Notes: Structural Actions, Form and Systems 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:

TensionCompression

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

Godden, B47

IdealizedReal

Basic Structural Elements: Tension—The Tie Rod

• Single, axial-force element• Studied in ENGRD 202

Notes: Structural Actions, Form and Systems 3

Real

Idealized

Basic Structural Elements: Tension--The Cable

• Single, axial, tensile force element• Form-active

Notes: Structural Actions, Form and Systems 4

Column

RC Shapes

Metallic Shapes

Beam-Column

Idealized

Real

Basic Structural Elements: Compression--The Column

• Multiple Force: Axial, Shear, Moment• Studied in ENGRD 202

Godden, F43

Notes: Structural Actions, Form and Systems 5

Basic Structural Elements: Compression--The Arch

Godden, B28

Real: 3 Hinges

RC ArchNo Hinges

Idealized

• Can be single force = Funicular, or...• Multiple Force: Axial, Shear, Moment• Can Have 1, 2, or 3 Hinges

Notes: Structural Actions, Form and Systems 6

Godden A56

Real

Basic Structural Elements: Flexure--The Beam

• Multiple Force: Shear, Moment, Axial• Studied in ENGRD 202

Multiple span continuous

Fixed-Fixed

Cantilever

Simply Supported

Beam: A Multiple Force Element

Idealized

Tapered/Haunched

Built-Up

Notes: Structural Actions, Form and Systems 7

1D Rod [Shear on non-orthogonal section]

2D Plate in Biaxial Tension (“Plane Stress”)[Note: if S1 S2, shear will be present]

Basic Elements May Be Simplifications of 2D and 3D Surface Elements

Notes: Structural Actions, Form and Systems 8

1D Beam[Torsion?]

2D Plate in Bending[Twisting possible]

Basic Elements May Be Simplifications of 2D and 3D Surface Elements

Real

Godden, F80

Idealized

Notes: Structural Actions, Form and Systems 9

Cable

Pressure Vessel/Membrane

Basic Elements May Be Simplifications of 2D and 3D Surface Elements

Real

Godden, E35.3

Idealized

Notes: Structural Actions, Form and Systems 10

Basic Elements Are Simplifications of 2D and 3D Surface Elements

Arch

Shell:eg. Dome

Godden E35.1

Real

Idealized

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 GeometryModel of Gear

Notes: Structural Actions, Form and Systems 12

Basic Elements Can Be Combined Into Structural Systems

Beams + Columns = Frame

IdealizedReal

Godden, F64

Notes: Structural Actions, Form and Systems 13

Basic Elements Can Be Combined Into Structural Systems

Tie Rods + Columns = Truss

Idealized

Real

Notes: Structural Actions, Form and Systems 14

Beam/columns + shell = aircraft fuselage

Idealized SectionRepresented with Finite Elements

Real

Basic Elements Can Be Combined Into Structural Systems

Notes: Structural Actions, Form and Systems 15

Some Planar Structural Systems Are Simplifications of 3D Systems

Plane Truss

Space Truss

Idealized

Godden, D67

Real

Notes: Structural Actions, Form and Systems 16

Some Planar Structural Systems Are Simplifications of 3D Systems

Plane Frame

Space Frame

Idealized

Godden, F62

Real