1. Choose the most appropriate answer from the options given in each case.

Tensile strength of concrete for pre-stressed concrete structure may be assumed as

0. 5 sqrt(fck)

0.8 sqrt(fck)

0.6 sqrt(fck)

0.70 sqrt(fck)

Minimum grade of concrete used for pre-tensioned concrete structures is

M 35

M 25

M 40

M 30

Ideal profile of pre-stressing cable for a beam carrying uniformly distributed load is

with uniform eccentricity

passing through neutral axis

parabolic

linearly varying

A bearing plate below an anchorage system

is desired

distributes the force evenly

is unsafe

increases stress intensity in concrete

Loss of pre-stress due to elastic shortening of the member occurs in

post-tensioned concrete structures

pre-tensioned concrete structures


both and

None of the above

Stress due to eccentric pre-stressing only, at an extreme fibre of a pre-stressed beam of cross-sectional area moment of inertia may be given as

A/P ± Pey/I


P/A ± I/PEY


P/A ± Pey/I

None of the above

Partial safety factor for live load for limit state of serviceability required for the load combination (DL LL WL) is

0·8

1·0

1·2

0·9

Write down any three advantages of pre-stressed concrete. Also indicate three applications of the same.

Explain the utility of Hoyer's long line system of pre-stressing with a neat sketch.

Explain the concept of load balancing as applied for pre-stressed concrete structures.

Discuss briefly the concept of pressure line.

Explain briefly the utility of high strength steel and high strength concrete for pre-stressed concrete structures.

Discuss briefly secondary stresses due to tendon curvature.

5. Write short notes on any two of the following:

Chemical pre-stressing

Pre-stressed concrete poles

Flexure failure of pre-stressed concrete beams

A pre-tensioned concrete beam of 200 mm x 450 mm has 6 wires of 7 mm diameter. The wires have initial stress of 1200 N/mm^2 and effective eccentricity is 70 mm. Calculate the loss of pre-stress due to creep of concrete, if Es 2 x 10^5 N/mm^2 Ec =30 x 10^3 N/mm^2 creep coefficient =1·6.

Discuss the losses of pre-stress due to anchorage slip and relaxation of steel.

Define tendon splices. Discuss the types of tendon splices in brief.

Calculate stresses at mid span in top and bottom fibres for a simply supported beam of 6 m span. The beam carries an imposed load of 10 kN/m and has cross-section of 250 mm x 400 mm (deep). Pre-stressing force of 400 kN is applied concentrically. Assume density of concrete as 24 kN/m^3.