Longitudinal Fillet Welds Research Articles

Numerical investigation of the behavior of combination connections with pretensioned high-strength bolts and longitudinal fillet welds

Numerical analysis is conducted to investigate the behavior of double shear combination connections made with pretensioned high-strength bolts and longitudinal fillet welds. The finite element (FE) models were validated using the results of an experimental investigation and utilized to develop a better understanding of the influence of critical input parameters on the connection behavior. Slip-dependent surface frictional and weld ductile fracture models were incorporated into the numerical models to simulate the nonlinear behavior of the connections. The numerical simulations confirm that at low slip displacements, the force carried by the combination connection can be estimated as the summation of the friction resistance introduced by the pretensioned bolts and the shear force carried by the fillet welds. The results also indicate that the behavior and capacity of the combination connection are not sensitive with respect to the weld location compared to the center of gravity of the bolts as long as no eccentricity is introduced within the force transfer mechanism. The paper also investigates the stress distribution within the connection plates and studies the effect of fillet weld size on the behavior of combination connections.

The effect of temperature actions on single‐sided fillet welds in small‐sized box girders of bridges

AbstractThe use of small‐sized box girders has shown to bring numerous benefits in the design of bridges with short to medium spans. Therefore, it has become an established construction method in Germany. However, the beams are not accessible for inspection due to their small size, requiring the girder to be welded airtight. The limited accessibility also has consequences on the manufacturing process. Two of the four longitudinal fillet welds can only be executed from outside resulting in single‐sided fillet welds. As a result of the airtight construction, temperature actions lead to fluctuation of the internal pressure of the box. The single‐sided fillet welds are consequently subjected to unscheduled bending stress, which has an unclear impact on the weld. Subject of the research project, presented in this paper, is the influence of this unscheduled load case on the load‐bearing capacity of the girder. To quantify the temperature which leads to changes of the internal pressure, numerical studies based on meteorological data are performed. The load‐bearing behavior of single‐sided fillet welds is investigated in experiments. It can be shown that the load‐bearing capacity is underestimated by simplified calculation methods.

Experimental Investigation into the Capacity of Concentrically Loaded Steel Connections with Pretensioned High-Strength Bolts and Longitudinal Fillet Welds in Combination

This paper presents the results of an experimental study aiming to investigate the behavior of steel connections that combine pretensioned high-strength bolts and longitudinal fillet welds on a common faying surface. A total of 75 double-shear tension splices were tested under direct tension loading to quantify the effect of various connection variables on the load-deformation behavior of the connection. These variables include the (1) bolt pattern (2×2 and 2×3), (2) bolt size (3/4 in. and 1 in.), (3) bolt grade (ASTM F3125 Grade A325, A490, and F1852), (4) bolt pretensioning method (turn-of-nut and tension control bolts), (5) faying surface class (Class A and B), and (6) weld/bolt strength ratio. The variation in the connection characteristics covered a wide range of weld/bolt strength ratios from 0.50 to 2.00. The bolts were installed in oversized holes, and the specimens were assembled in a negative bearing condition to allow for a maximum slip distance. The load-deformation behavior of the combination connections was recorded and compared to that of the bolted- and welded-only control specimens. In all tests, the addition of welds increased the capacity of the connection. The investigation shows that the capacity of the combination connection with pretensioned high-strength bolts and longitudinal fillet welds can be computed by adding the capacities of the individual connecting elements while considering the strain compatibility.

Overview on the fatigue strength of single-sided transverse and longitudinal fillet weld joints

In the present study, an overview on the fatigue performance of single-sided fillet welds is carried out. Both longitudinal load-carrying joints, for instance existing in beam structures and welded hollow sections, and transverse joints are considered in this work. Experimental data of such joints made of mild and ultra-high-strength steel (UHSS) is extracted from existing studies to evaluate the fatigue strength properties. The main characteristics affecting fatigue strength properties of these joints are discussed. Furthermore, the paper evaluates the fatigue strength of single-sided fillet weld joints in comparison with the joints with double-sided welds. The experimental results indicate that in the transverse welds, an increase in material’s yield strength shows a slight decrease in fatigue strength compared to mild steels, while in the longitudinal load-carrying seams, in the case of continuous weld root geometry, high fatigue strength can be achieved with UHSS materials. The double-sided welds provide one FAT class higher fatigue strength for transverse non-load-carrying joints, obtained in terms of mean fatigue strengths. In addition, in transverse joint configurations, intermediate welding was found to have no detrimental effect on the fatigue performance compared to the joints with continuous welds. In longitudinal load-carrying joints, double-sided welds do not provide any additional benefit unless full penetration and, thus, continuous longitudinal weld root shape is achieved with such weld preparation.

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.

Reliability assessment of connections with slip-critical bolts and fillet welds in combination

This paper quantifies the reliability level of connections combining slip-critical bolts and longitudinal fillet welds using a probabilistic approach that integrates finite element (FE) modeling, meta-modeling, and Monte Carlo simulation. The proposed approach relies on experimental results to calibrate a FE model and quantify the uncertainties associated with various input parameters. The calibrated FE model is next integrated into a low-rank tensor approximation process to provide the variance-based sensitivity measures associated with the considered random variables. The influential variables, along with the calibrated FE model, are then used to evaluate the reliability by means of accelerated Kriging Monte Carlo simulation (AK-MCS). Finally, the proposed approach is applied to combination bolted-welded connections under direct tension to evaluate their reliability considering different faying surface conditions. The results of the conducted sensitivity analysis indicate that variability in weld geometry, bolt pretensioning forces, and friction coefficient of steel surface would significantly contribute to the variability of the load-carrying capacity of the investigated connections. In addition, the reliability of the combination connections with Class A and B faying surfaces is evaluated based on code provisions.

An enhancement of the current design concepts for the improved consideration of residual stresses in fatigue-loaded welds

The consideration of residual stresses in fatigue-loaded welds is currently done only qualitatively without reliable knowledge about their real distribution, amount and prefix. Therefore, the tools which enable a more or less unsafe consideration in design concepts are mainly based on unsafe experiences and doubtful assumptions. Since the use of explicitly determined residual stresses outside the welding community is state of the art, the target of the presented paper is to show a practicable way for an enhanced consideration of residual stresses in the current design tools. This is not only limited on residual stresses induced by welding, but also on post-weld treatment processes like HFMI or shot peening. Results of extended experiments with longitudinal fillet welds and butt welds of low and high strength steels evidently show that an improved use of residual stresses in fatigue strength approximation enables a better evaluation of peening processes as well as of material adjusted welding procedures or post-weld stress relief treatments. The concept shows that it is generally possible to overcome the existing extremely conservative but although unsafe rules and regulations and may also enable the improved use of high strength steels.

Mechanical behaviour of longitudinal lap-welded joints of high strength steel: Experimental and numerical analysis

Mechanical behaviour of twenty-eight longitudinal lap-welded joints made of high strength steels (HSS) under tension load was investigated by experimental and numerical study. Weaknesses due to traditional deformation measurements for fillet welded joints can be perfectly solved by digital image correlation techniques (DIC). Distribution and development of strain field throughout the specimens along the whole loading process were recorded by DIC measurement. The effect of parameters (e.g. weld size, weld length and mismatch ratio) on mechanical properties (e.g. ultimate strength, failure modes, weld ductility and fracture angle) of longitudinal fillet welds and transverse fillet welds, which was introduced in detail in previous work by the authors, were compared. Generally, because of the difference on the combination of shear force and tension force, the fracture angle of longitudinal welded specimens (around 50∘) were much more divergent from transverse welded specimens (around 20∘) even though both of them failed at welded zone (welded zone only refers to weld metal in this paper), resulting that the mean strength of longitudinal welded specimens were only 0.58 time of transverse welded specimens. Conversely, the mean deformation capacity of longitudinal welded specimens was almost 4.0 times of transverse welded specimens. All longitudinal welded specimens have “platform” or “decline” feature while all transverse welded specimens have “rise” or “platform” feature load-deformation curves. Generally, the specimens with “rise” feature load-deformation curve are more likely to suffer sudden fracture, while specimens with “decline” or “platform” feature have satisfactory ductility performance. Based on the strain distribution and development features provided by DIC measurement, a new strength criterion, in which the ultimate strain obtained in relevant coupon tests was an indicator, was proposed and through the comparison between the numerical results and test results, its validation was verified by FE simulation. Moreover, it was confirmed that the predicted loads of EC3 and AISC Specification were close and slightly conservative for all specimens.

Experimental Assessment of Time-Limited Operation and Rectification of a Bridge Crane.

This paper describes a problem related to a casting bridge crane with a combined load of 200/50/12.5 t and a span of 18.6 m, working in a heavy metallurgical operation. Due to the specific stress of the structure after its long-term operation, longitudinal fillet welds between the upper flange and the web of the main box beam on the rail side of the 200 t trolley were irreparably damaged. As a result, the cross-section of the main beam had opened, thereby substantially reducing its strength and stiffness. This resulted in a disproportionate increase and undesirable redistribution of stresses in the beam and, at the same time, an increase in the probability of acute fatigue or the loss of stability of the elastic beam shape. Therefore, the rectification of the damaged load-bearing structure was carried out by specific structural modifications. Critical load-bearing elements were subjected to complicated strength and fatigue life analyses before and after rectification. These analyses were supported by experimental measurements. The applied modifications resulted in a partial strengthening of the lifting device with the possibility of its further operation, but only in a limited mode, with a limited period of operation with a time limit of 2 years and a reduced total load capacity of 150 t. The applied methods are also applicable for the fatigue analysis of load-bearing elements and equipment for bridge, gantry and tower cranes, crane tracks, road and railway bridges and support structures under machinery and other devices with a dominant transverse and rotating effect.

Fatigue life investigation of non-load carrying fillet weld of structural offshore steel S460G2+M using experiment and FEM simulation

This research deals with the fatigue life investigation using experiment and FEM simulation on longitudinal fillet weld of structural offshore steel S460G2+M with a thickness of 10mm. The experimental fatigue test is conducted based on nominal stress (NS) approach while the simulation uses the effective notch stress (ENS) approach for fatigue life assessment. The investigation begins with the preparation of the longitudinal fillet weld fatigue specimen using Milling Machine based on the IIW fatigue specimen design recommendation and joined using the semi-automatic GMAW process following the AWS D1.1 procedure. Fatigue testing on non-load carrying fillet weld is conducted using the Instron Fatigue Machine with a stress ratio of 0.1 with constant amplitude loading and stress loading from 50%-75% of the yield strength of the base material. For the simulation approach, the 3D longitudinal fillet weld geometry is created using CAD based on the ENS design procedures of IIW where the sizes and dimensions are similar to the experimental fatigue specimen. The static elastic stress analysis of the model is conducted using MSC Marc/Mentat FEM software. Based on the IIW fatigue data evaluation, it is found that the natural mean curve of the longitudinal fillet weld obtained 146 MPa of FAT class which exceeds approximately 106% from the IIW FAT class recommendation for a longitudinal fillet joint. However, the characteristic curve of 97.7% failure probability of the parts only attained 95 MPa of FAT class, but still exceeds approximately 33% form the IIW FAT class. In the ENS fatigue assessment of the 3D longitudinal fillet weld, it is found that the model obtained 195MPa of FAT class which is inferior approximately 15 % from the FAT class recommendation of IIW. Also, it is found that both S-N curves of NS after conversion to ENS system have a good agreement with the S-N curve of ENS of 3D longitudinal fillet weld model and the IIW recommendation due to only 16 % and 34% lower as compared with the IIW FAT class recommendation for ENS.

A beam-column model for evaluating the effects of residual stresses and geometrical imperfections

A numerical model within the framework of the finite element method is developed in order to perform second order analyses of steel columns and beam-columns by considering geometrical and material nonlinearities, and taking into account residual stresses and initial geometric imperfections. The model considers a displacement based beam element and adopts a distributed-plasticity formulation for the implementation of the steel nonlinear behaviour together with a Newton-Raphson algorithm for the solution of the resulting nonlinear governing equations. The results obtained from the developed model are compared with the results in the literature that were adopted for the calibration of the formulae in Eurocode regarding the buckling resistance of columns and beam-columns. Thereafter, the model is adopted to evaluate the applicability/accuracy of these formulae regarding the corresponding safety check. A detailed evaluation of the buckling resistance of columns with tubular cross-sections is presented, namely in what concerns the effect of the relative position of the longitudinal fillet weld to the direction of the considered geometric imperfection.

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.

BEHAVIORS OF SLIP-CRITICAL BOLTS IN COMBINATION WITH FILLET WELDS

According to the Specification for Structural Steel Buildings (AISC 2010), slip-critical bolts can only share load with longitudinal welds in a joint. Moreover, the bolt available strength shall not be taken greater than 50% of the bearing-type. This paper presents the result of a series of joint tests verifying the specification. The joints were tested in a manner similar to previous work (e.g. Manuel and Kulak 2000). The slip strength values of JIS F10T and F14T bolts were tested and compared. Transverse and longitudinal fillet welds with a leg size of 12 mm and the same amount of weld material were adopted and tested respectively. The strength ratio between bolts and welds changes from 5/8 to 6/9 in the combination joints. The result shows that in the combination with longitudinal welds, the bolts tend to slip and contact the plates, developing greater bearing strength. In the combination with transverse welds, the bolts slip and the pretension decreases greatly. But the combination also causes the fracture surfaces of transverse welds to change, providing additional strength to compensate the decrease in bolt slip strength. The combination joints therefore can develop strength greater than the sum of slip strength and fracture strength.

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.

Modular Multi-Process Welding System Used for HSLA Materials Joining

The development of welding technologies and techniques used for advanced materials joining should be closely linked with the design and development of equipment and also with the expectations of end-users involved in the cutting-edge manufacturing engineering. In order to reach this objective, the researchers, developers and producers should work together for designing new welding processes, technologies and equipment that meet the requirements of productivity and cost-effective manufacturing processes. Combining the multiple-arc & multi-process welding solutions, the system presented in this paper was designed to perform longitudinal butt and fillet welds of high-strength low-alloy (HSLA) steels plates of medium and large thickness, frequently encountered in shipbuilding, oil and gas onshore and offshore industries. The welding system can be easily used for achieving long seams specific to complex ship blocks or sections, pipelines sections, beams, girders and stringers for railway wagons. Based on the modularity concept, the architecture of this innovative welding system was designed as a structure of multiple interchangeable slides, used for positioning and assembling the welding heads typical for gas metal arc welding, submerged arc welding and Laser welding processes. Due to its versatility, adaptability and functionality, the system allows end-users to select the suitable combination of welding processes, in order to obtain butt and fillet HSLA steels welded joints. By controlling and monitoring the process parameters in real time, significant advantages such as weld geometry, high deposition rate and high penetration and, consequently, improved productivity, controlled cooling rate and, hence, reduced stress and strain are achieved. Due to its modularity and versatility, the system can be successfully used in different industrial applications, in several combinations of GMAW, SAW and LASER-hybrid welding processes, for joining of similar and dissimilar materials.

Problemi pojasnih lamela u građenju čeličnih mostova

As the plate elements of ordinary lamella flanges always exhibit unavoidable initial geometrical imperfections, a gap always occurs between them, into which the loaded lamella is pressed under load. Given the fact that the loading is many times repeated, the above phenomenon is also many times repeated, a pronounced cumulative damage process being thereby generated. As it was manifested during the authors' tests, this leads to the initiation and propagation of fatigue cracks in the longitudinal fillet welds connecting the individual lamellas, which can, of course, imperil the safety and useful lifetime of the bridge structure concerned.

Behavior and design of stainless steel tubular member welded end connections

Among the various alternatives to make a steel tubular member connection, making a slotted and gusset plate welded connection is one of the most frequently preferred alternatives. This type of connection is essentially an end connection that is made by slotting the tube longitudinally, inserting the gusset plate and then placing longitudinal fillet welds at the tube-to-plate interface. In this paper an experimental study on the behaviour of such connections in stainless steel is presented. 24 specimens were tested under concentrically applied axial tensile forces for varying tube-to-gusset plate weld lengths. Both circular and box section members were considered in the test program. Load-deformation curves were obtained and comparisons were made in terms of strength and ductility. The results obtained from the study were then critically examined and compared with currently available design guidance for slotted gusset plate welded tubular end connections. It is noted that no specific rules exist in international specifications on structural stainless steel which cover the design of such connections. Therefore, the results of this study are compared with the existing design rules for carbon steel.

Cyclic performance of flange-plate connection to box column with finger shaped plate

The objective of using the flange plate connection as one of the most popular indirect connections to the built-up box column is to avoid using long plates. In deep beams, the need to provide sufficient length to fillet welds necessitates using of long flange plates, which may cause brittle failure due to increasing the bending moments at the face of the column. In the present study, configuring the top flange plate with a finger slot shape type is proposed in order to diminish length of the flange plates. In the proposed configuration, the longitudinal fillet weld was used in flange plates in addition to the transverse fillet and slot weld in the top and bottom flange plates, respectively; in order to provide the required strength for welds. Two full-scale specimens fabricated based on the proposed design methodology were subjected to the cyclic loading. The study results indicated that the flange plate connection with a suggested modified configuration could be prequalified for use in the special moment frames. In a parametric analytical study, the best arrangement of the longitudinal as well as the transverse fillet weld in a top flange plate was proposed for flange plate connections.

Shear Strength and Failure Angle Analysis of Fillet Welds Based on Structural Stress Approach

With conventional shear stress formula given in AWS B4.0, huge difference of strength between longitudinal and transverse fillet welds exists, and different failure angle of two type welds could not be interpreted. In this paper, a mesh-insensitive structural stress based shear strength definition is presented for correlating weldment test data obtained from longitudinal and transverse fillet welds in literature. Finite element model were created according to the geometry of specimens, and shear stress at different cut plane of weld were calculated. Failure angle could be interpreted reasonably for two type fillet welds, and discrepancies in shear strength between transverse and longitudinal shear tests can now be reconciled, resulting in a single shear strength value regardless of specimen types and loading conditions with this proposed approach.

Fatigue tests on steel plates with longitudinal weld attachment strengthened by ultra high modulus carbon fibre reinforced polymer plate

ABSTRACTWelded steel connections of infrastructures are susceptible to fatigue failure. Advanced carbon fibre reinforced polymer (CFRP) has been demonstrated promising for fatigue strengthening of steel structures. Limited research was conducted on CFRP strengthening of welded connections. This paper focuses on the application of ultra high modulus (UHM) CFRP plates with a modulus of 460 GPa to strengthen steel plates with longitudinal fillet weld attachment using five CFRP strengthening configurations. A series of fatigue tension tests were carried out with constant amplitude fatigue loading. Beach marking technique was adopted to record the crack propagation process. Effects of CFRP bond length, bond width and bond locations on fatigue performance of welded steel joints were investigated. The experimental results showed that UHM CFRP plates could generally increase the fatigue life of the welded steel joints. It seems better to apply CFRP on the welding side of the specimen to achieve longer fatigue life. Then, the effects of weld and weld attachment on the CFRP strengthening efficiency was further studied by comparing experimental results of non‐welded steel plates with single side UHM CFRP plate strengthening. Finally, the classification method was adopted to assess the strengthening efficiency of the UHM CFRP plate to the steel plates with longitudinal weld attachment.