# Load-Carrying Capacity of Bailey Bridge in Civil Applications
## 3 Global Analyses
### Loads in Global Analysis  
In addition to the respective dead load corresponding to the layout of the superstructure and bridge deck, traffic loads and wind effects were taken into account. Within the scope of this study, wind loads were considered as \(F_{w}\)\({}^{*}\) according to Eurocode 1 [17] and were properly combined with the traffic loads. Accordingly, the wind pressure value of \(q_{p,z}=0.50\) kPa was considered acting uniformly for all analysed BB models. The effect of wind pressure acting on bridge deck combined with pressure on traffic load was transformed into the edge horizontal load, surface horizontal load and vertical surface load producing torsion of the deck around its longitudinal axis, as shown in Figure 10a. The values presented in Figure 10a were derived by utilizing the reference height of traffic load 2.0 m consistent with [17]. Accordingly, the wind load on structural members of BB panels was calculated as uniformly distributed load using the force coefficient \(c_{f}\) given in [17] with dependence on the shape of each cross-section, as shown in Figure 10b. Due to its variable nature, modelling of traffic loads presents the key input in the assessment of both the new bridges and, of course, existing ones. Load models defined in the current design, codes are often described as conservative, due to the limited traffic data used for their calibration and their integrated safety levels [18]. In addition, despite the harmonized design codes for almost all European countries, the structural safety levels and consequent capacities of similar bridges vary across Europe, as different national adjustment factors are defined in most of countries. Code load schemes are primarily developed for new-designed bridges expecting to be in service next hundred years, at least. Nowadays, extensive research is aiming to find out the 'actual tonnage' which can occur on the bridge without any traffic restrictions. Thus, for the load schemes representing the traffic load in the present study, it was decided not to use the load schemes given in Eurocode 1 [19]. The main reasons for avoiding the Eurocode statements for 'normal' traffic in the case of the Bailey bridges arose from the fact that it is still difficult to define which part of the LM1 scheme according to [19] can be considered as a representative vehicle. This problem is also evident from the experiences from recalculations of old bridges, supported by the extensive theoretical study presented in [20; 21]. Specifically, in [20], some results from the extensive study are published, based on several thousands of calculated bending moments and shear forces for bridges with different concepts of cross-sections and spans. In the follow-up research presented in [21], over 2800 load-carrying capacities for those bridges were quantified and compared, considering different load schemes, including possible alternatives from the Eurocode models [19]. In addition, different calculations of the current load capacity of the bridges were taken into account in those calculations, thus considering their possible poor condition. The final value of load-carrying capacity produced by representative loads depend also on mutual combinations of classification factors \(\alpha_{Qi}\) and \(\alpha_{qi}\)[19]. Moreover, in the case of short spans, LM1 causes disproportionately high effects because the dominant 'uniformly distributed load' (UDL)  
Figure 10: Example view from approximation of wind load: (**a**) left wind action on deck with traffic load on it; and (**b**) wind load assumed on main girders BB panels. as well as the dominant 'tandem system' (TS) are concentrated together in the same lane on the relatively small length section. The abovementioned phenomenon is even more visible in narrow bridges. Findings that the load schemes given in the Eurocode [19] are not very suitable for load-carrying capacity calculations of existing bridges are also supported by the conclusions in [22], which provides an extensive state of the art presentation of the traffic load models.