Grade 7 Unit 4 Topic 1 Types of Structures

An Overview Structure: An object with a definite size and shape, which serves a purpose or function. The parts of a structure have a specific arrangement that remains the same. Function: (of a structure or object) its main purpose.

An Overview – cont. To perform its function, every part of a structure must resist forces and loads that could change its shape or size. Force: Stresses such as pushes or pulls. Load: the weight carried or supported by a structure.

Types of Structures There are so many different structures that it is difficult to form a definition that fits them all. Instead of defining structures scientists, engineers, and designers group structures into classifications based on key factors.

Classifying Structures It is much more efficient to classify structures based on key common features such as: 1. The Structure’s origin 2. Its Function 3. Its Form 4. Its Design 5. The Materials and parts it made of 6. How it is held together.

The Structure’s Origin One common way to classify structures is to group them according to their origin. That is, are they natural or manufactured objects. Natural Structures Natural Structure: an object or structure not made by people.

The Structure’s Origin–cont. Natural Structures –cont. They have a definite shape. They can be made of many parts They could have simple or complex patterns They can serve many purposes. They can be from either the living or non-living part of the natural world. As both a feather and a sand dune can be considered structures.

The Structure’s Origin–cont. Manufactured Structures Manufactured Structures: An object or structure that is made by humans. Many manufactured objects are modeled after natural structures.

The Structure’s Design Structures can also be classified by the way they are built also known as the structure’s design. Design: the shape and size of a structure and the materials of which it is composed.

The Structure’s Design–cont. The 3 key types of designs are: 1. Mass Structures 2. Frame Structures 3. Shell Structures

The Structure’s Design–cont. 1. Mass Structures: Mass Structure: A structure, natural or manufactured, that is made by the piling up of materials; examples include a pyramid a mountain, and even a cake.

The Structure’s Design–cont. 1. Mass Structures – cont.: Advantages of mass structures include i. They are held firmly in place by their own weight. ii. If small pieces are worn away or broken it usually makes little difference. Mass structures are not always completely solid. Due to their large size and weight, mass structures must be carefully designed.

The Structure’s Design–cont. 1. Mass Structures – cont.: There are 4 main ways a Mass Structure can fail: 1. The mass of the vertical sections may not be enough to resist the forces and loads put upon it. 2. The mass structure itself may be so heavy that the ground underneath is pressed down unevenly causing instability.

The Structure’s Design–cont. 1. Mass Structures – cont.: 3. The structure may not be thick enough or fastened tightly together, so parts of it are dislodged, breaking the structure apart. 4. The structure may not be anchored firmly enough to the ground possibly causing it to tip over if too much force is put on the top of the structure.

The Structure’s Design–cont. 2. Frame Structures: Frame Structure: A type of structure in which a skeleton of materials supports the weight of the other parts.

The Structure’s Design–cont. 2. Frame Structures – cont.: Frame structures allow most of the inside of the building to be empty space. There are 2 types of walls in frame structures: 1. Load bearing walls – which hold up, and are part of, the frame structure. 2. Partition walls – these walls simply divide up the open space.

The Structure’s Design–cont. 2. Frame Structures – cont.: The level of complexity in frame structures varies from simple exposed frame structures (like ladders and spider webs) to more complex objects that have added parts to their frames (such as covering materials and subsystems).

The Structure’s Design–cont. 2. Frame Structures – cont.: The frames can be hidden or exposed They are relatively easy to design and build They are relatively inexpensive to construct.

The Structure’s Design–cont. 2. Frame Structures – cont.: All frame structures must overcome similar problems: 1. How should the parts be fastened together? 2. How do you make them strong without using too much material? 3. What shape or bracing should they have so that they will not bend or fall down?

The Structure’s Design–cont. 2. Frame Structures – cont.: Common design problems in frame structures are further complicated when the building needs to be: 1. Lightweight – such as a tent 2. Very tall – such as communications towers 3. Large complicated projects – such as bridges and buildings These challenges are often addressed using anchors, bracing, and low ranges of tolerance for parts.

The Structure’s Design–cont. 3. Shell Structures: Shell Structure: A type of structure that obtains its strength and rigidity from a thin, carefully shaped outer layer of material and that requires no internal frame; examples include an igloo and an egg.

The Structure’s Design–cont. 3. Shell Structures – cont.: Some shells, like those of a balloon, or parachute, are flexible. Shell structures have 2 very useful features: 1. They are completely empty 2. They use very little building material

The Structure’s Design–cont. 3. Shell Structures – cont.: The shape of the shell spreads the forces, experienced by the shell, through the whole structure, which results in each part supporting only a small portion of the load. This need to spread out the forces causes certain construction difficulties.

The Structure’s Design–cont. 3. Shell Structures – cont.: Problems facing builders of shell structures include: 1. Tiny weaknesses can cause the whole structure to fail. 2. Uneven cooling or drying can cause the whole structure to fail. 3. The rounded shape can make fitting flat material difficult. 4. Assembling flexible materials into a shell is also tricky.

The Structure’s Design–cont. Mix and Match: Many structures combine designs. For example: 1. Hydroelectric Dams are mass structures with large rooms that use frames to support the space. 2. Airplanes are built on a metal frame that is further strengthened by the metal skin that acts as a shell.

The Structure’s Design–cont. Mix and Match: Many structures combine designs. For example: 3. Domed Buildings usually used shell construction for the dome and frame construction for the rest of the building. 4. Warehouses are often a combination of frame structures, with thick walls of concrete that act as mass structures.