56 PROBLEMS IN STRENGTH OF MATERIALS 



can safely carry if the compression in the concrete is limited to 450 

 pounds per square inch. What is then the unit-stress in the steel rods ? 



535. What percentage of reinforcement must be introduced into a 

 concrete column designed to sustain a load of 650 pounds per square 

 inch, when the compressive unit-stress in the concrete is limited to 

 500 pounds per square inch ? 



536. Find the safe bending moment for a reinforced concrete beam 

 16 inches deep and 4 inches wide, having one steel rod J inch in 

 diameter, with its center 1J- inches above the bottom of the concrete, 

 if the tensile resistance of the concrete is neglected and the maximum 

 compressive stress in the concrete is 600 pounds per square inch. 



537. Find the safe bending moment for the beam of Problem 536, 

 if the concrete is to resist part of the tensile stresses with a maximum 

 tensile stress of 100 pounds per square inch. 



538. Determine the maximum bending moment for a reinforced 

 concrete beam 8 inches wide and 17 inches deep, with a 1-inch-square 

 steel rod placed with its center 2 inches above the bottom, if the con- 

 crete offers no tensile resistance and the maximum compressive stress 

 in the concrete is limited to 600 pounds per square inch. 



539. Solve Problem 538, if the maximum compressive stress in the 

 concrete is limited to 500 pounds per square inch. 



540. The beam of Problem 538 is supported at the ends of a 20-foot 

 span and bears a total uniform load of 5200 pounds. Determine the 

 unit-stresses in the concrete and in the steel, assuming that the con- 

 crete sustains none of the tensile load. 



541. A reinforced concrete beam 5 inches deep, 48 inches wide, 

 and 6 feet span has 2 square inches of steel placed 1 inch above the 

 bottom of the concrete and sustains a total -uniform load of 6000 

 pounds. If the beam is supported at the ends and the concrete offers 

 no tensile resistance, determine the position of the neutral surface 

 and the maximum unit-stresses in the concrete and in the steel. 



542. A concrete-steel beam 12 inches wide, 13^- inches deep, and 

 14 feet span, with supported ends, has 1 per cent of steel embedded 

 IT?- inches above the bottom of the concrete and bears two loads of 

 1300 pounds each at the third points of the span. Assuming that 

 the concrete offers no tensile resistance, find the maximum unit- 

 stresses in the steel and in the concrete. Consider weight of beam. 



