Download PTU (Punjab Technical University) B.Tech (Bachelor of Technology) / BE (Bachelor of Engineering) 2021 January CE 7th Sem 71868 Pre Stressed Concrete Previous Question Paper

Total No. of Pages : 03

Total No. of Questions : 18

B.Tech. (CE) (2012 to 2017) (Sem.?7)

PRE-STRESSED CONCRETE

Subject Code : BTCE-809

M.Code : 71868

Time : 3 Hrs. Max. Marks : 60

INST RUCT ION TO CANDIDAT ES :

1 .

SECT ION-A is COMPULSORY cons is ting of TEN questions carrying TWO marks

each.

2 .

SECT ION-B c ontains F IVE questions c arrying FIVE marks eac h and s tud ents

have to atte mpt any FOUR q ues tions.

3 .

SECT ION-C contains THREE questions carrying T EN marks e ach and s tudents

have to atte mpt any T WO questio ns.

4 .

Use of IS 1343 is pe rmitted in the ex aminatio n.

SECTION-A

Answer briefly :

1.

Give the range of w/c ratio of High strength mixes.

2.

What is the necessity of using high strength concrete in prestressed concrete?

3.

Define shrinkage of concrete.

4.

What is Pressure Line?

5.

What is Anchorage slip?

6.

What is the limiting value of effective reinforcement ratio of a bonded prestressed

concrete beam at failure?

7.

Name two ways of improving the shear resistance of structural concrete members by

prestressing concrete.

8.

Give any empirical formula for computing transmission length.

9.

What is the advantage of prestressing grid floors?

10. What is debonding?

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SECTION-B

11. What are Tendon splices? Sketch some common types of tendon splices.

12. A prestressed concrete pile 250 mm square, contains 60 pretensioned wires, each of 2mm

diameter, uniformly distributed over the section. The wires are initially tensioned on the

prestressing bed with a total force of 300 kN. Calculate the final stress in concrete and the

percentage loss of steel after all losses. Data given is modular ratio = 6.5, shrinkage due

to creep = 30 ? 10?6 mm/mm per N/mm2, relaxation of steel stress = 5% of Initial stress.

13. A prestressed concrete beam of rectangular section 120mm wide and 300 mm deep spans

over 6m. The beam is prestressed by a straight cable carrying an effective force of 200

kN at an eccentricity of 50 mm. It supports an imposed load of 4kN/m and EC = 40

kN/mm2.

Compute the deflection at the following stages :

a) Upward deflection under prestress + Self weight.

b) Final deflection under prestress + SWT + Imposed load including effects of creep &

Shrinkage.

14. A post-tensioned prestressed concrete T beam having a flange width of 1200 mm and

flange thickness of 200 mm, thickness of web = 300 mm is prestressed by 2000 mm2 of

high tensile steel located at an effective depth of 1600 mm. If fck = 40 MPa, fp = 1600

MPa ; estimate the ultimate flexural strength of unbounded Tee section, assuming

span/depth ratio as 20 and fpe = 1000 MPa.

15. Explain with sketches the effect of varying the ratio of depth anchorage to the depth of

end block on the distribution of bursting section.

SECTION-C

16. Design a partially prestressed post-tensioned beam to suit the following data :

Effective span = 30 m

Live Load = 9 kN/m

Dead load (excluding self weight) = 1 kN/m

Load factors : 1.4 for DL & 1.6 for LL.

fcu = 50 MPa

Strength of concrete at transfer = 35 MPa

Loss Ratio u = 0.85

Tensile strength of concrete = 1.7 N/mm2

Permissible tensile stress under service loads = 6 N/mm2

Maximum width of crack under service loads not to exceed 0.1 mm.

8mm high tensile wires having an ultimate tensile strength of 1500 MPa are available

for use.

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17. Design a post tensioned prestressed concrete two way slab 6m by 8m in size, to support a

live load of 3kN/m2. If cables of four wires of 5mm diameter stressed to 1000 N/mm2 are

available for use, determine the number of cables in the two principle directions. The

stresses in concrete not to exceed 15 MPa in compression and tensile stresses are not

permitted under service loads. The loss ratio is 0.7.

Check for limit states of service ability and collapse.

18. Write short notes on :

a) Shear and Principle stresses due to torsion

b) Methods by which bond between concrete and steel tendons can be improved.

NOTE : Disclosure of Identity by writing Mobile No. or Making of passing request on any

page of Answer Sheet will lead to UMC against the Student.

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This post was last modified on 26 June 2021