Issue 45

D. Yang et alii, Frattura ed Integrità Strutturale, 45 (2018) 45-52; DOI: 10.3221/IGF-ESIS.45.04 47 (a) (b) Figure 2: Finite-element model of Zheng Hongzhi. R ELEVANT SPECIFICATIONS he current calculation method for hot spot stress adopts the minimum distance between the extrapolation region and the weld toe, seeking to eliminate the impact of the local shape of the weld. Mechanically speaking, the weld size has a positive correlation with the distance between the extrapolation region and the intersection area, the most obvious variation place of stiffness. In other words, the SCF tends to decline with the increase in the weld size. Hence, it is assumed here that the weld size does have an impact on the SCF. The range of weld size must be determined before studying the effect of weld size on the SCF of welded joints. Below is a review of the relevant specifications on weld size. (1) For welded joints directly under fatigue load, the Technical Specification for Structures with Steel Hollow Sections (CECS 280:2010) [17] stipulates that the partial or full penetration weld should be adopted if the brace wall thickness t is greater than 8mm; the fillet weld can be used if the brace wall thickness is smaller than or equal to 8mm (Article 8.28). (2) For tubular T-joints with full penetration weld, the Technical Specification for Welding of Steel Structure of Building (JGJ 81-2002) [18] stipulates that the minimum weld size should be w0=0.5t1 at the chord-side and w1=6mm+0.767t1 at the brace-side (Article 4.3.6-1), where t1 is the brace wall thickness. That is, the minimum weld size-brace wall thickness ratio remains at 0.5 at the chord-size, and changes at the brace-side with brace wall thicknesses. Moreover, the ratio of weld-size to brace wall thickness should fall in 1.14~2.27 if the brace wall thickness varies between 4mm and 16mm (the brace wall thickness should not exceed 16mm) (Article 4.3.6-1). (3) For tubular T-joints with fillet weld, the Technical Specification for Structures with Steel Hollow Sections (CECS 280:2010)[17] stipulates that the weld thickness should not be smaller than brace wall thickness t1 (Article 8.2.8) and should not exceed twice the brace wall thickness (Article 7.1.1-4); the Code for Design of Steel Structures (GB 50017- 2013)[19] stipulates that the ratio of brace-side weld size to chord-side weld size can be 1: 1 (Article 8.2.8). In the right- angle fillet weld, the fillet weld size should be about 1.4 times of the weld thickness. In other words, the fillet weld size should not be smaller than 1.4t1, should not be greater than 2t1, and must not be greater than 2.8t1, where t1 is the brace wall thickness. (4) For tubular T-joints with partial penetration weld, the Technical Specification for Structures with Steel Hollow Sections (CECS 280:2010) [17] stipulates that the fatigue performance of the weld should be the same as that of fillet weld, that is, the weld size should not be smaller than 0.5t1 at the chord-side or smaller than 1.73t1 at the brace-side, where t1 is the brace wall thickness. F INITE - ELEMENT ANALYSIS Finite-element model eld configuration. Fig. 3 presents the three possible welds for the brace and chord of welded tube joints, namely, full penetration weld, partial penetration weld and fillet weld. Wingerde examined the weld configuration by finite-element method, suggesting that the effect of different weld configurations on the SCF is negligible [3]. Zheng Hongzhi also applied finite-element method to examine the impacts of different weld configurations on the SCF and concluded that the SCF of full penetration weld is less than 10% greater than that of the other two configurations under the same weld size and dimensionless parameters [16]. For reliability and accuracy, the three types of welds are all modeled according to the configuration of full penetration weld in this research (Fig. 3(a)). T W