Question
A prestressed concrete simply supported beam of span 6 m has a rectangular cross-section 300 x 600 mm and unit weight 24 kN/m3. The resultant prestressing tendon has zero eccentricity at ends and an eccentricity, e, at midspan, and linear profile. Under initial condition, the allowable stresses are 20 N/mm2 in compression and 2 N/mm2 in tension. Using this condition, determine the prestressing force, P, and the eccentricity, e, at midspan. The imposed loading is a single concentrated load, W, at midspan and the tendon undergoes loss in prestress of 25%. Determine W, if the final allowable stresses in compression and tension are not to exceed 15 N/mm2 and 1 N/mm2 respectively.