## 1 Introduction
[35] discussed the failure mode and degree of ground fissure activities of urban bridges in Xi'an through examples, and put forward a general prevention and control concept for bridge structures in response to ground fissure activities. Taking the cross-ground fissures in the elevated section of Xi'an Metro Line 3 as an example, it was proposed that when uneven settlement occurred in the foundation, the influence of ground fissures on the elevated line could be reduced by using a simply supported beam bridge and a line slope adjustment scheme [36]. [PERSON] et al. [37] studied the influence of ground fissure activity on pier stress and track deformation when a high-speed railway bridge traversed the ground fracture zone through a 1:20 model test. [PERSON] et al. [38] carried out a 1:5 model test of a bridge structure across a ground fissure, analyzed the strain situation of the bridge deck and pier during ground fissure activity, and discussed the failure mode of the bridge. Through physical model tests, [PERSON] [39] investigated the overall deformation, concrete pile stresses, and box girder strains of high-speed railway bridges under different ground fissure dislocation amounts and compared them with numerical simulations. [PERSON] et al. [40] established a numerical model of a high-speed rail bridge crossing ground fissures using Fast Lagrangian Analysis of Continua in 3 Dimensions (FLAC3D) and analyzed the deformation of the box girder and the force characteristics of the pile foundation. [PERSON] [41] simulated the hidden ground fissures across the simply supported girder bridges of high-speed railways and analyzed the box girder deformation, pile foundation settlement, and internal force changes when the ground fissures were active. [PERSON] [42] established a numerical model for steel-concrete composite girder bridges spanning ground fissures and investigated the internal force and deformation characteristics of steel-concrete composite girder bridges when ground fissures were active. [PERSON] [43] established a numerical model of a Cloud Rail simply supported girder bridge spanning active ground fissures and studied the displacement law of the rail girders with piers and pile foundations. [PERSON] et al. [44] investigated the impact of ground fissure activity on underground utility tunnels. At present, although some achievements have been made in the measurement of ground fissures in bridge projects, the current studies mainly focus on the analysis of the deformation and internal forces of simply supported girder bridges during ground fissure activities using examples, model tests, or numerical simulations, while a few studieshave been conducted for multi-span overpasses. Multi-span overpasses, which sacrifice the inclined deformation of the structure to ensure that the deck does not suffer crack damage, are a widely used form of overpass at present. However, there has been little study on multi-span overpasses crossing active ground fissures. The purpose of this study was to investigate the effect of ground fissure activity on urban multi-span overpasses by using a numerical simulation method and to provide references for the disaster mechanism and rational design of overpasses that have been built, or are under construction, and overpasses that will be built in future. In order to reduce the influence range of ground fissure activity on the overpass, a simple supported beam structure is adopted for bridges across ground fissure zones. Although this structure type has no significant effect on the internal force of the box girder, the excessive settlement displacement will reduce the contact area between the box girder and spacer and cause the lateral restraint of the girder to be reduced, which is a safety hazard. The interchange bridge has strict requirements on the longitudinal inclination angle of the box girder that is not easy to meet, and a larger span is needed to reduce the inclination angle, increasing the requirements for the construction of the interchange bridge.