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Posted Date: 01 Jul 2009 Posted By: Sunil Reddy Member Level: Platinum
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2009 Jawaharlal Nehru Technological University Civil Engineering IV B.Tech II Semester Regular Examinations, April/May 2009 JNTU Kakinada, PRESTRESSED CONCRETE Question paper
Code No: 2420105
IV B. Tech II Semester Regular Examinations, April/May 2009
PRESTRESSED CONCRETE
(Civil Engineering )
Time: 3 Hours Max. Marks 80
Answer any FIVE questions
All questions carry equal marks
********
1. (a) Differentiate between full prestressing and partial prestressing
(b) What are the factors influencing the creep and shrinkage of concrete?
2. (a) Explain the principle of post – tensioning.
(b) A prestressed concrete beam of rectangular cross section 300mm by
600mm is 12m long supports a live load 12 KN/m in addition to its own Self weight and
stressed to 800 N/mm2 .The cable is straight and located at a distance of 175mm from
the soffit of the beam. Determine the shift in the pressure line at one quarter span and
centre of span, when the beam Supports the service load.
3. (a) How do you compute the loss of stress in steel due to curvature and wobble Effect?
(b) A prestressed concrete girder is post-tensioned using a cable concentric at Supports
and having an eccentricity of 400mm at centre of span. The effective span of the girder is
25 m. the initial force in the cable is 400KN at the jacking end A. Determine the loss of
force in the cable due to friction and wave effect and the effective force in the cable at
farther end B. Assume coefficient of friction µ=0.30 and coefficient for wave effect
k=0.0043/m .
4. A post-tensioned bonded beam of rectangular section 300mm wide by 650mm deep
is stressed by 800 mm2 of high –tensile steel at an effective depth of 600 mm . The beam
is provided with two 25 m diameter, high-yield strength deformed bars both at the
compressive and tension faces with an effective cover of 50 mm. Given fc=40N/mm2 ,
fp =1600N/mm2, fy=460N/mm2 and (fpy/fpu ) =0.90, estimate the ultimate moment
capacity of the section using American code provisions .
5. Outline the factor influencing the ultimate shear resistance of prestressed
Concrete section with flexure- shear cracks.
6. A high –tensile cable comprising 12 strands of 15 mm diameter (12K15 of p.s.c
freyssinet system) with an effective force of 2500 KN is anchored concentrically in an
end block of a post –tensioned beam. The end block is 400 mm wide by 800 mm deep
and the anchor plate is 200 mm wide by 260 mm deep . Design suitable anchorage
zone reinforcements using fe-415grade HYSD bars using IS: 1343 code provisions.
7. (a) Briefly outline the method of estimating the deflection of composite
members in cases in of
(a) un propped construction and (b) propped construction
(b) Briefly outline the method of computing the ultimate flexural and shear
Strength of composite sections.
8. A concrete beam is prestressed by a parabolic cable having an eccentricity of
e1 towards the soffit at centre of span and an eccentricity of e2 towards the
top near support sections find the ratio of these eccentricities for zero
deflection at centre of span due to prestress only.
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