Statics & Strength of Materials
Problem Assignment (determinate) Stress/Strain 2
Find the
size cable required for a crane. Two cranes lift a concrete bridge beam. The beam is 80
feet long with a rectangular cross section 8 inches wide and 24 inches deep. The density
of concrete is 150 pounds per cubic foot. Each crane lifts an equal share of the weight.
The allowable tensile stress in the cable is 25,000 psi. Cable size is by 16ths to 1/2
inch, by 1/8ths to 2 inches and by 1/4 thereafter. (3/4")
The boom on
the crane is 100 feet long. Determine the weight of cable hanging from the boom when it is
fully extended. That is, how much does 100 feet of cable weigh. The density of steel is
490 pounds per cubic foot. (150 lb)
The ends of
the bridge beams in problem 1 rest on 8 inch wide steel plates. How long should the plates
be if the allowable bearing stress is 45,000 psi.? (.0223")
At one
point while the cranes in problem 1 are lifting the bridge beams in problem 1, their booms
are at an angle of 53 degrees. The cable at the top of the boom runs over a pulley held in
place with an axle. Assuming that the axle is solid steel, determine the minimum diameter
of axle required so that the shear stress in the axle material does not exceed the
allowable shear stress for hardened steel, 20,000 psi. The tension in the cable is
constant. Determine the shear force acting on the axle from static equilibrium. It
requires a drawing of the crane and then a free body diagram of the pulley assembly.
(d = .98")
A hammer
strikes a 12 penny common nail with a maximum force of 500 pounds. What is the compressive
stress in the nail? (29,064 psi., using nominal diameter)
A construction crane has a 3/4 inch diameter cable. The allowable working stress for the cable is 20,000 psi. Determine the maximum load that the crane can lift.(8830 lb)
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Topic 3: Stress, Strain
& Hooke's Law - Table of Contents
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