An unsymmetrical I-section prestressed concrete beam of span 9 meters…

Question

An unsymmetrical I-section prestressed concrete beam of span 9 meters. The beam has to carry a superimposed load of $20\text{ kN/m}$. The prestressing force is transmitted by tendons in two cables which are located at $120\text{ mm}$ from the soffit of the beam. In each cable the tendons consists of 14 wires of $5\text{ mm}$ diameter subjected to an initial stress of $1000\text{ N/mm}^2$. The sectional details are top flange, $250\text{ mm}$ wide and $100\text{ mm}$ thick; bottom flange $200\text{ mm}$ wide and $200\text{ mm}$ thick; thickness of web = $100\text{ mm}$; overall depth of beam = $800\text{ mm}$. Analyze the beam section at the centre for the stresses induced before and after the application of the superimposed load. Allow 15% loss of prestress.