## 1 Introduction  
Steel-concrete composite girder bridges are widely used in motorway and municipal bridges because they make full use of the properties of each material and have a high load-bearing capacity. The twin I-girder bridge has many advantages, such as easy and efficient construction, high industrialisation, simple structure construction, and high technology economy [1; 2; 3]. This type of bridge has been used in many applications. In fact, in this structure, the bracing system is part of the bridge load-bearing system, which not only provides overall stability for the main girders during the construction phase, but also withstands various lateral loads during the operational phase [4; 5; 6; 7; 8]. In the case of twin I-beam bridges, the cross frames' dimensions need to be increased to meet the stability requirements due to the large spacing of the main girders [9], whereas the crossbeams are simpler and more convenient to construct than cross frames. The crossbeam in twin I-girder bridges is subjected to horizontal forces brought on by wind loads and, in some cases, by the lateral torsional buckling of the compression member acting as a support. In the case of curved beams, the crossbeam is also subjected to the horizontal radial component of the axial force of the main beam because of the curvature of the curved beam [10]. The internal force components of the crossbeam are therefore mainly related to the distribution and the magnitude of these types of loads. At present, a series of studies has been carried out on the internal forces of crossbeams. The internal forces in crossbeams can be determined approximately using the V-load method. In fact, [PERSON] [11] documented the development of the V-load method. As for [PERSON] and [PERSON] [12], they concluded that, in the analysis of horizontally curved steel beams, the crossbeam forces can be determined according to the V-load method if the effects of curvature can be ignored. In addition, these authors present tables for the calculation of crossbeam end moments and shear forces for structures with 2 to 8 main beams and carry out internal beam force calculations using an example of a 5-main beam structure design. [PERSON] et al. [13] have also made use of the V-load method for the design of engineering examples. [PERSON] [14] extended the V-load method to the I-girder with arbitrary bracing structures and compared the results of the V-load method with finite element calculations for structures with three different lateral bracing systems under dead and live loads. It was shown that the results of the V-load method are relatively accurate under dead load, while, under live load, the outcomes are influenced by the lateral distribution of the load. Another conclusion was reached showing that the V-load method cannot be applicable to a closed-framed system with horizontal lateral bracing near, or in, the plane of the bottom flanges, as this would inhibit the lateral bending effect of the flange and, therefore, the V-load method would produce less accurate results [15; 16]. However, for twin I-girder bridges, the most common calculation method used by scholars is to simplify the spatial structure of the bridge consisting of steel main girders, cross girders, and deck slabs to a planar frame model in order to facilitate the calculation process. In their publication, [PERSON] and [PERSON] [17] studied the distribution of transverse moments in concrete slabs with crossbeam sections under external loads and proposed a frame model for crossbeam sections to analyse the transverse moment distribution coefficients. These coefficients can calculate the internal forces and moments of crossbeams under vertical loads on bridge deck slabs; however, the model is only applicable to the case where vertical loads are applied to the bridge deck slabs.