7 
212 APPLIED MECHANICS 
force on the rivets connecting the gusset to the rafter is the resultant 
4 
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of the forces acting along the various members, other than the rafter — | 
itself, connected to the gusset. 
Design the shoe and whatever other details of the truss have not 
already been arranged for. 
Fix the size of the purlins, treating them as beams carrying their 
load from rafter to rafter, and arrange for suitable joints in them. 
Settle any further details of the covering which may be necessary. 
Arrange for suitable wind ties if it is deemed prudent to fit these. 
Make complete working drawings of the whole roof, seeing that 
all the parts go together properly, can be easily made, and are in every 
way suitable for the functions which they have to perform. 
Exercises XIII. 
In the following exercises the various members must be proportioned pei 
to the loads which they have to carry, and working drawings of the various detat 
should be made. 
1. Design for a king-rod roof truss (Fig. 298). Span, 20 feet. Rise at centre, 
5 feet. Distance between principals, 6 feet. Assume that the truss has to 
support a total load of 2 tons per ‘‘ square” acting verti- peer 
cally. (A “square” is 100 square feet of area covered.) al 
The following sections are to be used.—Rafters, ‘tee ; = 
struts, angle; ties, flat. Material to be mild steel, and < 7 
the joints to be riveted. eo 20 ae 
2. Design a roof suitable for covering a shed with Fia. 298 
open ends. The span between the supports is 35 feet, a 
and the trusses are to be placed 8 feet apart. The principal rafters have a 
rise of 10 feet, and the tie bar has a camber of 2 feet. The form of truss to 
be used is shown in Fig 299. The covering is to be corrugated iron on angle iron 
purlins. The dead weight upon the roof may be assumed in the first instance © 
to be 10 lbs. per square foot. Snow, 6 lbs. per square foot, and horizontal wind 
pressure 50 lbs. per square foot. Lateral wind bracing is to be provided, 
Rolled steel sections and riveted joints are to be used. 
Fra. 299. Fra. 300. 
3. A design is required for a trussed roof of the saw-tooth pattern (Fig. 300). — 
There are several similar spans. The trusses over the first span are bolted to 
a wall at one side, and all the other supports are columns, as shown. The 
distance apart of the principals longitudinally is 7 feet 6 inches. The steep slope — 
is to be covered with glass, the other with slates on boarding. Take the dead 
weight of the roof as 18 lbs. per square foot, the weight of the snow as 6 lbs. 
per square foot, and the horizontal wind pressure as 50 lbs. per square foot. 
Round bars may be used for the ties, angles and tees for the other members. 
_ & Design for a slated roof. The trusses to be of the “ French” pattern. 
Pitch, }. Camber of tie rod, 2. Span, 50 feet. Distance apart of principals, 
10 feet. The covering to be Duchess slates laid upon 2 inch boarding supported 
by angle purlins. The roof is estimated to weigh as follows: Slates, 9 lbs. per 
square foot. Boarding, 7 lbs. per square foot. Purlins, 3 lbs. per square foot. 
One truss, $ ton. Snow, 6 lbs. per square foot, and the normal wind pressure ~ 
