12 : 15.8 :: 5000 : 6585 lbs.,

requiring a rod of ¾ of an inch diameter. The posts in this bridge correspond to the braces of the Howe Truss, but being vertical, are not so large.

Subjoined are two Tables, one by Prof. G.L. Vose, and one by Mr. Trautwine, giving principal dimensions for bridges of different spans of the Pratt type of Truss.

TABLE OF DIMENSIONS OF A PRATT TRUSS.
PROF. G. L. VOSE.

Span.Rise.Chords.End
Post.		Centre
Post.		End
Rod.		Centre
Rod.		Counter
Rod.
50102—8 x 105 x 54 x 42—1⅜2—11—1½
75122—8 x 106 x 65 x 52—1⅝2—11—1½
100153—8 x 107 x 76 x 62—1¾2—12—1⅛
125183—8 x 108 x 86 x 6 3—1⅞3—12—1⅜
150214—8 x 129 x 96 x 63—2⅛3—13—1⅛
200244—8 x 1610 x 106 x 65—1⅞5—13—1⅛

TABLE OF DIMENSIONS OF A PRATT'S TRUSS.

Clear Span in feet.255075100125150175200
Rise in feet69121518212427
No. of Panels.89101112131415
Upper Chord.
No. Pieces.33334444
Size.4 x 56 x 76 x 96 x 106 x 108 x 1010 x 1212 x 12
Lower Chord.
No. of Pieces.33334444
Size.4 x 106 x 106 x 116 x 126 x 138 x 1410 x 1512 x 16
Main Brace Rods.
No. Ctr.22222333
Size. Ctr.11-3/161-5/161-7/161½1-5/161⅜1½
No. End.22222333
Size. End.1⅜1⅞2⅛2½2⅞2½2¾3⅛
Counter Rods.
Number.11111222
Size.1-7/161⅝1⅞22⅛1⅝1-11/161-13/16
Posts.
No. End.33334444
Size. End.4 x 56 x 66 x 76 x 96 x 98 x 810 x 1012 x 10
No. Ctr.33334444
Size. Ctr.4 x 46 x 56 x 56 x 76 x 78 x 710 x 810 x 8

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.

Clear
Span,
Ft.		Chords each,
Ins.		Centre
Post,
Ins.		End Posts,
Ins.		At centre
of truss,
Diam. of
Rods.		At end
of truss,
Diam. of
Rods.		Centre
Counter,
Diameter,
Ins.		End Counter,
Diameter,
Ins.
309 x 114 x 97 x 911⅝1⅜1
4010 x 124 x 108 x 101⅛1⅞1⅝1
5010 x 145 x 109 x 101¼2⅛1¾1
6012 x 155 x 129 x 121⅜2⅜21
7012 x 176 x 1211 x 121½2½2⅛1