Gusset Welded Joints Research Articles

Fatigue strength improvement of longitudinal fillet welded out-of-plane gusset joints using air blast cleaning treatment

Blast cleaning treatments are used widely in newly built steel structures to clean forged surfaces and increase the adhesive properties of subsequent coatings. On the other hand, the beneficial effects of a blast cleaning treatment, which are similar to shot peening, on the fatigue strength of welded steel structures are not considered in the fatigue design procedure. In this study, fatigue tests were carried out on as-welded and blast-treated longitudinal fillet welded out-of-plane gusset joints subjected to three different cyclic loading conditions: uniaxial tension, out-of-plane bending and in-plane bending stress cycles. The effect of the blast cleaning treatment on the fatigue strength of the gusset joints was studied. The fatigue tests showed that the blast cleaning treatment increased the fatigue strength of the gusset welded joints, particularly at the lower stress range. A 19% increase in fatigue strength at 2 million cycles and 66% increase in fatigue limit could be realized using the blast cleaning treatment.

Numerical simulations of fatigue crack initiation and propagation based on re-tensile plastic zone generating load criterion for in-plane gusset welded joints

Many accidents are caused by fatigue in welded built-up steel structures, and so it is important to estimate the fatigue lives of such structures quantitatively for safety reasons. By assuming that fatigue cracks cannot grow without an accumulation of alternating tensile/compressional plastic strain, one of the authors identified an improved effective stress intensity factor range ΔK RPG based on the re-tensile plastic zone generating (RPG) load, which represents the driving force for fatigue cracks, and suggested that ΔK RPG should be used as the parameter to describe fatigue crack growth behavior. The “FLARP” numerical simulation code in which ΔK RPG is implemented as the fatigue crack growth parameter, was developed in order to predict fatigue crack initiation and propagation behavior. In this paper, it is demonstrated that FLARP gives accurate estimates for fatigue life by comparing the estimated fatigue crack growth curves and S–N curves with the experimental results for in-plane gusset welded joints, which are used in many welded steel structures. Moreover, the effect of induced bending moment due to the linear misalignment in the out of plane direction on the fatigue strength of in-plane gusset welded joints is investigated through numerical simulations.

Fatigue life prediction of in-plane gusset welded joints using strain energy density factor approach

Fatigue crack growth behavior of in-plane gusset welded joints is studied using the strain energy density factor approach. Fatigue tests were performed in order to estimate fatigue strength under tension. Fatigue crack growth analysis was carried out to show the effects of the initial crack shape, the initial crack length, and the stress ratio on the crack types of in-plane gusset welded joints. The assumed crack types were edge crack, semi-elliptical crack, and corner crack. Fatigue crack growth parameters were obtained from crack growth curves assuming constant crack shapes for the given crack types. The results of analysis for the assumed crack types agreed well with the experimental data. The fatigue life did not change as initial crack shape varied for a given initial crack length.

Fatigue life prediction of out-of-plane gusset welded joints using strain energy density factor approach

Fatigue growth behavior of out-of-plane gusset welded joints is studied using the strain energy density factor approach. Fatigue tests on two types of specimens with curvatures of ρ = 0 and ρ = 30 were performed in order to estimate fatigue strength under tension. Fatigue crack growth analysis is carried out to show the effects of initial crack shape, initial crack length and stress ratio. Fatigue crack growth parameters were obtained from crack growth curves assuming constant crack shapes. The results of analysis for the assumed crack shapes agreed well with the experimental data. Fatigue propagation life of the ρ = 30 specimen was larger than that of the ρ = 0 specimen.

面内ガセット継手の疲労き裂発生・成長シミュレーション

Welded built-up steel structures in service encounter many accidents caused by fatigue, and it is important for maintenance of social foundations and safeness to estimate their fatigue lives quantitatively.By considering that fatigue cracks cannot grow without the accumulation of alternating tensile / compressional plastic strain, one of authors identified that the effective stress intensity factor range ΔKRPG based on the Re-tensile Plastic zone Generating (RPG) load which represents the fatigue crack driving forces, and suggests that ΔKRPG should be applied as the parameter in order to describe the fatigue crack growth behavior. For predicting fatigue crack initiation and propagation, numerical simulation code “FLARP” based on ΔKRPG was developed.In this paper, it is confirmed that fatigue life estimation by FLARP gives accurate results by comparing the estimated fatigue crack growth curves with the experimental results for in-plane gusset welded joints which are used in many welded steel structures. Moreover, the effect of induced bending moment due to misalignment for the fatigue strength is investigated by the numerical simulations.

溶融亜鉛めっきを施した溶接継手の疲労強度（第３報） 溶融亜鉛めっきを施した部材の疲労強度に及ぼすめっき施工条件と鋼材の影響

Recently, the discussion on prolonging life of steel bridges such as life cycle cost and long life bridge is widely done, and main factors of the prolonging life are countermeasures against fatigue and corrosion. As a countermeasure against corrosion, galvanizing is one of the effective methods, and many galvanizing steel bridges have been constructed until now. It is also considered that residual stress of welded portion is reduced by the annealing effect due to immersing welded member into hot dip galvanizing tank of about 450°C and the stress concentration at the weld toe as an origin of fatigue crack is reduced if a part of stress is transmitted in the galvanizing layer. These are correspondent to the two methods for increasing the fatigue strength. However, the effect of the galvanizing on the fatigue strength of welded joints has not been made clear sufficiently at the present. This study aims at investigating fatigue strength of welded joint with galvanizing. For this purpose, fatigue tests have been carried out on out-of-plane gusset welded joints which are made of 3 kinds of steel and are galvanized in several conditions. Residual stress measurements and three-dimensional finite element stress analyses for them are also carried out.

溶融アルミニウムめっきを施した面外ガセット溶接継手の疲労強度

Hot dip metal plating is considered to be effective for increasing corrosion resistance in steel structures. The planting makes possible to reduce the residual stress in the welded portion due to annealing effect, and stress concentration at the weld toe is reduced by the plating if a part of stress is transmitted in the aluminum layer. Therefore, it is considered that fatigue strength can be improved by hot dip aluminum coating. These facts mean that the hot dip aluminum coating is one of useful countermeasure against the fatigue and corrosion, which are regarded as weaknesses of steel structures. However, it has not been clear how the planting influences the fatigue strength of a welded joint. This study aims at clarifying fatigue strength of welded joints coated with aluminum. For this purpose, out-of-plane gusset welded joints specimens were made of SM400 and were plated on two conditions of hot dip aluminum coating, then fatigue tests were carried out on these specimens. Furthermore, microstructures on the plating layer and fatigue crack origin were closely observed.

Fatigue Strength of Flange Gusset Welded Joints Repaired by Bolting-Stop-Hole Method

Fatigue Strength of Flange Gusset Welded Joints Repaired by Bolting-Stop-Hole Method

Fatigue strength of welded joints made of high‐strength steels

AbstractBy rearranging existing fatigue test results, fatigue performance of typical welded joints, (longitudinal, cruciform and out‐of‐plane gusset welded joint) are discussed with respect to the dependence on steel strength and on joint size. The relationship between fatigue strength and steel strength was not clear for longitudinal welded joints of small specimens and large‐scale girder specimens. For cruciform welded joints and out‐of‐plane gusset welded joints, fatigue strength of small joint specimens is independent of the steel strength, but that of girder specimens decreases with increase in steel strength. In addition, fatigue strengths of these two types of welded joints decrease with increase in joint size, especially for girder specimens.In order to discuss these relationships in detail, fatigue tests with out‐of‐plane gusset welded joint specimens and large‐scale girder specimens, including web gusset joints made of JIS SM570 and 900 MPa class steel were carried out. From the fatigue tests, similar tendencies were found to those obtained from existing test results. Although fatigue tests of joint specimens showed no difference in fatigue strength, crack initiation life and crack propagation rate between the steel strengths, fatigue strength of girder specimens made of 900 MPa class steels is much lower than for JIS SM570. In addition, fatigue strength of the girder specimens is considerably lower than that of the joint specimens. This difference results mainly from an increase in stress concentration due to joint geometry, and combination of nominal stress and shear stress in the girder specimens. It was found that the influence of the combination can be approximately evaluated from the nominal principal stress.

IMPROVING FATIGUE STRENGTH OF WELDED JOINTS BY HAMMER PEENING AND TIG-DRESSING

The effectiveness of fatigue strength improvement methods, namely TIG-dressing and hammer peening, were examined using out-of-plane gusset welded joints of high strength steel (SM570). In addition, the mechanism of each improvement method was discussed with respect to the decrease in stress concentration and residual stress at the weld toe. Finally, various methods for improving the effectiveness of these fatigue strength improvement methods are proposed.

Fatigue Strength of Gusset Welded Joints under Simulated Program Loading of Overhead Travelling Crane.

A survey of the degradation in overhead travelling cranes was performed. Fatigue cracks were often detected in highly stressed regions in cranes that had been in use for fifteen years or more. Service stresses of an overhead travelling crane with a lifting capacity of 50 kN were monitored and analyzed by the rain-flow method. A fatigue test of gusset welded joints made of SM490A steel was carried out under both constant loading and program loading determined based on service stress monitoring. The fatigue life of the gusset welded joints is dominated by crack initiation rather than propagation. The crack growth rate of the welded joints under program loading is correlated with an effective stress intensity factor range, ΔKRem estimated based on linear accumulation of the stress intensity factor range which takes into account residual stress at each step in a block. The prediction of fatigue propagation life using ΔKRem agrees with the experimental result in the range of error up to 15%, when the crack length is less than 20 mm.

Fatigue Strength of Gusset Welded Joints Under Simulated Program Loading of Overhead Traveling Crane.

A survey of degradation in overhead traveling cranes was performed and fatigue cracks were often detected in highly stressed regions in cranes that have been used for fifteen years or more. Service stresses of an overhead traveling crane with lifting capacity of 50 kN were monitored and analyzed by the rain-flow method. A fatigue test of gusset welded joints made of SM490A steel was carried out under both constant loading and program loading determined based on the service stress monitoring. The fatigue life of the gusset welded joints is dominated by crack initiation rather than propagation. The crack growth rate of the welded joints under program loading is correlated with an effective stress intensity factor range, ΔKrem, estimated based on linear accumulation of the stress intensity factor range which takes into account residual stress at each step in a block. The prediction of fatigue propagation life using ΔKrem agrees with the experimental result in the range of error within 15%, when the crack length is less than 20 mm.

付加物継手の疲労強度におよぼす継手端部形状の影響

Gusset welded joint is known as having the lowest fatigue strength among other types of welded joints. In order to improve the fatigue strength of gusset welded joints, the effect of the shape of weld ends on fatigue strength was investigated for three types of gusset welded joints using mild steel (SS41). Non-load carrying and load carrying gusset welded joints were examined, which were boxing fillet welding (type A and A'), side fillet welding (type B and B') and lengthened side fillet welding (type C and C') types.The test result indicates that the fatigue strength increases in the following order, type A and A'<type B and B'<type C and C' and that type C and C' are about 22% stronger than type A and A' at N=2×106. This result can be discussed in terms of difference in notch effect at the weld ends and in crack propagation process. The effect of residual stress may be insignificant.The effect of toe grinding was also investigated. Toe grinding increased fatigue strength of type A' and did not increase that of type C' while it changed location and appearance of the fracture.