Classifying Structures What forms do structures have?
Different structures have different functions. We can group structures based on their functions.
We can also group structures based on their forms. Structures have three basic forms: SOLID. FRAME. SHELL.
Complex structures are often combinations of these forms. Different structural forms can support different loads.
Solid Structures
A solid structure uses solid construction materials to support loads. A solid structure usually has a large mass. A well-made solid structure can last a long time.
A concrete dam, a wooden telephone pole, and a marble statue are examples of solid structures.
Figure 1 shows a concrete dam. The dam has thick concrete at the bottom where the load for des of the water are huge.
Frame structures
A frame structure uses a network, or skeleton, of materials that support each other.
Frame structures can be very strong. The parts of a frame work together to resist forces. Frame structures are also lighter than solid structures.
A frame structure may have a membrane stretched over it, but the membrane does not help support loads. For example, a tent may be made of a metal frame with fabric stretched over it. The fabric does not help support loads.
Shell structures
A shell structure has a hollow, curved shape. An egg and a bike helmet are shell structures.
Shell structures are strong and rigid, but they can also be very light.
Combination structures
Most structures are combination structures. They have solid, shell and frame parts.
For example, most buildings have a solid foundation. They also have a frame of wood or metal that supports a shell of brick or concrete.
Table 1 shows other examples of combination structures.
The human skeleton
The human skeleton is a combination structure. Bones can be considered solid structures. The network of bones is a frame structure. The skull is a shell structure.
