ESTIMATED QUANTITIES FOR STANDARD BEAM SPANS. IOWA HIGHWAY COMMISSION.

are given in Table I and Table II, Chapter X. The depths of I-beams for different spans for beam spans with plank floors designed to carry a 20-ton, a 15-ton, or a 10-ton auto truck with 30 per cent impact are given in Table IV. The minimum weights of I-beams are to be used in each

Clear Span.

Note: Outside Is to be
raised 1" above bridge

Seat, wrapped with mesh
and encased in concrete.

"Felt Exit

2" Coping

DATA FOR STANDARD BEAN SPANS -CONCRETE FLOOR
Dimensions 9 lines Quant. 18-0 Rowy change of Rome
Quant. For 2 FE

ABH St.St Con. Re. St St St Con. Re St 16. 5-06-0 1-2 9×21 3500 12.1 Y 1120 390.88 V 90 18' 6-0 6-01-310x25 4610 13.6 1230 510 .98 99 2016-08-01-310x25 5060 14.8 1350 560 1.06 107 227-08-0145 12x3156950 16.8 1460 770 1.18 116 24'8-08-0145 12×3157510 18.0 1580 840 1.25 124 26 9408401-5 12x3158080 19.2 1690 890.33 133 28916940-81542 11530 21.6 1820 1280 1.47 141 30 1069401-815-42 12290 228 1910 360 1.55 150 3211-6 940 1-8 15×42 13040 24.0 2040 1450 1.62 158 Note:- Add or subtract one I for each 2ft. change of roadway..

For handrail over wings add 1.9 yds. concrete and 180 16. reinforcing per bridge.

3 layers tar paper

31-0"

243"

10510578

91-100-20:3

FIG. 4.

5,000

$10,000

15 TON ENGINE

STANDARD BEAM SPANS Concrete Floor & Handrail lOWA HIGHWAY COMMISSION

STANDARD BEAM BRIDGE. IOWA HIGHWAY COMMISSION.

In the calculations it was assumed that one stringer carried that fraction of the concentrated load equal to the fraction found by dividing the stringer spacing by 6 feet for concrete floors, and by dividing the stringer spacing by 4 feet for plank floors. It will be noted that heavier beams are required for short spans with plank floors than with concrete floors.

case.

TABLE III.

DEPTH IN INCHES OF I-BEAMs for Different Spacings and Spans Required to CarRY 20-TON, 15-TON AND 10-TON AUTO Trucks and 30 PER CENT IMPACT. DEAD LOAD 100 LB. MINIMUM Weights of I-Beams are Used.

PER SQ. FT.

The proportion of the concentrated live load carried by one joist shall be taken equal to the spacing of the joists divided by six feet when reinforced concrete floor is used. The outside beams to be the same as the intermediate beams.

TABLE IV.

DEPTH IN INCHES OF I-BEAMS for Different SPACINGS AND SPANS REQUIRED TO CARRY 20TON, 15-TON AND 10-TON AUTO TRUCKS AND 30 PER CENT IMPACT.

MINIMUM

The proportion of the concentrated live load carried by one joist shall be taken equal to the spacing of the joists divided by four feet when timber floor is used.

The outside beams to be the same as the intermediate beams.

Details of standard beam spans designed by the Michigan State Highway Department are given in Fig. 6. The reinforced concrete floor has a bituminous wearing surface. Data and details are given in the cut.

The details of a beam bridge with a concrete floor has designed to comply with the author's specifications are given in Fig. 7.

Leg Bridges.-Beam and truss bridges are sometimes supported on steel legs in the place of abutments. A steel leg beam bridge is shown in Fig. 7, Chapter VIII. The legs are composed of I-beams supported on a timber or a steel channel mudsill. The backing is steel plate, or plank,

FIG. 5. STANDARD BEAM BRIDGE. IOWA HIGHWAY COMMISSION.

or stone. The legs should be designed to carry the thrust of the filling in addition to the live and dead load on one-half of the span. (For methods of calculation of thrust due to the earth filling, see Chapter XIX, and also the author's "The Design of Walls, Bins and Grain Elevators.") Truss leg bridges should be built with stiff lower chords designed to take the thrust due to the filling. Leg bridges, unless very carefully designed and constructed, are not to be recommended.

Panels 8-0" or less

Note: All reinforcement to be medium, open hearth steel

and wired securely with No. 18 wire.

22"Pipe

4"Tar Paper Joint

Section A-A

Elevation Pipe Rail

K-6"

K

-Bars-8"c. to c.

12

K

19'-6"

(With Pipe Railing) Typical Cross Section (With R. Concrete Railing)

FIG 6. STANDARD BEAM BRIDGE.

MICHIGAN STATE HIGHWAY DEPARTMENT.