1. 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

2. Notes: Structural Actions, Form and Systems
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

3. Notes: Structural Actions, Form and Systems
Basic Structural Elements: Tension--The Cable
Single, axial, tensile force element
Form-active
Idealized
Real
Notes: Structural Actions, Form and Systems

4. Notes: Structural Actions, Form and Systems
Basic Structural Elements:
Compression--The Column
Idealized
Column
RC Shapes
Metallic Shapes
Beam-Column
Multiple Force: Axial, Shear, Moment
Studied in ENGRD 202
Godden, F43
Real
Notes: Structural Actions, Form and Systems

5. Notes: Structural Actions, Form and Systems
Basic Structural Elements: Compression--The Arch
Can be single force = Funicular, or...
Multiple Force: Axial, Shear, Moment
Can Have 1, 2, or 3 Hinges
Godden, B28
Real: 3 Hinges
RC Arch
No Hinges
Idealized
Notes: Structural Actions, Form and Systems

6. Basic Structural Elements: Flexure--The Beam
Idealized
Basic Structural Elements:
Flexure--The Beam
Beam: A Multiple Force Element
Multiple Force: Shear, Moment, Axial
Studied in ENGRD 202
Simply Supported
Cantilever
Fixed-Fixed
Multiple span continuous
Tapered/Haunched
Built-Up
Godden A56
Real
Notes: Structural Actions, Form and Systems

7. 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

8. Basic Elements May Be Simplifications of 2D and 3D Surface Elements
Idealized
1D Beam
[Torsion?]
2D Plate in Bending
[Twisting possible]
Real
Godden, F80
Notes: Structural Actions, Form and Systems

9. Basic Elements May Be Simplifications of 2D and 3D Surface Elements
Idealized
Cable
Pressure Vessel/Membrane
Real
Godden, E35.3
Notes: Structural Actions, Form and Systems

10. Basic Elements Are Simplifications of 2D and 3D Surface Elements
Idealized
Arch
Shell:eg. Dome
Godden E35.1
Real
Notes: Structural Actions, Form and Systems

11. 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

12. Notes: Structural Actions, Form and Systems
Basic Elements Can Be Combined Into Structural Systems
Real
Godden, F64
Beams + Columns = Frame
Idealized
Notes: Structural Actions, Form and Systems

13. Notes: Structural Actions, Form and Systems
Basic Elements Can Be Combined Into Structural Systems
Tie Rods + Columns = Truss
Idealized
Real
Notes: Structural Actions, Form and Systems

14. Basic Elements Can Be Combined Into Structural Systems
Beam/columns + shell = aircraft fuselage
Real
Idealized Section
Represented with Finite Elements
Notes: Structural Actions, Form and Systems

15. Some Planar Structural Systems Are Simplifications of 3D Systems
Idealized
Godden, D67
Real
Plane Truss
Space Truss
Notes: Structural Actions, Form and Systems

16. Some Planar Structural Systems Are Simplifications of 3D Systems
Plane Frame
Space Frame
Idealized
Godden, F62
Real
Notes: Structural Actions, Form and Systems