Triangulation </li></ul><li>Structures and the environment </li><ul><li>Damage to the environment </li></ul></ul>Cover page
INTRODUCTION This chapter is about how materials can be formed into different shapes (or structures) to support loads and withstand pressures. Did you know you can make strong structures from fairly weak materials? Most structures are designed to support heavy loads. A bridge is an example of an everyday structure. Can you think of others? When you think of structures, you probably think of things like bridges, mobile phone masts and tall buildings. There are also other examples that we use every day, like chairs, tables, windows and presses. The two main kind of structures are: <ul><li>Frame structure: Frame structures are structures that have a “frame” or skeleton associated with them.
Shell structures: Shell structures rely on the shape they have been moulded into for their strength. They are usually lighter than frame structures. </li></ul>These structures may be man-made or may occur naturally . Cover page
Structural Members STRUCTURAL MEMBER A structural member is a part of a structure. Tension Compression Redundant REDUNDANT MEMBER A redundant member is a part of a structure that is neither in tension nor compression. Redundant members can be removed from structures without the structure weakening. A good design has not redundant members. Cover page
What is a force? A force is a push or a pull . Forces can make things move. Engines and motors make forces that cause machines to move. The force of gravity pulls everything downwards towards the earth. Force is measured in newtons (N), after Sir Isaac Newton. TYPES OF LOADS: Structures are built to support a load. Loads can be static (not moving) or dynamic (moving) Cover page
Types of forces that act on a structure <ul><li>Tension
Tension Tension is stretching, straining, pulling, tensile force. If something in tension is cut, the two ends will pull apart. <ul><li>Example: A rope with a weight hanging on the end of it is in tension. If it cut, it will pull apart.
Example: A coping saw always has its blade in tension. If the blade is cut, it will pull apart. </li></ul>Cover page
Compression / Pressure Compression means being pressed into less space or being flattened by pressure. Something under a heavy load is in compression. Certain materials under compression will get smaller. An object is under pressure if there is a compression force acting on it. Pressure = Force / Area This means that the smaller the area the force is applied to, the greater the pressure. This explains why someone leaning on you with their hand is a lot less painful than the same person leaning on you with a compass point. Cover page
Shear A shearing force is a tearing or ripping force that is trying to move one part of the material in the opposite direction to the other. <ul><li>Example, scissors cut through paper by applying a pair of forces on the paper, each force in the opposite direction. </li></ul>Shear force acts on the paper as the scissors try to cut through it. Cover page
Torsion Torsion is the act of twisting a structure. A torsion force causes something to twist or turn. The cube is in torsion, as it is being twisted. Cover page
Bending Forces can bend a structure. Example: A bar bends due to the weight of a gymnast swinging on it, or a long narrow shelf may bend with books on it. In these situations, the upper surface is in compression and the lower surface is in tension. The beam is being bent with the weight. Cover page
Types of structures / Parts of structures <ul><li>Beams
Beams A beam is a long rigid piece of wood or metal. It is the simplest way of supporting a load across a gap. It is the simplest structure, but it can also be part of a more complex structure. Circular section Square section Triangular section L-section beam I-section beam U-section beam T-section beam Cover page
Bridges A bridge is used to “bridge” a gap, usually between the banks of a river. A bridge has supports at two ends. The first bridges were simple wooden beams, but nowadays they are often huge, complicated structures. Golden Gate (St. Francisco) Tower Bridge (London) New River Gorge Bridge Fayetteville (USA) Cover page
Cantilevers Cantilevers are beams that are held and supported at one end only. They are brackets for supporting balconies, shelves, tree branches, etc. Cover page
Columns and pillars Columns and pillars are vertical beams, normally designed to support loads directly on top. Example: Table legs. Cover page
Ties A tie is a part of a structure in tension for keeping two objects from spreading or separating. Ties are usually thin. Example: The cross piece on a swing. Tensor Cover page
Struts A strut is a part of a structure in compression for keeping two objects from coming closer together. Struts are usually thick. Example: A pillar supporting a roof. The wires on either side of the flagpole are being stretched, and so, therefore, are the ties. The pole is in compression due to gravity, and so, therefore, is the strut. Cover page
Triangulation Triangulation means using triangles arranged together to form a frame or part of a frame, with increased rigidity . Structures made from triangles are strong. Eiffel Tower Pylon Tecnology Project Cover page
Structures and the environment While many structures are needed in our world to house people and allow them easy transport, structures also impact on our environment. Structures can impact positively by being beautiful and enriching people's lives or structures can be ugly and damage the environment. DAMAGE TO THE ENVIRONMENT The environment can be damaged from structures being built in some or all of the following ways: <ul><li>Grassland is destroyed by the structure.
There is pollution from the lorries and trucks used in the construction of the structure.
The iron, stone and other raw materials have to be sourced in quarries and mines, which damage the landscape. There is further environmental damage in converting the raw materials into a form that can be used in the structure.
Wildlife is disturbed and may no longer survive. </li></ul>Cover page