34 PKOBLEMS IN STKENGTH OF MATEEIALS 



300. Find the factor of safety for a 15-inch steel I-beam, 42 pounds 

 per foot, 1 6 feet span and supported at the ends, if it bears a concen- 

 trated load of 15,000 pounds at the middle. Neglect weight of beam. 



301. Solve Problem 300, considering the weight of the beam. 



* 302. Find the concentrated load at the middle of a 9-inch steel 

 I-beam, 25 pounds per foot, 14 feet span and supported at the ends, 

 for a factor of safety of 4. Neglect weight of beam. 



303. A cast-iron simple beam of 12 feet span has a section like 

 Fig. 19 with t r = t 2 = t = 1, d = 10, and b 1 = \ = 6 inches. Find the 

 concentrated load it can carry at its middle with a factor of safety 

 of 6. Neglect weight of beam. 



/ 304. Select the proper steel I-beam of 12 feet span, supported at 

 its ends, to carry two loads of 5000 pounds each, one at the middle 

 and the other 2 feet from the left end, with a factor of safety of 4. 

 Neglect weight of beam. 



305. A floor designed to carry a total uniform load of 180 pounds 

 per square foot is supported by steel I-beams of 20 feet span and 4 

 feet apart from center to center. Find the proper beam that should 

 be used for a factor of safety of 5. 



306. A floor which is to carry a total uniform load of 150 pounds 

 per square foot is supported by 9-inch steel I-beams, 35 pounds per 

 foot and 15 feet span. Find their distance apart from center to center, 

 if the factor of safety is 4. 



307. A cylindrical wrought-iron simple beam resting on end sup- 

 ports 24 feet apart sustains three concentrated loads of 400 pounds 

 each at distances of 4, 12, and 16 feet respectively from the left 

 support. What should be the diameter of the beam for varying stress ? 

 Neglect weight of beam. 



308. A 10-inch steel I-beam, 40 pounds per foot, 15 feet span and 

 supported at its ends, bears a concentrated load of 5 tons at its center. 

 Is it safe ? 



309. Select a steel I-beam 10 feet long and supported at its ends to bear 

 a total uniform load of 1500 pounds per linear foot with varying stress. 



310. A simple beam 16 feet span is loaded with 8000 pounds at 

 the middle and has a section like Fig. 18, with = ^ = 1, d = 10, 

 and I = 6 inches. Neglecting the weight of the beam, determine the 

 maximum fiber-stress, both tensile and compressive. 



