Question

. A symmetrical rectangle box section prestressed concrete beam of external width of 300
mm and external depth of 600 mm with a uniform thickness of 40 mm is prestressed with 7
numbers straight steel wires of 7 mm diameter located at a distance of 15 mm from the bottom
of the soffit and 5 number of 5mm diameter of the steel wires located at the 575 mm from the
bottom of the beam . The wires were initially tensioned on the prestressing bed with an initial
prestress of 1500 N/mm2
. The beam is subjected to point load of 55.4 kN at the center of the beam and a uniformly distributed load of 20 kN/m entire length
of the beam with a length of 10 m. Calculate the resultant stresses at the end and mid span
section with neat stress distribution diagram. Assume the density of the concrete is 24
kN/m3
.

b. In the above problem, how to control the resultant stresses such that they do not exceed
25 N/mm2 at mid span section.

Answer 1