Font size
WorksheetsDay 107-Jan 16-worksheet-Btech-Prestressed concrete 3
Total questions: 15
Worksheet time: 11mins
In a prestressed concrete beam, if the net loss of prestress is 10% and the final prestressing force is 750 kN, the initial prestressing force is
(a)
In post-tensioned members, prestress loss due to friction depends mainly on
Age of concrete only
Shrinkage strain
Curvature and wobble of tendon
Anchorage slip only
For a parabolic cable with zero eccentricity at supports, maximum friction loss occurs
At mid-span
At jacking end
At unjacked end
Uniformly along the span
The minimum grade of concrete specified for pretensioned prestressed concrete is
M20
M30
M40
M45
Which of the following losses occurs only in post-tensioned concrete members?
Shrinkage loss
Creep loss
Anchorage slip loss
Relaxation loss
The typical diameter of wires used in pretensioning system is
12–15 mm
10–12 mm
5–8 mm
2–3 mm
Friction loss of prestress occurs
Only in pretensioned beams
Only in post-tensioned beams
In both pre-tensioned and post-tensioned beams
Only under external loading
Net percentage loss of prestress is generally higher in pretensioned members than in post-tensioned members.
True
False
Anchorage slip is classified as a long-term loss of prestress.
True
False
Assertion (A): Friction loss of prestress is higher near the unjacked end in a one-end jacked cable. Reason (R): Prestressing force reduces exponentially along the length due to wobble and curvature effects.
A and R are true and R explains A
A and R are true but R does not explain A
A is true and R is false
A is false and R is true
Maximum loss of prestress in one-end jacking occurs at the (a) end.
A post-tensioned beam has an unjacked-end prestress of 800 MPa. Given K = 0.003/m, μ = 0.5, span = 8 m, and mid-span eccentricity = 125 mm. Calculate the percentage loss of prestress due to friction.
(a)
Part E – Numerical Questions. A prestressed beam has a final prestressing force of 800 kN after a net loss of 9%. Calculate the initial prestressing force.
(a)
. A 6 m long simply supported prestressed beam carries a uniformly distributed load of 6 kN/m. Effective EI = 2×104 kN·m 2 , effective prestressing force = 200 kN, cable eccentricity = 50 mm. Calculate the net increase in length of the prestressing cable.
(a)
Choose immediate losses from these
-Anchorage slip
-Friction-loss
-Relaxation
-Shrinkage
(a)
