Log Book – Weeks 1 & 2 Strength – how much force a material can withstand before breaking Stiffness – how flexible a material is. If a material is stiff it can’t bend very well. Shape – The shape of the material. Eg. Cylindrical, flat, thin etc. Material Behaviours – The way in which a material behaves when it comes in contact with other materials. Economy - How much the material costs. IMAGE 1 Sustainability – How well the material can withstand circumstances and remain in a stable condition. Eg. Weather, human engagement, corrosion etc.
Tension Vs Compression A tensile force is a pulling force for example a cable from a crane holding a load. Steel cables are commonly used to withstand tensile forces. A compressive force is a pushing force for example a brick on the bottom layer of a wall. The more down the wall the brick is the greater the compressive force is because each brick exerts its gravitational force down affecting the two bricks directly underneath it. Bricks and concrete are both strong when used under compression.
Practical 1. In the tutorial on Friday our task was to construct a tower that was wide enough inside to fit a toy dinosaur. The only material we had to use was small wooden blocks. To ensure we had maximum strength around the weakest point (the doorway) we made an archway that allowed the blocks to be in compression (timber is strong under compression rather than tension).
From the archway up we slowly began to close the roof off into a cone-like shape. This was also an unstable process as one uneven wall could put the whole tower off balance. After we closed off the roof we built up a bit more to increase the compression on each block. The higher the tower and the more layers of blocks that the tower has, the greater compression that each block undergoes.
Photos taken from tutorial on Friday 7 of March.
Because of these compressive forces the bottom of the tower is much stronger than the top. This is because each block splits its load down to the block directly beneath it. Therefore the bottom row of blocks will have each block’s passed on force.
Depending on what materials cities had in abundance depended on what the city was built out of. Melbourne – Bluestone Sydney – Sandstone Perth – Clay for bricks, & limestone
Dead load – a fixed object. Eg Walls of a house. Live load – something that is not fixed and can be readily moved if necessary. Eg Furniture. Newton’s third law states that for every action there is an equal and opposite reaction. That is why structures, for example the tower we built, remains stationary and doesn’t push through the floor. As we knocked down the tower from the bottom, it stayed upright. This was because of the strong compressive forces from the weight of all the blocks.
In comparison to other groups our structure reached the greatest height. Two of the other groups weren’t allowed to use the archway method and had to punch a hole in the side of the wall after their tower was finished. The archway strengthens the entrance much more than other methods, primarily because of the even compressive forces (shown above).
CONSTRUCTION SYSTEMS Enclosure system: Roof, walls, windows and doors. To shelter and protect the interior space from noise and weather and to provide privacy and security. Structural system: Columns, beams, the foundation. The structural system is basically to keep the house standing upright. It allows the weight forces to be transmitted to the ground safely.
IMAGE 3: The structural system of a chicken coop.
Mechanical system: The water, sewage, electrical and heating systems all make up the mechanical system. These systems are used to bring comfort to the occupants of the home. Performance requirements: fire resistance, insulation, protection from rain and water vapour, ability to cope with movement in soil, resistance to sound, easy to be maintained, readily changeable. Aesthetic qualities: Colour, surface material. Economic efficiencies: Initial building cost, lifetime costs (maintenance) Environmental impacts: Sustainability of materials. Use of nontoxic materials. Example of thermal mass
Environmentally Sustainable Design (ESD) Strategies: - Night air purging -Local materials
-Solar energy -Wind energy -Insulation -Thermal mass: materials that dont conduct heat easily. Eg concrete rather than metals. -Material efficiency -Water harvesting(Eg. Collecting water in tanks)
Practical 2. In our attempt to make a tower to the roof only out of balsa wood we decided to begin with a triangular base. We choose this rather than a square base to reduce the amount of wood that we used.
To increase stability we reinforced the joints by cutting small bits of balsa and putting them against the vertical beam and also put a bit across the horizontal strips of wood to reduce any movement. This made each â€˜floorâ€™ very stable. The main weakness was the middle of the long bits of balsa which began to bend as we continued to build. As we only had a limited supply of wood, we werenâ€™t able to diagonally support the tower. The red line shows a possible support line which would have stopped the tower from bending. However, the green line shows a much stronger support which would stop the bending of the tower especially the part where the arrow is pointing.
Photos taken from tutorial on14th of March.
Structural Joints Roller joints: allow rotation but not translation Pin joints: allow rotation but not translation Fixed (rigid) joints: resists movement in any direction and maintains the sameangle(usually 90 degrees)
GLOSSARY Load path: The path the weight forces take to get to the ground. Reaction force: The force opposing an initial force. Masonry: Individual blocks laid together and joined by a mortar. Eg. Bricklaying. Point load: The point where the structure transfers its weight to the foundation. Compression: A pushing force. >>|=|<< Beam: A long piece of timber or metal used to support the roof or floor of a construction. Structural Joint: The connection of two pieces of timber or metal. Frame: The skeletal part of a structure which gives support and shape. Bracing: The supporting timber or metal used to hold a construction up. Tension: A pulling force. <<|=|>> Column: A vertical pillar used to support a load. Works by using compression.
Reference list. IMAGE 1: Tension and Compression. http://hendrix2.uoregon.edu/~imamura/102/section2/chapter12.html IMAGE 2: Visitor, strong and hot (erâ€Ś). http://simpleglee.blogspot.com.au/2010_09_01_archive.html IMAGE 3: http://friendsoftheubcfarm.wordpress.com/2008/06/10/one-red-beacon-of-summer/ Ching, F. (2008) Building Construction Illustrated (4th ed.). Hoboken, New Jersey: John Wiley & Sons, Inc. (pp. 2.02-2.04)