Having determined the spacing of rivets connecting the web with flanges, it remains for the rivets in the latter alone merely to be so spaced as to stagger with them. The distance between the rows of rivets on the flange plate should not exceed 20 times the thickness of the thinnest plate; making in our girder the maximum allowable distance 30Ã--⅜=11 inches. For flange plates more than 12 inches wide it is the usual practice to put in 4 rows of rivets.

Except at the ends of the girder, no rivets in the bottom flanges should be countersunk, unless special allowance is made for the loss of sectional area, and where the leg of the stiffener angle fouls the rivet head, the former may be cut off enough to clear the latter.

As already said, every flange plate, except of course the one that covers the full length of the girder, should be extended far enough beyond the point at which it begins to form the necessary section of the flange, to take in the number of rivets whose total shearing strength will equal the strength of the plate itself. Thus the uppermost plate f (Pl. II), 12" Ã-- ⅜", which, according to our calculation, begins to form the necessary part of the flange area at about the point t is extended to take in (12 Ã--⅜ Ã--8,400)ö4,400=8 rivets to the point u. In the same way, in the bottom flange, the plate f', which is required to form the section at about the point t', is extended beyond that, to take in (10Ã--⅜ 9,600)ö4,-400=8 rivets.

The rest of the plates are proportioned in the same way.

Splicing

Particular attention should be given to splices in plate girders. Both flanges should be fully spliced, and no contact joint should be depended upon, although in all cases as good a contact should be given to pieces joined in the top flanges as possible.

In web splicing is often proportioned to the entire net strength of the plate, irrespective of the stress at the joint. It is, however, more proper to take the stress into consideration and make due allowance for the uncertainty of its action as well as for the imperfection attending such construction.

Girders whose lengths are less than 30 feet hardly require any splicing, as all the pieces, except perhaps web plates sometimes, can be obtained in full length.

In our girders, all the full-length pieces are to be spliced. Plates g and g'(Pl. II), are splices for the long flange plates which are joined in the middle. These splices must, of course, be long enough to take in on each side of the joint the number of rivets necessary to make their total shearing Strength equal to the strength of the plate. The stress is supposed to be transmitted in a manner something as is shown by the dotted lines in the figure.

Angles are spliced between a and d.

The splices may consist of two bars riveted on both legs of the angle, or, better, of cover angles, such as we have used. Cover angles are always given such a shape as to fit closely into the inside of ordinary angles. Since the flange angles are 3«Ã--5"Ã--3«," each having the sectional area of 4.0d," we take for splice the cover angle 3"Ã--4" Ã--⅝".

The web is spliced in the middle and near a and c. The maximum shear at a, with proper allowance for impact, has already been found equal to G3,000 lbs. The number of rivets required is, therefore, equal to63,000/4,700=13, against which we find several more to provide for the uncertainty of such joint to resist stresses which the web is called forth to sustain. The splice plates in the middle are made to fit tight between flanges, to serve as stiffeners there.