Structural Systems
Solid: early buildings such as the ancient Greek and Egyptian buildings composed of stone and brick and compression is the main structural action so arches are used well. Surface or shell: An example of a planar structure is the Sydney opera house. Skeletal or Frame: see it in modern construction, very efficient way of transferring loads through to the ground. Membrane: less commonly used in built environment. North court is an example membrane structure, also used in Sports stadiums exhibit this style. It is an economic and quick way of covering large areas. Hybrid system: Most structures are hybrid buildings, may have skeletal structure with membrane cladding, such as the Birds Nest of the Beijing Olympics.
LOGBOOK WEEK 2 – WILL CARDWELL
CONSTRUCTION SYSTEMS
Figure 1: Sydney Opera House Shell Structure (2014)
The construction systems include the Envelope or enclosure system, the structural system and the service system. When thinking about the structure, make decisions based on: performance requirements, aesthetic qualities (finishes), economic efficiencies and environmental impacts and constructability (context, climate, materials available) Performance requirements: Structural compatibility, fire resistance, comfort (insulation), rain protection, noise, soil movement, easily maintained, last long. Aesthetic qualities: proportion, colour, surface qualities and finishes (architecture). Economic: initial cost of building, life cycle costing (longevity of material and building performance to create comfort without air conditioning), efficient materials, access to site, prefabricated and in situ materials. Environmental impacts: embodied energy and efficiency of materials, air conditioning, natural or artificial lighting.
FRAMEWORK FOR ANALYSING FORM – ‘COLUMN AND WALL POINT AND PLANE’
Site conditions, need for facility, budget, materials Creative response to factors best architecture Strategies achieve this Building factors Column and wall, arcade consists of two vertical parallel planes, Point and plane, things begin at a point, then becomes a line and then a plane which then folding or bending to become a volume. 1 to 2 to 3d. Ends of line give the starting point. Large planes floors and walls of building, small planes modifying local spaces, lines which provide structure and spatial definition, small lines and planes which articulate the detail. Euclid is the key to both column and wall and point and plane. In column and wall clear demonstration of structure and construction, point and plane not sure what is structure and what spatial division is. Connection between design, construction and manufacture of materials.
ESD – Environmentally Sustainable Design – Things to consider when constructing a building to be environmentally sustainable include:
Orientation of the building: allowing in winter sun, protecting from hot summer sun. Water harvesting usage How ventilation is used to moderate temperatures. Building management lights being turned off when not needed, is air conditioning used or necessary? Green building strategies can reduce consumption significantly such as water, energy, CO2 emissions. Construction of buildings consumes large amount of resources. Making, transporting and constructing materials. Recycled materials. Design is crucial in environmentally sustainable buildings (architecture).
STRUCTURAL JOINTS The way loads are transferred depends on the joints and connections in the structure. There are three ways of joining structural elements:
ROLLER JOINT: loads transferred in one direction, loads from any other direction causes roller to move. Allow rotation but resist translation in a direction perpendicular into or away from their faces. Useful when a joint must allow expansion and contraction of a structural element to occur. Resists only vertical loads. PIN JOINTS: Common, useful to make calculations, in truss systems. Allow rotation but resist translation in any direction. Resists vertical and horizontal loads. FIXED JOINTS: Complex calculations, bending occurs, loads in one member can cause bending in joint. Maintain the angular relationship between the joined elements, restrain rotation and translation any direction, and provide both force and moment resistance. Resists rotational, horizontal and vertical forces, an example is a counter lever.
Figure 2: Joint Types (1995)
The Building (Ching, F., 2014) Buildings can be resolved to many interrelated systems forming a single structure. These systems can be categorised as the structural, enclosure and mechanical systems. Structural System: Designed and constructed to safely transfer gravitational and lateral loads to the earth, this means that the allowable stress limits for structural members cannot be exceeded. The superstructure is the vertical extension of the building above foundations. The roof and floor is supported by columns, beams and loadbearing walls. The substructure is the underlying structure forming foundation. Enclosure System: Shell or envelope of a building (roof, exterior walls, windows and doors). Walls and roof shelter from climate and control moisture, heat and air flow. Walls and roof also reduce the effect of noise and provide privacy and security for residents. Mechanical Systems: Provide essential systems to the building. This includes:
Water system. Sewage disposal. Heating, ventilation and air conditioning systems Electrical system (power, security, communication and lighting) Vertical transportation systems. (elevators in larger structures) Firefighting systems (sprinklers) Waste disposal and recycling systems.
The manner in which structures are composed of these systems depends on the performance requirements (fire resistance, prevention and safety, noise reduction, resistance to wear, structural compatibility), aesthetic qualities, regulatory constraints (zoning and building codes), economic considerations (initial cost materials, transport, equipment and labour), environmental impact (conservation of energy, energy efficiency and materials used) and construction practices (safety requirements, budget constraints, equipment required).
Figure 3: Building Systems (2014)
TUTORIAL SUMMARY
A counter lever is a structural member which has only one point of support. A span is the distance between two points of support, a spacing is the distance between like members. In order to allow beams to span longer distances, the depth of the beam must be increased. There is a limiting factor however, as a beam cannot get too deep to the point where it collapses under its own weight. In order to make beams span longer and increase depth without becoming too heavy beams can be hollowed out, or have holes made in the beam to decrease weight. This process forms a ‘truss’ however this is not a safe beam. The beam must be braced, using triangulation in both directions to resist lateral loads. Braces are formed in the triangle shape, because the triangle is the most stable shape. Another way to strengthen frames or structures is to add a shear panel using plywood.
TUTORIAL ACTIVITY The activity in the tutorial was to, in groups, construct a bridge made from plywood spanning 1500mm using glue, blu tac and a blade that could support the largest possible load. The group decided that by cutting the plywood into three pieces creating a joined single piece of 1250mm as well as 6 extra pieces giving a total length of 1520mm with supporting braces placed appropriately throughout the beam.
The design of the bridge encountered problems towards the end of construction as the beam was too wide and struggled to support its own weight across the span. The beam was 33mm wide with extra support weighing down in the middle. Another problem that arose late in the tutorial was the lack of strength at the end of the bridge, leading to added deflection with the heavy weight of the beam in the centre.
The result of the bridge was unsuccessful, with deflection due to weight of the bridge resulting in collapse as soon as pressure was applied. In an attempt to improve stability, the bridge was turned sideways, however this caused the weight to contort the bridge as it was now too narrow and it collapsed anyway.
In comparison to other groups, our bridge performed quite poorly, others elected to cut the plywood into many more, thinner pieces and glue together leaving spaces based on the truss principle. This functioned much better than ours as it significantly reduced the weight component.
The load path diagram for the bridge will show how the excessive weight flowed through to the edge but was too much for the bridge to sustain and pass through to the supports on either side.
GLOSSARY
Tension: When an external load pulls on a member, particles are pulled further apart from each other. Column: A structural member that supports compressive loads and is oriented vertically. They are short and thick, to prevent buckling to the side. Columns fail from crushing due to loads exceeding the strength of the column for compressive loads. Structural Joint: The way structural elements are joined, allowing forces to be transferred from on element to the next. Span: The distance between two points of support. Bracing: To improve the strength of a structure through triangulation, generally to resist lateral loads. The added elements are added in triangular shape, the only stable shape. Frame: A beam supported by two columns capable of resisting lateral forces.
A fixed frame is connected to its supports with fixed joints and is therefore more resistant to deflection however is vulnerable to thermal expansion and contraction and support settlements. A hinged frame is a rigid frame connected to supports with pin joints which prevent high bending stress by allowing the frame to rotate when strained by support settlements. A three hinged frame is composed of two rigid connections of pin joints and is more sensitive to deflection but less so to support settlements and thermal stresses.
REFERENCE LIST
Figure 1: “Sydney Ceramic Tile Pattern”. (2014). Retrieved from: http://www.sydneycloseup.com/ceramic-tile-pattern.html Structural Systems and Forms. (2014). Retrieved from : https://www.youtube.com/watch?v=l--JtPpI8uw&feature=youtu.be Construction Systems. (2014) Retrieved from: https://www.youtube.com/watch?v=8zTarEeGXOo&feature=youtu.be ESD and Selecting Materials (2014) Retrieved from: https://www.youtube.com/watch?v=8zTarEeGXOo&feature=youtu.be Structural Joints. (2014). Retrieved from: https://www.youtube.com/watch?v=kxRdY0jSoJo&feature=youtu.be Figure 2: Luebkeman, Chris H., & Peting, Donald. (1995). “Support and Connection Types”. Retrieved from: http://web.mit.edu/4.441/1_lectures/1_lecture13/1_lecture13.html Ching, F. (2014). Building Construction Illustrated. (5th ed.). Hoboken, New Jersey: John Wiley & Sons. A Framework for Analysing Form. (2014) Retrieved from: https://www.youtube.com/watch?v=KJ97Whk1kGU&feature=youtu.be