# Load-Carrying Capacity of Bailey Bridge in Civil Applications
## 2 Outline of the Study  
For the purposes of the analysis, the load-carrying capacity of individual bridge members was selected as a decisive criterion for the applicability of the BB system. Based on experience, double-truss and triple-truss main girders were taken into account as single-story and double-story alternatives:  
* Double-truss, single-story (DS) for a span with length of 12.196 m;
* Triple-truss, single-story (TS) for spans: 12.192 m, 15.240 m, 18.288 m and 21.336 m;
* Double-truss, double-story (DD) for spans: 21.336 m, 24.384 m and 27.432 m;
* Triple-truss, double-story (TD) for spans: 27.432 m, 30.480 m, 33.528 m, and 36.576 m.  
In Table 1, the seven chosen variants are presented, which were identified as most suitable and applicable after evaluating several alternatives.  
All bridges are supposed to act as simply supported, while the end verticals of BB are present on both ends of main girders. It is further assumed that standardized bearings of the BB system are used to transfer reactions from the superstructures to substructures.  
With respect to the structural arrangement of the BB system [3], the load-carrying capacities were derived from the resistance of following members or their cross-sections (the terminology of Bailey bridge from [3] is given in single quotation marks, if differ from the common bridge engineering terminology):  
* Old stringers made of the original cross-section.
- New stringers made of the cross-section IPN100.
- Alternative new stringers made of the cross-section IPN120.
* Cross beams--'transoms'.
* Upper chord.
- Bottom chord.
- Diagonals with U-shaped cross-section.
- Alternative diagonals with I-shaped cross-section.
- Verticals with U-shaped cross-section.
- Alternative verticals with I-shaped cross-section.
* End verticals--'end posts'.
* Inclined struts--'rakers'.
* Panel pin (hinged connection between panels).
* Bottom bracings--'sway brace'.
* Floor bolts (in double-storeys arrangement)--'chord bolts'.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Span** & **Truss** & **Story** & **Abbreviation** \\ \hline
40 ft/12.192 m & triple & single & TS-12 \\
60 ft/18.288 m & triple & single & TS-18 \\
70 ft/21.336 m & triple & single & TS-21 \\
80 ft/24.384 m & double & double & DD-24 \\
90 ft/27.432 m & double & double & DD-27 \\
110 ft/33.528 m & triple & double & TD-33 \\
120 ft/36.576 m & triple & double & TD-36 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Spans and BB arrangement of the chosen alternatives.  
The load-carrying capacity of the bridge deck was determined for two variants of the construction arrangement of cross beams according to Figure 5:  
* Three cross beams within each panel of the bridge--the spans of the stringers are then 1440 + 1290 + 318 mm.
* Two cross beams within each panel of the bridge--the spans of the stringers are then 1608 + 1440 mm (this alternative was applicable only for single-story systems).  
The variant with four cross beams within each panel was not considered in the study. In addition, two alternatives to the timber roadway deck cover solution given in Figure 6 were considered:  
* Standard solution of two layers of 2 \(\times\) 50 mm thick timber boards, where the bottom boards are placed perpendicular to the stringers, while the top layer is oriented in 45\({}^{\circ}\) degrees to the bridge axis;
* Stiffer roadway, where bottom supporting layer of the bridge deck is made of timber beams of 100 mm section height placed side by side perpendicular to the stringers, while the top layer stays the same as in the alternative a).  
Figure 4: Scheme of three-stringer panel.  
Figure 5: Two alternatives of construction arrangement of cross beams: (**a**) 3 cross beams within each panel; and (**b**) 2 cross beams within each panel.