USN

Time: 3 hrs.

t0cY74

Max. Marks:100

(10 Marks)

(04 Marks)

(10 Marks)

(04 Marks)

Seventh Semester B.E. Degree Examination, Dec.2013 lJan.20l4Design of Prestressed Goncrete Structures

a.

c.

2a.b.

6)oo:a

o()L

oxoo-o.;--y>6e-ooltroo.= c.lc+ir bOyool-O

o>o2

a::

o()(BO

50tr(d(d

-6

3o5.E

^X

oj

9E=ioaa L=€i!ox .:a>'!bovEOOo=sotr>VLo

U<iN

0)

o

o.

Explain the concept of usingstructures,What are thE advantages of prestressed concrete structures compared to R.C.C. structures?

(05 NIarks)With neat sketches,explain pre tensioning and post tensioning. State the advantages of these

Note: 7. Answer FIVEfull questions, selectingut least TWO questions from euch part.

2. Use of 151343-1930 is permitted.3. Assame any missing data suitably.

PART _ Ahigh strength concrete and high stfengt

With a neat sketch, explain Hoyes system of prestressing,

What are the important losses of prestress? Explain in detail.

List the factors influencing deflections.

A rectangular concrete beam,of cross section 30cm deep and 20cm wide is pre-stressed bymeans of l5wires of 5mm diameter located 6.5cm from the bottom of the beam and 3 wiresof diameter of 5mm. 2.5cmfrom the top. Assuming the pre-stress in the steel as 840 N/mm2,calculate the stresses at the extreme fibres of the midspan section when the beam issupporting its own weight over a span of 6m. If a uniformly distributed live load of 6kN/m is

imposed, evaluate the maximum working stress in concrete the density of concrete is 24kN/m3. (16 Marks)

3a.b. A rectangular concrete beam. 300mm deep and 200mm wide is prestressed by means of

flfteen 5mm diameter wires located 65mm from the bottom of the beam and three 5mmwires, located 25 from the top of the beam. If the wires are initially tensioned to a stress

of 840 N/mm2. calculale the peicentage loss of stress in Jeel immediately after transfer-allowing for the loss of stress due to elastic deformation of concrete. Take E, : 210 kN/mm2

4a.b. A concrete beam with a cross sectional area of 32 x 103 mm2 and radius of Gyration of

72mm is prestressed by a parabolic cable carrying an effective stress ol1000 N/mm2. Thespan of the beam is 3m. The cable composed of 6 wires of 7mm diameter, has aneccentricity of 50mm at the centre and zero at the supports. Neglecting all losses, find thecentral deflection of the beam for the following cases:

i) Self weight * pre-stress; ii) Self weight + pre-stress + live load of 2 kN/m. (08 Marks)A pre-stressed concrete beam of rectangular section 120mm wide and 300mm deep, spans

over 6m. The beam is prestressed by a straight cable carrying an effective force of 180kN atan eccentricity of 500mm. If it supports an imposed load of 4kN/m and the modulus ofelasticity of concrete is 38 kN/mm2. Compute the deflection at the following stages andcheck whether they comply with the IS code specifications:i) Upward deflection under (pre-stress + self weight) andii) Find downward deflation under (pre-stress + self weight * imposed load) inducing the

effects of creep and shrinkage. Assume the creep coefficient to be 1.80. (08 Marks)

c.

For More Question Papers Visit - www.pediawikiblog.com

For More Question Papers Visit - www.pediawikiblog.com

www.pediawikiblog.com

5a.b.

6a.b.

7a.b.

A pre-tensioned prestressed concrete beam having a rectangular section 150mm wide and350mm deep has an effective cover of 50mm. If fcr:40 N/mm2, &: 1600 N/mm2 and thearea of pre-stressing steel Ap : 461mm2, calculate the ultimate flexural strength of the.

PART _ BList and explain the types of flexural failure.

uslng IS: 1 343 code recommendations.

List and explain the types of shear cracks in structural concrete.

standard code IS : 1 343 ieCbmmendations.

The support section of a pre-stressed concrete beam 100mm widg and 250mm deep, isrequired to support an ultimate shear force 60kN. The compressive pre-stress at thecentroidal axi's is 5-N/mm2 the characteristic cube strength of concrete is 40N/mm2. Thecover to the tensiqn'reinforcement is 50mm. If the characleristic tensile strength of steel instirrups is 250 N/mm2, design suitable reinforcements it the section using the Indian

t0cY74

(08 Marks)

(05 Marks)

(08 Marks)

(06 Marks)

(06 Marks)

(08 Marks)

section using IS:1343 code provisions. (07 Marks)

c. A post-tensioned beam with unbounded tendons is of rectangular section 400 mm wide withan effective depth of 800 mm. The cross sectional area of the pre-stressing steel is 2840mm2.The effective pre-stress in the steel after all losses s 900 N/mm2. The effective span of thebeam is 16m. If f.r:40 N/mm2 estimate the ultimate moment of resistance ofthe section

c. The cross section of a pre-stie$sed concrete beam is rectangular with a width of 350mm andan overall depth of 700mm.'The prestressing force of 180kN acts at an eccentricity of190mm. If the bending and twisting momerlts at the section are 80 and 20kN-m respectively.Calculate the maximum principal tensile stress at the section.

i. '1

Explain the concept of stress distribtrtion in End block.The end block of a post tensioned pre-stressed member is 550mm wide and 550mm deep.Four cables each made up of 7 wires of 12mm diameter strands and carrying a force of1000 kN are anchored by plate anchorages 150mrn by 150mm, located with their centres atl25mm from the edges of the end block. The cable duct is of 50mm diameter the 28day cubestrength of concrete ler is 45N/mm2. the cube strength of concrete at transfbr f.i is 25N/mm2.Permissible bearing stresses behind anchorages should conform with IS I 343. Thecharacteristic yield stress in mild steel anchorage reinforcemqnt is 260N/mm2. Designsuitable anchorage for the end block. (12 Marks)

Design'a'pre-tensioned roof Purlin to suit the data below: Effective span : 6m, appliedload'* 5 kN/m, load factors: for dead load: 1.4, for live load: 1.6, concrete cube strength,f., * 50N/mm2, cube strength at transfer f"i : 30 N/mm2, tensile strehgth of concrete,ft : 1.7 N/mm2, modulus of elasticity of concrete, E. : 34 kN/mm2, loss ratio, 11 : 0.8,permissible stresses: at transfer :

compressive stress, f.t : 15N/mm2,tensile stress, fn: -1N/mm2 ,

atworkingload:compressivestressf.*:17N/mm2,tensilestressf*:0.7mm high tensile steel wires having an ultimate tensile strength, fp, : 1600 N/mm2 areavailable fort use. (20 Marks)

* ,,< * ,,< {<

2 of2

For More Question Papers Visit - www.pediawikiblog.com

For More Question Papers Visit - www.pediawikiblog.com

www.pediawikiblog.com