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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) What is the basic principle of prestressed Concrete?
(b) What are the main factors influencing the design of high strength concrete mixes?
2. (a) List the various types of tensioning devices used in prestressed concrete.
(b) A concrete beam with a double overhang has the middle-span equal to 10m and the
equal overhang on either side is 2.5m. Determining the profile of the prestressing cable
with an effective force of 250KN which can balance a uniformly distributed load of
8KN/m on the beam, which includes the self-weight of the beam. Sketch the cable profile
making the eccentricity of cable at the support and mid span.
3. (a) List the various types of loss of prestress in pretensioned and post-tensioned members.
(b) A post-tensioned cable of beam 10m long is Initially tensioned to a stress of
1000N/mm2 at one end. If the tendons are curved so that the slope is 1 in 15 at each end
with an area of 600 mm2, calculate the loss of prestress due to friction, given the
following data:
Coefficient of friction between duct and cable = 0.55; friction coefficient for wave effect
= 0.0015/m during anchoring, If there is a slip of 3 mm at the jacking end, calculate the
final force in the cable and the percentage loss of prestress due to friction and slip.
4. A double T-Section having a flange 1200 mm wide and 150 mm thick is prestressed by
4700 mm2 of high-tensile steel located at an effective depth of 1600 mm. The ribs have
a thickness of 150 mm each. If the cube strength of concrete is 40 N/mm2 and tensile
strength of steel is 1600 N/mm2, determine the flexural strength of the double T-girder
using IS:1343 provisions
5. What are the different ways of improving the shear resistance of structural concrete
members by prestressing techniques?
6. A Freyssinet Anchorage (125mm diameter), carrying 12 wires of 7mm diameter stressed
to 950 N/mm2, is embedded concentrically in the web of an I-section beam at the ends.
The thickness of the Web is 225mm. Evaluate the maximum tensile stress and the
bursting tensile force in the end block using Rowe’s methods. Design the reinforcement
for the end block.
7. (a) What are the advantages of using composite construction with prestressed and in situ
concrete in structural members.
(b) Sketch some typical cross-sections of composite bridges decks with precast
prestressed elements.
8. (a) Distinguish clearly between short-term and long term deflections of prestressed
concrete beams.
(b) Briefly explain the importance of creep of concrete in long term deflections of
prestressed members.
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