When beginning to design a new structure, the engineer or designer must consider the function of the structure. What is it supposed to do?

Many structures have more than one function. For example, think of a bridge. It needs to support cars, people, and most importantly, its own weight. Sometimes, designers have a hard time performing their structure to do everything well.

Another example is a running shoe. A plastic-covered running shoe works well to keep the water out, but it will also keep the sweat trapped in, so the designer will need to find a compromise.

The appearance of the structure must also be considered during the design process. Aesthetics is the study of beauty in art and nature. A designer or engineer might choose interesting textures, colours, or shapes that are repeatedly advanced. Sometimes the choice of materials and the methods used to make a structure can have a huge impact on aesthetics.

Almost all structures are designed and built with a margin of safety in mind. For example, an elevator might have a capacity limit posted, however the elevator is designed to hold much more than could ever fit inside one. In Ontario (and Canada) buildings are designed to support the weight of snow in the winter. Structures are designed to withstand conditions that might occur, or even rare events.

Choosing building materials is another very important part of designing a structure. Materials have different strengths.

To pick the most suitable material for a structure, engineers consider the following:

• Cost: Depending on the project, the cost of materials will vary. It is important to find a balance between materials that are inexpensive and materials that will last a long time and remain durable
• Appearance: Materials need to remain attractive and strong, even over time, without requiring expensive maintenance.
• Environmental impact: Using materials that are sustainable and derived from renewable resources is incredibly important when considering designing a structure. An engineer may avoid materials that require harmful chemicals, or materials that are difficult to dispose of.
• Energy efficiency: The cost of a structure includes more than materials and construction. Engineers also consider the amount of energy a structure might require (i.e. heating, cooling, refrigeration, etc.). They aim to reduce operating costs and preserve the Earth’s limited supply to non-renewable resources.

Materials that are used to fasten structures together are also very important to the design process of a structure. Structures are often their weakest where different parts are joined together, so choosing this material and design wisely is essential.

If you explored joints in your home or school, what might you notice?

You may notice rigid joints that attached two parts together, such as a hinge, fastener, adhesive, or interlocking shapes.

The magnitude of a force describes its strength.

How big is the force compared to the size and weight of the object?

The direction of a force describes the direction in which it is acting.

Where is the force coming from?

The point of application is the direct spot where the force is applied on the structure. Where does the force meet the structure?

The plane of application is the side of the structure that would be affected by the force. What part of the structure is affected by the force?

A natural structure occurs organically in nature. For example, a leaf is a natural structure and so is a spider’s web.

In a shell structure, the outside layer of the structure holds the whole object together. Typically, shell structures are hollow on the inside, such as a tin can, but have a solid outer layer. While they are incredibly strong, they require a very specific design by an engineer to function properly. The Rogers Centre in Toronto is one example of a shell structure.

A mass structure is sometimes called a solid structure and is usually made of one solid piece of strong material. A solid structure has little or no space inside and relies on its own mass to resist the forces that act upon it.

Frame structures are structures made up of various parts fastened together, called structural components. A framed structure can be 2D, such as a door frame or fence, or 3D, such as the wood framing for a house.

When engineers design frame structures, they really have to consider how each of the parts are attached. Frame structures are more flexible than other structures, but require specific engineer knowledge to assemble these structures in a specific way to ensure they are strong and stable.