically initiate at weld toes or within the heat-affected zone (HAZ), severely limiting the fatigue life of fabricated components. Traditional life prediction methods are complex, inefficient, and lack accuracy. This study proposes a machine learning (ML) framework for efficient fatigue life prediction of E36 welded joints. Welded specimens using SQJ501 filler wire on prepared E36 steel established a dataset from 23 original fatigue test data points. The dataset was expanded via Z-parameter model fitting, with data scarcity addressed using SMOTE. Pearson correlation analysis validated data relationships. After grid-optimized training on the augmented data, models were evaluated on the original dataset. Results demonstrate that the machine learning models significantly outperformed the Z-parameter formula (R² = 0.643, MAPE = 16.15%). The artificial neural network (R² = 0.972, MAPE = 4.45%) delivered the best overall performance, while the random forest model exhibited high consistency between validation (R² = 0.888, MAPE = 6.34%) and testing sets (R² = 0.897), with its error being significantly lower than that of support vector regression. Full article

Traditional methods of construction for reinforced concrete columns utilize longitudinal steel bars and transverse ties. Field experience has shown that such a transverse reinforcement method is labor-intensive, time-consuming, and prone to inconsistencies in quality. Welded wire reinforcement (WWR) offers a prefabricated alternative, forming a closed cage that simplifies installation and speeds up the fabrication process. This study investigates the potential of using WWR as a replacement for conventional ties in reinforced concrete columns in pure compression. To achieve this objective, eight one-third-scale columns (1000 mm height, 200 × 200 mm cross-section) were tested under concentric axial loading inside a Universal Testing Machine. Four of the specimens contained WWR, while the other four had conventional ties. The variables that were considered in this study include the concrete compressive strength (34.3 and 43.5 MPa) and the grid size of the WWR (25 and 50 mm). This study investigated the influence of the type of transverse reinforcement on the strength, modulus of elasticity, and ductility of the confined concrete within the core. The findings of the study showed that lateral reinforcement in the form of WWR can increase the concrete core strength by 2.7% relative to corresponding columns employing ties when f′_c = 34.3 MPa was used. Conversely, the utilization of ties proved to be more effective than WWR in improving concrete core strength by an average of 28.8% when f′_c = 43.5 MPa was used. Additionally, WWR reinforced columns demonstrated a marginal 2.0% rise in the modulus of elasticity and a remarkable 21.0% increase in the ductility of the confined concrete core compared with corresponding tied columns. Theoretical predictions of the axial compressive capacity of WWR reinforced columns subjected to concentric loading based on the ACI-318 code provisions underestimated the experimental results by 20%. These findings demonstrate that WWR can serve as an effective substitute for conventional ties, particularly in cases where rapid installation and reduced labor costs are prioritized. Full article

Single-layer spatial grid joints are crucial to structural safety, with commonly used welded hollow spherical joints and cast steel joints. However, these traditional joints face limitations, including a rigid design, excessive weight, and susceptibility to stress concentration. As engineering practices advance, these joints struggle to meet modern requirements. This paper introduces a generative method for designing rigid joints in single-layer spatial grid structures, based on Audze space-filling criteria. The method’s mathematical formulation is presented, followed by developing novel joint configurations by exploring various cross-sectional forms, retention mass, and geometric elements, while considering bending moments. A comparative analysis of static properties between the new and traditional joints shows promising results. The generative approach demonstrates significant innovation, producing lightweight, aesthetically pleasing, and structurally efficient joints. Compared to conventional welded hollow spherical joints, the new joints exhibit a 57% reduction in self-weight, a 51% decrease in maximum equivalent stress, and a 24% reduction in maximum displacement. This method enables versatile and optimized joint design for single-layer spatial grid structures, offering enhanced strength, safety, and aesthetic appeal. Full article

This paper addresses the issue of fatigue in grid structures, a topic of interest in engineering and academia. The goal is to establish a practical fatigue design calculation method for weld toes in welded hollow spherical joints (WHSJs). The study focuses on commonly used steel tube-WHSJs in grid structures, conducting 25 constant amplitude and four variable amplitude fatigue tests on tube–sphere joints (TSJs) to derive corresponding S-N curves. Using ANSYS, the hot spot stress concentration coefficient K_h at the weld toes in 22 TSJs was calculated, resulting in a numerical solution for K_h ranging from 2.0550 to 4.8600. Based on this, fatigue design methods were established using nominal stress amplitude and hot spot stress amplitude as fundamental parameters. Within a fatigue design reference period of two million cycles, the allowable nominal stress amplitude for TSJs is 22 N/mm², and the allowable hot spot stress amplitude is 66 N/mm². The study also conducted macroscopic and microscopic analyses on fatigue fractures of TSJs, revealing that the weld toe in the sphere of TSJs is the primary site for fatigue crack initiation. This research provides practical calculation methods for fatigue design in WHSJ grid structures, contributing to their broader application. Full article

Insufficient bearing capacity of compression bars in space grid structures can significantly reduce the collapse resistance of structures and cause immeasurable losses. Reactive powder concrete (RPC) with high strength, micro-expansion, and good ductility is used to reinforce the compression members of grid structures by infilling steel tubes. Axial compression tests on five types of high-frequency welded pipes with different section sizes and initial stresses were carried out. The results showed that compared to steel tubes alone, the bearing capacity of steel tubes reinforced by RPC could be increased by 75.77 to 218.34%. With a decrease of either the initial stress or confinement coefficient, the contribution of the material reinforcement increased. The failure mode of the specimen after RPC grouting was the same as that of the non-reinforced steel pipe, which was dominated by elastic-plastic buckling. The grouting hole after reinforcement did not fail prior to the instability of the member, which suggests that necessary measures to repair the hole should be taken. Based on the design method of axial compression bearing capacity of concrete-filled steel tubular members in six codes in China and abroad, the test results of this paper and 242 RPC-filled steel tubes were compared and analyzed. Finally, an equation of nominal bearing capacity, which estimates the ultimate bearing capacity of compressive members strengthened by filled RPC in grid structures, was proposed. Full article

For a typical pipeline-lifting deep-sea mining system, marine mining pipelines have higher requirements for steel welding. After the pipeline steel is welded, a large amount of residual stress will be generated inside the component because the heat treatment is not carried out, causing the pipeline to form stress corrosion cracks in the seawater environment. For high residual stress, the blind hole method has inaccurate measurement accuracy. Based on the theory of solid mechanics, this paper comprehensively considers the distance between the strain grid and the center of the hole. It introduces the ratio γ of the applied stress to the yield strength of the specimen. The strain relief coefficients under the values were investigated. The variation trend of the strain release coefficient distribution with the γ value of the three kinds of strain gauge flowers commonly used in China was discussed. Finally, the variation law of strain release coefficient with γ value was obtained by fitting. The strain release coefficient was corrected to improve the accuracy of the blind hole method for measuring high residual stress, which provides a reference value for the engineering application of the blind hole method. This has important theoretical significance and engineering value for guiding the welding construction of high-strength pipeline steel in a deep-sea environment. Full article

The temperature difference in the weld area during the process of welding, cooling the welded product, and post-welding affect the formation of distortion. Therefore, this study aims to evaluate the distortion formed and hardness behavior on the ASTM A36 (EN S275) steel plate while welding using different cooling media including air, water, and ice. This involved using the MAG (Metal Active Gas) method, which used the AWS A5.18 ER70S-6 electrode with a 1 mm diameter and an 8 mm plate thickness. The value of distortion on the MAG-welded steel plate was measured using a digital dial indicator and evenly distributed by first making a grid. Moreover, the measuring points from the transverse and longitudinal directions were placed at 20 and 8 rows with a distance of 10 mm between points for each variation of the cooling media, such that 10 mm each was allowed left-right and top-down. The results showed that the highest distortion value of 3.13 was formed on the second row of the air cooling media, and this media was also used to determine the contours and distortion profiles. Full article

This study considered the possibility of using steel gabion baskets made of welded mesh for a soil-strengthening function. Examples of such applications are known for meshes made of wires with diameters from 6.3 to 12.7 mm and mesh openings from 125 to 225 mm. In the case of a welded grid, the pulling resistance of fine-grained soil consists of two factors: frictional resistance and bearing resistance. Therefore, for the purposes of this issue, a simplified laboratory pullout test was carried out with four types of welded steel grid (common in Europe) embedded in the fine sand. The geometry of the grid (opening size: 76.2 × 76.2 mm), the type of steel (low carbon steel, tensile strength from 500 to 700 MPa), the diameter of the wire (2.7–4.5 mm) and its cover (ZN + PVC or ZnAl) were taken into account during the analysis. It was unequivocally stated that as the stiffness of the steel grid itself increases, its strength increases during the pullout test, which is not so obvious in the case of popular steel woven meshes. In addition, it has been shown that steel welded meshes with wire diameters less than 6 mm are suitable for soil reinforcement in structures with gabion facing, and the determined apparent friction coefficient (μ_k = 0.39–1.47) takes values similar to the friction coefficient given in references for welded meshes of larger diameters. This is a positive premise for starting further research on the use of wires of smaller diameters for welded mesh production used as soil reinforcement. Full article