Thickness Effect Criterion for Fatigue Strength Evaluation of Welded Steel Structures

Abstract

From a practical point of view, some measures to reduce the thickness effect backed by a reasonable criterion are required for fabricating structures with heavy section plates. In this study, the thickness effect was investigated by systematic experiments on welded steel joints with thicknesses ranging from 10 to 80 mm. Cruciform joints and T-joints with improved weld by overall profiling or toe-grinding were tested under pulsating tension and under pulsating bending, respectively. These experimental results were analyzed together with the previous results of as-welded joints. As a result, it was concluded that the thickness effect exponents for various conditions may be classified into three categories according to the combination of joint type and loading mode. As-welded joints under bending stress have the steepest thickness effect exponent of −1/3, while as-welded joints under tension with an exponent of −1/5 is milder in thickness effect than that specified in the existing codes. If the weld profile is improved by grinding, the thickness effect becomes much milder to an exponent of −1/10. The as-weld joints with constant-sized attachments also have an exponent of −1/10. Furthermore, thickness effect dependence on fatigue life and thickness effect under random stress were investigated. Based on these results, this study proposes a new evaluation criterion for design purposes.

Fatigue properties of arc‐welded lap joints with weld start and end points

“…The fatigue strength Δσ g for 2 × 10 6 cycles of the 2.3‐30/50 and the 3.2‐30/50 specimens, which have the same dimensions except in thickness, are plotted with the abscissa of thickness in Figure 10. The thickness effect exponent for the specimen is −0.86, which as an absolute value is rather large compared to that for butt joints, cruciform joints and tee joints of heavy steel plates (−0.1 to −0.3) 3,4 . The thickness dependencies of the stress‐concentration factor obtained by the finite‐element analyses for r = 0.5 mm and r = 1.0 mm, which will be mentioned later, were 0.61 and 0.53, respectively, and the same order as the thickness effect exponent.…”

“…The thickness effect exponent for the specimen is −0.86, which as an absolute value is rather large compared to that for butt joints, cruciform joints and tee joints of heavy steel plates (−0.1 to −0.3). 3,4 The thickness dependencies of the stress-concentration factor obtained by the finite-element analyses for r = 0.5 mm and r = 1.0 mm, which will be mentioned later, were 0.61 and 0.53, respectively, and the same order as the thickness effect exponent. However, the thickness dependency of the stress-concentration factor in the specimens with constraint under out-of-plane deformation was calculated as a half of those without constraint.…”