angles should be employed with the longer legs vertical; but for 4-angle sections it is economic to make the longer legs horizontal and connect the shorter legs by a single line of lacing placed between them. For very long struts it is economic to employ four angles in box section, connected by four lines of lacing.

In light bridges the posts can be made either of H section or of four angles with either a web or lacing between, rather than of two channels laced. This arrangement saves considerably in weight of details, but some of that saving is lost because of the greater sectional area required to allow for the reduced radii of gyration.

For compression members which carry shear, there should be one or more webs in planes parallel to the said shear. Such webs can be employed to advantage also in simple struts of large cross-section. If lacing can be omitted thereby, a saving of metal may result. On the other hand, the radius of gyration may be reduced by using such diaphragms, thus lowering the unit stresses.

In railway, deck plate-girders, as far as weight of metal is concerned, it is economical to use cover plates for top flanges, but this requires rivets and the variable dapping of the ties. Rivets increase the work of placing and maintaining the ties, and deep dapping is undesirable. The best railroad practice forbids the use of rivets through the upper horizontal legs of the flange angles of stringers when timber deck is employed.

Batten plates for large compression members must be excessively thick, unless they be properly stiffened by angles; and it will generally be found less expensive to adopt thin plates and stiffen them. Unless considerable metal be saved by that expedient, however, it is better not to do this, because the addition of stiffening angles increases materially the amount and cost of the shopwork—besides it may involve some difficulty in handling the members.

In compression members consisting of two built or rolled channels, it is usually economical of metal to turn the said channels in. However, this increases the cost of the shopwork, because lacing-rivets when the channels are turned in usually cannot well be machine driven.

In designing a built chord for a bridge, the sections must be determined by considering all panels of the chord simultaneously. It is well to adopt as few differing thicknesses of metal as practicable, and to arrange the various sections so as to avoid, to as great an extent as possible, the use of filling plates at the splices. In field splicing the loss of loose filling plates is a cause of serious trouble and expense; hence they should be avoided. For the sake of simplicity, it is frequently best to waste metal in some of the panels; but such waste should always be reduced to a minimum. When cover plates are employed, it is advisable to avoid changes in the location of the center of gravity of the section.

In detailing one should always endeavor to use metal to best advantage; and the strength of each detail or connection should be figured whenever