Intermittent Welding Research Articles

Nominal stresses in continuous and intermittent rail welds of crane runway beams

Crane runway beams of hot-rolled I sections are frequently the supporting structures of top-running overhead bridge cranes. In case of light crane service, the crane rails are usually fastened to the top flange of the crane runway beams by fillet welds. A survey among steel construction companies revealed that continuous rail welds as well as intermittent rail welds are commonly used. The rail welds are subject to multiaxial fatigue since they are exposed to normal and shear stresses due to the local wheel load introduction and global bending. Currently, the design standards EN 1993-1-9 (2005) and EN 1993-6 (2007) neither provide an appropriate detail category nor a nominal stress formula for rail welds. The paper focuses on the calculation of the nominal stresses in rail welds as basis of the fatigue action effect within the nominal stress method. It describes the differences in the nominal stresses of continuous and intermittent rail welds because of the contact between rail and top flange that has to be assumed for intermittent rail welds. Based on work samples, the contact conditions of intermittent rail welds are characterized as ‚technical contact‘ (in contrast to ‚ideal contact‘) due to imperfections within the contact surfaces that are described in detail. A Finite Element model is presented that accounts for the ‚technical contact‘ between rail and flange. This model is analyzed in a parametric study to identify the decisive parameters on the nominal stresses in intermittent rail welds.

Experimental investigations on the compression capacity of rectangular steel tubular columns strengthened with intermittently welded angle steel

Many steel structure buildings in China were built from the 1970s to the 1980s, and they have been in service for decades. However, due to factors such as changes in their functionality, prolonged disrepair, and erosion of the surrounding environment. Studying the strengthening of many existing steel structures will become an important measure during the “reinforcement period.” Welding angle steel on the surface of steel columns for reinforcement is a commonly used method in practical engineering. However, the traditional continuous welding of angle steel to reinforce rectangular steel tube columns results in a relatively large welding workload on the construction site, extending the construction period and increasing the engineering cost, which cannot guarantee high welding quality. To reduce the workload of on-site welding and the cost of construction reinforcement, intermittent welding is proposed. This article designed 9 test specimens for axial and eccentric compression tests to obtain the failure modes, ultimate bearing capacity, and stress distribution of the cross-section of steel tube columns reinforced with different intermittent welding angle steels. The experimental results indicate that intermittent welding can replace continuous welding for the reinforcement of steel tube columns, significantly reducing on-site welding workload and fully utilizing the role of angle steel reinforcement. If the length of the intermittent welding is too large, local buckling will occur, thereby weakening the reinforcement effect of the angle steel. The existence of batten plates can improve the ultimate bearing capacity of intermittent welded angle steel tube columns. Comparative analysis was conducted using a finite element model, which revealed the force transfer mechanism and ultimate bearing capacity of intermittent welding angle steel reinforced steel tube columns. The optimal weld spacing and weld length for intermittent welding of angle steel to reinforce rectangular steel tube columns provide a theoretical reference for the design and application of practical reinforcement engineering.

Fatigue lifetime assessment of weld ends with idealized or real geometry in steel joints for off-road vehicles using the Peak Stress Method

The Notch Stress Intensity Factors (NSIFs) for the fatigue analysis of welded structures can be rapidly estimated by FEM by applying the Peak Stress Method (PSM). Two steel welded joint geometries adopted for off-road vehicles and containing four intermittent fillet welds were tested under uniaxial loading. To apply the PSM, an idealized as well as the real 3D scanned geometry of the weld ends were implemented in the numerical analyses. The PSM properly anticipated where cracks initiated and estimated the fatigue lives in fairly good agreement with the outcomes of the fatigue tests.

Prediction of distortion in a thin-plate structure with intermittent fillet joints using a local-to-global approach

Fillet welds by intermittent welding are widely used in the welding of centrifugal fans, such as attaching a fan blade to the rear plate. The intermittent welding method transforms the full-length continuous weld into multiple short welds to minimize distortion by reducing the total heat input for a welded joint to control welding distortion. An infinite number of short welds are created during this process. However, depending on the complexity of the model, the computational cost of predicting welding distortion based on full-scale modeling is considerable. These numerous short welds undoubtedly complicate modeling and computations, limiting rapid distortion prediction for large and complex structures. This study develops an equivalent deformation calculation approach based on a local-to-global technique and applies it to predict distortion of a fillet joint welded specimen. The approach consists of two steps. First, the welding-induced structural deformation is calculated for a two-dimensional (2D) weld and a 2D heat-affected zone (local calculation). Second, the 2D structural deformation is applied to the full-scale welded structure using a nearest-point spatial interpolation algorithm to acquire the three-dimensional (3D) equivalent deformation (global calculation). Note that the weld shape was considered in both local and global calculations. In addition, welding tests were performed, and the coordinates of the key points were measured. The geometric parameters of the welds used in the numerical simulations were obtained from experimental observations. Finally, the key point coordinates obtained by the proposed approach were compared with experimental measurements. Furthermore, the distribution of out-of-plane distortion caused by the new approach was compared with the simulation results of the thermo-elastic-plastic method performed on a full-scale welded structure. The proposed approach can be verified by both comparisons.

Finite Element Analysis and Reinforcement of Steel Crane Beam under Eccentric Track Loading

The crane track of a steel structure workshop was installed eccentrically, and the crane operation caused a large deflection of the crane beam, requiring reinforcement measures. The finite element model of the crane beam was established by Midas Gen finite element software, and the maximum stress, deflection, and the stress amplitude of 9 m and 12 m steel crane beam under different track eccentricity values were analyzed. The results show that when there is no brake truss, the maximum stress and deflection of the crane beam will increase greatly under the action of eccentric loading. On the contrary, a brake truss can effectively reduce the adverse effect of eccentric loading; the fatigue strength of crane beam cannot be controlled under eccentric rail loading. The reason why steel crane beam is sensitive to track eccentricity is that its torsional stiffness is too small. As a reinforcement measure, welding angle steel or steel plate lower on the crane beam flange, forming a box section, can effectively increase the torsional stiffness of the crane beam; the residual stress can then be effectively reduced by applying intermittent welding and reinforcement using the same material.

Experimental and numerical study on the hysteretic behavior of a hybrid timber buckling-restrained brace with a cross-shaped steel core

In this study, a hybrid buckling-restrained brace (BRB) composed of a cross-shaped steel core and a timber casing has been developed for potentially enhancing the seismic performance of heavy-timber frame structures. For such a novel timber buckling-restrained brace (T-BRB), a simplified design procedure has been conducted to preliminarily determine its key design parameters. Then, for investigating the hysteretic behavior of the T-BRB, eight full-scale 3.6-m-length T-BRBs with various design parameters and configurations have been tested. The considered design parameters include the ratio between the Euler buckling load of the casing to the core yield force (i.e., constraint ratio), the fastener type, the fastener spacing, and the welding details of the steel core. Finally, a calibrated numerical model of the T-BRBs has been developed and used to further investigate the specific lower limitation of the constraint ratio, which should be carefully addressed during the engineering design of the T-BRBs. It shows that the T-BRBs can provide stable hysteretic performance with an ideal energy-dissipating capacity. Also, in the T-BRB with un-densified fastener spacing near its casing ends and in the T-BRB adopting an intermittent welding for its steel core, a premature splitting and rupture of the casing ends would occur based on the experimental results. It leads to the ratio between their cumulative inelastic deformation (CID) to their yield deformation to be less than the specified minimum ratio of 200. When using the bolts instead of the self-tapping screws as fasteners, the CID and the energy dissipation of the T-BRB can be enhanced by 43.74% and 39.60%, respectively. For the T-BRB with a cross-shaped steel core, the specific lower limitation of its constraint ratio is recommended to be 1.5.

A study of the mechanical behavior of rectangular steel tubular column strengthened using intermittent welding angle steel

From the perspective of the development of steel structures in China, the existing steel structure had experienced decades of service. However, due to the change of its functionality, and the erosion caused due to the surrounding environment, reinforcement of steel has become necessary. Thus, the research on reinforcement theory and methods of the existing steel structures has become an important measure in the “reinforcement period”. Steel angle welding on the surface of steel columns is a common method used in practical engineering. However, the traditional continuous welding angle steel reinforcement of rectangular steel pipe columns leads to a large amount of welding work on the construction site, thus prolonging the construction time and increase the project cost. Moreover, the quality of welding also cannot be guaranteed. Therefore, in order to reduce the cost of field welding and reinforcement of the construction project, intermittent welding is proposed in this work. In this paper, the finite element analysis of rectangular steel tube column models that were strengthened using different intermittent welded angle steel under axial and eccentric compression is discussed out and the results are compared with the experimental results for validation. Further, a large number of numerical models with different parameters are analyzed. From the analysis, the ultimate bearing capacity and the load transfer mechanism of the rectangular steel tube columns that were strengthened using intermittent angle steel under eccentric and axial compression are studied, and the optimal weld spacing and weld length are obtained. The results provide a theoretical base for future practical engineering applications.

Development of Methodology for Calculation of Discontinuous Circular Welds in Torsion

The main criterion for the performance of welds is the strength. The least durable ones are the corner joints used to perform various types of welded joints. In the literature, the methods of calculating the strength of welded joints with solid welds are considered in sufficient details. Methods of calculation of connection interrupted sutures absent. In this case, the greatest difficulty is the calculation of connections using circular intermittent welds, which are often performed in welded drums and pulleys; they work on torsion. Therefore, the development of methods for calculating circular intermittent welds for torsion is quite important.Shear stresses in welds from torque are determined depending on the value of the polar moment of resistance of its dangerous section. When determining the polar moment of resistance of the dangerous section of a circular discontinuous weld, it was represented by a set of sections in the form of a sector of a circular ring. The method of calculation of the polar moment of resistance of the rotated dangerous section of a circular discontinuous weld, which takes into account the relative length of the weld areas and their number, as well as the method of accurate and approximate calculation of shear stresses in the weld.

Generalization of the Vlasov theory for lateral torsional buckling analysis of built-up monosymmetric assemblies

The present study provides a formal generalization of the elastic lateral torsional buckling solution based on the Vlasov theory, initially intended for monolithic sections, to extend its applicability to any number of cross-sections connected together to form a monosymmetric assembly. The theory applies the well-known Vlasov kinematic assumptions to each of the components and augments them by assuming no relative slip between the components, as would be the case when components are bolted or welded. The formulation naturally leads to general expressions for effective sectional properties for the assembly (e.g., location of the shear centre, warping constant, monosymmetry parameter, and the Saint-Venant torsional constant). By adopting the effective sectional property definitions arising from the theory, the resulting lateral torsional buckling variational principle for the assembly is cast in a form analogous to that of monolithic sections. Alternative techniques are proposed to estimate the effective warping constant and monosymmetry parameter for assemblies. The solution shows that assemblies of sections connected through plug welds have lower critical moments than those continuously welded at the edges, while assemblies with intermittent welds have intermediate critical moment values. It is shown that treating the assembly as a monolithic section yields higher critical moments than assemblies with plug welds. The theory is used to quantify the critical moments in a number of built-up applications. Comparisons with the predictions of shell finite element model in Abaqus and S-Frame demonstrate the validity of the formulation.

Welding Seam Trajectory Recognition for Automated Skip Welding Guidance of a Spatially Intermittent Welding Seam Based on Laser Vision Sensor.

To solve the problems of low teaching programming efficiency and poor flexibility in robot welding of complex box girder structures, a method of seam trajectory recognition based on laser scanning displacement sensing was proposed for automated guidance of a welding torch in the skip welding of a spatially intermittent welding seam. Firstly, a laser scanning displacement sensing system for measuring angles adaptively is developed to detect corner features of complex structures. Secondly, a weld trajectory recognition algorithm based on Euclidean distance discrimination is proposed. The algorithm extracts the shape features by constructing the characteristic triangle of the weld trajectory, and then processes the set of shape features by discrete Fourier analysis to solve the feature vector used to describe the shape. Finally, based on the Euclidean distance between the feature vector of the test sample and the class matching library, the class to which the sample belongs is identified to distinguish the weld trajectory. The experimental results show that the classification accuracy rate of four typical spatial discontinuous welds in complex box girder structure is 100%. The overall processing time for weld trajectory detection and classification does not exceed 65 ms. Based on this method, the field test was completed in the folding special container production line. The results show that the system proposed in this paper can accurately identify discontinuous welds during high-speed metal active gas arc welding (MAG) welding with a welding speed of 1.2 m/min, and guide the welding torch to automatically complete the skip welding, which greatly improves the welding manufacturing efficiency and quality stability in the processing of complex box girder components. This method does not require a time-consuming pre-welding teaching programming and visual inspection system calibration, and provides a new technical approach for highly efficient and flexible welding manufacturing of discontinuous welding seams of complex structures, which is expected to be applied to the welding manufacturing of core components in heavy and large industries such as port cranes, large logistics transportation equipment, and rail transit.

Additive Manufacturing of Reinforced Concrete—Development of a 3D Printing Technology for Cementitious Composites with Metallic Reinforcement

Reinforced concrete (RC) is by far the most widely used composite material in the world. Despite the enormous economic importance of RC construction, there is a lack of viable concepts for its digital fabrication. While 3D printing of plain concrete has been pushed forward by a growing research community in recent years, methods for integration of steel reinforcement have only scarcely been researched and little attention has been payed to meet the practical requirements of construction sites and prefabrication plants. Therefore, full-scale implementations of current approaches are hardly available. Based on both, a sound review of R&D for digital fabrication of RC structures and an analysis of practical requirements, the present paper proposes a novel 3D printing process for RC structures, called Additive Manufacturing of Reinforced Concrete (AMoRC), viable for real-world application. In this hybrid process, consisting of an intermittent stud welding process and a continuous concrete extrusion process, segmented steel reinforcing bars are joined to form a three-dimensional reinforcement mesh and simultaneously encased with extruded concrete. The paper describes the conceptual design and development of the process and demonstrates the results of preliminary investigations on its feasibility. As AMoRC enables the operation of rebar welding and concrete extrusion process with synchronized feed rates, combination of both processes in one hybrid print head for digital fabrication of RC is a key-advantage of the proposed method.

Mechanical behaviour of angles used to strengthen rectangular steel columns

Welding angles onto the surfaces of steel columns is a commonly used method to strengthen rectangular steel columns in practical engineering. However, continuous welding requires extensive welding work in the field, which increases project costs significantly and extends the construction period. Intermittent welds can reduce both the field welding work and the cost of the reinforcement. The main objective of this study was to investigate the reliability of substituting intermittent welding for continuous welding through an experimental study. The mechanical behaviour of the intermittently welded angles was also investigated. The influences of the use of steel battens, the number of weld zones, the weld length and the intermittent length of the weld seam on loading capacity were examined and a design recommendation is proposed. The findings of this study indicate that intermittent welding can be used as a substitute for continuous welding.

Mechanical and seismic behaviors of bottom-flange-bolted upper-flange-welded through-diaphragm connections

The through-diaphragm connection to a square steel tubular column is a regular connection type that is used widely in Asian countries. However, connections with traditional welded flange designs often fail through bottom flange to diaphragm weld fractures owing to the unstable quality of on-site intermittent welding. Therefore, a new type of bottom-flange-bolted upper-flange-welded through-diaphragm connection is presented to avoid premature fracture failure at the bottom flange. The construction process of the new connection is more convenient than the traditional construction. In this study, three specimens were designed and tested to investigate the mechanical properties and seismic behaviors of this new connection, and different web connecting methods were considered. The failure modes, hysteretic curves, backbone curves, and energy dissipation abilities were evaluated. Together with finite element simulations, the deforming pattern and load bearing performances were discussed in comparison with the traditional welded flange. The results indicate that the bolt and plate slip would present a slight reduction in the energy dissipation ability of the new connection. However, the strength development is similar to that of the traditional welded flange connection, and the ductility satisfied the seismic provisions in moment frame connections. A two-row regular-bolted web connection can ensure a sound load transfer at the beam web.

Framework of computational approach based on inherent deformation for welding buckling investigation during fabrication of lightweight ship panel

During the fabrication of lightweight ship panel, thin plates are usually employed and welding induced buckling may be generated, which will significantly influence the manufacturing integrity and performance. Computational approach based on inherent deformation was proposed, and its framework and application were introduced in this study. In detail, typical fillet welded joint was experimentally conducted and its solid elements FE model was numerically examined with experimental validation. Then, welding inherent deformation was evaluated based on computational results; elastic FE analysis with welding inherent deformations as input parameters was implemented to predict out-of-plane welding distortion and critical welding buckling condition. As the practical technique, intermittent welding procedure was employed to decrease the magnitude of welding inherent deformation, and sequentially avoid the occurrence of welding induced buckling. With this holistic investigation, welding induced buckling during thin plate section assembly was represented; critical welding buckling condition and mitigation technique were also demonstrated.

Numerical simulation and experimental investigation on static behavior of cold formed steel beam with trapezoidally corrugated web by varying depth-thickness ratio

This paper presents a numerical simulation and experimental investigation on the static behavior of cold-formed steel beams with trapezoidally corrugated web has been carried out to find its structural performance of simply supported beam under pure bending. The steel beams with corrugated steel webs represent a new innovative which has emerged in the past decade for short- and medium-span beams. The thin corrugated web affords a significant weight reduction of these beams, compared with hot-rolled beams. In the initial solution, the flanges are made of flat plates, welded to the trapezoidal web sheet, requiring a specific welding technology. The connecting between flanges to the web can be done by means of intermittent welding. The paper summarizes the experimental and numerical investigations carried out at the Hindustan University and, at the end, presents the flexural behavior of cold-formed steel beams with trapezoidally corrugated web. To find the effect of web corrugation, 12 experiments were conducted on cold-formed steel beams. Beams having two different web depth-thickness (dw/tw) ratio 60 and 80 and with three types of web corrugation angles 0°, 30° and 45° were tested. Two beams were tested in each series. The static performance of the three different corrugation angles, including failure mode, load–deflection curves, strength capacity, load–strain curves, moment–curvature curves, flexural stiffness and ductility, are compared and discussed in detail based on the experimental results. Finally, numerical analysis using ANSYS Workbench results are analyzed and the experimental results were validated with the results obtained from the finite element analysis.

Axial compression performance of steel box columns with different strengthening schemes

Welding the reinforced component on the surface of a steel structure is a common method to reinforce steel structures in practical engineering. Work efficiency is low in actual construction because of continuous welding. Intermittent welding was adopted in this study to address this issue. The axial compression performance of reinforced steel columns in an actual project was studied through experiments and with the numerical method. The influence of different intermittent welding reinforcement schemes on the reinforcement of steel box columns was analyzed. Steel box columns with different weld intervals were placed relatively close because of their failure mechanism. The discontinuous welding reinforcement scheme reduced cost and improved efficiency. A simplified numerical model was established to conduct a parametrical analysis. An improved reinforcement scheme was proposed based on the analyzed results. The improved reinforcement scheme enhanced the load conditions and strength of steel angles.

Evaluation of welded joints of vertical stiffener to web under fatigue load by hotspot stress method

The feasibility of intermittent fillet weld at the connection of vertical web stiffener and web plate in steel box girder bridge was studied considering vehicular fatigue loading. The study was conducted using FEM models taken from real three span steel box girder bridge with three box-girders connected by reinforced concrete deck. Web-to-stiffener connections at the middle of span and near the support of the bridge were studied in detail using refined 3D linear finite element analysis. Then, using structural hot spot stress approach, fatigue load induced stress was evaluated on the welded parts, and parametric study was conducted on a range of intermittent fillet weld parameters to evaluate the maximum fatigue load induced stress. The results of the parametric study are compared with maximum fatigue stress thresholds specified in design codes to verify the applicability of the proposed detail. Finally, some conclusion and recommendations are given on the applicability of intermittent fillet weld for web-to-stiffener connections of steel box girder bridges.

Recent research on welding distortion prediction in thin plate fabrication by means of elastic FE computation

Elastic FE simulation with inherent deformation and interface element is an ideal and practical computational approach for predicting welding distortion in production of thin plate structures. In this study, recent researches on inherent deformation theory and welding induced buckling investigation of ship panel were sequentially introduced. Taking bead-on-plate welding as research objective (plate with 2.28 mm in thickness), integration approach with inherent strain was proposed to accurately and conveniently evaluate magnitude of inherent deformation. Also, average temperature to clarify the mechanism of influential effect of plate width on magnitude of inherent deformation was presented and examined. With the mechanism investigation of welding induced buckling by elastic FE analysis using inherent deformation, an application for predicting and mitigating the welding induced buckling in fabrication of ship panel with thin plates by employing different welding procedure patterns was carried out. Examined intermittent zigzag welding procedure is effective to reduce the magnitude of in-plane inherent shrinkages and control the possible welding induced buckling.

Strengthening under Load: The Effect of Preload Magnitudes

Strengthening existing structures under load by welding plates is often conducted but little research into this subject was presented. Some researchers claim that the column strengthened under load has the same ultimate capacity as the column welded without preloading. Others disagree and recommend safe design not allowing the steel to yield. The paper presents the parametric study of wide flange columns HEA 100 strengthened under load via two plates parallel to flanges conducted on numerical models validated by experiment. The varying parameters are thickness of strengthening flange, column length, initial bow imperfection, preload magnitude and direction of the axis which is pinned while the other axis is fixed. The experimental research consisted of two columns welded without preload and two columns strengthened under preload ratios (preload magnitude divided by base column ultimate strength) equal to 0.5 (200 kN) and 0.75 (300 kN). All columns were 3 m long and the boundary conditions were determined by knife-edge bearings which ensured pinned supports in the direction perpendicular to the strong axis and fixed perpendicular to the weak axis. All strengthening plates were welded to columns with intermittent welds. All columns failed via flexural buckling. The numerical models used for the parametric study were created in ANSYS software. Design values and procedures recommended by EN 1993-1-5, Annex C were used. The most commonly used steel grade S235 was selected for all plates. Shell 181 element type was used for mapped meshing of steel plates. Element birth and death feature was convenient to simulate strengthening under load.

Study on Welding Distortion of Stiffened Thin-Plate Structures Using Idealized Explicit FEM

In this research, to evaluate the welding distortion of stiffened thin-plate structures, an analysis method was developed that considers large deformation theory in elastic analysis using inherent strain based on Idealized Explicit FEM with shell elements. The developed method was applied to the analysis of stiffened thin-plate structures. The following factors were considered in the analysis to investigate their influence on welding distortion: heat input and welding processes such as double-sided continuous fillet welding, single-sided continuous fillet welding, double-sided intermittent fillet welding, and staggered fillet welding. From the analysis, it was clear that a buckling-type deformation is generated when the heat input is large. Regarding the welding method, the largest deformation was observed in double-sided continuous fillet welding. In addition, to show the applicability of the developed method to large-scale problems, the developed method was applied to the analysis of the car deck of a pure car carrier ship. As a result, it was found that the developed method can analyze the welding deformation of a large-scale stiffened thin-plate model in practical computing time.