PROF.  G. L. VOSE.

End   Centre    End     Centre  Counter
Span.  Rise.  Chords.     Post.    Post.     Rod.      Rod.      Rod.

50   10   2—­8x10   5 x  5   4 x 4  2—­1-3/8   2—­1   1—­1-1/2
75   12   2—­8x10   6 x  6   5 x 5  2—­1-5/8   2—­1   1—­1-1/2
100   15   3—­8x10   7 x  7   6 x 6  2—­1-3/4   2—­1   2—­1-1/8
125   18   3—­8x10   8 x  8   6 x 6  3—­1-7/8   3—­1   2—­1-1/3
150   21   4—­8x12   9 x  9   6 x 6  3—­2-1/8   3—­1   8—­1-1/8
200   24   4—­8x16  10 x 10   6 x 6  5—­1-7/8   5—­1   3—­1-1/8

TABLE OF DIMENSIONS OF A PRATT’S TRUSS.

|    |    | Upper   |  Lower  |  Main Brace Rods.  |  Counter  |   |     |          |
Clear|    | No.| Chord.  |  Chord. |                    |   Rods.   |   |     |  Posts.  |
Span |Rise| of |---------|---------|--------------------|-----------|   |     |----------|
in  | in |Pan-|No.|     |No.|     |No.| Size |No.|Size.|Num|       |No.| Size|No.|Size. |
feet.|feet|els.|Pcs|Size.|Pcs|Size.|Ctr|Centre|End| End.|ber| Size. |End| End.|Ctr|Centre|
-----|----|----|---|-----|---|-----|---|------|---|-----|---

|-------|---|-----|---|------|
25 |  6 |  8 | 3 | 4x5 | 3 | 4x10| 2 |1     | 2 |1-3/8| 1 |1-7/16 | 3 | 4x5 | 3 |  4x4 |
50 |  9 |  9 | 3 | 6x7 | 3 | 6x10| 2 |1-3/16| 2 |1-1/8| 1 |1-5/8  | 3 | 6x6 | 3 |  6x5 |
75 | 12 | 10 | 3 | 6x9 | 3 | 6x11| 2 |1-5/16| 2 |2-1/2| 1 |1-7/8  | 3 | 6x7 | 3 |  6x5 |
100 | 15 | 11 | 3 | 6x10| 3 | 6x12| 2 |1-7/16| 2 |2-7/8| 1 |2      | 3 | 6x9 | 3 |  6x7 |
125 | 18 | 12 | 4 | 6x10| 4 | 6x13| 2 |1-1/2 | 2 |2-3/8| 1 |2-1/8  | 4 | 6x9 | 4 |  6x7 |
150 | 21 | 13 | 4 | 8x10| 4 | 8x14| 3 |1-5/16| 3 |2-1/2| 2 |1-5/8  | 4 | 8x8 | 4 |  8x7 |
175 | 24 | 14 | 4 |10x12| 4 |10x15| 3 |1-5/8 | 3 |2-3/4| 2 |1-11/16| 4 |10x10| 4 | 10x8 |
200 | 27 | 15 | 4 |12x12| 4 |12x16| 3 |1-1/2 | 3 |3-1/8| 2 |1-13/16| 4 |12x10| 4 | 10x8 |

This table is partly given in Trautwine’s Engineer’s Pocket Book, and partly made up from directions therein given.

TABLE OF DIMENSIONS FOR SMALL SINGLE TRACK PRATT TRUSSES.

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.