## 7 Design Applications
### Environmental Wind  
To add the effect of wind gust to the fatigue calculation and assess the fatigue life of structural joints based on combined stress ranges from vehicle buffeting and external wind, the European standard [45] can be used to start the calculation. For structural joints involving hollow cross sections, hot spot S-N curves from \"CIDECT Design Guide 8\" [46] were used to start the fatigue assessment postprocessing routine. The total fatigue damage due to a combined stress cycles (vehicle and environmental induced cycles) can be assumed to be the sum of the damage due to each cycle. As the fatigue damage due to one cycle with stress range \"S\" in most popular design codes is defined as 1/N times the total fatigue life of the structure at the particular location\(\backslash\)joints, the total sum of stress cycles at different ranges (by linear Miner rules or rain flow counting scheme) can be used to inspect the fatigue life by estimation of the number of repetitions \"N\" from the S-N curve. Figure 14 shows the gantry structural joints and their FE simulations for fatigue hot spot estimations. Some initial assumptions can be made to start the fatigue life calculation under both environmental wind gust and HSV buffeting; namely,  
* For stress cycles below the threshold limit \(\Delta\sigma_{\text{D}}\), if all the stress ranges can roughly fall below the threshold (no large stress cycles), it can be assumed that no fatigue damage is considered to have been done in the joint zone (European standard [47] can be used to define the \(\Delta\sigma_{\text{D}}\)). * For the stress cycles with a stress range less than \(\Delta\sigma_{\text{L}}\), it is assumed that stress cycles can cause no fatigue damage and can be ignored (\(\Delta\sigma_{\text{L}}\) can be defined as \(\Delta\sigma_{\text{L}}=0.549\)\(\Delta\sigma_{\text{D}}\) according to the European standard [47]). * For joints with exposure to stress cycles larger than \(\Delta\sigma_{\text{D}}\), the damage from all service life cycles is summed. The damage from a cycle with stress range \(\Delta\sigma\) is considered to be 1/N (times the joint failure damage), where N is obtained from the S-N curve for the joint. Figure 14: (a) Local/detailed CAD model of gantry boom, (b) its high-resolution zonal stress results, (c) fatigue calculation for baseplate welding, and (d) boom-leg joints. The fatigue life calculation can then be performed for each structural joint based on its own S-N curve. To account for the number of stress cycles for environmental wind gust, let us consider the equation [45]  
\[\Delta S/Sk\ =\ 0.7\cdot\left(\log\left(N_{g}\right)\right)2-17.4\cdot\log\left(N_{g }\right)\ +\ 100 \tag{45}\]  
where \(\Delta S/Sk\) is an effect from gust wind loading as a proportion (generally in percent) of the effect of the 50-year peak wind loading (the 50 year return period wind gust), while \(N_{g}\) is the number of times that this effect is expected to be exceeded in 50 years of service life (i.e., number of times a wind gust of each magnitude is expected to occur during 50 years). The pulse transient loading for these wind gust events can be defined using the 10 min wind mean speed according to the European standard [45]. The assumed gust pressure can be a constant multiple of basic wind pressure for the full wind exposure (without obstacles). A gust pressure factor of 3 can be used [45] for the gantry structure herein, which implicates the wind gust speed of \(\surd 3\) times the 10 min mean wind speed. Figure 15 shows typical S-N curves [46; 47] for the reference stress of \(\Delta\sigma_{\text{C}}=100\) along with a graphical representation of the wind gust effect [45] and the cumulative 3 s transient pulse loadings for excitation scenarios. Figure 15: (a) Typical S-N curves for fatigue calculation based on the European Standard [47] and Cidect guide [46]; (b) transient factors for pulse loading pattern representing wind gust loading.