Structures I Week 1 Principles of Statics

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Structures I - Week 1 Principles of Statics
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Structures 1 - Week 1 Principles of Statics -
Revision

• Equilibrium
• Properties of Forces
• Concurrent Forces
• Non-concurrent Forces
• Resolution of Forces
• Moment of a Force
• Couples
• Equivalent Force Systems

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Structure

• A body at rest or in a state of
• static equilibrium
• under the action of a force system

Function of a Structure
To support loads or to transmit loads to the
Ground
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Properties of Forces
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Quiz

• Question
• If there are only two forces acting on a body
  and the body does not move, suggest what
  conditions must be satisfied by those forces

• Answer
• They must be equal
• They must be opposite
• in direction
• They must be collinear

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Concurrent ForcesAddition - Resultant /
Equilibrant

• Graphical Solution for 2 forces (parallelogram or
  triangle of forces)
• Mathematical Solution for 2 forces
• Graphical Solution for 3 or more forces

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If three coplanar non-parallel forces are in
equilibrium then they must be concurrent

• Example

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Non-concurrent ForcesAddition

• Graphical Solution for 3 or more forces

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Resolution of Forces

• Examples

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Moment of a Force

• Rotational effect of a force applied at a
  distance (lever arm) from a given point or axis
• Example

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Couples

• A couple consists of two forces
• equal in magnitude
• parallel
• opposite in direction
• A couple has the same value of moment about any
  point or any axis

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Equivalent Force Systems

• Two co-planar force systems are equivalent when
• a) they produce the same resultant forces in two
  mutually perpendicular directions and
• b) they produce the same moment about any chosen
  point or axis
• e.g. eccentrically applied load

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Resources
www.civl.port.ac.uk

• Megson T.H.G. , (1996), Structural and Stress
  Analysis, Arnold
• Croxton P.C.L., Martin L.H. (1987), Solving
  Problems in Structures, Vol..1, Longman
• Cain J., Hulse R. (1990) Structural Mechanics,
  Macmillan
• Marshall W.T., Nelson H.M., (1990), Structures,
  3rd Edition, Longman