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! ! ! Log Book - Week 5!

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Short & Long Columns
 Short column: Short and fat.
 Primarily concrete or masonry are used. Timber is hard to come by in a short and fat state and is therefore used as a long column instead.
 Short columns are structurally adequate if the force pushing down doesn't exceed the compressive strength of the material. If it does the material, for example concrete, can crack and become structurally unstable. It becomes shorter when a compressive load is applied and then fails by crushing when the compressive strength of the material is exceeded. Two ways in which the column could crush could be applying a load too great or having a crosssection too small.
 Compressive Strength(Pa)= load(N)/area(m^2)
 A concrete slab is approximately 30MPa.

IMAGE 1: A short, concrete column that has had a load greater than it’s compressive strength. You can see the reinforcing steel bars have buckled under this load. 



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Long Column: Long and slender.
 Primarily steel or timber.
 Long columns fail if too much force is applied from above and this causes them to buckle. Different methods of fixing the columns from above and below affects how the beam will buckle. 
 To be considered a long column, the column has to have a ratio of greater than 1:20. Eg. 100mm wide 2000mm(2m) high.


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A diagram showing the effects of a load applied to a column with different joints.


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Structural Frames!

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Concrete: The beam is interconnected into the column to make a rigid joint(moment joint). The column is then connected to the footing system which is firmly attached to the ground.


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Timber(post & beam): The corners of a timber frame can be braced to reinforce the structure and to increase lateral stability.! 


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IMAGE 2: A timber frame of a house. Bracings are shown at the top of each of the columns connected to the beams. This is to reduce the compressive force pushing down and assists in preventing buckling of the column.


 
 
 


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Steel: Commonly used in cantilevers to reduce the weight of the dead loads.
 Steel joists, beams and columns are all supported on girders that attach the cantilever to the building. The frame of the Architecture Building is a prime example of this in action as all of the components help each other.
 The long diagonal beam shown in the photograph is under an enormous amount of tension. Without this beam in place, the cantilever wouldn't have enough strength to hold itself up.

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 IMAGE 3: A cantilever at Melbourne University’s new Architecture Building. This image shows what makes up the frame of a cantilever.


Load Bearing Walls
 Concrete: Used to support the weight of the above structure instead of just a wall which is used just to enclose the house. They can be used around lift wells or stair wells. They use their compressive strength to hold up loads and then transfer the load into the foundation.


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Reinforced Masonry: Masonry walls that are built from concrete blocks can be reinforced by placing rods through the centre of the blocks and then grouted in place with a mortar mix. 
 Bond beams over openings are created by using special concrete blocks that are filled with concrete and held together to cure. Once the concrete is set, the blocks need no support to hold themselves up.

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Solid Masonry: Load bearing walls that are created with one or multiple skins of masonry units or clay bricks. The skins of masonry can be joined together either with wall ties or by using a brick with the header showing in the face of the wall).
 A lintel(made out of steel) is used in openings.! Cavity Masonry: Usually formed with two skins of masonry.
 The perpends(vertical mortar in-between bricks) on a masonry wall can be left hollow to allow an exit for any water. These gaps are called weep holes.

A steel lintel supporting above a window/door.

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A weep hole that is located at the bottom of one of the perpends at my house. Weep holes are usually located towards the bottom of a wall to allow any water absorbed above the hole to be drained out.


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Stud Framing! 


Metal and Timber Stud Framed: The thinner vertical studs mean that they needed to be repeated more often to oppose this loss in strength. Another approach could be to construct less studs and make them thicker. The noggins are then placed to prevent the long, thin studs from buckling.

Plywood can act as a bracing when used as a sheet. This allows the structure to more stable without being affected by sheer forces as shown in the diagram below.

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Brick veneer construction: One layer brick and one layer timber. The load is carried down the timber studs, through the bottom plates, onto the joist, onto the bearers then down to the foundation. The brick masonry forms the exposed exterior of the building.


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IMAGE 4: The base of a brick veneer wall showing the bottom of a column and the first 5 layers of brickwork. The masonry wall isn’t taking any of the load so therefore it can be created more aesthetically than structurally stable.


! Knots: A knot in a piece of timber is considered a weak spot because the knot causes a slope in the grain. In the Constructing Environments Workshop some of the ‘bridges’ that we built broke due to knots in the timber. To avoid this, ‘clean’ timber can be used which is knot-free. If there is a knot in a beam for example, the knot should be towards the top of them beam as the beam will be in compression at the top and tension at the bottom. The tension is what causes the area around the blemish to crack open. IMAGE 5: A knot that has causes the grains to go around it making the piece of timber structurally week. A resulting crack is shown where the grain has had to avoid the knot and take a 45 degree angle instead of staying horizontal.

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Timber Properties and Considerations
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! Properties


The characteristics and properties of wood depend on the type.
 Hardness- Fairly low as it is easily able to be marked.
 Fragility - Depending on the shape of the timber, however usually low.
 Ductility - Low, but can be manipulated into a curved form.
 Permeability - High, therefore it needs to be protected from weather.
 Poor conductor of both electricity and heat.
 Very durable but does depend on finishing and the weather it’s exposed to.
 Generally cheap however labour may cost for onsite work.

Softwood - Radiata pine, cypress pine, hoop pine and douglas fir. (pines)
 Hardwood - Victorian ask, brown box, spotted gum, jarrah, tasmanian oak and balsa wood.!


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! Timber is graded according to its strength. Fgrade and MGP gradings are commonly used.


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The issues with timber that need to be taken into consideration are water, insects such as termites, fire and weak points such as knots. Some timber products come with an insect repellent. You can also paint the exterior of the timber with a waterproof cover to avoid rotting from rain and this cover can also be semi fireresistant. 


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IMAGE 6: A fire retardant coating that is painted on in three layers. As fire is one of the biggest weaknesses for a timber construction, being able to withstand fire for an extended period of time may save the structure. Most commonly used in bushfire prone areas.

From Wood to Timber
 
 Seasoning is another way of saying drying. Timber is seasoned to increase it’s stability and so it is appropriate for the intended use. 
 The moisture can be removed by air seasoning which is cheap but takes 6 months to 2 years per 50mm of thickness.
 A quicker way of removing water is kiln drying which typically takes between 20 and 40 hours to dry 12% of the timber. There needs to be less than 15% of moisture left for timber to be classified as seasoned timber.

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IMAGE 7: A digram of how kiln drying is used in action. A fan pushes are through heating coils and then is allowed to flow through the gaps inbetween the pieces of timber. This is much more effective than air seasoning as the air is heated and it is constantly circulating.


! ! ! ! ! ! ! The grain direction helps us determine the strength of the wood. If a force is applied parallel to the grain the timber will remain stiff. If forces are perpendicular to the grain, either pulling or compressing, this is a weakness and could cause the timber to crack.

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 As the amount of rainfall varies annually, this creates the alternating light and dark rings inside the tree. Generally there is only one ring each year however some climates may have more than one growth season producing multiple rings each year. Another factor can be fire or disease which can produce another ring.

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 IMAGE 8: The cross-section of a tree showing each of the rings produced annually. Not only can these rings tell you the age of the tree but they can give you information about bushfire activity in the life of the tree.

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! ! ! ! ! Green Sawing!

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Quarter Sawn: Growth rings parallel to short edge. The advantages of quarter sawing are that the grain can be shown on the surface, it’s good for floors and furniture and it can be readily coated.
 The disadvantages however are when nailing into the wood it’s prone to splitting along the rings.


 


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Back Sawn: Rings parallel to long edge of piece. More commonly uses in structural timber.
 The advantages of back sawing are less prone to splitting when nailing, fewer knots and the piece of timber and wide pieces are possible compared to quarter sawing.
 Disadvantages are that it has a higher chance of warping than quarter sawing and it shrinks

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Radial Sawn: A wedge is cut out of the timber when radial sawn.
 The benefits of radial sawing are it has high stability, it’s less prone to warping and theres less wastage of timber.
 The wedge shape gives the timber some negative attributes; it’s difficult to stack and difficult to detail.!

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Plywood: Because timber has grains, the plywood must be made in such a way so it doesn't crack down the grains and makes it a lot more stable. To do this, each layer of the plywood is glued together alternating from vertical to horizontal as shown in the diagram above. Plywood can be used structurally as a sheeting brace for a wall. This eliminates the effect of sheer forces trying to push the structure over. (refer to stud framing sketch)

LVL(laminated veneer lumber): Sheets of thin timber with grains running in the same direction. In strength it is comparable to solid timber or concrete. It’s manufactured by putting thinly sliced timber veneers under heat and pressure.!

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IMAGE 9: A LVL piece with all grain running in the same direction. Similar in looks to plywood except for the grain pattern.


A knowledge table of the key points from Peter Ashford’s lecture. !

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Practical - Model Oval Pavilion !

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The section of the Oval Pavilion that we had to build was the south-west section including the cantilever. We had to build this at a scale of 1:20. As the scale of the plan was 1:20 this worked out well. However, we had to double each distance due to the plan being at the size of A1, not A3.

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We constructed the beams out of foam board and the columns out of cardboard. This was a useful material is it was relatively easy to cut with a basic stanley knife. This quickened construction time and the materials, once glued together, were sturdy.


To increase the stability of the columns we cut out holes 6mm in diameter in the base to allow for the columns to fit into them. As the super glue works better the more surface area it has joining two materials, the edges of the hole we cut(compared to the column just sitting on the base) will increase surface area allowing the glue to attach more of the column to the base.

! The material we used for the columns was cardboard. We rolled it up into a cylindrical shape to increase stability by making the column solid rather than hollow. This decreased the chance of it buckling under the weight of the cantilever and roofing system.

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! ! We decided that by cutting the supports parallel to the above beam it would increase the available surface area for the glue to stick. Thus increasing the overall strength of the structure and also quickening the construction time.

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! ! ! When we came to gluing the cantilever to the main truss we found that it was going to be a challenge to glue it on without any support on the other end. We decided to construct two supports(one shown in the picture) to hold the cantilever in place until the glue was dried.

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Our model was only a section of the Oval Pavilion. One of the other groups did the basement and first floor of the building which proved to be quite challenging. This was because the plans weren’t as straightforward as the cantilevered section. Most builders would have built many floors, walls and basements in their lives so the detail of the plan doesn't need to be as precise. However, a cantilever (this cantilever in particular) is sometimes an odd shape and is much more uncommon than a room.

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The first problem that they encountered was that the glue wasn’t strong enough to hold the load-bearing walls in place. They therefore had to use masking tape which maybe be stronger in the short-term but can weaken as it is stored for extended periods of time. They did also find it difficult to read directly from the plan as it wasn’t as clear as other parts of the structure.

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The third group constructed the other half of the cantilevered section. They encountered the same problem as the other group as their glue wasn’t drying quick enough. They therefore had to resort to using masking tape. Their model did manage to stand however it was quite flimsy due to the columns being weakly attached to the ground.

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Finished product
 The finished product of the model turned out quite well. We did however encounter a few problems; one of them being the foam board becoming weak due to over-handling. In the bottom of both of these pictures, it is evident that the foam board has broken. Also, some of our measurements were slightly wrong but only by a few millimetres. However, in a real life construction, even a few millimetres can be the determining factor whether someone gets fired or not. Because of our short time period to complete this task, we managed to get to a pretty accurate finalisation of the model.

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Glossary! Stud: The long vertical components used in framework.
 Noggin: A short, horizontal piece of timber attached to the studs that is used to support a framework.
 Lintel: A support made out of steel, timber or concrete across the top of a door or window.
 Axial Load: Vertical loads that are usually found in columns.
 Buckling: When a load to great is forced upon a column or long vertical beam, the column fails and collapses.
 Seasoned Timber: Timber that has been dried leaving under 15% moisture left.!

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References:
 
 E-learning:
 https://app.lms.unimelb.edu.au/bbcswebdav/courses/ENVS10003_2014_SM1/WEEK%2005/ SHORT%20AND%20LONG%20COLUMNS.pdf 
 http://www.youtube.com/watch?v=Vq41q6gUIjI&feature=youtu.be 
 http://www.youtube.com/watch?v=YJL0vCwM0zg&feature=youtu.be 
 http://www.youtube.com/watch?v=ul0r9OGkA9c&feature=youtu.be 
 http://www.youtube.com/watch?v=0YrYOGSwtVc&feature=youtu.be 
 
 
 IMAGE 1: http://www.polycount.com/forum/showthread.php?t=62741 
 IMAGE 2: http://woodframesystem.wordpress.com/wood-frame-system/components/ 
 IMAGE 3: http://nadaaa.com/blog/?cat=76 
 IMAGE 4: http://www.boral.com.au/bricks/brickInsights/bricks_mortar.asp ! IMAGE 5: http://www.123rf.com/photo_20270578_old-wooden-board-with-timber-knot-forbackground-or-texture-macro-shot.html 
 IMAGE 6: http://www.spec-net.com.au/press/0208/cea_060208.htm 
 IMAGE 7: http://www.physics.otago.ac.nz/nx/eman/abstract---c-davis-phd-energymanagement.html 
 IMAGE 8: http://disjointedthinking.jeffhughes.ca/2010/12/contesting-christianity-young-earthcreationism/ 
 IMAGE 9: http://www.diytrade.com/china/pd/7299040/Laminated_veneer_lumber_LVL_LVB.html 
 http://www.woodsolutions.com.au/Wood-Product-Categories/Laminated-Veneer-Lumber-LVL 
 


Ching, F. (2008) Building Construction Illustrated (4th ed.). Hoboken, New Jersey: John Wiley & Sons, Inc. (pp. 5.16, 5.17)


Log Book - Week 5  
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