## 1 Introduction
In this paper, a stepwise algorithm is proposed to determine the reasonable completion state of the hybrid girder cable-stayed bridge, and the improved genetic algorithm is used in order to optimize the cable force of the hybrid girder cable-stayed bridge of Jiujiang No. 2 Bridge under dead load. Compared with the traditional method of determining the cable force, this algorithm avoids the later work of cable adjustment. [PERSON] et al. [9] used the evolutionary nondominated sorted genetic algorithm (NSGA) to solve the multiobjective optimization problem of multispan cable-stayed bridges. The genetic algorithm only takes a few seconds to find the nondominated solution set comprising the Pareto front. In addition, many scholars have extended this kind of method to the field of bridge structure optimization design, which makes its application scope more extensive. The latest cable force optimization algorithms suitable for cable-stayed bridges have been increasingly paid attention by scholars. [PERSON] et al. [10] proposed an optimal design method for cable-stayed bridges by combining an influence matrix method with genetic algorithm and applied it to the preliminary design of the cable-stayed bridge with two towers and two cable planes located in Ferrara, Italy. At present, the main method of introducing the swarm intelligence optimization algorithm to realize cable force optimization of cable-stayed bridges is based on the interaction between programming language and large general design software. [PERSON] et al. [11] used a multipopulation genetic algorithm to optimize the cable force of long-span cable-stayed bridges under reasonable completion state by establishing the parametric analysis model with APDL (Ansys Parametric Design Language). The research proves the feasibility and validity of the multipopulation genetic algorithm in the optimization of the cable force of long-span cable-stayed bridges considering nonlinearity. It is undeniable that ANSYS is an excellent fine analysis software. For example, scholars such as [PERSON] et al. [12] have used ANSYS for fine analysis and obtained satisfactory results. However, Ansys, as large general finite element design software, is still lacking in the professional bridge module compared with the special software for bridges. [PERSON] et al. [13] and [PERSON] et al. [14] developed a program for automatic optimization of cable forces in Python language based on FBR_CAL_SUO, a planar rod mechanical calculation software developed by Professor [PERSON] of Changsha University of Technology. The particle swarm intelligent optimization algorithm and the reasonable state of cable-stayed bridge proposed by [PERSON] are the theoretical bases. The automatic optimization of cable-stayed bridge cable forces and the determination of reasonable state are finally completed. However, the number of users of the finite element software is not substantial, and the ultimate choice of the most optimal solution for the Pareto front solution sets depends largely on individual judgment. [PERSON] et al. [15; 16] write code in MATLAB based on the OAPI (Open Application Programming Interface) function of SAP2000 to realize the interactive use of MATLAB and SAP2000. Finally, the Java optimization algorithm was successfully applied to optimize the tension forces of a single-tower cable-stayed bridge and a multitower cable-stayed bridge, and the internal forces and alignment of the cable-stayed bridge were still more reasonable under the premise that the total weight of the cable was reduced from the initial basis. However, the current problem is that SAP2000 has separated its bridge module from SAP2000V15.1.0/1, which means that SAP2000 software itself in the field of bridge application does not have the characteristics of further promotion, even if its OAPI function is very powerful.