4. Definition
A couple is system of forces that consists of
two parallel forces that has equal magnitude,
oppositely directed and do not act in a straight
line but are separated by a perpendicular
distance.
6. Expressions
The magnitude of the couple is
given by
F
C=Fd
d
Here, F are the two forces
and d is the perpendicular
distance between the forces
or is the moment arm.
F
7. Properties
Couple does not produce any translational
movement but rotational.
The resultant force of a couple is zero. but the
resultant moment is not zero.
8. Properties
Couple is independent of the moment center.
d’
F
The moment of couple about
d
the point A,
M(A)
A
d’’
F
= +F*d” – F*d’
M(A)
= +F(d”-d’)
M(A)
= +Fd
**[Anti-clockwise= +ve]
9. Is Torque and Couple same thing?
In engineering mechanics, torque is the resultant moment of
a couple.
In general physics, it represents the moment of a force.
Expression: t or C= Force * perpendicular distance
10. Couple in Reinforced Concrete
The concept of couple is consider in reinforced concrete
member.
Here, reinforcement takes tension and concrete takes the
compression so the two materials form a resisting couple
against the external moment
acting on the member.
11. Couple in Pre-stressed Concrete
One of the general principal of pre-stressed Concrete is
directly governed by the concept of Couple.
In this type of member, by pre-stretching and anchoring
the steel in the bottom of concrete member, we produce
compressive stress in bottom fiber and tensile stress in top
fiber. So when a external load act on that member and try
deflect it downward, the internal resisting couple generated
by high-strength steel counter that force.
