248 APPLIED MECHANICS 
between the two main girders the wind pressure acting on the bridge. It 
rm 
: 
. 
S = 
oe 
C Sway Bracing. mie 
Fia. 380. 
also has the effect of resisting the distortion. of the bridge due to the 
deflection of the cross girders as the 
travelling load passes. 
When the trusses are too low 
to admit of any overhead bracing, 
gussets may be introduced instead, 
connecting the vertical’ members 
with the cross girders, as shown in 
Fig. 370, p. 243. 
To resist lateral distortion, 
deck bridges are invariably braced, 
as shown in Fig, 381. See also Fig. 372, p. 243. 
227. Open Web Girder Bridge—Worked Example.—To indicate 
the method of procedure, the design of an open web girder bridge to 
fulfil the following conditions will be considered. T'ype—single track, 
through bridge. Span—150 feet. Travelling load—a train of “ eight- 
wheeled” coaches, headed by three locomotives of the type shown in 
Fig. 382. 
Fig. 381. 
o- 8 See 4 
oo err toor’: 
- 1 
te B-G ot ~~ 23-6 -- ee BE | HOHE Em 8 “Sie 9-8 He 7-S ee 3H ie 
Wie - -- tee OM pit Ae She os Se MR om aa 
Coach Locomotive 
Fig. 382. 
Type of Main Girders.—As typical of normal British practice for 
spans of the length given and carrying such a load, an N girder with 
curved top flange will be adopted. 
Actual Span.—Fix as accurately as possible the actual span of the 
girder, Where rocking bearings are employed it is the distance from 
centre to centre of the pins, in this case 150 feet exactly. This span 
will be used for all calculations. 
Depth of Girder and Number of Panels. _‘The depth at the vit of 
the span should be from one-twelfth to one-eighth of the span, the number 
of panels being chosen to correspond, due consideration having been given 
