directly under the panel-points and using the new floor system for carrying traffic and for running out material for the trusses; it permits the posts to be bolted to the floorbeams and released from the tackles on the travelers; it fixes the exact position of the shoes on the piers so that we can proceed with the erection from the center either toward the fixed or the roller end, as we may prefer; it has the advantage of giving more opportunity for jacking up the spans in order to secure proper camber; and it requiers a minimum amount of blocking. There are other features which render it desirable, where possible, to erect the floor system in advance of the trusses. Over dangerous streams, however, where there is a possibility of loss during the erection, it is sometimes desirable to erect the trusses first, so as to have as little material on the falsework as practicable and thus minimize the amount endangered. There are also sometimes certain local conditions which make it imperative that the trusses be erected first; and, therefore, it is important, wherever possible, that details be so arranged that either method can be used. In the erection of through, riveted, lattice spans, it is customary to place the floor system first, then to put the lower chords in position, set up the web members, and put the top chords on last. Therefore, it is more advantageous to have the gusset-plates connecting the web members with top chord riveted to the top chord sections rather than to posts or diagonals, as the rivets in gusset-plates connecting top chords with web members are more easily driven in the web members than in the top chord sections.

In the case of through plate-girders, the details of the floor system should be so arranged that the stringers and floor-beams can be put in place, panel by panel, without the necessity of spreading the main girders. Particularly is this the case in "Rolling Lift Bridges," which, in the majority of cases, have to be erected in an upright position, and where it is extremely dangerous and practically an impossible operation to spread the trusses in order to put in place the floor system.

Top chord sections with half pin-holes, having a hinge-plate on each section, are undesirable. When half pin-holes are used, if possible put a hinge-plate on one section only and make it long enough to rivet or bolt to the adjoining section when in place. Hinge-plates should be arranged so as to give two full pin-holes in center chord sections, and should be put on the ends farthest from the center on the other sections, except in special cases when it is necessary to commence raising spans from the end instead of the center.

Entering connections are usually the most difficult and expensive to make; and where at all possible, entering connections of any character should be avoided, but where they must be used, particular attention should be given to insure necessary clearances. An entering connection is not only an expensive and dangerous operation, but in a great many cases it cannot be accomplished on account of the interference with back walls, adjoining spans, etc.

It is of the greatest importance to allow ample clearance where members are packed inside of chords, posts, etc., as lack of proper clearance causes much trouble and expense, not only augmenting the cost of erection by increasing the time required for making the span safe, but adding materially to the risk. In putting in tie-bars and diagonals, it is customary to connect them on the bottom chord pins first, and then swing them into the chords and posts around the lower pins as a center. All rivet heads coming in the path of bars swung in this way should be cleared. Too much attention cannot be given to this matter of proper clearance. Particularly is this the case in through and deck riveted lattice spans, which are being erected now more than ever before with the use of a derrick car with one boom; and the appliances for pulling tight-fitting members into place are not always present, as was the case formerly when these spans were erected by a gantry traveler. For adjustable rods packed close together, the sleeve nuts should be staggered. Attention should he given to the field connections so that enough space is allowed around all field rivets to enable them to be driven.