## 7 Conclusions  
* The stress integration approach for the 3D solid elements showed that the structural stress does not change significantly with the parameters \(w\) (width of the isolated body) and \(\delta\) (the distance between the crack propagation surface and the reference surface). In order to simplify the calculation, \(\delta\) was set as 0, and \(w\) can be set as the mesh size along the weld length direction. * When the mesh size is no more than 0.5 times the deck thickness, the mesh insensitivity of the stress integration approach is obviously better than that of the extrapolation hot spot stress approach. The mesh size in the stress integration approach is recommended to be 0.25 times the deck thickness, and the calculation error is approximately 2%. * The slope of the master S-N curve at high cycles (\(N>10^{7}\)) significantly affects the bridge fatigue life, and the slope \(m_{2}=5\) at high cycles is more reasonable. * The weld parameter analysis for Jiangyin Bridge showed the following: (1) The change of weld size caused by weld manufacturing errors can obviously affect the bridge fatigue life. The fatigue life of five different weld types varies from 51 years to 113 years under a standard vehicle load. The weld fatigue life increases with the decrease of the angle \(\alpha_{2}\) between the deck and the rib and the increase of the weld area. (2) A new grinding treatment type that does not weaken the deck is proposed. It is more beneficial to improve the fatigue life of the deck-rib welding details, and the fatigue life increases by approximately 5% when the grinding radius increases by 2 mm. (3) The fatigue life with 80% partial penetration is slightly higher than that of 100% full penetration. (4) In practice, the most favorable weld type is WT-3 with an angle \(\alpha_{2}\) of 30 degrees and an area of 48 mm\({}^{2}\). The grinding type that does not weaken the deck is more conducive to improving the bridge fatigue life. The 80% partial penetration of the deck-rib welding details condition is recommended. All authors discussed and agreed on the idea and scientific contribution. [PERSON] did the mathematical modeling, performed the simulations and contributed to the writing. [PERSON], [PERSON], [PERSON] and [PERSON] contributed to the revisions and discussion of the results. Figure 25: FEM of 80% partial penetration and 100% full penetration. (**a**) 80% (**b**) 100%. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Penetration Rate** & \(\sigma_{s}\) **(MPa)** & \(S_{s}\) **(MPa)** & \(N_{a}\) **(Years)** \\ \hline
80\% & 41.67 & 54.64 & 89 \\
100\% & 42.21 & 55.35 & 84 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Comparison of structural stress and fatigue life under different penetration rates. **Funding:** This research was funded by the [National Basic Research Program of China (973 Program)] grant number [2015 CB060000], the [Key Program of National Natural Science Foundation] grant number [51438002], the [Program of National Natural Science Foundation of China] grant number [51578138, 51608258], the [Fundamental Research Fund for the Central Universities] grant number [2242016K41066], the [Fundamental Research Funds for the Central Universities and graduates' Science and Innovation Foundation of Jiangsu Province] grant number [KYLX16_0250], and the [A Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)] grant number [1105007002]. **Acknowledgments:** The authors gratefully acknowledge the National Basic Research Program of China (973 Program) (no. 2015 CB060000), the Key Program of National Natural Science Foundation (no. 51438002), the Program of National Natural Science Foundation of China (no. 51578138, 51608258), the Fundamental Research Fund for the Central Universities (no. 2242016K41066), the Fundamental Research Funds for the Central Universities and graduates' Science and Innovation Foundation of Jiangsu Province (no.