# Influence of Girder Flaring on Load Effect in Girders of Composite Steel Bridges
## 5 Parametric Study
### Dead Load Effect in Girders  
In this study, both shared and unshored construction methods are studied and applied to the reference bridge to understand the behavior of splayed girder bridges under the influence of dead load. Finite element models are developed for both cases and the results are compared with hand calculations for the composite girder of the bridge loaded with the same dead loads based on the tributary area concept. In shared construction, the composite girder resists all dead load components, including the girder and deck slab self-weight, parquet weight, and future wearing surface (FWS). In the analytical approach, a single composite girder of the bridge is loaded with the concrete deck slab self-weight, where the deck slab width is taken as half of the girder  
Figure 24: Effect of girder spacing on shear GDF: (**a**) slab thickness; (**b**) cross-bracing spacing; (**c**) number of girders; (**d**) girder web depth; (**e**) span length. Figure 25: Comparison between the finite element and AASHTO shear GDF: (**a**) interior girder; (**b**) exterior girder. spacing from each side. This approach results in a linearly variable slab width along the span length equal to the girder spacing, resulting in a trapezoidal load on the composite girder. The steel girder self-weight is also represented by a uniform load along the composite girder's length assuming the girder was supported during erection. Regarding the superimposed load from parapet weight and future wearing surface, the AASHTO LRFD Bridge Design Specifications [1] suggest distributing it equally among the girders if sufficient curing of the concrete slab has taken place. Therefore, the parapet weight is represented by a uniform load along the span and its magnitude is taken equal to the summation of parapet loads at both edges of the bridge divided by the number of girders. However, due to the bridge splayedness, the FWS load varies along the girder length, and it is represented by a trapezoidal load with a magnitude at any section equal to the total FWS load per unit width at that section divided by the number of girders. Cross-bracing, if present, is represented by point loads along the span of the composite girder; these loads vary in magnitude from one point to another based on the cross-bracing weight, where it changes due to the variable girder spacing along the span. The composite girder dead load for the reference bridge B1 is shown in Figure 26. The composite girder is then analyzed as a line element using statics, and the moment at the midspan is computed to find the elastic stress at the bottom flange of the girder in the composite section at the midspan. The ensuing stress due to analytically calculated dead load is compared with the one obtained from the finite element (FE) results at the midspan, as shown in Table 3.  
It is clear from the results included in Table 3 that the stresses are very close to each other. The magnitude of the stress resulting from the analytical approach using the transformed composite girder geometric properties is greater than the corresponding stress from the finite element model by 4.2% for the first interior girder and by 5.5% for the intermediate girder, but lower by 1% for the exterior girder. This finding indicates that the analytical approach provides a reasonable approximation of the dead load effect in individual girders for the shored construction method in splayed girder bridges. In the unshored girder construction case, the composite girder resists loads resulting from FWS and parapet weight, while the non-composite girder resists all other dead loads. Therefore, in the analytical approach, the composite girder is only loaded by the trapezoidal load representing the FWS and the uniform load representing the parapet weight, as shown in Figure 27 for reference bridge B1. Both load components are assumed to be distributed equally among the bridges' girders, as suggested by the AASHTO LRFD specifications,