Forces “A force is any influence that produces a change in the shape or movement of a body” (Ching Building Construction illustrated 4th ed 2.11) forces are vector quantities represented by arrows whose orientation represents the direction of the force and size the magnitude. Collinear forces Occur along the same line of action. The resultant force is the algebraic sum of the component forces. Concurrent forces Have lines of action that intersect at a single point. Their effect is equal to their vector sum. This can be found by resolving the vectors into their horizontal and vertical components or adding the forces graphically ‘head to tail’ A Moment is a force that causes a body to rotate about a single point. Similarly a couple is a pair of parallel forces acting in opposite directions but along different lines that cause rotation. Buildings can be overturned by lateral loads above a buildings centre if they are not counterbalanced by the restoring moment of the structures dead weight
Site Analysis take into account Area & shape of site defined by its legal boundaries Area required for the building, any landscaping or future development Topography, soil conditions, drainage patterns and water table depth. Vegetation, waterways or heritage features that should be preserved Climatic conditions including path of the sun in various seasons, prevailing wind direction etc. Availability and location of on-site of utilities such as water, phone lines & electricity. access to roads & how to circulate foot and vehicle traffic on site context of the site as part of a larger area, eg character of the neighbourhood, sources of noise or congestion, desirable or undesirable view
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Loads Forces acting on a building that it must withstand Static Loads Are applied slowly to a structure without rapid fluctuations in size or position. Dead load are permanent Static loads such as the structures self-weight, and act vertically downwards Live loads Are applied movable loads, such as those that result from occupancy or the accumulation snow water or sand. Typically act vertically downwards but can also act horizontally moving
Materials Properties to consider Strength Stiffness/flexibility Shape - Monodimensional (linear) - Bidimensional (planar) - Tridimensional (Volumetric) Material Behaviours Economy – Price, availability, efficiency, transport distance Sustainability, of production as well as over the buildings life.
Dynamic Loads Loads that may be suddenly applied to a structure and will vary rapidly in magnitude, direction and point of application
Material Property Isotropic materials such as steel and other metals Perform well in both compression & tension Anisotropic materials are stronger in one than the other, for example Masonry is strong in compression but not tension
Wind Loads Are exerted horizontally by the force of moving air against a building on vertical surfaces and those with a slope of greater than 30 degrees. Exerts positive pressure on the windward side of a building and negative pressure on the leeward side
Material “MDF” or Medium Density Fibreboard. Is used everywhere in furniture construction because it is cheap. Dangerous to inhale dust when cut as it contains formaldehyde, some architects Specify EO MDF which does not. Disintegrates when wet
Earthquake Loads Are exerted horizontally at ground level. The upper levels of the structure are generally held in place by inertia while the base is translated horizontally. Causing a lateral force on the structure called base shear.Taller thinner structures or those built on soft soils are more vulnerable to earthquakes
Material “Melbourne Bluestone” or volcanic basalt native to the Melbourne area, Dark navy colouring. Very hard material, used in roads and the foundations of older buildings in Melbourne. This wide use of this gives Melbourne its dark colour
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Studio 1 - Mass Tower. Objective – to build a tower as high as possible using only the supplied MDF bricks, which must accommodate a Godzilla toy supplied by our tutor In choosing a site to build our tower we looked for flat a section of carpet (some had lumps in it). This meant our tower would have a stable footing. A wide base with walls the thickness of 3 bricks end to end for stability was laid out in the shape of a rectangle with rounded corners. The corners are intended to allow the upper layers of the structure taper inwards, as this is a more efficient use of materials & will make the tower lighter The straight edges are to allow an opening with a straight load bearing beam across the top as the entrance for the object provided by our tutor (A Plastic Godzilla). The length of these sides was minimised where possible but needed to be at least 6 bricks wide to accommodate Godzilla
Layout of Tower Base
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From here 3 separate stretcher bond walls with a gap of about a 1cm between them were constructed on this base. These walls were 4 blocks high this style was chosen because is stronger than a stack bond as the load on each brick is distributed between the two bricks beneath it, (see load path diagram) and once enough load is applied the bricks act like an interlocking network, held in place by the weight of those on top of them. The use of the stretcher bond system also allowed us to leave a gap between bricks without reducing the strength of the structure. This meant we were more efficient with our use of bricks and also reduced the structures weight, and thus the selfload on its lower levels Next two bricks were placed over this linking the 3 layers. This was Influenced by the use of braces between separate layers of masonry in Brunelleschi’s Dome of the Basilica di Santa Maria del Fiore (Kevin McCloud’s Grand Tour, Lecture 1) Two separate walls of the same stretcher bond pattern as previously described 5 bricks high were built on top of this, before being joined by a single brick.
Construction of Base
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On top of this a single stretcher bond wall was built, with the bricks resting on their narrow sides This method allowed construction to progress very rapidly, as we were operating in a short time frame and had found our previous construction methods to be prohibitively slow. It also had the advantages of using half as many bricks to achieve the same height as when they were lain flat, which in turn increased our material efficiency and reduced the dead load on the buildings lower levels, most importantly the door Walls constructed in this way are less stable than when the bricks are laid flat as they have a higher centre of gravity and smaller base area so are less likely to form a restoring moment if a lateral load is applied Interchanging layers of flat bricks and bricks on their side were used on higher levels of the building as this provided greater stability The door to Accommodate Godzilla was constructed out of a lintel made of bricks held together with elastic bands, which distributed the weight of the bricks above two columns. Two lintels were used to reduce the load on each by sharing it.
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When the Deconstruction of the tower began we found The whole outer wall of bricks could be removed from the base of the tower without affecting its stability, as most of the towers self-load was being transferred by the most direct route to the ground through the inner two walls. Where the tower tapered to two walls the outside wall could also be removed for the same reasons described above. Narrow rounded holes could be made in the walls of the tower without it collapsing as the stretcher bond brick pattern would distribute the load around them, behaving like and arch. The Tower completely collapsed when we attempted to make larger holes in the side that were wider and non – rounded as they no longer acted like archways In comparison with other group’s towers, ours had a much larger base area. This put us at a disadvantage as for each layer of bricks added to the tower we required more time and materials. This resulted in our tower not reaching the same heights achieved by other groups.
Tower with Narrower Base, More Efficient.
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Wk 1 References ENVS10003 (2014, March 6). Melbourne’s Bluestone. Retrieved March 11, 2014, from http://youtube.com/watch?v=CGMA71_3H6o&feature= youtu.be ENVS10003 (2014, March 5). Introduction to Materials. Retrieved March 11, 2014, from http://youtube.com/watch?v=s4CJ8o_1jbg&feature=you tu.be ENVS10003 (2014, March 5). W01 s1 Load Path Diagrams. Retrieved March 11, 2014, from http://www.youtube.com/watch?v=y__V15j3IX4&featur e=youtu.be McCloud, K. (Presenter). (2009). Episode 2 [television series episode]. Kevin McCloud’s Grand Tour. England: Channel 4 [UK] Ching, F. (2008) Building Construction Illustrated (4th Ed.). Hoboken, NJ: John Wiley & Sons.
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Types of Structure Solid – Stone, bricks, Compression, arches efficient Surface/Shell - Planar Frame/Skeletal - long, ridged elements, some in compression and some in tension, very efficient at transferring loads to the ground. Membrane – Everything in tension, like sails Hybrid – A combination of at least two of the above. almost all structures are hybrid to an extent
Membrane Structure: Retrieved March 19, 2014 from http://www.structureflex.com.au/PVCMembr anes.php
Structural Joints Roller joint, only vertical load, moves when lateral load applied, good when thermal expansion must be considered Pin Joints, allow attached members to pivot but not translate, used in truss systems. Fixed Joints – does not allow for rotation or translation of attached members, means one member deforming can cause others to.
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Considerations When Building Precedent is often a good guide Regulatory Constraints Aesthetic Economic – Initial Cost & life cycle cost (longevity and cost to run over lifetime) Environmental Impact – Linked to lifecycle cost. Good design can reduce electricity & water use & waste during construction. Consider embodied energy/CO2– the amount of Energy/CO2 used in sourcing manufacturing & transporting a product. Recyclability of products, try to think of construction process as a circle not linear. Common ESD Strategies – local materials, material efficiency, thermal mass, night air purging, solar & wind energy, cross ventilation, insulation, water harvesting & recycling, smart solar design Performance Requirements – Insulation of heat & Noise, fire resistance, resistance to corrosion, strength Constructability – Difficulty of construction. Labour, equipment, access to site.
Building Systems. A system is “an assembly of interrelated … parts forming a more complex and unified whole and serving a common purpose” Ching (2008) Ch2.02. Some systems present in buildings are Structural System – Supports and transmits to the ground loads applied to the building (superstructure above ground, substructure below ground) Enclosure System – skin of the building, shelters interior spaces from weather, noise etc. Service Systems – delivers services (electricity, sewage) Some ESD Considerations
Some arrangements of form Column & Wall Arcade an example, two parallel vertical planes, one with arches cut out, when viewed along length columns appear solid in the distance. Apparent how the structure works Point & Plane Points become lines, lines planes, Contains no volumes, implied by different planes, not apparent what is structural and what is defining space as they rarely join in a single form
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Studio 2 – Frame Tower Objective: To construct a frame tower that reaches the roof of out tutorial room without collapsing using only the one sheet of balsa wood provided and glue to connect members.
Our group elected to build a triangular prism shaped tower with a 600mm equilateral triangle base. Vertical elements 600mm in length joined two identical triangles to form a triangular prism The tower then tapered inwards to a triangular prism with 400mm horizontal sides, before finally tapering in again to a triangular prism with 200mm vertical sides This shape provided a compromise between the stability of the wide base and the material efficiency of a narrower tower. The balsa wood was cut into 40 very narrow strips (around 2.5mm thick). These strips were extremely light as well as weak in compression and relatively strong in compression The superglue joints acted like fixed joints as they did not allow translation or rotation of adjoined members relative to each other
Fixed Joints
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The vertical members of the structure behaved like narrow columns when subject to compression loads because of the towers dead load. This caused them to buckle because of their relative slenderness (600mm x 2.5mm) and the use of fixed joints. To counteract this they were diagonally braced. At Higher levels the diagonal braces were abandoned due to material shortages and the negligible dead load on these structural members because of the lightness of the balsa wood. The tower was able to support its own minimal self-load, but when live loads were applied it was apparent that the building had many weak points where it was likely to fail, especially along it vertical members Most of these were due to the design of the tower not suiting the nature of the materials used. The upper levels of the tower behaved like a narrow column and were susceptible to buckling under the slight applied load and would have snapped under any significant load
Upper Levels Behaving like Narrow Column
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Due to the length of their vertical members relative to their thickness and the lack of supporting braces to make the structure rigid The vertical members of the structures at lower levels were also prone to buckling along their length. The braces used to prevent this were largely ineffective because they were attached around 100mm from the top of the vertical element. This simply resulted in a 500mm column like vertical member which was only slightly less prone to deforming than an unbraced element as it was still very tall relative to its with Another reason the braces were not very effective was that they were attached to the vertical elements with fixed joints. This caused the braces to also deform when the column like elements did so that a constant angle was maintained between them. If they had been attached by pin joints they would have been more effective as they would have been acting in tension rather than having a lateral force applied to them
Braces not attached to point most prone to buckling
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Braces Bending to Maintain Fixed Angle Wk 2 References Envs10003 (2014, March 9). W02 c1 Construction Systems. Retrieved March 13, 2014, from http://www.youtube.com/watch?v=8zTarEeGXOo&featu re=youtu.be ENVS10003 (2014, March 9). W02 s1 Structural Systems. Retrieved March 13, 2014, from http://www.youtube.com/watch?v=l-JtPpI8uw&feature=youtu.be ENVS10003 (2014, March 9). W02 s2 Structural Joints. Retrieved March 13, 2014, from http://www.youtube.com/watch?v=kxRdY0jSoJo&featur e=youtu.be ENVS10003 (2014, March 9). ESD & Selecting Materials. Retrieved March 13, 2014, from http://www.youtube.com/watch?v=luxirHHxjIY&feature =youtu.be ENVS10003 (2014, March 9). Framework for Analysing Form. Retrieved March 13, 2014, from http://www.youtube.com/watch?v=KJ97Whk1kGU&feat ure=youtu.be Ching, F. (2008) Building Construction Illustrated (4th Ed.). Hoboken, NJ: John Wiley & Sons.
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Glossary Tension forces Occur when part of a structure is pulled and particles in it move apart. The amount a material stretches depends on the magnitude of the load, its cross sectional area and the individual properties of that material Compression forces Occur when a force part of a structure and particles move closer together. This shortens the material. Columns Relatively thin, rigid vertical structural members designed to support axial compression loads applied to their ends Beams Rigid horizontal structural members Designed to transfer vertically applied loads laterally across space to supporting members. Subject to bending which must be resisted by materials internal strength.
Load Path The Path through which a load on a building is transferred to the ground. Loads always take the most direct route possible. Reaction Force The force applied by the ground on structural members that push down on it, in accordance with newtons third law. For a structure to be stable this must be equal and opposite too the applied load, holding it still. Point Load A load that acts on a structural member at a specific point rather than being distributed across it.
Stability The likelihood of a structure to collapse. Its ability to resist external forces applied to it and those of its own self load. Bracing The use of diagonal member(s) to strengthen a square frame structure against lateral loads Masonry Discrete building blocks (eg stone, bricks, concrete blocks) held together with mortar. Masonry walls are strong in compression but weak in tension
Structural Joint The means by which two discrete structural members are fixed to each other and how loads or forces are transferred from one to the other. Frame A type of structure composed of long, ridged elements, some in compression and some in tension, very efficient at transferring loads to the ground. Page | 14