Beam Supports & Equilibrium Equations
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Questions and Answers

Match each support type with its corresponding description:

Simply Supported = A beam resting on supports at both ends, allowing rotation but resisting vertical movement. Cantilever = A beam fixed at one end and free at the other, resisting both rotation and vertical movement at the fixed end. Overhanging = A beam that extends beyond its supports, creating both a simply supported section and a cantilevered section.

Which of the following statements accurately describes the behavior of a simply supported beam?

  • It is fixed at one end and free at the other.
  • It is rigidly fixed at both ends, preventing rotation and vertical movement.
  • It extends beyond its supports, creating a cantilevered section.
  • It is supported at both ends, allowing rotation but resisting vertical movement. (correct)

A cantilever beam is characterized by being supported at both ends, similar to a bridge.

False (B)

Describe the primary difference between a statically determinate and statically indeterminate structure.

<p>Determinate structures can be fully analyzed using statics equations alone; indeterminate structures require additional compatibility equations.</p> Signup and view all the answers

For a structure to be statically __________, the number of unknown reactions must be less than or equal to the number of equilibrium equations.

<p>determinate</p> Signup and view all the answers

What condition defines an unstable structure in terms of reactions (R) and number of equilibrium equations (N)?

<p>$3N &gt; R$ (C)</p> Signup and view all the answers

Improperly constrained structures always maintain stability regardless of load application.

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

Explain why a structure is considered 'improperly constrained' when force reactions converge at a single point.

<p>Convergence at a single point means the reactions cannot independently resist all potential loading scenarios, leading to instability.</p> Signup and view all the answers

A ________ support resists both vertical and horizontal forces but allows rotation, whereas a fixed support resists vertical and horizontal forces and also prevents ________.

<p>pinned, rotation</p> Signup and view all the answers

For a 2D problem, how many independent equilibrium equations can be applied to solve for unknown forces and moments?

<p>3 (B)</p> Signup and view all the answers

In a rigid frame, joints are assumed to allow free rotation without transferring any moment.

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

Define the term 'hinge' within the context of structural analysis and explain its effect on moment transfer.

<p>A hinge is a structural connection that allows rotation but does not transmit moment. It introduces an internal zero-moment condition.</p> Signup and view all the answers

The determinacy of a structure is evaluated by comparing the number of unknowns (reactions) with the number of available __________ __________.

<p>equilibrium equations</p> Signup and view all the answers

Which type of support is most suitable for allowing thermal expansion of a long beam without inducing significant stress?

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

A statically indeterminate structure will always experience lower stresses compared to a statically determinate structure under the same loading conditions.

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

Flashcards

Roller Support

A support that resists vertical forces but allows rotation. It has one unknown reaction force.

Pinned Support

A support that resists both vertical and horizontal forces, but allows rotation. It has two unknown reaction forces.

Fixed Support

A support that resists vertical and horizontal forces and prevents rotation. It has three unknown reaction forces.

Simply Supported Beam

A beam supported at both ends, free to rotate at the supports.

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Cantilever Beam

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

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Overhanging Beam

A beam that extends beyond one or both of its supports.

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Statically Determinate

The condition where the number of unknown reactions equals the number of equilibrium equations.

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Statically Unstable

The condition where the number of unknown reactions is less than the number of equilibrium equations.

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Statically Indeterminate

The condition where the number of unknown reactions is greater than the number of equilibrium equations.

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Improperly Constrained

A structural system where all force reactions converge at one point.

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Study Notes

  • There are three types of supports for beams: simply supported, cantilever, and overhanging.

Homework 5 & 6

  • Problem 2.29, which is similar to problem 2.28 and considers joint C, involves calculating forces by setting the sum of forces in the x and y directions to zero.
  • Trigonometric functions are used to resolve forces into x and y components to solve for unknown forces Sca and Scb.
  • Problem 2.30 discusses a eyebolt in equilibrium, and it's analyzed as a point in space.
  • Two unknowns, P and α, can thus be solved with two equilibrium equations ΣFx=0 and ΣFy=0.
  • Problem considers joint A, resolving forces and then solving for an angle.

Reading assignment

  • Book 1 includes pages 84-94.
  • Book 2 includes chapter 13.

Determinacy and Stability

  • There are three equations of equilibrium in a 2D problem: ΣFx=0, ΣFy=0, and ΣM=0.
  • The total number of unknowns equals R = R' + 2 x the number of hinges, and the number of equilibrium equations is 3 x N.
  • Reactions with equations of equilibrium are determinate when 3N = R (statically determined).
  • A structure is statistically determinate if this is the case.
  • Rigid body moves and will not stand if 3N > R (unstable).
  • Equations of equilibrium alone aren't enough if 3N < R (statically indeterminate).
  • Compatibility equations are used in this case.
  • Instability can result from improper constraints, which is also when force reactions converge at one point.

Homework 7

  • Refers to the provided link
  • Using the video to define a roller, pinned and fixed supports

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Description

Exploration of beam supports (simply supported, cantilever, overhanging) and equilibrium equations (ΣFx=0, ΣFy=0, ΣM=0) in 2D problems. Includes homework problem-solving with trigonometric functions and joint analysis. Reading assignment spans pages 84-94 of Book 1 and chapter 13 of Book 2.

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