228 . APPLIED MECHANICS 
limited to 7 tons per square inch, the best section, found after a number 
of trials, is as follows :— , 
Two angles 4 inches x 4 inches x } inch, less one }4 inch 
rivet hole in each = 46 tons 
Three flats 12 inches x 2 inch, less two 33 ‘inch rivet ‘holes 
ineach . = 82 tons 
One flat 12 inches x ve inch, less two iE inch ‘rivet holes = 32 tons 
Total : - 160 tons 
Setting these off upon the diagram, the necessary length of each plate 
is at once apparent. The 1g inch plate placed outside must be 18 feet 
6 inches long, the next two 3 inch plates 24 feet and 29 feet long, while — 
the inside plate and the angles will be carried the full length of the — 
girder. It will be observed that an extra rivet pitch or two have been — 
allowed in the various lengths. 
In this design the top boom will be made of exactly the same 
pattern, length of plates, etc., as the bottom boom; that is to say, the 
rivet holes will be subtracted from the area .of the section both for — 
compression and tension. If it is thought desirable to take the area of — 
the compression boom as the gross area, not subtracting the rivet holes, 2 
another diagram of the same type for the compression boom will be — 
necessary. It is doubtful in the present case if such alteration would 
save money. 
Set out the Girder.—Start with two horizontal centre lines 24 inched 
apart. Erect the centre lines of the stiffeners. Next put in the rivets, 
those in the flanges being staggered with regard to those in the web, 
due regard being paid to local conditions, taking on of cross girders, ete., 
remembering that a simple uniform pitch is to be aimed at. Next, on 
this skeleton outline, put in the outlines of the plates and angles. 
Joints.—The longest boom plate in the design has a length of — 
38 feet 5} inches. It will be advisable to make a joint in this, although — 
it might possibly be obtained in one piece. This joint will be placed so- 
that the outer ¢ inch plate produced will form a cover. The cover 
being single, the rivets are in single shear, each worth 2°59 tons, and : 
since the cut plate was worth 27} tons, 12 rivets will be required through — 
each half of the cover, as shown: 
If the joint occurs in the bottom boom to the left of the centre of the 
girder, it may be placed to the right in the top flange. 
~The web plate will also be made in two pieces, and the joint placed at — 
the centre, where the shear is least. If the joint be designed to carry the 
shearing force only, the shear per inch of depth diagram which determined — 
the longitudinal riveting will determine that in the transverse seam also. — 
It will be seen that a 6 inch pitch would be more than sufficient at the 
joint under consideration. Actually a single riveted butt joint with double 
cover straps and rivets of 4 inches pitch will be used as shown. “a 
Stiffening at Ends.—The reaction at each end is 38 tons. A bolster 
plate 1 foot square will be riveted to the bottom of the girder at each end — 
to limit the span, and between this and the wall plate sheet lead is placed. — 
The reaction must be distributed over the depth of the web plate through 
the vertical stiffening at the end. There are 8 rivets in the end 
angles, and 7 in the first stiffener. The load on each of these rivets is — 
