. A symmetrical rectangle box section prestressedconcrete beam of external width of 300
mm and external depth of 600 mm with a uniform thickness of 40 mmis prestressed with 7
numbers straight steel wires of 7 mm diameter located at a distanceof 15 mm from the bottom
of the soffit and 5 number of 5mm diameter of the steel wireslocated at the 575 mm from the
bottom of the beam . The wires were initially tensioned on theprestressing bed with an initial
prestress of 1500 N/mm2
. The beam is subjected to point load of 55.4 kN at the center ofthe beam and a uniformly distributed load of 20 kN/m entirelength
of the beam with a length of 10 m. Calculate the resultant stressesat the end and mid span
section with neat stress distribution diagram. Assume the densityof the concrete is 24
kN/m3
.
b. In the above problem, how to control the resultantstresses such that they do not exceed
25 N/mm2 at mid span section.
