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9. Beams Subjected to a Moment

Beams subjected to a moment are a vital consideration in structural analysis and design, as they involve the rotational forces that can significantly impact the stability and safety of various structures. A moment, often referred to as a bending moment, is the force that causes a beam to rotate about a specific axis, inducing internal stresses that must be accounted for in the design process.

Idea

Example 1

A simply supported beam of span \(2.5\ m\) is subjected to a uniformly distributed load and a clockwise couple as shown in Figure 34. Draw the shear force and bending moment diagrams for the beam. \(x_2 = x_3 = 1 m\), \(W_1 = 2 kN/m\), \(W_2 = 2 kNm\).

clockwise-couple-1q
Figure 34. Clockwise couple.
Solution:
clockwise-couple-1a
Figure 35. Clockwise couple.

Idea

Assignment 1

Analyse the beam shown in Figure 36 and draw the bending moment and shear force diagrams. Locate the points of contraflexure, if any. \(x_1=x_2=2.5 m\), \(x_3=4m\), \(x_4 = 1m\), \(\theta = 30^{\circ}\), \(W_1=6.5 kN\), \(W_2=1.5 kN/m\), \(W_3 = 3 kN\)

inclined-load-1q
Figure 36. Inclined load.
Solution:

Please attempt this assignment.

Idea

Assignment 2

A horizontal beam \(6\ m\) long is loaded as shown in Figure 37. Draw the shear force, bending moment and thrust diagrams for the beam. \(W_1\ =\ 5 kN, \theta_1\ =\ 35^{\circ},\ x_1\ =\ 1\ m,\) \(\ W_2\ =\ 6 kN, \theta_2\ =\ 40^{\circ},\ x_2\ =\ 1.5\ m,\) \(\ W_3\ =\ 7 kN, \theta_3\ =\ 55^{\circ},\ x_3\ =\ 2\ m,\ x_4\ =\ 1.5\ m\)

inclined-load-2
Figure 37. Inclined load.
Solution:

Please attempt this assignment.

Idea

Assignment 3

A horizontal beam \(x_1\ =\ 11\ m\) long is carrying a uniformly distributed load of \(W_1\ =\ 1.5\ kN / m\). The beam is supported on two supports \(x_3\ =\ 6\ m\) apart. Find the position of the supports, so that bending moment on the beam is as small as possible. Also draw the shear force and bending moment diagrams.

simply-supported-distributed-load-1
Figure 38. Simply supported beam with a distributed load.
Solution:

Please attempt this assignment.



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Comments (7)

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Brenda

Ae we doing chapters 6, 7, 8 & 9?

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Dr. Sam

No. That's for Solid II.

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Elsie

Kindly confirm for us the formula for volumetric strain

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Brenda

Hello, are the notes here all we will have for SSM2 or is there a possibility for addition?

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Dr. Sam

Solid Mechanics II starts from chapter 6.

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Robert

Could you confirm if in example 1 the shear force diagram is correct since from my shear force calculations the forces are positive meaning the diagram ought to be upwards

(Edited)
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Dr. Sam

Yes, in example 1, the shear force diagram is correct. There are two point loads acting downwards, which tend to shear the bar in the negative direction.