Structural Classification
Structures can be classified into three main types:
- Frame Structures
- Shell Structures
- Solid Structures
Frame Structures
Definition
Frame Structure
A structure made of beams and columns that can support its own weight without needing an outer shell.
Key features:
- Lightweight and material-efficient
- Often hollow or open in form
- Require bracing to prevent collapse
- Can be easily modified or expanded
- Efficient load distribution
Example
- Bicycle frame
- Greenhouse or tent poles
- Steel framework in skyscrapers
- Bridges (e.g. truss bridges)
Tip
When designing frame structures, consider the material properties and joint connections to ensure stability and durability.
Shell Structures
Definition
Shell Structure
A 3D hollow structure with thin walls relative to its overall size.
Key features:
- Lightweight but strong
- Can cover large areas without internal supports
- Distribute forces smoothly across the surface
- Smooth, flowing forms are visually striking
Example
- Helmet or dome
- Car body panel
- Plastic bottle
- The Millennium Dome (The O2 Arena)
- Clamshell packaging
Analogy
- Think of a shell structure like an eggshell.
- Its curved shape distributes pressure evenly, allowing it to withstand significant force despite its thinness.
Solid Structures
Definition
Solid Structure
A structure with few or no internal spaces that resists shape change when under load.
Key features:
- Resistant to external forces and environmental conditions
- Usually heavy as it provides stability through mass
- Resistant to compression
Example
- Brick wall
- Dam
- Concrete block
- Stone sculptures or monuments
Common Mistake
- Don't assume solid structures are always stronger than frame or shell structures.
- Each type has its own strengths and weaknesses depending on the application.
Comparing Structural Types
| Structure Type | Characteristics | Applications |
|---|---|---|
| Frame | Lightweight, flexible, efficient | Bridges, buildings, furniture |
| Shell | Curved surfaces, minimal material use | Domes, car bodies, helmets |
| Solid | Heavy, dense, durable | Dams, statues, foundations |
Note
- While frame structures excel in flexibility and material efficiency, shell structures offer aesthetic appeal and aerodynamic properties.
- Solid structures provide unmatched durability and stability but at the cost of increased weight.
Common Mistake
Forgetting that one product can sometimes use more than one type of structure
Self review
Choose three everyday products (e.g. water bottle, chair, bicycle, shoe, helmet, packaging). For each product, complete the following:
- Name of the product
- Type of structure it uses
- Frame, shell, or solid (or a combination)
- Evidence from the product to support your classification
- Describe the shape, thickness, materials, or how it supports loads
- Reason for choosing that type of structure
- Consider weight, cost, strength, material efficiency, or aesthetics
Example (for a sports helmet):
- Product: Bike Helmet
- Structure Type: Shell
- Evidence: Thin, curved plastic outer layer with foam inside; no internal frame or solid core
- Reason: Lightweight protection, distributes impact force across surface, easy to manufacture
