# Influence of Girder Flaring on Load Effect in Girders of Composite Steel Bridges
## 3 Approach
### Information on Parametric Study  
A simply supported, splayed girder bridge with selected dimensions and material properties is chosen as a reference bridge. The considered parameters are the girder spacings (small spacing S\({}_{1}\) and large spacing S\({}_{2}\)), and span length (L), slab thickness (t\({}_{5}\)), cross-bracing spacing (D), girders' web depth (d), and number of girders (n). The small and large girder spacing at the two extreme ends of the bridge were within the range of 1500-3000 mm and 3750-5250 mm, respectively. The span length varied between 30,000 and 50,000 mm, while the concrete deck slab thickness varied between 150 and 300 mm. The spacing of the cross-bracing was as small as 5 m and as large as the bridge length, i.e., no intermediate cross-bracing was present. The number of girders within the superstructure was 3, 5 and 7. While the dimensions of top and bottom flanges of the steel girders were kept constant, the depth of the web varied between 1400 and 2000 mm. The deck slab overhang ranged between 500-1250 mm at the supported narrow width of the bridge and 1000-1750 mm at supported wide width of the bridge. The range of variables considered in the study represent practical values that are encountered in real-life applications. In the parametric study, one parameter is increased and decreased beyond the reference value, while all other parameters are kept unchanged. As the girders in this study are splayed by changing the spacing at the beginning and end of the bridge, a girder spacing parameter is changed four times using two different aspect ratios. The first aspect ratio is (S\({}_{2}-\)S\({}_{1}\))/L, which represents the degree of splayedness of the bridge, and by varying this parameter twice--once up and once down--the girder spacing is changed at one end and kept constant at the other. The second aspect ratio is the S\({}_{1}\)/S\({}_{2}\) ratio, where the degree of splayedness ((S\({}_{2}-\)S\({}_{1}\))/L) is kept constant by changing the girder spacing of the end that was kept constant through the first aspect, which also generates two different bridges. The overhang cantilever width from the edge of the parquet to the centerline of the exterior girder (OH) is taken one-third of the interior girder spacing in all bridges, which is in line with common practice. The symbol OH\({}_{1}\) represents the overhang width at the narrower girder spacing end and OH\({}_{2}\) represents the overhang at the wider girder spacing end. A total of fifteen bridges are modeled by the computer program ANSYS to carry out the parametric study. The steel girders used in all the bridges considered consist of a 30 mm \(\times\) 300 mm top flange, a 60 mm \(\times\) 600 mm bottom flange, and a 15 mm thick web with varying girder depth (d), as shown in Figure 3a. The chosen cross-bracing consists of  
Figure 2: Finite element model used in the study. two or three equal-angle sections of 150 mm \(\times\) 15 mm, as shown in Figure 3b. The concrete parapet cross-section is 300 mm wide and 1000 mm in height. The fifteen bridges considered, shown in Table 1, are modeled using the finite element software ANSYS to determine the flexural and shear girder distribution factors for the critical interior and exterior girders. In all 15 cases, the line of support at the abutments is taken perpendicular to the central girder, which is the shortest in length among all the girders within the superstructure. In addition, two more bridges that are similar to the reference bridge B1 are considered, with the exception that the line of support at the abutments is either perpendicular to one of the exterior girders (B1-a) or one of the first interior girders (B1-b). The truck position is changed in each model to maximize the live load effect in the transverse and longitudinal directions for bending moment and shear force. The truck rotational angle within the bridge plan is also examined to maximize this effect, as elaborated in detail later in the paper.