Question

a. 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 48 + 0.2 (54) 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 . Use BS8110 code

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