Welded Connections Research Articles

Seismic design and hybrid tests of a full‐scale three‐story buckling‐restrained braced frame using welded end connections and thin profile

SUMMARYA series of hybrid and cyclic loading tests were conducted on a three‐story single‐bay full‐scale buckling‐restrained braced frame (BRBF) at the Taiwan National Center for Research on Earthquake Engineering in 2010. Six buckling‐restrained braces (BRBs) including two thin BRBs and four end‐slotted BRBs, all using welded end connection details, were installed in the frame specimen. The BRBF was designed to sustain a design basis earthquake in Los Angeles. In the first hybrid test, the maximum inter‐story drift reached nearly 0.030 rad in the second story and one of the thin BRBs in the first story locally bulged and fractured subsequently before the test ended. After replacing the BRBs in the first story with a new pair, a second hybrid test with the same but reversed direction ground motion was applied. The maximum inter‐story drifts reached more than 0.030 rad and some cracks were found on the gusset welds in the second story. The frame responses were satisfactorily predicted by both OpenSees and PISA3D analytical models. The cyclic loading test with triangular lateral force distribution was conducted right after the second hybrid test. The maximum inter‐story drift reached 0.032, 0.031, and 0.008 rad for the first to the third story, respectively. This paper then presents the findings on the local bulging failure of the steel casing by using cyclic test results of two thin BRB specimens. It is found that the steel casing bulging resistance can be computed from an equivalent beam model constructed from the steel core plate width and restraining concrete thickness. This paper concludes with the recommendations on the seismic design of thin BRB steel casings against local bulging failure. Copyright © 2011 John Wiley & Sons, Ltd.

Numerical investigation of the effects of connection rotational stiffness on block shear capacity of coped beams with a welded end connection

In order to investigate the effects of connection rotational stiffness on the block shear capacity of coped beams with welded end connections, a numerical investigation was conducted. Parametric study is conducted based on the validated finite element model. Based on the mechanical model of double angle connection, the pitch and the beam element length-to-angle thickness (L/t) ratio of the outstanding leg are selected as two important parameters to consider the effects of the connection rotational stiffness. The results of parametric study show that the connection rotational stiffness has a great influence on the block shear capacity of coped beams with double welded clip angle connection. The results of parametric study also show the pitch has no significant effect on the block shear capacity. Based on the results of finite element analysis, the design equation proposed by Yam et al. (2007) was modified to account for the effects of the connection rotational stiffness.

Finding Suitable Indexes to Detect the Locations of Omitted Spot Welds in Structural Joints Using FE Model and Modal Parameters

Resistance spot welding is one of the mostly used methods in joining different pieces of complex sheet metal structures such as automotive BIW. Some manufacturing inaccuracies, accessibility difficulties to some locations and large quantity of spot welds, may lead to missed out substantial number of spot weld connections. In present work, it is tried to find suitable Indexes to detect the locations of omitted spot welds in a structural joint using finite element method and modal analysis. Two different special modal indexes derived that can be used to detect the missed out location of a spot weld in a lap joint of two flat plates. One modal index derived from computations on high range natural frequencies of the structure and the other one was achieved by searching on a special case of MAC values of modal vectors at joint region. Finally, using artificial neural networks and the developed indexes in present work, the location of an absent spot weld in the investigated structure detected successfully.

상수도강관 용접접합의 방법별 비교분석

The welded connection is known as an essential factor for establishing qualified construction and/or maintenance of wrapped steel pipe. In this study, welded connection conditions in the coated pipes with large diameter (over 700 mm) in Korea water distribution systems were estimated for suggesting technically and economically available welded connection method. For the study analysis, current steel pipe usage and accident cases were investigated. In addition, the characteristics of each welded connection method and automatic or manual connection techniques were also compared and estimated. As results, automatic welded connection method is superior than manual welded connection method in aspect of pure construction cost (average 9%) or pure welded connection cost (average 13.5%). When the poor welding-working situations in Korea are considered such as high tolerance of out-of-roundness in KS regulation, a number of lap joint welded connections, the real cost benefits of automatic welded connection should be much higher than those of manual welded connections.

Quality assurance on the welding work during the assembly of Wendelstein 7-X

At the Max-Planck-Institut für Plasmaphysik (IPP) in Greifswald (Germany) the stellarator experiment W7-X is presently being assembled. During this assembly many different weld connections are made, which are very important for the proper functionality of the experiment. This concerns mainly the structural integrity and the leak tightness. The quality requirements for the weld seams are high (mainly class B according to DIN EN ISO 5817), because the complex machine must operate reliably for more than 15 years and the possibility of any repair or change of important components is very small. To guarantee a high quality of the welds they are submitted to different tests. The applied test methods are depending on the function of the weld, the wall thickness, the seam geometry, and the material. The main test methods are visual testing (VT), penetrant testing (PT), radiographic testing (RT), ultrasonic testing (UT), leak testing (LT), permeability testing and macros. The paper will describe the application of these test methods and show their need by examples of typical weld imperfections.

Closure: Design and Behavior of Multi-Orientation Fillet Weld Connections

Closure

Discussion: Design and Behavior of Multi-Orientation Fillet Weld Connections

Discussion

Mechanical Properties on the Welded Connection of Pipe and Hollow Spheres Joints

Taking pipe - hollow spherical node as the object, and using ANSYS finite element analysis software, established five kinds of finite element model to analyze the stress concentration at the weld connection of the different connections of steel structures - hollow ball under the uniaxial tension. Obtained this node’s stress concentration factor, stress distribution, by changing the hollow spherical diameter and wall thickness, pipe’s diameter and wall thickness, obtained the trend of the stress concentration factor under different control ball matches. Take static tests on typical structures of two specifications 6 hollow sphere nodes, get the measured stress concentration factor, and stress distribution of this node. Through comparative analysis of theoretical analysis and experimental results, show that the two rules are consistent. The research results can provide basis for improving the pipe - hollow spherical joints connecting structural.

Calculation Method of Butt-Welded Connection of Steel Structure Post Fire

In order to study the load-bearing properties of butt-welded connection of steel structure post fire, the strength design value of weld connection post-fire is proposed based on the experimental data and theoretical analysis. Considering the influence of different high temperatures and cooling patterns on strength damage of the weld, a revised checking method for strength of butt-welded connection of steel structure after high temperature is established on the basis of the analysis method for strength of butt-welded connection of steel structure at room temperature. The method can be used for damage assessment and strengthening technique of steel structure post fire.

A New Connection Structure Between Hydrogen Nozzle and Sphere Head in a Hydrofining Reactor

This paper presents a study of the residual stress in the welding connection between hydrogen nozzle and spherical head in a hydrofining reactor. A sequential coupling finite element program is developed to analyze the residual stress in nozzle-to-sphere connection. The results show that large residual stresses are generated in the weld and weld/parent interface during the welding of hydrogen nozzle. Large axial stress is generated on the internal surface of hydrogen nozzle due to the angular deformation, which has a great effect on hydrogen induced cracking (HIC) and stress corrosion cracking (SCC). Based on the residual stress distribution character, a new connection structure between hydrogen nozzle and head is developed. A stressless flanging is proposed to insert into the nozzle to isolate the residual stresses, which can be useful to prevent HIC and SCC. To cover all the residual stresses effectively, the arc length of flanging should be not less than 80 mm.

Measuring Transducer Of Vibration-Type

The measuring transducer includes at least one measuring tube communicating with a line connected during operation for conveying a medium to be measured, and a support element oscillatably holding the at least one measuring tube. Additionally, it is provided that the support element contains at least two passageways, via which the at least one measuring tube communicates with the line, and that the at least one measuring tube is affixed, especially releasably, at at least one end to the support element by means of a screwed-fitting at one of the passageways. Alternatively or in supplementation thereof, it is further provided that the at least one measuring tube is, at least in part, made of cold-strengthened, for instance cold-stretched or autofrettaged, material. As required, the measuring transducer can further include at least two measuring tubes communicating with the line for conveying the medium; each of these two measuring tubes is to be connected to an inlet-side distributor element and an outlet-side distributor element. In such case, at least one of the two distributor elements can be embodied as an integral component of the support element, so that the support element can be kept, at least in the area of this at least one distributor element, free of materially bonded, joined locations, especially free of solder, braze or weld connections. The measuring transducer of the invention is especially provided also for applications in which the medium to be measured acts with a pressure of more than 500 bar, especially over 700 bar, on the measuring tube.

Numerical Investigation on Block Shear of Coped Beams with a Welded End Connection

A numerical investigation on the block shear failure behavior of coped beams with double welded clip angle connection was conducted. Parametric study was conducted based on the validated finite element model. The parameters included the web block aspect ratio and the connection rotational stiffness. Based on the mechanical model of double angle connection, the pitch and the beam element length-to-angle thickness (L/t) ratio of the outstanding leg were selected as two importance parameters to consider the effect of the connection rotational stiffness. The results of parametric study show that the connection rotational stiffness has a great influence on the block shear capacity of coped beams with double welded clip angle connection. This is contributed to the fact that for the connections with a smaller connection rotational stiffness, the shear stresses of the shear area were much less than those of the connections with a larger connection rotational stiffness.

Welded T-joint connections of square thin-walled tubes under a multi-axial state of stress

T-joint connections are used extensively in industry as parts of machine components and structures. The T-joint connection is typically constructed through the welding of its tubular members, with significant stress and strain concentrations occurring at the toe of the weld under loadings. In this paper, a welded T-joint connection of square hollow-section (SHS) tubes subjected to a multi-axial state of stress is examined both numerically and experimentally. The hot spot strains and stresses in the connection are determined through a detailed finite element (FE) analysis of the joint. The weld geometry is accurately modelled using FE. To model the weld, several full-scale welded T-joints were cut at the connection to obtain the size and depth of penetration of the weld. For the experimental study, a test rig with a hydraulic actuator capable of applying both static and cyclic loadings is designed and used. Strain gauges are installed at several locations on the joint to validate the FE model. The verified FE model is then used to study the through-the-thickness stress distributions of the tubes. It is shown that the membrane stresses which occur at the mid-surface of the tubes remain similar regardless of the weld geometry. The weld geometry only affects the bending stresses. It is also shown that the stress concentrations are highly localized at the vicinity of the weld toe. At a distance of about half of the weld thickness from the weld toe, the effect of the weld geometry on the bending stresses becomes insignificant as well. To reduce the stress concentrations at the T-joint, plate reinforcements are used in a number of different arrangements and dimensions to increase the load-carrying capacity of the connection.

A REVIEW OF CANDU FEEDER WALL THINNING

Flow Accelerated Corrosion is an active degradation mechanism of CANDU feeder. The tight bend downstream to Gray loc weld connection, close to reactor face, suffers significant wall thinning by FAC. Extensive in-service inspection of feeder wall thinning is very difficult because of the intense radiation field, complex geometry, and space restrictions. Development of a knowledge-based inspection program is important in order to guarantee that adequate wall thickness is maintained throughout the whole life of feeder. Research results and plant experiences are reviewed, and the plant inspection databases from Wolsong Units One to Four are analyzed in order to support developing such a knowledge-based inspection program. The initial thickness before wall thinning is highly non-uniform because of bending during manufacturing stage, and the thinning rate is non-uniform because of the mass transfer coefficient distributed non-uniformly depending on local hydraulics. It is obvious that the knowledge-based feeder inspection program should focus on both fastest thinning locations and thinnest locations. The feeder wall thinning rate is found to be correlated proportionately with QV of each channel. A statistical model is proposed to assess the remaining life of each feeder using the QV correlation and the measured thicknesses. W-1 feeder suffered significant thinning so that the shortest remaining life barely exceeded one year at the end of operation before replacement. W-2 feeder showed far slower thinning than W-1 feeder despite the faster coolant flow. It is believed that slower thinning in W-2 is because of higher chromium content in the carbon steel feeder material. The average Cr content of W-2 feeder is 0.051%, while that value is 0.02% for W-1 feeder. It is to be noted that FAC is reduced substantially even though the Cr content of W-2 feeder is still very low.

Seismic Resistance Capacity of High-Rise Buildings Subjected to Long-Period Ground Motions: E-Defense Shaking Table Test

A series of large-scale shaking table tests is conducted for a high-rise building structure subjected to long-period ground motions. A test method is developed to preserve the original dimensions of structural members of a prototype building that has 21 stories with a total height of 80 m. The test specimen consists of a four-story, two-span by one-bay steel moment frame and three substitute layers placed on top of the moment frame. The substitute layers, which consist of concrete slabs and rubber bearings, are arranged to represent the upper stories of the prototype. From preliminary vibration tests, equivalence between the test specimen and the prototype is verified in terms of the lower mode natural periods and corresponding mode shapes. The test specimen when subjected to long-period ground motions exhibits cumulative ductilities more than four times those expected in Japanese seismic design, while the maximum story drifts remain nearly the same as those considered in the design. A number of cyclic inelastic deformations caused fractures at the bottom flanges of beam ends. According to these observations, the combination of large cumulative ductility demand, the weld quality of the field weld connections, and the promotion of strain concentrations at the toe of the bottom flange weld access hole by the presence of floor slabs caused the fractures and resultant smaller cumulative ductility relative to that observed in the bare beam tests.

Modeling of Crack Propagation in Weld Beam-to-Column Connections Submitted to Cyclic Loading with a Cohesive Zone Model

Abstract During the earthquakes in Japan and California in the 1990s, cracks appeared in some weld beam-to-column connections of heavy rigid frame steel buildings. This prompted the necessary assessment of the performance of weld connections in terms of rotation capacity and crack propagation. In the present study, experimental tests were performed where weld connections were submitted to cyclic loadings with increasing amplitude until a macrocrack event was reached. However the crack phenomenon depends on many parameters: The geometry, the material, the welding process…. For this reason, it was interesting to develop a finite element modeling of these connections in order to complete these experiments and perform a parametric study. This paper describes the finite element model development, its material parameter identification, and its comparison with experimental results. The weld connections were modeled by using three-dimensional mixed solid elements. The constitutive laws applied were elastoplastic with isotropic hardening identified for the base metal and the weld metal. Crack propagation was modeled by a cohesive zone model. The parameters of this cohesive zone model were identified by an inverse method with the modeling of three-point bending tests of pre-cracked samples performed on the base and weld metals. The fatigue damage generated by the cyclic loading was computed by the fatigue continuum damage model of Lemaitre and Chaboche, which was coupled with the cohesive zone model.

Wedge Design: A Reduced Beam Web (RBW) Connection for Seismic Regions

After the Northridge earthquake, it became clear that welded flange-bolted web connections for deep beams do not have adequate ductility when subject to seismic loading. Previous experimental tests on two such connections for shallow beams based on “wedge design” had achieved adequate strength and ductility. Such beams have a wedge removed from the web and flanges are then reattached. This study aimed to investigate the strength and ductility of “wedge design” connections for deep beams. The finite element method was used to model two pre-tested post-Northridge connections for deep beams of different depths. Wedge design was then applied on these connections, with results showing inadequate connection ductility. A parametric study was therefore carried out to find the best wedge detail. The effects of using different stiffener configurations and double wedge details on the strength, ductility and initial stiffness of connections were also investigated. Finally, the most effective stiffener configuration for the connection is proposed.

Finite element analysis of plastic failure in heat-affected zone of welded aluminium connections

Finite element analyses of plastic failure in the heat-affected zone of a generic welded aluminium connection are presented. The analyses include process history through multi-scale modelling. The heterogeneous material properties of the heat-affected zone are calculated using welding simulations to obtain the temperature history as input to coupled precipitation, yield strength and work-hardening models. Thermal history-dependent material parameters are mapped as field variables onto the finite element model to account for their spatial variation inside the heat-affected zone. The welded connection is modelled using shell elements, solid elements and cohesive-zone elements. Convergence studies show that very small elements are needed (much less than the plate thickness) to resolve the large strain gradients within the HAZ and to obtain converged solutions. Non-local regularization is vital in shell element analyses to obtain accurate estimates of the ductility of the welded connection. Two methods for estimating the ductility in the welded aluminium connection with coarser meshes are proposed.

Design and Behavior of Multi-Orientation Fillet Weld Connections

Several independent research projects have demonstrated that the strength and ductility of fillet welds are a function of the angle between the weld axis and the line of action of the applied load. It has been demonstrated that transverse welds are about 50% stronger than longitudinal welds, but have considerably lower ductility. This difference in behavior can have a significant impact on the design of welded connections with multiple weld orientations within the same joint. Tests on concentrically loaded welded double lapped joints have recently been conducted to investigate the strength of connections with multiple weld segments of different orientations. The tests indicate that these joints possess capacities significantly lower than the sum of the individual weld segment strengths. The tested connections' capacities are a function of the interaction of the load versus deformation characteristics of the individual weld segments. A general approach for the design of welded joints that combine welds in various directions that reflects the individual segments' load versus deformation interaction is recommended.

LOCAL ELASTO-PLASTIC BEHAVIOR OF STEEL BEAM TO CONCRETE-FILLED SQUARE STEEL TUBE COLUMN MOMENT CONNECTIONS USING ELECTROSLAG WELDING

Subassemblage tests were conducted on steel beam to concrete filled square steel tube (CFT) column moment connections to investigate the structural behavior of electroslag welding connections between internal diaphragms and steel tube. The writers propose an ultimate strength equation for these connections, based on combined stresses on a fracture line within the steel plate of the CFT column. They have already proposed a model for a load-displacement relation for predicting the local tensile elasto-plastic behavior of CFT column to steel beam moment connections using internal diaphragms. This paper proposes an improved load-displacement relation model for these connections including an ultimate strength equation for electroslag welding connections in the load-displacement relation model. The improved model is found to agree approximately with this experimental result up to large deformations.