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Posted By: Sri Member Level: Gold Posted Date: 13 Dec 2007
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2005 Jawaharlal Nehru Technological University B.Tech Civil Engineering III/Sem1 Regular (NOV'05)Set 1,Concrete Technology and Prestressed Concrete Question paper
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Code No: RR310101 Set No.1
III B.Tech. I Semester Regular Examinations, November -2005
CONCRETE TECHNOLOGY AND PRESTRESSED CONCRETE
(Civil Engineering)
Time: 3 hours Max Marks: 80
Answer any FIVE Questions
All Questions carry equal marks
1. (a) Discuss the chemical composition of ordinary Portland cement.
(b) What are the Indian Standard specifications as per I.S. 269-1989 for 33 grade
ordinary Portland cement with respect to chemical requirements. [8+8]
2. (a) What is fineness modulus of aggregates? What does it indicates?
(b) In laboratory explain how you will conduct test to obtain fineness modulus of
aggregates? [8+8]
3. (a) How does the maximum size of coarse aggregate affects the strength of Hardened concrete.
(b) Laboratory experiments conducted in Mumbai on a particular mix showed a strength of 33 MP a for a fully matured concrete. Find whether form worm can be removed for an identical concrete placed at Jammu at the age of 15 days when the average temperature is 60C. The stripping stress in concrete may be taken as 25 Mpa. The Plowman’s Constants may be assumed as 21
and 61. [8+8]
4. (a) Discuss the various requirements as per ACI method, for w/c ratio and strength
for special exposure conditions.
(b) Discuss the various factors in the choice of Mix Proportions. [8+8]
5. (a) Give the classification of the various methods and systems of prestressing.
(b) With the help of neat sketches explain any one method of pre-tensioning and
post-tensioning. [8+8]
6. (a) A straight post-tensioned concrete member 14m long with a cross-sectional area 920mm2. This steel is made of four tendons with 230mm2 per tendon. The tendons are tensioned to a stress of 1200N/mm2. determine the loss of prestress in each tendon due to elastic shortening of concrete. Find also the average percentage loss of prestress. If it is desired that after the last tendon is tightened a stress of 1200N/mm2. be maintained in each tendon, 6. compute
the actual stresses to which the individual tendous should be tightened m=6
(b) Determine the loss of stress in tendons due to shrinkage of concrete in a post-
tensioned beam if the age of concrete at transfer is 28 days. Take ES =
207kN/mm2. [8+8]
7. Design a prestressed concrete beam to the following requirements:
(a) Span : 15 m
(b) Superimposed load : 34 KN/m
(c) Cube strength of concrete at 28 days : 35N/mm2
(d) Safe stress in concrete at transfer of prestress fs : 0.5fck
(e) Safe stress in concrete due to final prestress fc : 0.4 fck
(f) Total loss of prestress : 20%
(g) Allowable tensile stress in concrete : 0.129 pfck
(h) Ultimate stress in steel: 1500N/mm2
(i) Safe stress in steel : 60 % ultimate stress [16]
8. A prestressed concrete beam section has the sectional properties and the stresses
as follows:
Width of Top flange : 2400 mm
Depth of Top flange : 400 mm
Web width : 600 mm
Depth of web : 1000 mm
Width of bottom flange : 1200 mm
Depth of bottom flange : 900 mm
Max bending stress at top fibre : 13N/mm2
Max bending stress at bottom fibre : 0N/mm2
Shear stress at Neutral axis : 2.36N/mm2
Shear stress at Junction of web and bottom flange : 2.26N/mm2
The total vertical shear in concrete at the section is 2360 KN. Find the principal
tensile stress at the centroidal axis and at the Junction of the web with the lower
flange. [16]
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