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ESE 2021 Technical Quiz || Prestressed Concrete - 1

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Question 1

A pre stressed concrete beam is provided with a parabolic tendons as shown in figure. Which is tensioned from both the ends. If the stress in the tendons at the ends in 2000 N/mm2. Calculate the loss of pre stress from the ends to the centre.

Take, μ = 0.035 and K = 0.0015 per metre.

Question 2

If the loading on a simply supported prestressed concrete beam is uniformly distributed, the centroid for the pre-stressing tendon should be as

Question 3

A concrete beam prestressed with a parabolic tendon is shown in the sketch. The eccentricity of the tendon is measured from the centroid of the cross–section. The applied prestressing force at service is 1620 kN. The uniformly distributed load of 45 kN/m includes the self–weight.

The stress (in N/mm2) in the bottom fibre at mid–span is

Question 4

A prestressed concrete beam (pretensioned) has the following cross section as shown in figure below. Initial prestress = 1200 N/mm2 (in both wires).

Young’s modulus of steel, ES = 210 × 103 N/mm2, Young’s modulus of concrete, EC = 36 × 103 N/mm2
What will be the loss of pre-stress (in N/mm2) in top steel wires due to elastic shortening?
[Assume moment of Inertia about centroid axis = 8575 × 106 mm4]

Question 5

Which of the following assumptions regarding pre-stressed concrete are CORRECT?
A- Plane section before bending remains plane after bending
B- Hooke’s law is applicable to steel and concrete within the limit of elasticity.
C- The stresses in tendon does not change along the length.
D- Variation of stresses in tendon due to change in external loading is considered.
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