Year+7+Structures

toc = =

= Introduction - Structures = By examining structures in nature we can see where the design principle exists and see how these principles are incorporated in man-made structures built today. One thing we have to keep in mind when comparing natural and man-made structures is that nature uses live materials while man uses ones and the two do not always behave in the same manner.

= Research =

= Knowledge & Understanding =
 * A structure must be able to:**
 * **support itself...**
 * **...and withstand the forces that act on it.**
 * If it can't do these things, it's not a structure!**

Natural structures can be divided into three categories: Force and stability are important factors when designing and building structures. Instability can be caused by various natural forces, for example winds and earthquakes. Loads applied to structures can also affect the stability of a structure. All structures are effected by equilibrium and gravity. Loads on structures can be divided into two main categories: "the natural forces due to gravity and the dynamic force due to wind" The four primary loads are: More specialized loads on structures are referred to as secondary loads, such loads include:
 * ~ Structure in Plants ||~ Structure of Animals ||~ Structures made by Animals ||
 * [[image:http://larvalsubjects.files.wordpress.com/2009/02/maple_leaf_structure.jpg?w=300&h=193 width="210" height="122"]] || [[image:adult-female-leopard-tortoise-20071.jpg width="166" height="124"]] || [[image:http://worldbridgermedia.com/blog/wp-content/uploads/2007/04/honey-comb.gif width="134" height="126"]][[image:http://www.alanbauer.com/images/Patterns%20in%20Nature/Spider%20web%20with%20dew.jpg width="175" height="126"]] ||
 * Primary Loads**
 * Dead loads - for example in a building these are defines as the weight of the permanent elements of the building
 * Imposed or Live loads - for example, static and movable fixtures and fitting, and people using the space!
 * Snow loads - Weather conditions can add a load to a building. Snow and rain - 1litre of water = 1kg
 * Wind loads - the pressure and force of the wind beating and gusting against buildings
 * Secondary Loads**
 * Shrinkage loads
 * Thermal loads
 * Settlement loads
 * Dynamic loads

There are three types of structures:
 * Solid structures
 * Skeletal structures - frames
 * Surface structures - shell

All structures have forces acting on them including **tensile**, **compressive** and **shear** forces, follow this link [|www.technologystudent.com] The part of the structure that has a tensile force acting on it is called a **TIE** and the part that has a compressive force acting on it is called a **STRUT**. Follow this link [|www.technologystudent.com] = Bridging the Gap = There are three major types of bridges: Simple Beam: this is where you have a single span bridge constructed from a beam of steel or reinforced concrete. Trussed Beam: In this system is usually used where the span exceeds 45m and it can be simply supported or cantilevered. Truss bridges are mainly used for long spans as in the example shown above. Cantilever Beams: The cantilever bridge is based on the same principle as that of the cantilever beam it is supported at either end and has a suspended section in the middle. The piers at each end act as anchorage points and the bridge is built from each of these points. ||  || The masonry arch bridge has been in existence for many years Modern arch bridges are constructed form reinforced concrete and steel. There are different types of arch bridges and an example of the stiffened tie-arch or bow-string girder bridge is shown above. ||  || As can be seen form the photo there is a central span with two side spans.The cables exert forces on the piers but due to the fact that the cables are pulling in opposite direction the resulting force is almost vertical. ||
 * ~ The **beam bridge** ||~  ||~ The **arch bridge** ||~   ||~ The **suspension bridge** ||
 * [[image:http://www.toothpickdesign.com/images/clip_image004.jpg width="185" height="153"]][[image:msc-ks3technology/beam_bridge_1.jpg width="256" height="154"]] ||  || [[image:http://www.toothpickdesign.com/images/clip_image008.jpg width="219" height="158"]] ||   || [[image:http://www.toothpickdesign.com/images/clip_image012.jpg width="221" height="160"]] ||
 * Beam, including truss and cantilever.

The biggest difference between the three is the distances they can cross in a single **span**. A span is the distance between two bridge supports, whether they are columns, towers or the wall of a canyon. What allows an arch bridge to span greater distances than a beam bridge, or a suspension bridge to span a distance seven times that of an arch bridge? The answer lies in how each bridge type deals with two important forces called **compression** and **tension**: A simple, everyday example of compression and tension is a spring. When we press down, or push the two ends of the spring together, we compress it. The force of compression shortens the spring. When we pull up, or pull apart the two ends, we create tension in the spring. The force of tension lengthens the spring. Compression and tension are present in all bridges, and it's the job of the bridge design to handle these forces without buckling or snapping.
 * **Compression** is a force that acts to compress or shorten the thing it is acting on.
 * **Tension** is a force that acts to expand or lengthen the thing it is acting on.
 * Buckling** is what happens when the force of compression overcomes an object's ability to handle compression, and **snapping** is what happens when the force of tension overcomes an object's ability to handle tension.

media type="custom" key="4226259"

The best way to deal with these forces is to either dissipate them or transfer them. To **dissipate** force is to spread it out over a greater area, so that no one spot has to bear the brunt of the concentrated force. To **transfer** force is to move it from an area of weakness to an area of strength, an area designed to handle the force. An arch bridge is a good example of dissipation, while a suspension bridge is a good example of transference. Extract by: Morrissey, Michael. "How Bridges Work." 01 April 2000. HowStuffWorks.com. <[]> 16 August 2009.

= Design & Specification =

= Make & Manufacture =

Diary of Making
= Testing & Evaluation = To test the bridge there are some details required in order to compare against other structures that have been built in the class. Using the testing equipment as seen below: Your structure is mounted safely into the testing structure, then the position of the deflection arm is noted, and taking turns 100g weights are added, each time being careful to observe and listen to the behaviour of the structure and the changes in deflection.

= Assessment & Grading Criteria =

= Extension Activities =
 * 1) Work your way through this website, some interesting information about bridges []
 * 2) Here is a whole section about structures for you to investigate []
 * 3) Try West Point Bridge Builder, download the software and experiment with it and build the most efficient structures and bridges. []


 * Quiz **

= Links & Resources = Example of students working on their structures (Sept 2008) media type="custom" key="4222757" Some interesting and useful websites:
 * Photographic examples and brief notes about the properties of each type of concrete bridge are discussed. Bridge types are: slab, I-girder, box girder, segmental, spliced girder, arch and cable stayed.[| http://www.nationalconcretebridge.org/bridgetypes.html]
 * Looking at man-made and natural structures. The effects of load and stability, and forces on structures, very detailed information easy for you to understand with great examples: [|http://www.ul.ie/~gaughran/Gildea/menu.htm]
 * http://stephanyid3124.wikispaces.com/Bridges_notes