175 | 24 | 14 | 4 |10x12| 4 |10x15| 3 |9x11| 3 |8x8 | 2 |8x8 | 3 |2-5/8 | 3 |1-1/4
200 | 27 | 15 | 4 |12x12| 4 |12x16| 3 |9x12| 3 |8x10| 2 |8x10| 3 |2-7/8 | 3 |1-3/8

Both of these tables were calculated for a single Railroad track, and
would answer equally well for a double Highway Bridge. In the bridge
according to Trautwine's Table, each lower chord is supposed to have a
piece of plank, half as thick as one of the chord pieces, and as long
as three panels, firmly bolted on each of its sides, in the middle of
its length.

* * * * *


=PRATT'S BRIDGE.=

This is opposite in arrangement of parts to a Howe Bridge, as the
diagonals are rods, and sustain tension, and the verticals are posts,
and suffer compression:

_Example._--Span = 100 feet.
Rise = 12 "
Panel = 10 "
Weight per lineal ft. = 3000 lbs.

The tension on the lower, or compression on the upper chord, will be

300000 x 100
------------ = 3333333 lbs.
96