A prestressed concrete girder is simply supported over a span of 20 m as shown in...

 

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A prestressed concrete girder is simply supported over a span of 20 m as shown in Figure 3. In service condition, the superimposed loads are g- 6.0 kN/m and q = 10.0 kN/m. Assume that the tendon is placed with an eccentricity of 300 mm at the mid-span section. At transfer, what is the maximum prestressing force at mid span section to ensure that the stress in the bottom fibre does not exceed the allowable stress of 0.5f? With this maximum amount of prestress, calculate the stress at the top fibre at the mid span section and show that it does not exceed the allowable tensile stress of 0.25√ (50 Marks) (b) At service, what is the minimum prestressing force at mid span section to ensure that there is no tension at the bottom fibre, i.e. o,=0? With this minimum amount of prestress, calculate the stress at the top fibre at the mid span section and show that it does not exceed the allowable compressive stress of 0.45f. (50 Marks) If the total time-dependent losses of prestress at mid span are estimated to be 10%, what would be the appropriate prestress at transfer at mid span section? (25 Marks) (d) If the friction losses between the live end and mid span are 5%, what is the required jacking force at the live end? What are the stresses at the jacking end (Section A-A)? (25 Marks) BEAM ELEVATION 900 225 275 10 m SECTION A-A 300 + 350 450 A A 150 Centre of gravity 10 m Ą, -246 x 10³ mm² Z₁ = 47 x 10³ mm³ Zbor = 48.5 x 10 mm² = 21.5 x 10 mm Selfweight = 5.9 kN/m fp = 50 MPa f = 65 MPa Take, Eccentricity at mid span = 300 mm Eccentricity at end = 0 mm Figure 3. Refer to Question 3 A prestressed concrete girder is simply supported over a span of 20 m as shown in Figure 3. In service condition, the superimposed loads are g- 6.0 kN/m and q = 10.0 kN/m. Assume that the tendon is placed with an eccentricity of 300 mm at the mid-span section. At transfer, what is the maximum prestressing force at mid span section to ensure that the stress in the bottom fibre does not exceed the allowable stress of 0.5f? With this maximum amount of prestress, calculate the stress at the top fibre at the mid span section and show that it does not exceed the allowable tensile stress of 0.25√ (50 Marks) (b) At service, what is the minimum prestressing force at mid span section to ensure that there is no tension at the bottom fibre, i.e. o,=0? With this minimum amount of prestress, calculate the stress at the top fibre at the mid span section and show that it does not exceed the allowable compressive stress of 0.45f. (50 Marks) If the total time-dependent losses of prestress at mid span are estimated to be 10%, what would be the appropriate prestress at transfer at mid span section? (25 Marks) (d) If the friction losses between the live end and mid span are 5%, what is the required jacking force at the live end? What are the stresses at the jacking end (Section A-A)? (25 Marks) BEAM ELEVATION 900 225 275 10 m SECTION A-A 300 + 350 450 A A 150 Centre of gravity 10 m Ą, -246 x 10³ mm² Z₁ = 47 x 10³ mm³ Zbor = 48.5 x 10 mm² = 21.5 x 10 mm Selfweight = 5.9 kN/m fp = 50 MPa f = 65 MPa Take, Eccentricity at mid span = 300 mm Eccentricity at end = 0 mm Figure 3. Refer to Question 3

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Solution 900 2251 275 allowable MAL W1 8 350 450 s... View the full answer