Answer ALL Questions
PART A – (10 x 2
= 20 Marks)
1. Define Prestress
2. Draw the deflected shape
diagram the following cases a) parapolic
tendons (centroidal axis) b) pointed
tendon or sloped tendon
3. What is meant by deflection
4. Define thrust live of beam
5. Write the deflection formula
for simply support with mid point load (external load)
6.What is the value of young
modulus of steel and concrete.
7.DefineAnchortage.
8. Define long time deflection
9. Define Grouting
10. Draw the diagram of spacing
of Groups of Cables.
PART B
(5x16=80Marks)
1. A rectangular concrete beam
250 mm wide by 300 mm deep is prestressed by a force of 450 KN at a constant
eccentricity of 60 mm. T he beam supports a concentrated load of 68 KN at the
centre of a span of 3 m. Determine the location of the pressure line at the
centre, quarter span and support sections of the beam. Neglect the Self weight
of the beam.
2. A Prestressed concrete beam
supports a live load of 4 KN/m over a simply supported span of 8 m. The beam
has an I- section with an overall depth of 400 mm. The thickness of the flange
and web are 60 and 80 mm, respectively. The width of the flange is 200 mm. The
beam is to be prestressed by an effective prestressing force of 235 KN at a
suitable eccentricity such that the resultant stress at the soffit of the beam
at the centre of the span is zero. a)
Tind the eccentricity required for the force. b) If the tendon is concentric,
what should be the magnitude of the prestressing force for the resultant stress
to be zero at the bottom fibre of the central span section.
3. A Pretensioned beam, 200 mm
wide and 300 mm deep, is prestressed by 10 wires of 7 mm diameter initially
stressed to 1200 N/
,
with their centroids located 100 mm from the soffit. Find the maximum stress in
concrete immediately after transfer, allowing only for elastic shortening of
concrete.
If the concrete undergoes a further shortening
due to creep and shrinkage while there is a relaxation of five percent of steel
stress, estimate the final percentage loss of stress, estimate the final
percentage loss of stress in the wires using the Indian Standard Code IS: 1343 regulations, and the
following data.
4. A rectangular concrete beam of
cross section 150 mm wide and 300 mm deep is simply supported 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 beam at mid span and 125 mm from the top of the
beam at support sections. If the force in the cable is 350 KN/m and the modulus
of elasticity of concrete is 38 KN/
,
Calculate a) The deflection at mid span
when the beam is supporting its own weight,
b) The concentrated load which must be applied at mid span to restore it
to the level of supports.
5. .An
unsymmetrical I-section beam is used to
support an imposed load of 2 KN/m over a span of 8m. The sectional details are top flange ,300mm wide and 60mm
thick,bottom flange,100mm wide and 60mm
thick ,thickness of the web equal to 80mm,overall depth of the beam equal to
400mm. At the centre of the span, the effective prestressing force of 100KN is
located at 50mm from the soffit of the beam. Estimate the stresses at the centre of the span section of the beam
for the following load conditions:1. Prestress +self weight
2.Prestress+self
weight +live load
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