Articles Jaap Wardenier* Peter de Vries Gerrit Timmerman
DOI: 10.1002/stco.201710011
Evaluation of cracks in an offshore crane runway girder This paper deals with the evaluation of fatigue cracks in a box type radial crane runway girder with full penetration welds between the web and flange. After 20 years of service fatigue cracks were observed which were initiated in the flange at the toe of the full penetration weld with the web. The observed cracks in the crane runway girder vary in length from a few mm to 330 mm with a summation of the lengths of all observed cracks being 750 mm, on a total length of 56000 mm, thus being only 1.3 %. The investigation consists of the fatigue analysis described in this paper and additional experimental investigations with scale tests of approximately 1:2 on equivalent I sections with a concentrated load and with a line load to investigate whether cracks stop when they have grown through the residual tensile stress field. For this analyzed crane runway girder with multi-layered full penetration welds and with small cracks at the weld toes in the flange, based on EN 1993-6 the damage would be 1.0 for a design class 98 which is not far from the “class” 92 found by Kuhlmann et al, [1] for tests with rolling wheels, however, related to weld failures from the root of not fully penetrated fillet welds in combination with crack initiations at the weld toe.
1 Introduction This paper deals with the evaluation of fatigue cracks in a box type radial crane runway girder with full penetration welds between the web and flange. After 20 years of service fatigue cracks were observed which were initiated in the flange at the toe of the full penetration weld with the web. It is expected that they curve underneath the weld but, due to the limited possibility for inspection, this could not be clearly determined. The observed cracks in the crane runway girder vary in length from a few mm to 330 mm with a summation of the lengths of all observed cracks being 750 mm, on a total length of 56 000 mm, thus being only 1.3 %. The objective of the evaluation is to explain the observed cracks and to investigate whether the cracks could become critical and repair is required. The investigation consists of the fatigue analysis described in this paper and additional experimental investigations with scale tests of about 1:2 on equivalent I sections with a concentrated load and with a line load to investigate whether the cracks stop when they have grown through the residual tensile
* Corresponding author: j.wardenier@tudelft.nl
stress field. This paper describes the assessment of the fatigue cracks in the actual crane runway girder; publication of the experimental investigations will follow. The results of this analysis supports the results of the recently completed German AIF/Fosta research program [1] by the University of Stuttgart on the fatigue behaviour of crane runway girders under a rolling wheel. All other literature studied, only provides qualitative evidence but not evidence really based on a rolling wheel.
2 Background of the crane runway girder The crane runway girder with a cross-section shown in Fig. 1, consists of a box section with a 75 mm rail plate located on top of the 75 mm flange and above one of the 65 mm webs. The web is extended and fully supported beneath the box section, thus no in-plane bending stresses occur in the web and the overall shear stresses are neglectable. The full penetration welds between the web and the flanges are made with a foot print nearly equal to the thickness of the web. Details of the dimensions and details of the steel grades are, as far as available, given in Table 1. The loads with the number of cycles per year are given in
Fig. 1. Crane girder detail with location cracks with estimated weld detail
© Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin · Steel Construction 10 (2017), No. 1
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