Structural Form
The part of a structure that must transmit applied loads is the structural system.
The mode of transmission is a function of geometrical configuration, or form.
The basic modes, or “actions” may be:
Tension
Compression
Flexure (Bending)
Shear
[Torsion (Twisting, Shear)]
These may be combined in many structural forms, as seen in the following examples:
Notes: Structural Actions, Form and Systems
1
Basic Structural Elements: Tension—The Tie Rod
• Single, axial-force element
• Studied in ENGRD 202
Godden, B47
Idealized
Real
Notes: Structural Actions, Form and Systems
2
Basic Structural Elements: Tension--The Cable
• Single, axial, tensile force element
• Form-active
Idealized
Real
Notes: Structural Actions, Form and Systems
3
Idealized
Basic Structural Elements:
Compression--The Column
• Multiple Force: Axial, Shear, Moment
• Studied in ENGRD 202
Column
Beam-Column
Metallic Shapes
Godden, F43
Real
RC Shapes
Notes: Structural Actions, Form and Systems
4
Basic Structural Elements: Compression--The Arch
• Can be single force = Funicular, or...
• Multiple Force: Axial, Shear, Moment
• Can Have 1, 2, or 3 Hinges
Idealized
RC Arch
No Hinges
Godden, B28
Real: 3 Hinges
Notes: Structural Actions, Form and Systems
5
Idealized
Basic Structural Elements:
Flexure--The Beam
Beam: A Multiple Force Element
Simply Supported
• Multiple Force: Shear, Moment, Axial
• Studied in ENGRD 202
Cantilever
Fixed-Fixed
Multiple span continuous
Godden A56
Tapered/Haunched
Built-Up
Real
Notes: Structural Actions, Form and Systems
6
Basic Elements May Be Simplifications
of 2D and 3D Surface Elements
1D Rod [Shear on non-orthogonal section]
2D Plate in Biaxial Tension (“Plane Stress”)
[Note: if S1  S2, shear will be present]
Notes: Structural Actions, Form and Systems
7
Basic Elements May Be Simplifications
of 2D and 3D Surface Elements
Idealized
1D Beam
[Torsion?]
Godden, F80
Real
2D Plate in Bending
[Twisting possible]Notes: Structural Actions, Form and Systems
8
Basic Elements May Be Simplifications
of 2D and 3D Surface Elements
Idealized
Cable
Godden, E35.3
Real
Pressure Vessel/Membrane
Notes: Structural Actions, Form and Systems
9
Basic Elements Are Simplifications
of 2D and 3D Surface Elements
Idealized
Arch
Godden E35.1
Real
Shell:eg. Dome
Notes: Structural Actions, Form and Systems
10
It May Not Be Feasible/Useful to Simplify Complicated Solids
Real Gear
Idealized Transmission
Represented with Finite Elements
Idealized Geometry
Model of Gear
Notes: Structural Actions, Form and Systems
11
Basic Elements Can Be Combined Into Structural Systems
Beams + Columns = Frame
Godden, F64
Idealized
Notes: Structural Actions, Form and Systems
Real
12
Basic Elements Can Be Combined Into Structural Systems
Tie Rods + Columns = Truss
Idealized
Real
Notes: Structural Actions, Form and Systems
13
Basic Elements Can Be Combined Into Structural Systems
Beam/columns + shell = aircraft fuselage
Idealized Section
Represented with Finite Elements
Real
Notes: Structural Actions, Form and Systems
14
Some Planar Structural Systems
Are Simplifications of 3D Systems
Idealized
Plane Truss
Godden, D67
Real
Space Truss
Notes: Structural Actions, Form and Systems
15
Some Planar Structural Systems
Are Simplifications of 3D Systems
Idealized
Plane Frame
Godden, F62
Real
Space Frame
Notes: Structural Actions, Form and Systems
16