Solid Mechanics: Shear Force and Bending Moment

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Questions and Answers

Which type of beam is supported at both ends and is free to rotate?

  • Overhanging Beam
  • Cantilever Beam
  • Simply Supported Beam (correct)
  • Fixed Beam

A beam is subjected to a uniformly distributed load (UDL). How does the shear force vary along the length of the beam?

  • Parabolically
  • Cubically
  • Constant
  • Linearly (correct)

What is the sign convention for shear force if the resultant of the forces to the left of the section is upward?

  • Zero
  • Negative
  • Unpredictable
  • Positive (correct)

In pure bending, what is the value of shear force?

<p>Zero (D)</p> Signup and view all the answers

For a cantilever beam with a point load at the free end, how does the bending moment vary along its length?

<p>Linearly (A)</p> Signup and view all the answers

A simply supported beam has a concentrated load at its center. What are the reactions at the supports?

<p>Half of the load (B)</p> Signup and view all the answers

What type of loading is represented by 'UVL'?

<p>Uniformly Varying Load (A)</p> Signup and view all the answers

If a beam deflects such that the top fibers are in compression and the bottom fibers are in tension, what type of bending moment is it experiencing?

<p>Sagging (C)</p> Signup and view all the answers

Under what condition is a beam said to be in a state of pure bending?

<p>Shear forces are zero (A)</p> Signup and view all the answers

A cantilever beam of length L carries a point load W at the free end. What is the bending moment at the fixed end?

<p>$W \times L$ (B)</p> Signup and view all the answers

What is the bending moment at the free end of a cantilever beam?

<p>Zero (B)</p> Signup and view all the answers

For a simply supported beam with a uniformly distributed load (UDL) of 'w' per unit length over the entire span 'L', what is the maximum bending moment?

<p>$wL^2/8$ (B)</p> Signup and view all the answers

What is the characteristic of a 'fixed' beam?

<p>No rotation at supports (D)</p> Signup and view all the answers

Which of the following is true for an overhanging beam?

<p>It extends beyond one or both supports. (B)</p> Signup and view all the answers

How is the bending moment calculated?

<p>The product of the force and the perpendicular distance from the section. (D)</p> Signup and view all the answers

What does a bending moment diagram (BMD) represent?

<p>Variation of bending moment along the beam. (C)</p> Signup and view all the answers

Which type of beam has more than two supports along its length?

<p>Continuous Beam (B)</p> Signup and view all the answers

For a uniformly varying load (UVL) on a beam, how does the intensity of the load change?

<p>Changes linearly (B)</p> Signup and view all the answers

What does a positive bending moment typically indicate?

<p>Sagging (C)</p> Signup and view all the answers

How is shear force related to the load applied on a beam?

<p>Shear force is the integral of the load. (B)</p> Signup and view all the answers

If the bending moment is constant over a certain length of a beam, what does that signify about the shear force in that region?

<p>Shear force is zero. (C)</p> Signup and view all the answers

Which of the following diagrams helps in visualizing the internal forces in a beam?

<p>Shear Force and Bending Moment Diagram (A)</p> Signup and view all the answers

What is the correct expression for the relationship between bending moment (M), shear force (V), and distributed load (w)?

<p>$V = dM/dx $ (C)</p> Signup and view all the answers

What causes hogging in a beam?

<p>A negative bending moment (B)</p> Signup and view all the answers

How does the bending moment at a section affect the stress distribution across the cross-section?

<p>Bending moment causes linearly varying stress (D)</p> Signup and view all the answers

A beam of length 'L' is fixed at both ends and carries a uniformly distributed load 'w' per unit length. What is the bending moment at the supports?

<p>$wL^2/12$ (A)</p> Signup and view all the answers

Which of the following loads causes only shear force in a beam but no bending moment?

<p>Transverse load (D)</p> Signup and view all the answers

For a pure bending condition in a beam, what is consistent along the length of the beam?

<p>Bending moment (B)</p> Signup and view all the answers

Which support type provides both horizontal and vertical reaction forces as well as a moment reaction?

<p>Fixed Support (A)</p> Signup and view all the answers

Flashcards

Shear force and bending moment diagrams

Diagrams showing the variation of shear force and bending moment along the length of a beam.

Simply supported beam

A beam supported at both ends.

Cantilever beam

A beam fixed at one end and free at the other.

Overhanging beam

A beam extending beyond its supports.

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Continuous beam

A beam supported by multiple supports.

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Point load

Types of force concetrated at a single point.

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Uniformly Distributed Load (UDL)

Force evenly, equally distributed over a length.

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Uniformly Varying Load (UVL)

Load uniformly changing, varying, increasing or decreasing intensity along length

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Positive Shear Force

Shear force is positive if the resultant of forces to the left of the section is upward.

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Sagging Bending Moment

If beam bends downwards (like a smile).

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Hogging Bending Moment

If a beam bends upwards (like a frown).

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Pure Bending

Condition where shear forces are zero across a beam's cross-section, subjected only to constant bending moment.

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Study Notes

  • MEC201 Solid Mechanics, Unit 4 focuses on shear force and bending moment.
  • Diagrams are used to represent the variation of shear force (SF) and bending moment (BM) along a beam's length.

Types Of Beams

  • Cantilever beams have one end fixed and the other end free.
  • Simply supported beams are supported at both ends.
  • Overhanging beams extend beyond one or both supports.
  • Fixed beams are supported/fixed at both ends.
  • Continuous beams have more than two supports.

Types Of Loads

  • Point loads (i.e W(N)) are concentrated at a single point.
  • Uniformly Distributed Loads (UDL) are evenly spread across a section of the beam, measured in N/m.
  • Uniformly Varying Loads (UVL) increase (or decrease) linearly across the section.

Sign Conventions

  • Shear force is considered positive if the resultant of forces to the left of a section act upwards.
  • Bending moment is positive if it causes sagging (i.e. "happy" curvature).
  • Bending moment is negative if it causes hogging (i.e. "sad" curvature).

Hogging

  • A negative bending moment results in hogging.

Sagging

  • A positive bending moment results in sagging.

Pure Bending

  • A beam is in a state of pure bending when shear forces are zero across any cross-section perpendicular to its longitudinal axis.
  • This implies F = 0, and dM/dX = F = 0
  • Thus, M is constant.

Shear Force & Bending Moment Diagrams for Cantilever Beams with Point Loads

  • Key aspects to note are the specific calculations and shapes of the diagrams for cantilever beams under point loads, UDLs, and UVLs to accurately represent internal forces and moments.

Uniformly Distributed Load (UDL)

  • Focus on how to calculate SFD and BMD.

Uniformly Varying Load (UVL)

  • Focus on how to calculate SFD and BMD.

Simply Supported Beam

  • First find the reaction forces and mark them on the diagram.
  • Bending moment at points A & B is zero.

Overhanging Beam Notes

  • Bending moment at points C and E is zero.

Simply Supported Beam with Moment Couple Notes

  • Focus on how to calculate SFD and BMD.

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