Structural Technology Foundations of Technology Standard 20: Students will develop an understanding of and be able to select and use construction technologies.

What is a Structure? A structure is a group of elements somehow united to support a load with stability. Examples of structures are bridges, electricity pylons or dams. Can you think of others?.

Shell Structure A shell structure is one in which the strength reloads into the outer surface. They are usually lighter than frame structures. For example, a turtle, an egg, an airplane, a boat, a lobster or a car has a shell structure.

Frame Structure They are structures that have a skeleton associated with them. An example are leaves with frame structures and skin on them. If they have no “skin” on them, they are called “open frame”. An example of a natural open frame structure is the spider's web.

Spider web stronger than steel? sCpU98 sCpU98

What is a force? In a structure we can define a force as any agent that causes stress or compression in a fixed body – Pull force -> Stress effect – Push force -> Compression effect The force of gravity pulls everything downwards towards the earth. There are forces acting on us all the time. Force is measured in Newtons (N).

Compression The movement of two forces pushing together.

Tension The movement of two forces moving away from each other. In a structure, the forces cause the object to be pulled apart.

Tension Test Use link below if video does not load. stuff-stronger.html stuff-stronger.html Go to 5:50

Bending Force A force applied between at least two fixed points. The force produces tension on one side of an object and compression on the other side.

Torque A rotational or twisting force Torque is the base unit of measurement and is measured in foot pounds.

Shear Force Sliding forces that act in opposite directions. For example, in a teapot, there is a shear force in the surface between the handle and the body. You want to move the teapot up, while the load is downwards.

Considering Forces All these forces must be taken into account in designing structures. If the designer does not consider these forces, there is a big risk of crumbling, distortion, deformation or falling in all types of structures (bridges, buildings.. ) To prevent disaster, most structures are designed to withstand greater force than would be expected.

Structural Member A structural member is a part of any structure or building. All structural members have a mechanical function, so each of them supports a force (tension, compression, flexion).

Redundant Member A redundant member is a part of a structure that has no mechanical function, so there is no force applied to the element. So, if there are no forces, redundant members can be removed from structures. An example in a house is a brick. If you push down a wall in your living room to make that space bigger, the building would be affected.

Loads Structures are built to support static (dead load) and dynamic (live) loads. In a building, static loads are anything that is part of the structure. – For example, the weight of beams, cement, windows, etc. Dynamic loads are the objects you can move temporarily in, on or off the structure. – For example, furniture, people, computers, tables, etc. Dynamic loads are more important that Static loads because….. – In a chair, the design is made to support the heaviest person sitting on it ( static load ), but if a boy starts to jump on it ( dynamic load ), the chair is more likely to break.

Beams The simplest way of supporting a load across a gap is to use a beam. A beam is a horizontal support within a structure. This is the simplest form of bridge, using a tree trunk to span a stream. What is actually happening is that the forces that act upon the beam or bridge, caused by any load upon it and the weight of the beam itself, are being transferred to the support either side, as in Figure on the left. If the beam has a force that acts in the middle ( it could be its own weight ), then the forces at either end are equal. In this figure, we have that Force at Point x = Force at point y = 500 N

What happens in a beam? When beams bend, the top surface is compressed and the bottom surface is stretched as shown in the picture below. You can see, therefore, that the important areas for a beam to be strong are the top and bottom. The strength at the centre is not so important.

What happens in a beam? In practice the major design issue with beam construction is making the beam as light as possible without reducing its strength. This is called the strength-to-weight ratio. The cross- sectional shapes of modern beams have enabled them to become lighter without compromising strength.

Types of Beams This figure shows a range of beam sections.

Structural Elements In this illustration we have: 1.Foundation: Made of reinforced concrete that supports all the weight. 2.Columns: They are vertical supports in a structure. They transmit the building's weight to the foundations. They are also known as studs. 3.Primary beam and secondary beam are arranged to support the floor (Blue area)

Arch Bridge Arch bridges are one of the oldest types of bridges and have great natural strength. Instead of pushing straight down, the weight of an arch bridge is carried outward along the curve of the arch to the supports at each end. These supports, called the abutments, carry the load and keep the ends of the bridge from spreading out.

A Truss m/watch?v=eJSf1f_E2Q 8&feature=related m/watch?v=eJSf1f_E2Q 8&feature=related Go to 4:49

Keystone In the keystone the top end is bigger than the bottom end so the stone never falls and the arc is formed. The weight is shared by the lateral faces of the stones until it reaches the foundations. vid_bbarch/

Suspension Bridge A suspension bridge is a type of suspension structure. There are several beams which are held by dozens of steel wires or cables. They could have two or more columns, which support all the weight. The space between two columns is called the span. Most of the weight of the bridge is carried by the cables to the anchorages, which are imbedded in either solid rock or massive concrete blocks. Inside the anchorages, the cables are spread over a large area to evenly distribute the load and to prevent the cables from breaking free. This type of structure is very good for covering large distances (large span) but are very expensive. 0&feature=related

Cable Stayed Bridge Cable-stayed bridges may look similar to suspensions bridges—both have roadways that hang from cables and both have towers. But the two bridges support the load of the roadway in very different ways. The difference lies in how the cables are connected to the towers. In suspension bridges, the cables ride freely across the towers, transmitting the load to the anchorages at either end.

Cable Stayed Bridges In cable-stayed bridges, the cables are attached to the towers, which alone bear the load. The cables can be attached to the roadway in a variety of ways. In a radial pattern, cables extend from several points on the road to a single point at the top of the tower. In a parallel pattern, cables are attached at different heights along the tower, running parallel to one other.