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t0cY74
USN
Seventh Semester B.E. Degree E
.2015/Jan.20l6
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Design of Prestressed
Structures
Time: 3 hrs.
Max. Marks:100
Note: 7. Answer any FIVE full questions, selecting atleast TWO questions from each purt. 2. Use of IS 1343-1980 is permitted.
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Explain Magnel
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post-tensioning.
Blaton post tensioning
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system with a neat sketch. "' ''
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(06 Marks) (08 Marks) (06 Marks)
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b. Distinguish between pre-tensioning
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PART_A H prestressed g I a. Define concrete. State advantages as over reinforced concrete. ,,,
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(04 Marks) E 2 a. Explain load balancing concept in a prestressed concrete members. b. A simply supported concrete of rectangular x cross section 400 600 mm is loaded with a $g total UDL of 60 kN/m over a span of 6 m. Draw the distribution of stress at mid span. If the gE prestressing force of 1920 kN and the parabolic profile of the tendon has an eccentricity of EA -qp]^ l00mmatends and200 mmatmidspan. (t6Marks) doo
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A prestressed concrete beam of inverted T-beamp5p*hown in Fig.Q3 and is simply supported oYer a span of 16,.*. The beam is post-tensionffirith a 3-Freyssinet cables, each contay:yg l? wrres ur / rrur ula pracgo as snown a[ ["ff) r]1lo span. lI Ine mrtlal prestress ls IUUU N/tlm-, calculate maximum uniformly distributed,rlggd if the maximum compressive stress in concrete is hmited to 14 N/mm2 and tensile stress ls hmiteO to I N/mm'. Assume loss of' prestress r'-"-' as 15010.
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4 a. List the K&bffi losses in pre-tensioned and p-ost tensioned beams. (04 Marks) po.sffiioned b. A prestress concrete beam of 30 m span is subjected to a prestress force of 250_#$"At 28 days strength. The profile of cable is parabolic with maximum eccentricity of ?qmffi* at mid span. Determine the loss of prestress and has a cross section of *q$00mm x 800mm deep beam is prestressed with 9 cables each consists of 12 wires of 5 mm L.p-bia. Take E. :2.1x10s LJ-hia. 2.lx10s N/mm2 and E. 3.5x10a N/mm2. The cable is tensioned at time. (l6Marks)
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PART-B :"Wa. Explain 5 the load deflection characteristics of typical prestressed concrete beam under flexure ?\ -j N with a diagram. (06 Marks) g b. A rectangular concrete beam of cross-section 150 rlm x 300 mm deep is simply supported z
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over a span of 8 m and is prestressed by means of a symmetric parabolic cable at a distance of 75 mm from the bottom of the be.am at mid span and 125 mm from the top of the beam at ypport section. If the force in the cable is 350 kN and the modulus of elastfoity of concrete is 38 kN/mm2, calculate (i) The deflection at mid span when the beam is supplrted its own weight and (ii) the concentrated load which must be applied at mid span to restore it to the level of supports. (14 Marks)
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(06 Marks) Explain the mechanism of shear failure in PSC beams. A pre-stressed T-section has a flange width of 300 mm and the thickness of the flange is 200 mm. The rib is 150 mm wide by 350 mm deep. The effective depth of the cross section is 500 mm. Given Ao : 200 ffiffi2,- fr : 50 N/mm2 and fo : 1600 it/**'. Determiffi flexural strength of the section.
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What is transmission length? List the factors influencing transmission lengthffi S foo Marks) A pretensioned beam is prestressed using 5 mm diameter wires with ang{pjtifl stress of 80 r -,V-{, strength of peicent of the ultimate tensile strength of steel, fp, = 1600 N/mmffiXdube concrete at transfer is 30 N/mm'. 11 Calculate the transmissio, lr$glpr- (ii) Compute the bond stress at ll4 and the transmission length from the ped Ma (iii) Calculate the overall average bond stress (14 Marks) M
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Explain end zone (04 A pre-tensioned beam of 8 m span has a symmetriqul I-sbction. The flanges are 200 mm wide and 60 mm thick. The web thickness is 80 and the overail"ite tff.6ffiffU€pqFux-'Tn1 400 mm. The member is prestressed by 8 wires pf +nm diameter located on the tension side such that the effective eccentricity is 91 mm. -$&'dinitial stress in the wires is 1280 N/mm2 and the cube strength of concrete at transfer is,'42 N/mm2. Determine the maximum verticaltensile stress developed in the transfer zone and Design suitable mild steel rejefi*f;Pement assuming the permissible stress in steel as 140 (16Maiks)
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