"― ()*5 • 
Stresses due to Curv- 
ature. 
Clear Boaslwav. 
those of two hundred and fifty (250) to three Inin cl reel (300) feet for 
lorty (40) pounds por square foot. Tho area subjected to wind 
pressure is to be llgiu-ocl as just described ； and tho greater stress 
】)y oitber method of computation is to be used in determining the 
sectional area of the bracing. 
In through briilgcs aud pony trusses the wind pressure on the 
tram is to be assumed as taken up by the lower lateral system, and 
m deck bridges by tlie upper lateral systen"). Tlic wind pressure on 
tlio l)i*i(lgo itself is to bo divided botwoen tlie upper and lower systems 
according to tlio proportion of total area above and below the 
niidtllo horizontal plane of the structure. 
When a structnro is upon a curve the stresses in chords and 
lateral sj’stcms and in tlio one! transverse sway bracing of deck 
bridges due to tho centiifngal force of the heaviest assumed train 
moving at a velocity of sixty (00) miles per hour are to be pvoviiled 
for. These stresses arc to be coii.sidci.od (if iis importance as 
an y o 山 ei. stress iu tlic membors aftectod Uioruby. 
In all tlirough bridges ami pouy trusses the clear distance 
between nearest 11101 labors of trusses «hall l»e at least twelve (12) 
focr six (0) i nc lies for single track 1) ridges and twenty- two (22) feet 
ior donblo track bridges* 
Len ßUi of Span. 
LanRths of 
?,f au Different 
Hear Roadways. 
、\ lien such a structure is upon a curve, these minimnm widths 
are to be increased b} r the product of tlic radius and tlie versed sine 
oj one half tlie arc of the curve which is Hubtemled by the span, 
plus seven (7) times llio .super* elevation of tlie outer rail above tlic 
centre line of the track. 
The longtli of span is to be understood as the distance between 
centre of cml pins for trusses and between centres of bearing plaU'H 
foi. aU rolled beam ami plate ginler spans. 
The greatest lengths of span for the different clear road vv fly s 
are to be taken from tlie following table • 
CWi ， Hoadway. 
Greatest Lon^fh of 8pan. 
12 . 5 ， 
75， 
13.0’ 
120* > 
J 3 . 5 ’ 
り。， 
14 .o’ 
lg 。， 1 
14.5 ， 
210’ f 
15.0’ 
240 ， _ 
15.5， 
27O ’ 
30 o' ! 
