Search Results (37)

Metal inert gas (MIG) brazing was used to join galvanized thin sheets with thicknesses in the range of 0.8 to 2 mm in a lap joint configuration using CuAl₈ wire as filler. The process was used to manufacture built-up cold-formed steel beams composed of corrugated steel webs and flanges made from thin-walled cold-formed steel lipped channel profiles. The effect of heat input and sheet thickness on joint properties, such as macro- and microstructure, wettability, and mechanical characteristics such as microhardness and tensile strength were investigated. The bead geometry was assessed by studying the wettability of the filler material. The microstructure was investigated by digital and scanning electron microscopy, and the composition in the heat-affected zone (HAZ), interface, and bead was determined by energy dispersive spectroscopy. Formation of Fe–Al intermetallics was observed in the bead at the bead–base material interface. Some pores were noticed that formed due to the evaporation of the zinc coating. The bead shape and mechanical properties were found to be the best when 1.2 and 2 mm sheets were brazed using a heat input of 121.4 J/mm. This suggests that not only the heat input but also the thickness of the sheet metal play a crucial role in the production of MIG brazed joints. Full article

This study investigates a novel steel grid shear wall (SGSW) structure with lightweight and discrete lateral-resistance members, focusing on its structural behavior in lateral resistance. By comparing the characteristics of the thin steel plate shear wall, the mechanism of the steel grid components in both the tension zone and compression zone was briefly described. The formulas of lateral-resistant capacity and initial stiffness of the SGSW were derived through the static equilibrium method. Then, the influence laws of the span–height ratio, steel member spacing and section size of the steel members on the lateral-resistant performance of the SGSW were determined through a parametric analysis. In addition, the accuracy of the calculation formula was validated. The results showed that the strains of the steel grid components in different positions were all the same when the bending stiffnesses of the edge members were significantly large. The lateral-resistance capacity of the SGSW increased with the span-to-height ratio, while it decreased as the spacing between the steel components increased. Compared with the effects of web height, web thickness and flange width, increasing the flange thickness exhibited the best effects on improving the lateral capacity. As the flange thickness increased from 7 mm to 13 mm, the lateral-resistant capacity showed an improvement of 35.45%. Additionally, the formula derived in this study demonstrated high accuracy and reliability, with the error not exceeding 8% between the formula calculation and the simulation results. Full article

Kinematically exact rod models were a major breakthrough to evaluate complex frame structures undergoing large displacements and the associated buckling modes. However, they are limited to the analysis of global effects, since the underlying kinematical assumptions typically take into account only cross-sectional rigid-body motion and ocasionally torsional warping. For thin-walled members, local effects can be notably important in the overall behavior of the rod. In the present work, high-fidelity simulations using elastic 3D-solid finite elements are employed to provide input data to train a Deep Neural Newtork-(DNN) to act as a surrogate model of the rod’s constitutive equation. It is capable of indirectly representing local effects such as web/flange bending and buckling at a stress-resultant level, yet using only usual rod degrees of freedom as inputs, given that it is trained to predict the internal energy as a function of generalized rod strains. A series of theoretical constraints for the surrogate model is elaborated, and a practical case is studied, from data generation to the DNN training. The outcome is a successfully trained model for a particular choice of cross-section and elastic material, that is ready to be employed in a full rod/frame simulation. Full article

The failure mode of thin-walled C-channel beams typically manifests as premature local buckling of the compression flange, leading to insufficient utilization of material strength in both the flange and the web. To address this issue, this study adopts the approach of increasing the number of bends to reinforce the flange and adding V-shaped stiffeners in the middle of the web to reduce the width-to-thickness ratio of the plate elements, thereby delaying local buckling and allowing for greater plastic deformation. However, the challenge lies in the irregular cross-sectional shape and complex buckling patterns. Therefore, this paper aims to explore a suitable cross-sectional form to expand the application of stainless steel members. Subsequently, three-point bending tests were conducted on the optimally designed stainless C-channel beam with folded flanges and mid-web stiffeners. The finite element simulation results were compared and analyzed with the experimental results to validate the model’s effectiveness. After verifying the correctness of the finite element model, this study conducted numerical parameterization research to investigate the effects of the shear span ratio, complex edge stiffeners, web height–thickness ratio, and V-shaped stiffener size on the shear performance of stainless steel folded flange C-beams. The results show that changing the shear span ratio has a significant impact on the shear capacity and vertical deflection deformation of components; increasing the web height–thickness ratio can enhance the shear capacity of the component; elevating the V-shaped stiffener size can slightly improve the shear capacity of components; and for the stainless steel C-shaped beam with folded flanges and intermediate stiffening webs, adding edge stiffeners cannot remarkably promote the shear capacity of the component. Full article

Composite box girders with corrugated steel webs (CBGCWs) have attracted increasing attention in bridge engineering. However, the shear lag effect has an impact on the mechanical behavior of thin-walled box girders and the impact of transverse deformation on this effect is usually neglected. In this study, a modified energy variational method is proposed to quantify the shear lag effect on CBGCWs. The shear deformations of each flange are analyzed based on the mechanical properties of the corrugated steel webs. A shear-lag warpage displacement function is introduced for each flange to account for the shear lag effect due to transverse deformation of the top flange. The formulation for the shear lag effect on CBGCWs is then derived using the principle of the energy variational method. The feasibility and accuracy of the proposed method are validated through a numerical study of a simply supported CBGCW subjected to uniform loading. In addition, a parametric analysis of the shear lag effect on CBGCWs is conducted. The results demonstrate that local bending deformation of the top flange leads to an uneven distribution of shear lag effects and the shear lag effect on corrugated steel webs is significantly influenced by the width–to–span ratio. Full article

The article provides information about strengthening cold-formed thin-walled steel beams made of the sigma profile. An innovative concept for sectional transverse strengthening of thin-walled beams subjected to concentrated forces was investigated. The proposed solution’s novelty lies in attaching the sectional transverse strengthening to the beam’s cross-section, employing a point crimping technique. This technique requires a specific modification of the cross-section edges, necessitating double-lipped flanges. This strengthening method is innovative, as it has not been previously applied to cold-formed structures. Typically, strengthening is achieved using other cold-formed elements or materials, such as timber, lightweight concrete, or CFRP tapes. The laboratory experimentally validated the proposed method using short- and medium-length beams. The experimental results were then compared with the results of the numerical analyses and the conventional design approach described in EC3. The results demonstrated the feasibility of implementing this type of strengthening, its reliability under load, and the confirmation of an increase in the load-bearing capacity of the experimental samples by 11–24%. Full article

We develop a new analytical and numerical approach, based on existing models, to describe the onset of lateral–torsional buckling (LTB) for simply supported thin-walled steel members. The profiles have uniform I cross-sections with variable lengths of the flanges, to describe also H cross-sections, they are prestressed by external tendons, and they are subjected to fire and various loadings. Our approach manages to update the value of the prestressing force, accounting for thermal and loads; the critical multipliers result from an eigenvalue problem obtained applying Galërkin’s approach to a system of nonlinear equilibrium equations. Our results are compared to buckling, steady state, and transient state analyses of a Finite Element Method (FEM) simulation, in which an original expression for an equivalent thermal expansion coefficient for the beam–tendon system that accounts for both mechanical and thermal strains is introduced. Our aim is to find estimates for the critical conditions with no geometric imperfections and accounting for the decay of material properties due to fire, thus providing limit values useful for conservative design. This approach can surpass others in the literature and in the existing technical norms. Full article

Thin-walled channel beams such as cold-formed steel purlins are primarily used to withstand wind forces in the roofing and walling systems of buildings. Traditionally, these types of members are usually designed for bending moments, with the effects of torsion ignored. However, the loading on thin-walled channels can be much more complicated than simple bending actions. Because of the position of the shear centre outside the section, channels can undergo bending and torsion when subjected to vertical load on the top flange. The applied torsion may cause significant stresses in the channel, which may need to be accounted for in design. There appears to be no research on quantifying the effects of torsion on thin-walled channels subjected to a uniformly distributed load acting on the top flange. In this paper, a theoretical solution is derived for calculating the longitudinal stresses in thin-walled channels subjected to torsion caused by a uniformly distributed load acting on the top flange. The theory is validated by modelling the channels in a finite-element analysis. The theoretical results include calculations of the twist rotation, bimoment, sectorial coordinate and longitudinal stresses, while the results from the finite-element analysis include the twist rotation and longitudinal stresses. The results show that the longitudinal stresses caused by torsion can significantly exceed those caused by the bending moment. Practical advice is also given for engineers on how to minimize torsion in cold-formed steel purlins. Full article

In this study, we have developed an electrostatically suspended accelerometer (ESA) specifically designed for ground use. To ensure sufficient overload capacity and minimize noise resulting from high suspension voltage, we introduced a proof mass design featuring a hollow, thin-walled cylinder with a thin flange fixed at the center, offering the highest surface-area-to-mass ratio compared to various typical proof mass structures. Preload voltage is directly applied to the proof mass via a golden wire, effectively reducing the maximum supply voltage for suspension. The arrangement of suspension electrodes, offering five degrees of freedom and minimizing cross-talk, was designed to prioritize simplicity and maximize the utilization of electrode area for suspension purposes. The displacement detection and electrostatic suspension force were accurately modeled based on the structure. A controller incorporating an inverse winding mechanism was developed and simulated using Simulink. The simulation results unequivocally demonstrate the successful completion of the stable initial levitation process and suspension under $\pm 1g$ overload. Full article

A structure for joining thin-walled 6061-T6 aluminum alloy tube (outer tube) and Q195 steel tube (inner tube) by electromagnetic flanging process was proposed. The formation process, mechanical properties, failure modes, and morphology of the joint were investigated. The results showed that the outer tube impacted the inner tube, the flanges of the prefabricated holes on the outer tube were embedded into the prefabricated holes of the inner tube under the action of Lorentz force, and thus the mechanical locking joint was obtained. There were two tensile failure modes for the joints: Pull-out and fracture. Specifically, when the discharge energy was relatively high, the failure mode changed from pull-out to fracture. Combining the results of tensile tests and morphology observations, the maximum loads of the joints increased with the discharge energy. However, excessive discharge energy would lead to the brittle fracture of the inner tube, which was not beneficial to the service. Better discharge energy and the maximum load of the joint at this discharge energy were obtained. Full article

A thin-walled head with a lateral normal flanged hole is a key part of a propellant tank, and its low-cost and high-precision forming process is very challenging. In this paper, a two-step method is proposed to preform the head via marginal-restraint mandrel-free spinning and then to realize the flanging of the lateral normal hole using a punching–spinning method. Finite element analysis of round-hole punching–spinning flanging shows that the larger the thinning ratio and the roller fillet radius, the lower the rebound and contour rise amount; the larger the feed ratio, the lower the rebound and the higher the contour rise amount. Further study on the effects of round-hole punching–spinning flanging on the secondary deformation of thin-walled heads shows that the deformation of the head in the area around the flanging hole is less severe than that of the flat blank, and the deformation in the circumferential direction is different from that in the busbar direction. Finally, it is verified through experiments that the two-step method can realize the spin forming of thin-walled heads with lateral normal flanged holes. Full article

Composite structural insulated panels (CSIPs) are eco-friendly, high-performance materials, which not only good have mechanical properties, but also good waterproof, moisture-proof, fire-proof, and anti-corrosion characteristics, so they have been used to build envelope structures in recent years. However, how to improve stiffness of CSIPs remains unsolved. The poor stiffness is one of the biggest obstacles for the application of CSIPs in the load-bearing members of civil engineering. In this study, the layout of glass–polypropylene (PP) laminate layers is designed to enhance its stiffness, and this study applies CSIPs as load-bearing members of civil engineering for the first time. Thus, the bend model of CSIP thin-wall box-beams under uniform loading is built, based on Timochenko’s theory. The deflection curve equation is presented, considering shearing deformation. The expressions for the bending of normal strain flanges of the beam and the equation considering principal shearing strain at the beam’s web are obtained, respectively. Finally, mechanical properties of the thin-wall box-beam under uniformly distributed loads were performed by FE. FE results are entirely consistent with the theoretical results, thereby making the theoretical method applicable for the design of thin-wall box-beams, which are made of composite materials. Different from other beams, the shearing deformation is a critical factor that influences the deformation of thin-walled box-beams. Full article

The buckling failure of the afterburner cylinder is a serious safety concern for aero-engines. To tackle this issue, the buckling simulation analysis of the afterburner cylinder was carried out by using finite element method (FEM) software to obtain the buckling mode and critical buckling loads. It was found that the afterburner cylinder was susceptible to buckling when subjected to differential pressure or the compressive force of the rear flange. Buckling would occur when the differential pressure reached 0.4 times the atmospheric pressure or when the axial compressive force on the rear flange reached 222.8 kN. Buckling was also found at the front of the cylinder under the auxiliary mount load. Additionally, under various loads on the rear flange, buckling occurred in the rear section, with the buckling mode being closely related to the load characteristics. Based on the simulation results and structural design requirements, two structural improvements were proposed, including the wall-thickening scheme and the grid reinforcement scheme. FEM simulation analysis results showed that both schemes would improve the rigidity and stability of the afterburner cylinder. For the 0.3 mm increase in the wall thickness scheme, the critical buckling load increased by 17.86% to 66.4%; for the grid reinforcement scheme, the critical buckling load increased by 169% to 619%. Therefore, the grid reinforcement scheme had a stronger anti-buckling ability and was deemed the optimal solution. The findings of this paper could provide technical support for the structural design of large-sized and thin-walled components of aero-engines. Full article

At present, the development of green building materials is imminent. Traditional wood structures show low strength and are easy to crack. Steel structures are also prone to instability. A novel rectangular-section composite beam from the welded thin-walled H-shape steel/camphor pine was proposed in this work. The force deformation, section strain distribution law, and damage mechanism of the combined beam were studied to optimize the composite beam design, clarify the stress characteristics, present a more reasonable and more efficient cross-section design, and promote green and environmental protection techniques. Furthermore, the effect of different factors such as steel yield strength, H-type steel web thickness, H-type steel web height, H-type steel flange thickness, H-type steel upper flange covered-board thickness, and combined beam width was investigated. The ABAQUS simulation with the finite element software was also performed and was verified through empirical experiments. According to the results: (1) the damage process of the composite beam was divided into three steps, namely elastic stage, elastic–plastic step, and destruction stage, and the cross-middle section strain met the flat section assumption; (2) additionally, the bond connection was reliable, the two deformations were consistent, and the effect of the combination was significant. The study of the main factors showed that an increase in the yield strength, the H-type steel web height, the steel H-beam upper flange thickness, and the combined beam width caused a significant enhancement in the bending bearing capacity. The combined beam led to high bending stiffness, high bending bearing capacity, and good ductility under bending. Full article

Complex edge stiffeners are widely used because of their superior performance over simple edge stiffeners in limiting flange buckling and improving local stability. However, most of the studies on complex edge stiffeners are qualitative. In this paper, the criterion to judge the stiffening adequacy based on the buckling half-wavelength and buckling coefficient is proposed. It is considered as the criterion that the edge stiffeners’ stiffness is not less than the minimum stiffening stiffness or the half-wavelength of buckling is not more than the width of the flange. The criterion is followed for the minimum limits of the edge stiffener width−thickness ratios; whether the flange buckling occurs before the edge stiffener buckling and the economic implications are the criteria that should be followed for the maximum limits of the edge stiffener width−thickness ratios. Using the finite strip method, the feasibility of the criteria was verified by comparing them with the rules of simple edge stiffeners. The detailed design requirements for the width−thickness ratio limits of thin-walled steel elements with complex edge stiffeners were first given from an extensive parametric analysis. Based on the optimization algorithm, the suggestions and optimum sizes of complex edge stiffeners for thin-walled steel elements are provided, considering the sections’ economy and performance. It is considered that a ratio of 1:1 between the primary and the secondary edge stiffeners’ widths is the best configuration for elements with complex edge stiffeners. Full article