All splices in columns are to be full, butt splices, located preferably about two (2) feet above the points where the sway-diagonals connect, shingle-splicing being avoided because of the trouble it gives during erection.

The best span lengths for trestles are generally those which make the total cost of structure a minimum, the tower length varying from twenty (20) feet for low trestles to thirty (30) feet for very high ones, and the intermediate spans varying from thirty (30) to sixty (60) feet for the same limiting heights. Any length of girder exceeding sixty (60) feet would probably necessitate the employment of a too long, heavy, and expensive traveller, or else the use of bents of falsework between the towers.

For elevated railroads the sections of main members shall be as follows: Longitudinal girders, preferably plate girders, or, if necessary, open-webbed, riveted girders; cross-girders, plate girders ; columns for structures without longitudinal or tower bracing, two channels with an I beam riveted between; and columns for structures with longitudinal or tower bracing, four Z bars with a web-plate.

All columns for elevated railroads are to have both ends fixed, being held rigidly at the top by either the longitudinal girders or by deep struts that carry the thrust of braked trains from the track to the columns, and their sectional areas are to be figured accordingly for both direct load and bending.

Longitudinal girders in elevated railroads shall, generally, be riveted into the cross-girders and not rest thereon, except under certain conditions for the sake of clearance beneath, in which case the top flanges of the half-through girders must be stayed at the ends and at intermediate points, as specified for plate-girder spans.

On all curves in elevated railroads, special lateral bracing of angles, riveted at intersections to the longitudinal girders and carried over and riveted to the columns, must be employed.

Where brackets for columns can be used advantageously in elevated-railroad work, they must be put in, and must be built of solid web plates and angles.

In general, the limiting length of structure between expan-