# Strength of Materials Questions and Answers – Polar Modulus and Torsional Rigidity

This set of Strength of Materials Multiple Choice Questions & Answers (MCQs) focuses on “Polar Modulus and Torsional Rigidity”.

1. A circular shaft of diameter 30 mm is tested under torsion the gauge length of test specimen is 300 mm. A torque of 2kNm produces an angle twist of 1°. Calculate CJ.
a) 0.432 × 106 N/mm2
b) 0.324 × 106 N/mm2
c) 0.46 × 106 N/mm2
d) 0.532 × 106 N/mm2

Explanation: Angle of twist = 1° = π/180 radians.
Polar moment of inertia = π/32 × 304mm4.
To find CJ: T/J =C× twist angle
C = Tl/J×twist angle = 2×106 ×300 / π/32 × 304mm4× π/180.
C = 0.4323 × 106 N/mm2.

2. __________ has perfect control on river flow.
a) Barrage
b) Weir
c) Marginal bunds
d) Guide banks

Explanation: Barrages are much more costly than weirs. Gates are raised off the high flood to pass floods. They have perfect control of the river flow.

3. When the gross length is more than 6 metres between the face of abutment it is called as ________
a) Cause way
b) Bridge
c) Culvert
d) Cassion

Explanation: When the gross length is more than 6 m between the faces of abutment measured at right angles is called a bridge. If a bridge supports a road way over a railway then it is called Road over a bridge.

4. The minimum straight approach provided on either side of bridge is ___________
a) 12 m
b) 15 m
c) 20 m
d) 22 m

Explanation: The bridge site should be far away from the confluence of tributaries as far as possible the straight approaches are to be provided on either side of the bridge for at least 15m.

5. ________ should be taken below the deepest scour level.
a) Foundation
b) Sub structure
c) Structure
d) Parapet

Explanation: Foundations to be provided for approaches abutments, piers etc., by considering the water in the river, sub soil conditions etc., a foundation should be taken below the deepest scour level.

6. ___________ formula is used for calculating the depth of the foundation.
a) Gordon’s
b) Rankine’s
c) WH Smith’s
d) Falcon

Explanation: Rankine’s formula is used for calculating the depth of the foundation.
h=P/w × (1-sin/1+sin). Minimum depth is restricted to 90 cms.

7. _______ foundation is used when the depth of water is more.
a) Pile
b) Caisson
c) Raft

Explanation: The caisson foundation is used when the depth of water is more. The spread Foundation is used when good hard soil is available at shallow depth.

8. _____________ foundation is used when bed soil is soft.
a) Raft
b) Pile
d) Well

Explanation: Pile foundation is adopted when the bed soil is soft and hard soil is available at great depth and also the well foundation is adopted when river bed having sand and good soil is available at a reasonable depth.

9. The intermediate support of a bridge superstructure is called as ___________
a) Abutment
b) Pier
c) Wing wall
d) Approach

Explanation: The intermediate support of bridge superstructure for a multi span bridge is called pier.
Functions:
i. To divide the total length of bridge into suitable spans.
ii. To distribute the load from the superstructure of the bridge.

10. ___________ piers are adopted for well foundations.
a) Masonry
b) RCC
c) Dumb bell
d) Pile bent

Explanation: Dumb-bell piers are light in weight as compared to solid piers. These piers are suitable when well foundations are adopted. It consists of two columns connected by web for the full height.

11. _______ piers are used, when the height of pier is large as in case of viaducts, fly overs.
a) Column Bent
b) Pile bent
c) Trestle bent
d) Abutment pier

Explanation: It consists of vertical, horizontal and diagonal members. Trestle bents may be of steel or concrete. These piers are suitable when the height of pier is large as in case of viaducts.

12. The projection of the piers on the upstream side is known as ________
a) Cut waters
b) Ease waters
c) Sharp waters
d) Para waters

Explanation: The projection of the piers on the upstream side is known as cut waters. The cut waters are provided for easy passage of water. The shape may be triangular, semi-circular & parabolic etc.

13. The end support of a bridge is __________
a) Pier
b) Abutment
c) Wing wall
d) Approach

Explanation: The end support of a bridge superstructure is known as an abutment. The functions of abutment are
i. To retain the earth filling of approaches
ii. To finish up the bridge with necessary approaches.

14. The projection of the pier on the downstream side is known as ________
a) Ease water
b) Cut water
c) Bridge pier
d) Dumb pier

Explanation: The projection of the pier on the downstream side is known as “ease waters”. They prevent the formation of eddies and their scouring effect.

15. ____________ piers are suitable when foundations are of steel cylinder caisson type.
a) Masonry
b) Trestle bent
c) Cylindrical
d) Pile

Explanation: Cylindrical piers are made of mild steel filled with concrete and connected by horizontal and diagonal steel bearings. These are suitable when foundations of Steel cylinder caisson type.

Sanfoundry Global Education & Learning Series – Strength of Materials.

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