# Load-Carrying Capacity of Bailey Bridge in Civil Applications
## 3 Global Analyses
### Loads in Global Analysis
Thus, the schemes shown in Figures 11 and 12 were taken into account. These schemes come from the former Slovak national code and were slightly modified for the purpose of narrow bridges. These load schemes, utilized for several decades, reflect more to the traffic situations in narrow bridges [21], especially, when the load-carrying capacity of the bridge will be probably limited by the elements of member steel deck. Another advantage is that the required vehicle weight, which represents the instantaneous permissible weight of vehicle passing the bridge, is relatively clearly defined therein [20; 21]. Thus, the load scheme in Figure 11 is a better approximation for the possible traffic situation on such a narrow temporary bridge, with one of the lorries being considered as the _normal load-carrying capacity_\(V_{n}\). The 'normal load-carrying capacity' represents the maximum permissible weight of any vehicle on the bridge without any restrictions or addition regulations in traffic within the road section on the bridge. Geometric parameters of the load scheme are presented in Figure 11.  
_The exclusive load-carrying capacity_\(V_{e}\) represents maximum permissible weight of a single lorry on the bridge, while no other vehicles on the bridge are allowed at the same time, e.g., by other traffic signs. In the case of analysed Bailey bridges, which are the narrow one-lane bridges, this can be easily specified by the traffic sign of minimum following distance between vehicles. Alternatively, in some countries, the additional text table to normal load carrying capacities sign can be installed where the text concerning the maximum weight of the only vehicle on the bridge is specified. In the present study, for the 'exclusive' load scheme, it was decided for practical reasons to use the heavy truck scheme shown in Figure 12 instead of the schemes given in [19], which again differ among countries. To cover all the alternatives in that table, fourteen different trucks should be evaluated. Thus, the adopted scheme from Figure 12 is able to produce more efficient load effect with the simpler load-modelling, as only the distance of middle axes \(d\) has been changing from 4.0 m to the most severe alternative 1.20 m. That means that the vehicle should be the only traffic load on the bridge as discussed previously. Figure 11: Load scheme used for normal load-carrying capacity. Heavy vehicles from the schemes given in Figures 11 and 12 could be placed in any position within the cross-section of free width 3.30 m between timber curbs, as can be seen in Figure 13.  
The longitudinal placement of the load patterns was applied on the basis of moving load module considering their possible relief effects along the bridge. Hence, up to more than a hundred positions were analysed for each Bailey bridge model, depending on the BB system configuration. The load factors were taken according to Eurocode 1 for traffic loads on bridges [19]. As this standard does not define separate dynamic load effects for road traffic load, dynamic factors \(\phi\) calculated according to Equation (1) were considered in the analyses. \[\phi=\frac{1}{0.95-(1.4L_{d})^{-0.6}}\leq 1.50 \tag{1}\]  
In Equation (1), the abbreviation \(L_{d}\) represents the effective length in meters for each type of member. In the case of main girders and their components, the theoretical span can be taken into account. Thus, the dynamic factor applied to main girders internal forces varied from the value \(\phi\) = 1.17 in the case of longest analysed span with the length of 36.576 m, up to \(\phi\) = 1.30 in the case of span 12.196 m long. Similarly, the dynamic factors \(\phi\) = 1.48 for inclined struts (rakers) and \(\phi\) = 1.50 for all other members of BB superstructure were considered.