Clear ITcadway. 
— 66 — 
Styles of Bridge for 
Different Span*-, 
Limitiiif ： Depths of 
Pony Trustic.s. 
Limiting Slope fm’ 
Batter liraces of 
Pony TruBH^s. 
Limiting LungHi of 
Span for Dimlilf In- 
tersection Biitljfes. 
Side Braces, 
Limiting Sizes of Sec- 
tions. 
Limiting Widtlis of 
riates. 
Limiting Sizes of Up- 
per Lateral Rods. 
Expansion. 
Anchorage. 
Tlie clear headway or vortical distance between tlio upper sur- 
face of the rails and the lowest part of the overliead bracing shall 
be at least twelve (12) feet six (6) inches. 
Spans below fifteen feefc are to consist of rolled beams ; spans 
between fifteen (15) and sixty (GO) feefc of rivofcted plate girders ; spans 
between sixty (60) and seventy (70) or eighty (80) feet of pony 
trusses or deck bridges, and spans above seventy (70) or eighty 
(80) feet of through or clock truss bridges. 
Tlie groatost allowable dq)tli, measured from centre to centre 
of chords, for pony trusses is uino (0) foot. 
The least allowable slope for batter braces of pony trusses is to 
bo two (2) horizontal to ono (1) vortical. 
The least allowable lengths of span for double intersection 
trusses arc one luuulrcd ami seventy (170) feet fov single track 
bridges and one hundred and fifty (150) feet for doable track 
bridges. 
Tlie least allowable batter for side braces in pony trusses is five 
(5) inches to tlio foot ; and all side braces are to be made to resist 
both tension and compression. In no case is a side brace to have 
loss streiigth than tlmt of a 3" x 3" — 7* angle iron. All pony 
trusses arc to be provided with side braces. 
No vouncl rods less than oue (1) inch in diameter nor square 
ones less than seven eigfchs (5) of an inch on a sido are to be used : 
110 bars less than five eigfchs (J) of an inch thick for diagonals, no 
large plates less than five sixteenths ( T 5 ff ) of an inch thick, nor, 
except for filling plates, any iron less tliaii a quarter of tin inch in 
thickness anywhere in a bridge. The least allowable depths for 
channels aro four (4) inches for lateral systems, five (5) inches for posts 
in pony trusses aiul six (0) inches for posts in trusses of through 
anil deck bridges. 
Tlie unsupported width of any plate subjected to compression 
must never exceed thirty (30) times its thickness. 
The least allowable sizes of upper lateral rods are tlioso given 
in Table XIII. 
All spans shall bo proviiled with some means of expanding and 
contracting longitiulinally witli a variation in temperature of one 
hundred anti fifty (150) degrees Falir. as must also the track stringers 
wliore they rest upon tlio piers or abutments. 
Spans of over sovonfcy-fivo (75) feet in length are to have at 
one ciul two nests of turned wrought iron motion rollers running 
between planed surfaces. 
One eml of every span must be firmly anchored to the 
masonry, and the other end must be so attached thereto as to 
prevent vertical and lateral and permit 01 longitudinal motion. 
