Make a design for a pair of rafters, connected by a tie-beam, for
a roof 30 feet span, showing the dimensions of the several parts and
the manner of connecting them. State in detail your method of
obtaining the several dimensions.
76. How do you apply the principle of the parallelogram of forces in
determining the strain on the various members of a structure?
Illustrate graphically.
77. What should be the thickness at the top and base of a retaining
wall 15 feet high, built to retain ordinary earth? Show your method of
obtaining the required dimensions, also a sketch of the wall, showing
how it should be founded.
78. A reservoir is to be built, depth of water 10 feet. If the walls
are built of masonry, find the thickness of the same, and state how
they should be built. Show your work.
79. What is an arch, of how many forms, and of what may it be
constructed?
80. Can you state how you would find the thickness of an arch of
stone, span and rise being given?
81. Define the intrados and extrados of an arch.
82. Where should the line of resistance to pressure be found in an
arch in order to retain its stability?
83. Can you find the thickness of the abutments, the rise and span of
the arch being given?
84. In a semicircular arch, where is the horizontal thrust greatest
and where least?
85.
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