A prestressed concrete beam has a width of 250 mm and an overall depth of 500 mm. Prestressing bars are placed at a distance e below the centroidal axis of the beam and a prestressing force of P is applied on it. Assume a prestress loss of 25%.
1. Calculate the value of P when the compressive stress in the entire section is 18 MPa.
2. Calculate the value of P when the compressive stress at the bottom fiber is 10 MPa and the tensile stress at the top fiber is 3MPa.
3. Calculate the value of P when the compressive stress at the bottom fiber is 16 MPa and the stress at the top fiber is 0 MPa.