HINT; IF Standard is required use AS3600 Question 3 (35 Marks) - Prestressed Concrete A prestressed concrete

HINT; IF Standard is required use AS3600

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Question 3 (35 Marks) - Prestressed Concrete A prestressed concrete 1-Girder is simply supported over a span of 18m and has the cross section as shown in Figure 3. In service conditions the superimposed loads are g-4.5kN/m and q= 15kN/m. Assume than the tendon is placed with an eccentricity of 300mm at the mid-span section. i. 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 0.5fcp? Show that with this maximum amount of prestress, the top fibre stress at the midspan section does not exceed the allowable tensile stress of 0.25√/Tep (8 Marks) ii. At service, what is the minimum prestressing force at mid span section to ensure that there is no tension at the bottom fibre? Show that with this minimum amount of prestress, the top fibre stress at the mid span section does not exceed the allowable compressive stress of 0.45fc. (8 Marks) iii. If the total time-dependent losses of prestress at mid span are estimated to be 11% what would be the appropriate prestress at transfer at mid span section? (5 Marks) iv. If the friction losses between the live end and mid span are 3.5% what is the required jacking force at the live end? What are the stresses st top and bottom at this jacking end (Section A-A)? V. (6 Marks) During stacking this girder has been placed upside down by mistake, with supports placed at the two ends. Briefly discuss the consequence of this including any possible damage to the girder. (8 Marks) 10.000m BEAM ELEVATION 600 4.50 1150 500 SECTION A-A Figure 3 Refer to question 3 950 450 500 SECTION BB The End 10.000m 1150 A, -317 x 10' Z-82.9 x 10 mm Z-91.1 x 10 mm 1,- 49.90 x 10 mm Self weight-7.95 KN/m f-32 MP -40 MP 3 Question 3 (35 Marks) - Prestressed Concrete A prestressed concrete 1-Girder is simply supported over a span of 18m and has the cross section as shown in Figure 3. In service conditions the superimposed loads are g-4.5kN/m and q= 15kN/m. Assume than the tendon is placed with an eccentricity of 300mm at the mid-span section. i. 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 0.5fcp? Show that with this maximum amount of prestress, the top fibre stress at the midspan section does not exceed the allowable tensile stress of 0.25√/Tep (8 Marks) ii. At service, what is the minimum prestressing force at mid span section to ensure that there is no tension at the bottom fibre? Show that with this minimum amount of prestress, the top fibre stress at the mid span section does not exceed the allowable compressive stress of 0.45fc. (8 Marks) iii. If the total time-dependent losses of prestress at mid span are estimated to be 11% what would be the appropriate prestress at transfer at mid span section? (5 Marks) iv. If the friction losses between the live end and mid span are 3.5% what is the required jacking force at the live end? What are the stresses st top and bottom at this jacking end (Section A-A)? V. (6 Marks) During stacking this girder has been placed upside down by mistake, with supports placed at the two ends. Briefly discuss the consequence of this including any possible damage to the girder. (8 Marks) 10.000m BEAM ELEVATION 600 4.50 1150 500 SECTION A-A Figure 3 Refer to question 3 950 450 500 SECTION BB The End 10.000m 1150 A, -317 x 10' Z-82.9 x 10 mm Z-91.1 x 10 mm 1,- 49.90 x 10 mm Self weight-7.95 KN/m f-32 MP -40 MP 3

Answer rating: 100% (QA)

900 225 275 Superimposed loads allowable A P MDL w1 A 350 P... View the full answer