The design method used in the current steel structure design code is the

The approximate probabilistic limit state design method is to introduce the design parameters of variability into structural design using probabilistic analysis. It is divided into three levels according to the degree of applying probabilistic analysis. That is, semi-probabilistic limit state design method, approximate probabilistic limit state design method and full probabilistic limit state design method.

According to the probabilistic limit state design method, structural reliability is defined as the probability that a structure will fulfill its intended function within a specified time and under specified conditions. It is a general term for structural safety, serviceability and durability. When the structure or its components exceed a particular state can not meet the design requirements of a function, this particular state is called the function of the limit state.