ASSIGNMENT

STRUCTURE- IV

1. A prestressed-concrete rectangular beam 500 mm by 900 mm has a simple span of 8 m

and is loaded by a uniform load of 40 KN/m including its own weight. The prestressing

tendon is located as shown and produces an effective prestress of 1700 KN. Compute top

and bottom fiber stresses in the concrete at the midspan section, using 1st concept.

2. Consider the same problem stated in question 1. Compute top and bottom fiber stresses

in the concrete at the midspan section, using 2nd

concept.

3. Consider the same problem stated in question 1. Compute top and bottom fiber stresses

in the concrete at the midspan section, using 3rd

concept.

4. A straight pre-tensioned concrete member 15 m long, with a cross section of 420 mm

by 420 mm, is concentrically prestressed with 760 mm2 of steel wires with a stress of

1040 MPa. If Ec = 33000 MPa and Es = 200,000 MPa, compute the loss of prestress due

to the elastic shortening of concrete at the transfer of prestress, using elastic analysis with

transformed section.

5. Consider the same member as in question 4, but post-tensioned instead of

pretensioned. Assume that the steel is made of 4 tendons with 190 mm2 per tendon. The

tendons are tensioned one after another to the stress of 1040 MPa. Compute the loss of

prestress due to the elastic shortening of concrete.

6. A pre-tensioned concrete member with a cross section of 250 mm by 350 mm, is

concentrically prestressed with 580 mm2 of steel wires with a stress of 1035 MPa.

Assume, n = 6, compute the stress of concrete immediately after transfer of prestress,

using elastic analysis with transformed section (an exact solution).

7. A pre-tensioned concrete member with a cross section of 200 mm by 350 mm, is

eccentrically prestressed with 580 mm2 of steel wires with a stress of 1035 MPa. The

centre of steel is 125 mm above the bottom fiber. Assume, n = 6, compute the stress of

concrete immediately after transfer of prestress, using elastic analysis with transformed

section (an exact solution).

8. A post-tensioned beam has a mid-span cross section of 220 mm by 350 mm with a

duct of 50 by 70 mm. it is prestressed with 590 mm2 of steel to an initial stress of 1035

MPa. Immediately after transfer the stress is reduced by 10% due to loss. Compute the

stresses in the concrete at transfer.

9. A post-tensioned bonded concrete beam 300 mm by 550 mm has a simple span of 11m

and has a prestress of 1570 kN in the steel immediately after prestressing, which

eventually reduces to 1370 kN due to losses. The beam carries two live loads of 50 kN

each in addition to its own weight of 4.5 kN/m. Compute top and bottom fiber stresses in

the concrete at the midspan section, (a) under the initial condition with full prestress and

no live load and (b) under the final condition after the losses have taken place and with

full live load.

10. For the same problem as in problem 9, compute the concrete stresses under the final

loading condition by locating the center of pressure C for the concrete section.