2 PROBLEMS IN STRENGTH OF MATERIALS 



ultimate tensile strength, the unit-elongation for the elastic limit and 

 for rupture. 



10. A cast-iron bar has an elliptical cross-section with axes 6 and 4 

 inches. Find the unit-stress under a tensile load of 120,000 pounds, 

 and the factor of safety. 



11. A brick column 2 feet square and 8 feet high sustains a load 

 of 50 tons. What is the factor of safety ? 



12. What load can be borne by a brick pier whose cross-section is 

 2|- x 3^ feet, with a factor of safety of 15 ? 



13. Find the weight of a wrought-iron bar 1J X 2 inches section 

 and 12 feet long, and of a cast-iron bar of the same size. 



14. Find the cross-section area of a wooden beam which weighs 

 10 pounds per foot. What would be the cross-section area of a steel 

 beam weighing the same per linear foot ? 



15. What must be the height of a brick tower if the com- 

 pressive unit-stress on the lowest brick is one third of its ultimate 

 strength ? 



16. A cast-iron cylindrical rod 1500 feet long is suspended verti- 

 cally from its upper end. What is the unit-stress at this end, and the 

 factor of safety ? 



17. Calculate the length of a cast-iron bar, supported vertically at 

 its upper end, that will break under its own weight. 



18. The maximum steam pressure in a steam engine is 120 pounds 

 per square inch and the piston area is 200 square inches. Find the 

 diameter of the steel piston-rod for a factor of safety of 8, if lateral 

 bending is prevented. 



19. Find the height of a brick wall of uniform thickness for a 

 factor of safety of 15. 



20. What must be the diameter of a hard steel piston-rod, if the 

 piston is 18 inches in diameter and the maximum steam pressure is 

 110 pounds per square inch? Consider length of rod less than ten 

 times its diameter. 



21. A short wooden post is 6 inches in diameter. What compres- 

 sive load can it bear with a factor of safety of 8 ? 



22. A sandstone column bears a load of 6 tons. Find the area 

 of its base for a factor of safety of 20, if the ultimate compressive 

 strength is 3600 pounds per square inch. 



