• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.1
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• pp.129-136
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• 2018

The estimation of the fatigue design life for large welded structures is usually performed using the liner cumulative damage method such as Palmgren-Miner rule or the equivalent damage method. When a fatigue crack is detected in a welded steel structure, the residual service life has to be estimated base on S-N curve method and liner elastic fracture mechanics. In this study, to examine the 3D fatigue crack behavior and estimate the fatigue life of out-of-plane gusset fillet welded joint, the fatigue tests were carried out on the model specimens. Investigations of three-dimensional fatigue crack propagation on gusset welded joint was used the finite element analysis of FEMAP with NX NASTRAN and FRANC3D. Fatigue crack growth analysis was carried out to demonstrate the effects of aspect ratio, initial crack length and stress ratio on out-of-plane gusset welded joints. In addition, the crack behaviors of fatigue tests were compared with those of the 3D crack propagation analysis in terms of changes in crack length and aspect ratio. From this analysis result, SIFs behaviors and crack propagation rate of gusset welded joint were shown to be similar fatigue test results and the fatigue life can also be predicted.

• International journal of steel structures
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• v.18 no.5
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• pp.1631-1638
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• 2018

In the periodic repainting of steel bridges, often the steel surface has to be prepared by using power tools to remove surface contaminants, such as deteriorated paint film and rust, and to increase the adhesive strengths of the paint films to be applied newly. Surface preparation by bristle roll-brush grinding, which is a type of power tool, may additionally introduce compressive residual stress and increase the fatigue resistance of welded joints owing to the impact of rotating bristle tips. In this study, fatigue tests were conducted for longitudinally out-of-plane gusset fillet welded joints and transversely butt-welded joints to evaluate the effect of bristle roll-brush grinding prior to repainting on the fatigue resistance of the welded joints. The test results showed that bristle roll-brush grinding introduced compressive residual stress and significantly increased fatigue limits by over 50%.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.3
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• pp.48-55
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• 2013

In this study, fatigue tests were performed on longitudinal out-of-plane gusset fillet welded joints and transverse non-load-carrying cruciform rib fillet welded joints, and then applicability of hammer-peening treatment on improvement of fatigue life for fatigue damaged weld joints were investigated. Fatigue tests were carried out on three types of gusset and rib welded specimens: as-welded specimens, post-weld hammer peened specimens and hammer peened specimens at 50% of as-welded specimen's fatigue life. Before and after hammer peening treatment, the geometry of weld toes and surface stresses near weld toes were measured. As a result of hammer peening treatment, compressive residual stresses of 30-83MPa were introduced near weld toes of the gusset and rib welded joints, and 130% increase in fatigue life and fatigue limit of the welded joints could be realized by hammer peening treatment at 50% fatigue life of as-welded conditions.

• Journal of Korean Society of Steel Construction
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• v.20 no.5
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• pp.583-590
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• 2008

Blasting has been applied in newly-built steel structures for cleaning forged surfaces and increasing the adhesive property of applied painting systems. However, the effect of the blast cleaning on fatigue behavior of welded joints is not clear. In this paper, fatigue tests were carried out on out-of-plane gusset welded joints and the effect of the blast cleaning on the fatigue behavior was studied. The curvature radius at the weld toe of the surface-treated specimens by using the blast method is larger than that of as-welded specimens. By the blast cleaning compressive residual stresses were induced into weld toes. The experimental results showed that the fatigue life of surface-treated specimens is longer than that of as-welded specimens, even though the fatigue life of surface-treated specimens and that of as-welded specimens are not clearly different in the high stress range. About a 160% increase in fatigue limit could be realized by using blast cleaning.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.1A
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• pp.1-13
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• 2008

The web of a horizontally curved plate girder bridge is, in general, subject to not only longitudinal flexural in-plane stress but also out-of-plane bending stress. Therefore, the induced stresses in the fillet welded joints at the intersection of the web and flange plates in the curved plate girder bridge can be considerably high, and the welded joints of gusset plates connecting the main girder to the floor beams or sway bracings can be subject to much more severe situation than those in the ordinary straight plate girder bridge. In order to investigate the cause of fatigue crack occurred in a curved girder bridge that has been served in about 23 years, in this study, field load tests have been performed to obtain the stress characteristics at the welded joint under the real traffic flow. Using the test results, we have investigated the causes of the occurrence of various fatigue cracks and have estimated the fatigue lives for the cracks. In addition, the characteristics of structural behavior at welded joint of the curved girder bridge have been examined by comparing the FE analysis and the field test result.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.2
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• pp.179-188
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• 2011

Steel structures have been allowed to have fatigue damage tolerance in fact. If it would be assessed whether fatigue crack is growing or not and How fast fatigue crack is propagating, we should make a rational decision on methods and a period of reinforcement in the maintenance. In this study, fatigue crack growth tests on two kinds of through-thickness cracked steel plates and a out-of-plane gusset welded joint were conducted to evaluate fatigue crack growth rate using the COD(Crack Opening Displacement), and COD measurement using strain gauges was examined to offer a practical method. As a result, we proposed a reasonable assessing method for fatigue crack growth rate using the COD and it was experimentally proved practical to estimate the COD through measuring strains.