COMPOUND COLUMNS AND BEAMS 55 



527. A 10-inch steel I-beam, 30 pounds per foot, resting on sup- 

 ports 20 feet apart, carries a load of 6000 pounds at its middle point. 

 Determine the maximum horizontal unit-shear if the center of gravity 

 of each half section is 4.5 inches from the neutral axis. 



528. An 8-inch steel I-beam, 18 pounds per foot, resting on sup- 

 ports 15 feet apart, carries a load of 5000 pounds at its middle point. 

 Determine the maximum horizontal unit-shear, if the center of gravity 

 of each half section is 3.6 inches from the neutral axis. 



XII. COMPOUND COLUMNS AND BEAMS 



529. A vertical bar 10 feet long and 1 inch square is compounded 

 by fastening together rigidly at the two ends a bar of steel and a bar 

 of copper of equal size. When a load of 12,000 pounds is applied at 

 the lower end of the compound bar, how much of this load will be 

 sustained by each of the component bars, and what will be the elonga- 

 tion of the compound bar ? 



530. A compound column 4 feet in length is formed by bolting two 

 I -inch steel plates, 8 inches wide, to the 8-inch sides of a piece of 

 timber 6x8 inches in section area. When the column sustains an 

 axial load of 120,000 pounds what is the compressive unit-stress in 

 the steel and in the timber ? 



531. A flitched timber beam 15 feet long, supported at its ends, 

 has a timber section 8x12 inches, with two steel plates \ x 9 inches 

 bolted to the 12-inch sides. When the beam supports a total uniform 

 load of 16,000 pounds, find the factors of safety for the timber and 

 the steel. 



532. Aflitched beam consists of two timbers, each 10 inches wide and 

 14 inches deep, with a steel plate | inch thick and 7 inches wide 

 bolted between them on the 14-inch sides. Find the unit-stress in the 

 steel when the unit-stress in the timber is 900 pounds per square inch. 



533. A concrete column 12 feet high and 12 x 12 inches in section 

 area has four vertical steel rods, each 1J- inches in diameter, placed 

 near the corners. Compute the unit-stresses in the concrete and steel 

 due to their own weight and to an axial load of 30,000 pounds. 



534. Find the load that a short' concrete column 24 inches square, 

 reinforced with 4 round, vertical, steel rods 21- inches in diameter, 



