Roll. Number

Un ivers ity C o lle g" of Effi tri'a Lt*:noT:u,* 5:111"0";;;;"r"1 ii;rn" re cf, n o I o g i cat Unive r s itv Kakinada

*. ,.lilft#ster [Dr] (R13) {"eurq llty"utions' Aug-20t4

PRESTRESSEDCOI{CRETE(Cf - Structu ral E'n gineerit'g)

ivlax Marks: 60

Time: 3 hrs.

,{{b)nr)

Answer anY FIVE questions

All questions carry equal marks

Note: All parts ";ilJil;stionmust be answered at one place'

Explain general principals of pre tensioning and post tensioning systems?

;ffi;;?J b"theen ii" t""on"d and post tensioned members?

Exptain the various O"rt;;i;;;;t"il tur.a o, wedge action with neat sketches?

Explain different types of losses in pre strgssing]^ . r,The Indian ,t*a*o "J,

is, i:+l.pecifies diffbrent strains for different pre-

tensioned and post t""tion"O membeis '' Explain wi'th reasons?

Distinguish between cable line and Pressure line with sketches in a typical

ft ,

""f*"J'J, ffiH ; ;il*'i".p.

"rreiy. rhe overall depth,:_l *. 1".:1 I

s^

il,: T*trprestressed concrete beam ?

f":H'""H""i:H-d;metricar I-section snanl]nq lf li:^tlsi'yl1l #b)

Ti:ff :il:J#,ilL";;;i0ilft 'u"u-isry3stres!11-o1-:,1::1b:H:*:"#l::Ino tnlcKness ur urs wwu rr with an effective force

;;;;;.t"t*, or ts'-* at the oentre and zeroat,tht:"1ryf^ *^-a Aiamqm qr rhe:? i;fffii:?i!',iJ"''1,;;; *;; * '

oryi" ?'"-" lt*:i:E?ffit{i}: -). h*t-qt '::# H;tixtl1lliff: :;X"-Fffii,;6htGsitv or concrete - 24ro{/m3) and

iiiipr" stress * self weight + live load

4.a) Distinguish between web shear, flexural and flexure shear cracks in concrete beams

) with sketches ? lqr'L b) h:[',"1'#:T$:,ifiiJi^"J;:*?T::':,?',"'1ti:$ilr"]'i,i1]J*?:Tl'l;::;

1-l ''the centroidal axis is 5 Nimm':i; characteristic cube strength of concrete is 40

Nlmm2- Th" corer to the tension reinforcement is 50 mm' if the characteristic lotl"r

strength of sti*ups is 415 N/*#, -;.sign

suitable shear reinforcements in the section

usingls code recommendations ?

Design the pre stressing force required for the tie member of reinforced concrete

truss. The service rouJ-i"rrrion in the tie member is 360kN. and the thickness of the

member is fixed as. 150 mm. The permiisible compressive stress in concrete at

transfer is 15 N/mm' ""i i*!i,"gg?, r;rmitted undgr:grvice loads' The loss ratio

is 0.8. High-tensite wires 6ffim4-1iuffiss of 1000 N/mm2

and having an fe,Ji;'d;*'f ;;; ;;uiiaure for use. The tensile strength of

concrete is 2.5 Nl-*f.-a load factor of 1'7 at the limit state of collapse and l'2

against cracking i, ," i" p'"'iJ"O i" the design I

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e)

A composite bridge deck of span r 2m is made up of a pre cast pre stressedsymmetrical I section and an in situ cast slab. The pre cast I beams are spaced at750 mm centers and the top slab of the in situ concrete is 120mm thick. The crosssectional details of the pre cast I beams are as follows: thickness ofthe top and bottomflanges : I l0 mm, width of top and bottom flanges : 200mm, thickness of web : 75mm, depth of pre cast I beam : 500 mm, self-weight of pre cast concret e = 24 kN/m3self weight of cast in situ concrete : 23 .5a kN/m3, the pie stressed beam is un proppedduring the placing of in situ concrete. The form work load is estimated tl be0'2kNim. of the span. If the compressive pre stress in the beams is 15 N/mrn2 atthebottom and zero at the top , calculate the maximum stresses developed in the pre castand in situ cast concrete under an imposed load of 5 kN/m2, assuming the modularratio of cast in situ to pre cast concrete to be I .0.

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b)

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7 9)."Distinguish cleafly between short term deflections and long term deflections of-/ prestressed concrete members ?

Discuss various methods of predicting long term deflections of pre stressed concretemembers ?Explain the importance of creep of concrete in long tenn deflections of prestressed

6) . Exptain with sketcles the effect of varying the ratio of depth anchorage to the depth of endblock on the distribution ofbursting tgnsion.

b) The end block of a pre stressed concrete beam, rectangular in section, is 120 mmwide and-300-mm deep" The pre stressing force of 250kN is transmitted to concreteby.distributiofr plate, i20mm'rvid" unJ 7r '"* ;",p, ;;r;;;i;;iil"i;.uiJu, ,r,"ends. Calculate the position artd magnitude of the maximum tensile stress on thehorizontal section through the centre of the end block using the Guyon method.Yield stress in steel = 260 N/mm2.

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