" " 17 "
" " 4, " " 16 "
" " 5, " " 16 "

Now, using the formula

2240 b d cubed
--------- = W,
L squared

[TeX: $\frac{2240 bd^3}{L^2} = W$]

we shall have, in round numbers, the following dimensions:

For the 1st panel, 25 feet long, 8 x 10
" 2d " 37 " " 8 x 10
" 3d " 49 " " 8 x 10
" 4th " 64 " " 8 x 10
" 5th " 78 " " 8 x 10

For the lattice work, a double course on each side of each truss, in
long spans; and a single course, in shorter spans, of 3 x 6, or 2 x 9
plank, bolted at intersections, is sufficient.

GENERAL TABLE OF DIMENSIONS FOR ARCH BRACE TRUSS.

G.L. VOSE.

Span. Rise. Chords. Ties. Braces. Lattice.
50 10 2--8 x 10 1--8 x 10 2--6 x 6
75 12 2--8 x 10 1--8 x 10 2--6 x 6 2 x 9
100 15 3--8 x 10 2--8 x 10 3--6 x 6 or
150 20 4--8 x l2 3--8 x 10 4--6 x 8 3 x 6
200 25 4--8 x 16 3--8 x 10 4--6 x 9

The arch braces must all foot on an iron thrust block, of which a view
is given in Fig. 4, Pl. III; and the centre of pressure of the braces
must be directly over a bolster, to prevent crippling.

The several sticks forming a brace must be blocked together at
intervals, and When they are spliced,--a butt joint Should be
used--and it should come in the centre of a panel. Below are given the
dimensions of the Thayer Engineering School model.

Height Ins. 12
No. Panels 8
Chords Ins. 2--1 x 1/2
Posts Ins. 1--2/3 x 5/6
Braces Ins. 2--1/2 x 1/2
Lattice Ins. 1/4 x 1/2
Width Ins. 13

There are several other forms of Bridge, the most notable among which
are the Whipple, McCallum's, Post's, Towne's, Haupt's, and Burr's. But
enough has been said to give the student an idea of the general
arrangement of the different parts of a Truss, and to enable him to
determine the strains to which the various members are subjected.
Nothing will be said in regard to Wooden Arches, as our space is too
limited.

=Pile Bridging.= A bridge of this description is useful in crossing
marshes, or in shallow water. Fig. 5, Pl. III, gives a good example of
this kind of bridge, under 20 feet in height. If on a curve, there
must be extra bracing on the convex side.

=Trestle Work.= This is a combination of posts, caps, and braces; and