Week 3:
Today we went to have a look at some buildings around the University. The Architecture building spans over six levels and 17,488 square metres. Downstairs in the basement there are a two 120 seat lecture theatres and one 500 seat lecture theatre. There is a hanging studio in the atrium with a capacity of around 30-‐50 students. The library is down in the basement, with study spaces on the level 1 atrium. The rest of the floors from 1-‐5 are tutorial rooms and staff/academia offices, with access by 2 flights of stairs and 5 lifts. Structural components of the building The building has a basement level and 5 floors. The basement retention system consists of 12m bored piles with ground anchors and a capping beam cast on top of them. The basement has a reinforced suspended slab and the rest of the floor slabs from Ground, 1-‐5 are Bondek composite slabs with post tensioned 600mm beams. The columns in the building are all precast to save time compared with insitu and the lift and stair core are also precast panels. Concrete panels with a smooth white off form finish are cast in to the slab beam system (shown on the right). These act as shear walls and are precast with mesh as reinforcement. Later the outer zinc façade screens will be bolted with 4 x M20 High strength bolts to the panel which will connected it. The façade serves no structural purpose and is a layer for aesthetics. Lastly for the Joseph Reed Façade (below) that is being incorporated in to the new design is being supported by a retention system to prevent it stability from lateral loads until structurally attached to the rest of the building. This retention system consists of temporary and permanent system of steel UB and UC (similar to the Oval Pavilion Canopy). The permanent retention system is cast in to the slab and welded with angled brackets and stitch plates.
Slabs, Footings and Foundations There is a basement floor in this building, so there are strip footings that the basement slab sits on. Part of this basement retention system is bored piles held in by ground anchors. This is structurally connected to a capping beam, strip footings and both the ground and basement slab. Depending on the soil conditions effects the centre to centre spacing of the bored piles. The bearing capacity of the soil, depends on the area of the footings, however the depth of the footings depends on how reactive the soil is. Slab and Beam system The slab is a Bondek permanent formwork system, where the Bondek acts as bottom reinforcement in tension. The beams are post tensioned. The slabs and beams are poured at the same time as well as the columns for that floor. Columns transfer load down to beams, then through slab and so on for each floor until it gets to the foundations.
To the right, it shows loads of the 800mm thick beam. The beam takes the uniformly distributed load of the slab and transfers it to the beam. As the arrows along the beam show, the forces are then transferred along the beam to the supports (columns) at each side. The columns 600 x 600 then transfer the loads through compression down to the footings and then to the foundation.
Week 4 Today we learned scale, annotation and working drawing conventions with the Oval Pavilion drawings.
The notes on the ground floor plan 1. Erection sequence 2. Legend 3. Consultants 4. Client 5. Revision no. 6. Drawing title 7. Project number 8. Title
Drawings 1. Ground Floor Plan (1:100) 2. Sections 3. Elevations (dosent show structural components 4. Structural Services 5. Details (Wall typically 1:20 or 1:5) 6. Roof Plan 7. Window schedule
Legend for Structural Drawings 1. Concrete beam sizes and reinforcement and ligatures 2. Depth of concrete slab 3. Columns schedule 4. Masonry schedule 5. Grade of Concrete 6. Spacing of Ligatures 7. Lap length and cog length of steel reinforcement.
Above are some of the things we looked at. There are always many consultants on the job, so there name is on the drawings as a sign of
their approval as they all have expertise in certain fields to help the drawings become certified and meet Australian standards. Some may to make sure the bench height is right, it has enough space to serve food etc. The are consist of Food service consultants for like kitchens engineers which inspect structural drawings, electrical for services and mechanical. There are heritage consultants that help consider the best way to incorporate facades or vegetation. Landscape architects consider the terrain, soil and gradient of the site. Architects are in it is for its use. charge of making sure it fits the clients criteria in terms of interior fittings, size and how appropriate
Figure 2: Consultants for Project Figure 1: From Oval Pavilion
Bricks Manufactured from clay or Shale, then hardened by a firing process, can have holes in the middle for reinforcement. Can be used for walls, arches and paving. Mortar are in between the joints, an are 10mm thick. There are different finishes due to its exposure to weather, or the final finish. Bricks are relatively strong and durable, it is brittle but has good compressive strength, however hard to be shaped. Medium density and cost effective. Disadvantages, labour intensive, need regular expansive joints due to it absorbing moisture and expanding. Corrosion may occur if exposed to salty air and this can effect it visually.
Figure 4 : These are the dimensions of a brick. When the width 110mm is doubled it equals 220, with room for 10mm of mortar, makes the length be 230mm
Figure 3 : Types of patterns that bricks can be arranged in, with 10mm thk mortar in-‐between. Depends on the visual effect with different patterns or may be for a window opening or work around an object.
In-‐situ Concrete • • • •
Liquid, Plastic texture, once set, good compressive Sequence: Formwork, Reinforcement (Mesh, bottom or top reinforcement, ligatures and starter bars may be placed) , Pour or pump, vibrate and curing. Curing: Chemical process of hydration and hardening of the concrete. Control Joints, for when concrete shrinks, still have to structurally connect the two different pours together.
Figure 5: Shotcrete, High slump, sticky, pressurized to compact the concrete at time of placement. Good for retention systems basement
Week 5 Columns Slenderness of the column is the width to length ratio. It determines the compressive strength of the column, short columns are usually used when structurally important and if only part of secondary structure, slender columns are used. Slender long columns are more likely to fail through buckling. Buckling is when there is excessive bending and causes the column to fail. We prefer columns to fail by crushing, which is from shear force where the compressive strength is exceeded. To increase strength of column • • • • •
Add another column (hence distribute the load over two supports instead of one.) Increase concrete strength, ie 50MPa compressive strength is better than 20MPa. Increase size of ligatures of main bars of steel reinforcement (ligatures stop the main bars from buckling outwards) Increase cross sectional area to distribute the force over a grater area. Make the column shorter, or fix the ends as a rigid or pin connection to allow a smaller K constant and hence reduce buckling failure.
Timber Properties Hard and easily marked, can be bent into new shapes from steam pressure, it is a poor conductor of heat and electricity. Made up of fibres and needs to be protected as it quite porous and can absorb moisture. Timber has a low embodied energy and is quite renewable depending on country and if it is renewably sourced. Strength graded , either visually or machine graded, to find the load it can take. Can be seasoned or unseasoned. Seasoned reduces variation in size of timber If it has more than 15% moisture content is unseasoned, or if less than 15 % moisture content is seasoned (note a growing tree is 100 %). Can do this through air drying, or kiln drying 48 hours but more energy costs. May need to be treated to reduce termites or fungi from growing, depends on climate. Look at the grain of the timber, and don’t put knots in the tension side as wood is stronger in compression than tension. Knots are stronger in compression than tension. Timber is relatively good in tension and compression parallel to i Figure 7: The fibres when subject to tension and compressive forces in the parallel direction to the grain is relatively strong Figure 6: The strength of wood is not very effective when subject to compression and tension forces perpendicular to the grain, so the direction of the grain needs to be considered
Walls, Grids and Columns Light Gage Cold form steel, could be Cee or Zed Purlins, keeps the dead loads down and are used for roofing systems. Steel frames are good for temporary supports and also for reducing weight and floor space when compared to concrete. Universal columns are equal sizes for the flanges and webs to allow compressive forces to not buckle in either direction. Universal beams need to have a deeper flange than web, this is due to the bending moment of a beam spanning over supports. Load bearing walls have steel reinforcement inside it and are either insitu or pre cast. Reinforcement can be grouted inside masonry to make reinforced masonry. Steel lintel can be used to transfer forces around window openings. The options for solid masonary are concrete masonry units or clay bricks. They can be double skinned or brick veneer (one layer of bricks and timber stud). The two skins are connected together with metal cavity wall ties.
Timber stud frame is needed to be braced and noggings to reduce its effective length. It is usually covered up with timber plywood. The weep holes and damp proof course show that the wall is a cavity and has double skins, rather than a solid wall.
Week 6 Roofing Primary function is to provide shelter and protection for the users of the building. There a range of roofing systems from steep gable roofs, timber or steel structure or even a concrete slab as a flat roof (3 degree angle). Flat Roof • • • • •
Concrete slab with a waterproof membrane Metal decking or plywood as formwork Could have lightweight precast planks sitting on concrete or steel beams and columns. Can be useful to create roof gardens or carparks. Can consist of lightweight concrete insulation, membrane and rubber coat to prevent wearing.
Pitched Roof • • • • • •
Pitch greater than 3 degrees Tiles need to be at a greater slope than sheet metal, due to waterproofing and the profile of it. Roof beams and purlins on top which roof sheeting connects to. Portal frames have rigid connections between beams and columns and span large distances. Z or C shaped purlins to hold roof sheeting. Timber gable roofs consists of Ridge beams, rafters, joists, ceiling top plates, under purlins. Hip roofs are similar to Gable and are used around irregular shapes/ folds around a corner i.e. a L shape roof -‐Common Rafters
-‐Ceiling Joists
-‐Ridge -‐Valley Rafter -‐Hip Rafter
Trusses • •
Efficient beams, span long distances with relatively low materials. Timber and Steel usually. Bracing allows better stability.
Space Frames CHS RHS or SHS , accommodate two way spans for large areas of glazing, often used for train stations, atriums or shopping malls. Site Visit Presentations Through the site visit presentations I found one groups sit of a medium rise development for apartment buildings quite interesting. Some of the key features was precast concrete and steel structure. This allowed for faster speeds of construction as no time was wasted for stripping and propping formwork as well as no need to wait for curing of concrete when poured insitu. A big issue for many buildings were the compliance with the Building Code Australia and Australian Standards to provide fire safety. For wall framing systems, special fire rated plywood was used and designs to that the building will collapse in and not out which would harm the people on the street and adjacent buildings. Usually fire ratings of 120 minutes are needed so that in multistorey buildings people can evacuate safely before the spreading of the fire. However for buildings with a sole-‐occupancy, where escape and exit routes are easier, fire ratings are less strict.
This week I had the Construction workshop on. • To the right is our “winning” design, where it took a total of 550kgs of a point load at mid span • The deflection was only around 30mm compared to others with up to 85mm deflection • Below on the left is another teams, which using similar material was only able to achieve around half the load capacity of our groups. • Materials were pine wood 30 x 30 x 1200 and Plywood sheet. • Plywood was strong in tension, however we used it to provide sheer strength and help bond the pine wood together. • Tools were a screwdriver, nails, hammer, saw and drill.
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Our design was based on the bending moment and sheer force diagram for a point load over a span. Bending moments show internals stresses inside the structural component due to an external stress (point load). Sheer forces are unaligned forces, pushing a one part of a body one way and another part in the opposite, hence the change in direction at the point load. We decided that the cracks or failure was most likely to occur at mid span The shape of our design followed the bending moment diagram and we tried to make it as thick as possible in the middle. The cracks still occurred at the middle although it was had 4 layers in the middle ½ of the span and only 2 layers at ¼ spans.