EFFECTIVE LENGTHS.

Effective lengths shall be as follows:

For pin-connected spans, the effective length shall be the distance between centres of end-pins of trusses.

For riveted girders, it shall be the distance between centres of bearing-plates.

For stringers, it shall be the distance between centres of cross-girder webs.

For cross-girders, it shall be the perpendicular distance between central planes of trusses.

For columns and posts, it shall be the greatest length between points of axis that are rigidly held in the direction in which the strength is being considered.

These effective lengths are to he used in calculating moments, stresses, and working strengths.

EFFECTIVE DEPTHS.

Effective depths shall be as follows:

For pin-connected trusses, the perpendicular distance between gravity lines of chords, which lines must pass through centres of pins.

For plate-girders and open-webbed riveted girders, the perpendicular distance between centre lines of gravity of upper and lower flanges; but never to exceed the depth from out to out of flange angles.

STYLES OF BRIDGES FOR VARIOUS SPAN LENGTHS.

For spans under fifteen (15) feet, rolled I beams.

For spans between fifteen (15) feet and eighty-five (85) feet, plate girders.

For spans between eighty-five (85) feet and one hundred and twenty-five (125) feet, "A" truss, pin-connected spans, or riveted, open-webbed girders of single cancellation.

For spans between one hundred and twenty-five (125) feet and one hundred and seventy-five (175) feet, riveted, open-webbed girders of single cancellation, or  pin-connected trusses