cover-plates for top chords and inclined end posts, where the limit may be increased to forty (40) times the thickness. Where webs are built of two or more thicknesses of plate, the rivets that are used solely for making the several thicknesses act as one plate shall in no case be spaced more than (12) inches from each other, or from other rivets connecting said component thicknesses together. The least allowable thickness for such compound web-plates shall be one (1) inch.

The open sides of all compression-members composed of two rolled or built channels, with or without a cover-plate, shall be stayed by tie-plates at ends and by diagonal lacing-bars or lacing angles at intermediate points. Lacing-bars may be connected to the flanges by either one or two rivets at each end; but lacing angles, which are used for members of heavy section only, must be connected by two rivets at each end.

The tie-plates shall be placed as close as practicable to the ends of the compression-members. Their thickness shall not be less than one fiftieth (1/50) of the distance between the centre lines of the rivets by which they are connected to the flanges, unless said tie-plates be well stiffened by angles, in which case they may be made as thin as three eighths (3/8) of an inch. The length of a tie-plate shall never be less than its width, or one and one-half (1 1/2) times the least dimension of strut (unless it be close to a web diaphragm of the member, in which case it may be made as short as twelve (12) inches), and seldom greater than one and one-half (1 1/2) times its width.

The thicknesses of lacing-bars shall never be less than one fiftieth (1/50) of the length between centres of the end rivets, measuring between inmost rivets in case that there be more than one rivet at each end.

The smallest section for a lacing-bar shall be one and three-quarter (1 3/4) inches by five sixteenths (5/16) of an inch, which size may be used for channels under eight (8) inches deep; and the largest section shall be two and a half (2 1/2) inches by seven-sixteenths (7/16) inch, which size shall be used for channels fifteen (15) inches deep. For intermediate sizes of channels, the sizes of lacing bars shall be interpolated. For all built channels of  greater  depth  than fifteen (15) inches,  and