## 1 Introduction
The upper bound of the probability distribution of the TR1 rule can be expressed; the maximum of combination extreme is obtained according to the lower bound of the TR rule probability distribution. This rule is called the TR2 rule, and the lower bound of the probability distribution of the TR2 rule can also be expressed. [PERSON] et al. [16; 17; 18] extended the TR1 and TR2 rules to the situation where the load effect components are related, and noted that the accuracy of the combination rule is related to the correlation coefficient of the effect component, the probability distribution type, and the quantile level. When one of the load effect component amplitudes is significantly larger than other components, the TR1 and TR2 rules are more accurate. [PERSON] and [PERSON] [4; 19; 20] studied the combination rules of wind load effects, and the results showed that when the effect components are strongly correlated or have large amplitude differences, and the effect components have non-zero mean values, the TR1 and TR2 rules are more accurate, but when the effect components are partially correlated or uncorrelated, the TR1 and TR2 rules will underestimate the combination extreme. Some approximate combination rules have also been adopted in practice for the convenience of calculation, i.e., 40% rule and 75% rule. [PERSON], [PERSON] and [PERSON] [21] used the external dodecagon of an ellipse as the envelope of the most unfavorable condition for the combination of downwind and crosswind combination responses. On the basis of [PERSON]'s method, [PERSON] [22] made use of the external octagon of an elliptic trajectory to estimate the most unfavorable response. In the wind-resistant design of building structures, it is necessary to directly multiply the extreme value of the wind load effect component by the combination coefficient to obtain a simple Equation for the combination extreme of the effect, and the accuracy of the combination extreme should meet the engineering requirements. Therefore, it is very important to determine the simple and reasonable combination rules for extreme value combinations of wind load effect components. The TR rule is based on engineering experience and does not have a rigorous theoretical foundation. In contrast, the CQCrule is based on reliability theory and has rigorous theoretical foundations, but it is not convenient in engineering applications, especially when multi-effect components are combined. This paper derives the probability distribution expressions of combination extremes of wind load effect components according to CQC combination rules and Turkstra and its approximate combination rules, and proposes simplified combination Equations and combination coefficients of CQC combination rules and Turkstra approximate combination rules. The approximate combination Equations and combination coefficients proposed in this paper enable engineers to calculate the extreme values of the wind load combination effect directly and simply by applying the extreme values of effect components in engineering design. The combination Equation and Monte Carlo simulation method are used to analyze the accuracy of Turkstra and its approximate combination rules, and the application range of relative error within 10% is proposed. The simplified combination Equations and combination coefficients of the CQC rule and Turkstra approximation rules proposed in this paper provide a theoretical basis for the extreme value combination method of wind load effect components of a building structure, which is convenient for engineering application.