Structures need to be strong enough to do the job they are made for
The strength of structures depends on their design and the materials used
Models of structures can be tested
Sometimes the real structure has to be tested
EXAMPLE QUESTIONS
When do you need a test structure?
Why do some structures need to be tested for strength?
What other kinds of things can structures be tested for?
THE STRENGTH OF A STRUCTURE DEPENDS UPON ITS DESIGN AND MATERIALS
Forces can change the shape of an object (for example, a hammer can change the shape of a piece of clay).
Structures need to be designed in a way that will ensure that they can withstand the forces that are likely to act upon them.
Two things are important here: first, the design of the structure, and second, the strength of the material, or materials, used to build the structure.
The most efficient structures are those which successfully combine design with material strength in an economic way.
THE SHAPE OF A STRUCTURE IS IMPORTANT
Some shapes are stronger than others.
The shape of a structure depends upon the materials from which it can be made.
Materials can be rigid (like steel bars or pine logs) or flexible (like plastic sheeting or rubber).
Some materials can be given extra strength by careful design and shape (for example, a spider’s web or a wicker basket) or by being combined with other materials in the structure (such as the poles and guy ropes of a tent).
Some structures, such as buildings and bridges, can be made from a variety of materials.
STRUCTURES HAVE FORCES APPLIED TO THEM
Essentially, structures are designed to withstand forces. For example, a building must not collapse, a crash helmet must protect the head, and a shell must protect its contents.
STRUCTURES MAY NEED TO BE TESTED
Sometimes the only way of finding out if a structure works is by testing the real thing.
In some cases, however, the real structure cannot be tested to destruction (bridges, ships, or buildings, for example).
Instead, the strength of the design and materials is tested using scale models before the full-size structure is built.
Often, different model designs are tested to determine the best structure to fit the requirements.
Critical structures are usually designed with a wide margin of safety; that is, the structure are designed to withstand forces and conditions far more destructive than might reasonably be expected.
