WORLD FOR CIVIL

Statics & Strength of Materials

Problem Assignment (determinate) Stress/Strain 2

1. 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")

2. 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)

3. 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")

4. 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")

5. 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)

6. 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)