Formation of Structures
Bars → trusses
Theory and Design of Structures I
Elementary Theory of Structures
Seawall
Blocks → walls
Other examples:
Brick walls
Pyramids, etc.
The design process
Classification
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Classification
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Superimposition
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Actual and Idealized Structures
Actual and Idealized Structures
Actual and Idealized Structures
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Supports and Reactions
Hinge support
Supports and Reactions
Roller support
R

Supports and Reactions
Fixed support
Supports and Reactions
Clamped roller support
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Supports and Reactions
Elastic support
Joints
Pin joint or hinge joint
Joints
External Forces
Rigid joint
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Internal Forces
Internal Forces
Internal Forces
Free Body Diagrams
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Overall Rigid Body Stability and External Determinacy of
a Planar Structure
2 reaction components: Unstable
3 reaction components:
Stable and statically determinate
4 reaction components:
Stable and statically
indeterminate to the first degree
No. of redundant components of reaction =
degree of statical indeterminacy
Note that there are 3 equations of equilibrium for planar
structures.
Geometric Instability
Geometrically Stable Structure
• A structure is geometrically stable if for any
incipient movement, a resistance to this
movement is developed.
• This requires the presence of at least three
non-concurrent non-parallel forces.
• A structure that has sufficient number of
reactions but incorrectly placed for stability
is geometrically unstable.
Equations of Condition
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External Determinacy
r<c+3
r=c+3
r>c+3
Two-force members
Unstable
Determinate (provided there is no geometric
instability)
Indeterminate
Geometrically Stable Structure
The End
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