At centre At end Centre End
Clear Chords Centre End of truss, of truss, Counter, Counter,
Span, each, Post, Posts, Diam. of Diam. of Diameter, Diameter,
Ft. Ins. Ins. Ins. Rods. Rods. Ins. Ins.
30 9 x 11 4 x 9 7 x 9 1 1-5/8 1-3/8 1
40 10 x 12 4 x 10 8 x 10 1-1/8 1-7/8 1-5/8 1
50 10 x 14 5 x 10 9 x 10 1-1/4 2-1/8 1-3/4 1
60 12 x 15 5 x 12 9 x 12 1-3/8 2-3/8 2 1
70 12 x 17 6 x 12 11 x 12 1-1/2 2-1/2 2-1/8 1
This bridge possesses an advantage over the Howe Truss, for the panel
diagonals can be tightened up by screws, so that every part of the
truss can be forced to perform its work. In Howe's bridge the
adjustments must be made by wedging the braces and counters.
Below are given the dimensions of a Howe bridge on the Vermont Central
R.R., at South Royalton, (single track, deck.)
No. of Upper Lower
Span. Rise. Panels. Chord. Chord. Braces. Counters.
150 20 12 4--6-1/2 x 13 4--6-1/2 x 13 2--8 x 9 1--8 x 9
Rods. Transverse Bracing.
Braces. Rods.
3--1-1/4" 6 x 8 7/8
The bridge over the White River, on the Passumpsic R.R., is a Howe
Truss, strengthened by an arch. The verticals are of wood, and the
diagonals foot on steps formed by enlarging the ends of the verticals.
The counters are in two lengths, and are adjusted by wedges at the
points where they intersect the braces. The bridge is in two spans,
and has a double track, and consequently three trusses. There are two
timber arches to each truss, and the truss is supported on them by
connecting them to the verticals by short cross pieces notched into
the posts, and resting on the upper surface of the arches. It is a
very stiff bridge, and similar to the one at Bellows Falls, both
having their axis oblique to the channel of the stream they cross. The
timbers could hardly be procured now, except at great expense.
No.
of Upper Lower
Span Pan- Rods Chord Chord Braces Counters Uprights Arches
els
182 14 21 2--8 x16 2--8 x17, 1--21 x8 1--8 x10 21 x11 2--8 x9
1--5 x16 2--4 x17,
1--5 x17,
Diagonals 6 x 8, Rods 7/8. Floor timbers suspended both from
arches and truss, 9 x 13; stringers 10 x 14.
In the Cheshire Bridge, the braces are only 20x8, and the span is only
175 feet, the number of Panels being 14, as in the W.R. Bridge--the
other dimensions are the same. Below are given the dimensions of a
Howe Truss of 108 ft. span, weight to be borne on upper chord.
No.
of Upper Lower E. Floor
Rise Camber Pan- Chord Chord Braces Counters Rods Timbers
Ft. Ins. els Ins. Ins. Ins. Ins. Ins. Ins.