Fillet-welded Connections Research Articles

Experimental and numerical study on fatigue damage evolution of Q690D welding details

Steel structures are widely used in various types of structures, and welding details, which are fatigue-prone constructions, are typically utilized in steel constructions. In this study, regarding the high cycle fatigue performance and fatigue damage evolution behaviors of high strength steel welding details, experimental and numerical studies have been carried out on two typical types of Q690D high strength steel welding details, including butt-weld connections and cruciform load-carrying fillet weld (CLFW) connections. High cycle fatigue tests have been conducted, SN curves based on effective notch stress have been established and compared with the suggested curves in IIW specification, showing that FAT200 is more suitable for fatigue evaluation of high strength steel welding details. Fatigue damage evolution model and numerical simulation methods for Q690D welding details based on effective notch stress and continuum damage mechanic have been established and validated. Damage evolution analysis of welding details has been conducted based on the proposed numerical simulation method. The simulation method enables accurate characterization of fatigue damage locations.

Deformation behaviour of high‐strength steel welds using DIC

AbstractThis paper focuses on the deformation and strength behaviour of high‐strength steel (HSS) transverse fillet welds. The behaviour of six lap‐welded fillet joints made of high‐strength steels (HSSs) is investigated under tension load through experiment. Due to some weaknesses in the deformation measurement using traditional techniques, the digital image correlation technique (DIC) is used to measure the deformation of transverse fillet weld connections. The development of the deformation on the specimen throughout the loading process was analysed using DIC measurement. The deformation of transverse fillet lap‐welded connections from HSS is always less than 1 mm. The strength calculated from the weld's fracture surface area shows better results than the theoretical weld area because it provides the real strength of the weld. In most cases, the weld failure did not occur along the throat section. Moreover, it is confirmed that the analytical models offered by prEN 1993‐1‐8:2020 are conservative for all the specimens.

Residual shearing strength of fillet weld connections after exposure to elevated temperature

Experimental and analytical studies are carried out to investigate the residual shearing strength of fillet welded connections after exposure to elevated temperatures. Transverse fillet welds and longitudinal fillet welds were designed in the test, and four weld leg heights were considered. Fourteen specimens were manufactured for each weld leg height, including seven heating temperatures and two cooling methods, obtaining a total of 112 specimens, along with 8 unheated specimens for comparison. The load-displacement curves and stress-load ratio curves were obtained to evaluate the shearing strength, residual deformation, stress development, stiffness and ductility of the fillet welds. Test results exhibit the transverse fillet welds are mainly integral fracture, while longitudinal fillet welds occur obvious local and global cracks. The weld leg height has the greatest influence on the shearing resistance of fillet welds, followed by the elevated temperature and cooling method. When the heating temperature is between 400 °C-600 °C, an increasement in residual shearing strength can be noticed. Meanwhile, the residual deformation is positively correlated with the weld leg height. Additionally, water-cooling fillet welds are superior to room-temperature-cooled fillet welds in terms of stiffness and ductility. Moreover, the formulae for predicting the residual shearing strength of the fillet welds after exposure to elevated temperatures are proposed.

Low-cycle fatigue of fillet-welded steel plate connections

The present study focuses on the mechanical behavior of fillet-welded steel plated joints and the development of a strain-based fatigue assessment procedure, motivated by the seismic response of unanchored steel tanks that exhibit repeated uplifting, leading to low-cycle fatigue failure of the base plate connection with the tank shell, due to cyclic inelastic deformation. Low-cycle fatigue experiments on small-scale fillet-welded joints are performed, representing the welded connection the tank base plate with the tank shell, aimed at determining the relationship between the strain range developed at the welded vicinity and the corresponding number of cycles to failure. Prior to fatigue experiments, material tests have been conducted, to determine the mechanical properties of the base plate material, and the weld has been examined with stereo optical microscopy and micro-hardness measurements. In addition to experiments, numerical simulations are also performed, to elucidate special features of joint behavior, and calculate accurately the local strain at the weld region, complementing the experimental results and observations. The numerical simulations employ an advanced cyclic-plasticity model, based on the bounding-surface concept, implemented into the finite element model using an in-house material user subroutine. The experimental and numerical result enable the development of a strain-based fatigue curve, which can be used for the seismic design and assessment of liquid storage tanks. It is further concluded that the fillet-welded connections under consideration are capable of sustaining substantial strain levels for a significant number of cycles, until low-cycle fatigue failure occurs.

Application of strain-life fatigue-corrosion model for fillet-welded connections of sign support structures

Fatigue-related corrosion is a complex phenomenon that induces damage accumulation and electrochemical deterioration throughout the service life of the structure. This article presents a previously proposed and modified strain-life Smith–Watson–Topper corrosion model for details on fillet-welded connection of highway sign support structures. To evaluate the degree of corrosion activity, hot-dip galvanized, weathering, and low-carbon steel are investigated with respect to chemical compositions, material properties, and the corresponding corrosion resistance indices. The existing fatigue testing data were analyzed and used to evaluate fatigue resistance under various corrosion environments. A modified Smith–Watson–Topper corrosion model is further utilized to determine acceptable constant amplitude fatigue thresholds for the American Association of State Highway and Transportation Officials fatigue limits under each corrosion category. It was found that low constant amplitude fatigue threshold values were observed for ASTM A588, A595, and A572 steels in locations with corrosion categories exposed to severe corrosive environments. Under these conditions, hot-dip galvanization or other surface treatments of the steel components of the sign supports are recommended to achieve higher constant amplitude fatigue threshold values.

An Analytical Shear Strength Model for Load-Carrying Fillet-Welded Connections Incorporating Nonlinear Effects

AbstractIn this study, an analytical formulation of a weld throat stress model is presented for defining limit state condition of fillet-welded connections incorporating plate-to-plate contact cond...

Investigation of fatigue resistance of fillet-welded tube connection details for sign support structures

Stiffened and unstiffened fillet-welded tube-to-transverse plate connection details are widely used for mast-arm and base-plate connections for highway sign structures. However, due to repetitive wind loads, cyclic fatigue stresses are induced and they are the primary source of failure in welded connections at these locations. The resistance of fatigue critical details has been an on-going research topic because of limited experimental results and the variability in existing fatigue testing results. The main objective of this study is to evaluate fatigue resistance of fillet-welded tube connection details by utilizing the advanced fatigue tool in ANSYS Workbench platform. Finite Element (FE) models development and model validation using existing test data was presented. The resulting fatigue resistance from FE analysis was expressed in terms of fatigue life, fatigue damage, and fatigue safety factor to determine the fatigue performance of fillet-welded connections. Existing fatigue test data was grouped to perform a synthetic analysis and then analysis results were provided to determine input data and fatigue limit for the fatigue module. The local stress level at fatigue critical locations was evaluated using a static FE model for different number of stiffeners and boundary conditions. The results of this investigation provides fatigue resistance of fillet-welded connection details in the form of fatigue life, fatigue damage and safety factor for various connection parameters and structural conditions.

Block shear strength of cold-formed austenitic stainless steel (304 type) welded connection with base metal fracture

In this paper, the block shear fracture behavior of base metal in austenitic stainless steel (STS304, corresponds to ASTM 304 type) fillet-welded connection has been investigated through experimental and numerical methods. Even though the block shear fracture strength of welded connection thanks to stress triaxiality effect differs from those of bolted connection under monotonic tension, block shear strength equations of welded connection with base metal fracture in the design codes are identical to those of bolted connection. Main variables are weld method (TIG and Arc welding) and weld length (transverse and longitudinal to the direction of loading). It is found from study results that welding method did not affect the strength of welded connection. Block shear strengths by current codes (KBC2016, AISC2016 and EC3 1–3) and other researchers’ proposed equations were compared with those of experimental results and finite element analysis results. Finite element analysis (FEA) model was developed based on previously test data. Also, parametric study for investigating the weld length effect on strength has been performed with the developed finite element analysis procedures. Consequently, condition of weld length and end distance perpendicular to the direction of applied force for fracture mode transition boundary from tensile fracture to block shear fracture in welded connection was investigated. In addition, block shear strength equation with modified tensile stress and shear stress factors of base metal fracture in austenitic stainless steel (STS304) welded connection is suggested considering stress triaxiality.

Strength of duplex stainless steel fillet welded connections

Standard uniaxial tests were conducted on round bar specimens made of stainless steel and the corresponding weld metal. The stress-strain curves of both base metal and the corresponding weld metal were obtained. The constitutive relationship for base metal and the corresponding weld metal were calibrated against the test results and were taken into consideration for further finite element analysis on stainless steel fillet welded connections. Six transverse fillet welded connections and five longitudinal fillet welded connections were tested to investigate the strength, deformation, and fracture angle of stainless steel fillet weld connections. According to the test results, the average angle of stainless steel transverse fillet weld was 29°; the average angle of stainless steel longitudinal fillet weld connection was 46°. The ultimate strength for a transverse fillet weld connection was 1.5 times than that of a longitudinal fillet weld. Relevant numerical models using ANSYS were calibrated against experimental results. Further parametric studies were conducted to investigate the effect of weld length and weld size on the strength of stainless steel fillet welded connections. Finally, both the experimental and numerical results were compared with the current design provisions. The conservatism of the European, American, and Chinese design codes was discussed. A revised prediction of fillet weld strength was proposed based on the strength of the longitudinal fillet weld strength.

Investigation on Ultimate Strength of STS304L Stainless Steel Welded Connection with Base Metal Fracture Using Finite Element Analysis

Many studies on the application of stainless steels as structural materials in buildings and infra-structures have been performed thanks to superior characteristics of corrosion resistance, fire resistance and aesthetic appeal. Experimental investigation to estimate the ultimate strength and fracture mode of the fillet-welded connections of cold-formed austenitic stainless steel (STS304L) with better intergranular corrosion resistance than that of austenitic stainless steel, STS304 commonly used has carried out by authors. Specimens were fabricated to fail by base metal fracture not weld metal fracture with main variables of weld lengths according to loading direction. All specimens showed a block shear fracture mode. In this paper, finite element analysis model was developed to predict the ultimate behaviors of welded connection and its validity was verified through the comparison with test results. Since the block shear behavior of welded connection due to stress triaxiality and shear-lag effects is different from that of bolted connection, stress and strain distributions in the critical path of tensile and shear fracture section were investigated. Test and analysis strengths were compared with those by current design specifications such as AISC, EC3 and existing researcher’s proposed equations. In addition, through parametric analysis with extended variables, the conditions of end distance and longitudinal weld length for block shear fracture and tensile fracture were suggested.

Fatigue Reliability Assessment of Potential Crack Initiation of Tube-to-Transverse Plate Connections for Cantilever Sign Support Structures

AbstractTube-to-transverse plate stiffened connection details are widely used in cantilevered sign support structures in New Jersey and many other states. This stiffened fillet-welded connection sh...

Ultimate strength of austenitic stainless steel fillet-welded connections with weld metal fracture

This study investigates ultimate behaviors such as ultimate strength and weld metal fracture mechanism of austenitic stainless steel (304 type) fillet-welded connections with TIG (tungsten inert gas) welding through experimental method. Main variables of test specimens are weld length and welding direction against applied force. Specimens are fabricated with transverse fillet weld (TFW series), longitudinal fillet weld (LFW series) and full fillet weld FW series against loading direction. Specimens of TFW series, LFW series and FW series failed by tensile fracture, shear fracture and block shear fracture in the weld metal of connections. Test ultimate strengths were compared with predictions based on the design specifications, AISC (American institute of steel construction) and ASCE (American Society of Civil Engineers) and existing researcher's equations. Current design equations underestimated excessively the strength of welded connections with weld metal fracture. Consequently, modified design formula is suggested considering actual fracture path and the effect of stress triaxiality on welded connections and its validation was verified in this paper.

A quantitative weld sizing criterion for fatigue design of load-carrying fillet-welded connections

Fillet welded connections are most commonly used for construction of engineering structures that are often subjected to various forms of cyclic loading in service. There exist two potential fatigue failure modes, i.e., weld root cracking through weld throat and weld toe cracking into plate thickness. The former should be prevented at design stage through a proper weld sizing. However, due to difficulties in determining stress concentration at weld throat, existing fatigue design rules, particularly on weld sizing, are largely empirical and often result in excessive conservatisms, leading to oversized welds. As structural light weighting becomes increasingly important, there is an increasing demand for more quantitative fatigue-based fillet weld sizing criterion. By taking advantage of a comprehensive set of fatigue test results on load-carrying fillet-welded cruciform joints and associated analytical developments reported by Xing et al. (2016), an analytical weld throat stress model taking into account of weld penetration and joint misalignments is presented in this paper for determining critical weld size beyond which weld throat failure become unlikely. Then, it is shown that a weld sizing criterion can be analytically developed and expressed as a function of weld penetration and joint misalignments, which are shown to agree well with the large amount of test data reported by Xing et al. (2016), including a systematic validation by means of a logistic regression method on the same test data. As a result, the present developments provide both analytical and experimental basis for achieving quantitative weld sizing so that weld throat fatigue failure mode can be effectively prevented with a clearly defined confidence level without the need of over-sizing.

Analysis of fatigue failure mode transition in load-carrying fillet-welded connections

In load-carrying fillet welded connections, two distinct fatigue failure modes are possible depending upon fillet weld leg size and loading conditions. One is weld toe cracking through base plate thickness and the other is through weld metal, often referred to as weld root cracking. Based on a recent comprehensive fatigue testing program in support of construction of lightweight ship structures, this paper examines a number of stress based fatigue parameters that can be used to formulate an effective criterion for determining failure mode transition from weld root to weld toe. A closed form solution has been developed for analytically determining the weld throat critical plane on which a traction stress based fatigue parameter attains its maximum and can be compared with that corresponding to weld toe cracking. It is found that both an effective weld throat stress based criterion by combining normal and shear traction stresses and an equivalent effective stress based criterion based on the master S-N curve formulation can be used for the determination of the minimum fillet weld leg size beyond which weld toe fatigue failure dominates. The proposed fillet weld sizing criteria are then validated using a large amount of fatigue test data on load-carrying cruciform fillet welded specimens.

Experiment on strength of transverse fillet weld connections after high temperature treatment

Experiment on strength of transverse fillet weld connections after high temperature treatment

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

Closure

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

Discussion

Dubai Metro footbridge design

The Dubai Metro light-rail scheme is a flagship project in the United Arab Emirates and the longest fully automated rail system in the world. The first line of the rail system was opened in September 2009 with a second line due for completion in 2010. These first two lines include 35 elevated stations along their combined 76 km length. This paper describes the design and construction of the steel truss footbridges developed as part of the station context planning work for all of the elevated stations. The footbridges are all fully enclosed, air-conditioned corridors with the widths of many dictated by the provision of automated walkways. A key aspect to the footbridge design concept was to develop a modular system that could be rapidly designed for scores of differing span arrangements to be suitable for each unique location. Several of the footbridge truss elements comprised structural hollow sections, and the new rules in Eurocode 3 were adopted to design many of the connections between such members. With simply supported spans up to 45 m long and external cladding creating irregular shaped cross-sections, wind tunnel testing was required to demonstrate aerodynamic stability of the footbridges. Several erection methods were also considered to minimise the installation time of completed footbridge spans over the major Dubai highways, and the pre-camber and deflection analysis associated with the methods adopted for lifting were also important aspects considered in the design. Other critical design issues resolved included the design of fillet-welded connections in place of full-strength full-penetration butt welds and the design of several special spans for connecting into non-standard stations and entrance structures.

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.

Fatigue Capacity of Load Carrying Fillet-Welded Connections Subjected to Axial and Shear Loading

The status on current design recommendations concerning the fatigue capacity of load carrying fillet welds was presented by Maddox (Maddox, S., 2006, “Status Review on Fatigue Performance of Fillet Welds,” Proceedings of the OMAE Conference, Hamburg, Germany, Jun., Paper No. OMAE2006-92314) based on a literature survey. In order to examine the validity of the recommendations and to supplement the fatigue test database, a test matrix with 33 specimens was developed. This included 8 simple fillet-welded cruciform joints that were subjected to axial loading and 25 fillet-welded tubular specimens that were subjected to axial load and/or torsion for simulation of a combined stress condition in the fillet weld. The data obtained from these fatigue tests are presented in this paper. The test data are also compared with design guidance from IIW (1996, Fatigue Design of Welded Joints and Components: Recommendations of IIW Joint Working Group XIII-XV, A. Hobbacher, ed., Abington Publishing, Cambridge), Eurocode 3 (1993, Eurocode 3: Design of Steel Structures—Part 1–1: General Rules and Rules for Buildings), and DNV-RP-C203 (DNV, 2005, DNV-RP-C203, Fatigue Strength Analysis of Offshore Steel Structures).