## 2. CQC Combination Rules and Simplified Combination Coefficients
The expressions of the maximum and minimum of the combined effect can be obtained from Equation (2):  
\[R_{\text{max}}=(\mu_{1}+\mu_{2})+g_{R}\sigma_{R}, \tag{7}\]  
\[R_{\text{min}}=(\mu_{1}+\mu_{2})-g_{R}\sigma_{R}, \tag{8}\]  
In the Equation, \(g_{R}\) represents the peak factor of the combined effect, and its expression [24] is as follows. The peak coefficient \(\text{K}_{\text{P}}\) in the EN 1991-1-4 is changed from 0.5772 in Equation (9) to 0.6:  
\[g_{R}=\sqrt{2\ln\left(v_{0,R}^{+}T\right)}+\frac{0.5772}{\sqrt{2\ln\left(v_{ 0,R}^{+}T\right)}}, \tag{9}\]  
Assuming that the peak factors of the effect component and the combined effect are approximately equal:  
\[g_{R}\cong g_{1}\cong g_{2}\cong g, \tag{10}\]  
Then, we can obtain:  
\[F(R)=\exp\left[-v_{0,R}^{+}T\cdot\exp\left(-\frac{(R-\mu_{1}-\mu_{2})^{2}}{2 \sigma_{R}^{2}}\right)\right], \tag{2}\]0  
Substituting Equation (11) into Equation (7) yields the maximum of the combined effect:  
\In the Equation, \(\lambda_{\text{2,min}}\) is called the combination coefficient of extreme value \(R_{\text{2 min}}\), and its expression is:  
\[F(R)=\exp\left[-v_{0,R}^{+}T\cdot\exp\left(-\frac{(R-\mu_{1}-\mu_{2})^{2}}{2 \sigma_{R}^{2}}\right)\right], \tag{2}\]1  
Derived above is the simplified Equation for the combination of the two effect components according to the CQC rule, and the extreme combination coefficient of the two effect components is proposed. Extending the above principle to the combination of multi-effect components, the maximum of the combination extreme of the scalar sum of \(n\)-effect components can be written as:  
\[F(R)=\exp\left[-v_{0,R}^{+}T\cdot\exp\left(-\frac{(R-\mu_{1}-\mu_{2})^{2}}{2 \sigma_{R}^{2}}\right)\right], \tag{2}\]2  
In the Equation, \(\lambda_{i,\text{ max}}\) is called the combination coefficient of the \(i\)-th effect component extreme value \(R_{i\text{max}}\), and its expression is:  
\[F(R)=\exp\left[-v_{0,R}^{+}T\cdot\exp\left(-\frac{(R-\mu_{1}-\mu_{2})^{2}}{2 \sigma_{R}^{2}}\right)\right], \tag{2}\]3  
In the Equation, \(\rho_{jk}\) is the correlation coefficient of \(R_{j}(t)\) and \(R_{k}(t)\); \(c_{ji}\) is the ratio of \(\sigma_{j}\) to \(\sigma_{i}\); \(c_{ki}\) is the ratio of \(\sigma_{k}\) to \(\sigma_{i}\). The minimum of the combination extreme of the scalar sum of \(n\)-effect component can be written as:  
\[F(R)=\exp\left[-v_{0,R}^{+}T\cdot\exp\left(-\frac{(R-\mu_{1}-\mu_{2})^{2}}{2 \sigma_{R}^{2}}\right)\right], \tag{2}\]4  
In the Equation, \(\lambda_{i,\text{min}}\) is called the combination coefficient of the \(i\)-th effect component extreme value \(R_{\text{min}}\), and its expression is:  
\[F(R)=\exp\left[-v_{0,R}^{+}T\cdot\exp\left(-\frac{(R-\mu_{1}-\mu_{2})^{2}}{2 \sigma_{R}^{2}}\right)\right], \tag{2}\]5  
In engineering design, the maximum and minimum combination coefficients of each effect component can be calculated according to Equations (17) and (19), and the maximum and minimum values of the extreme value of combined effect can then be calculated according to Equations (16) and (18). Structural wind-resistant design can then be carried out. It can be seen from Equations (17) and (18) that the combination coefficient is related to the correlation coefficient, variance ratio, mean value, and fluctuating value. The combination coefficients proposed above provide convenience for engineers to directly apply combination coefficients to combine extreme values of wind load effect components in structural wind-resistant design. In addition to the CQC rule, the widely used load effect combination rules also include the TR rule. The following is a study of the TR rule and its approximate combination rules.