Log book, jshue

Week 1: Introduction to Construction

Structural

Timber (high Concrete grade)

Materials

Non Structural

Steel (UC and UB)

Aluminum

Brick Veneer

Forces: Tension and Compression Depending on the type of the material they have different properties that effect their capacity to take tension or compression. Concrete shows properties of very good compression while cannot take much load in tension. On the other hand, steel is very ductile and works well in taking loads in tension, it can take some compression loads as well. But given the cost of it concrete does it better and more efficiently.

We talked about how these two materials, having different properties work together to form a composite material, reinforced concrete.

Here are some examples on the right -­‐Single span: Concrete slab has a Uniformly distributed load over the span and the top part of the slab will act in compression and the bottom half in tension as a result of the load.

-­‐Continuous span: Concrete slab will experience tension over the supports (Top) as well as mid span (Bottom). If there is tension in the bottom half of the slab, the top is usually in compression, and vice versa.

Something to note, is that continuous spans are used as some large spans will not be able to be achieved with just a single span and a support or several will be needed in-­‐between to break up the spans.

Glass

Plastic

Ceramic tiles

Building Structure of a typical residential timber frame stud house.

-­‐Ridge: Connects the two rafters together

-­‐Rafters: Roof sheeting is attached to it and provides stability for suction and downward forces.

-­‐Struts: Reduces effective length of rafters and help provide lateral stability.

-­‐Ceiling Joists: Hold the roof structure together.

-­‐Top Plate: Connects roof to the walls

-­‐Stud: Transfers the vertical load from the roof down to the ground.

-­‐Bottom Plate: Transfers all the above load into the ground slab or timber flooring.

Materials used for construction are based on the supply and how readily available they are. Melbourne has an abundance of timber and most of the residential buildings are made out of timber. Hong Kong on the other hand may not have as much forests as land is very scarce there. They may tend to go for concrete buildings.

Before the 1900s before the industrial revolution they started using brick masonry to build, and when it got to producing 20 story buildings that were high for standards back then, they had to have the ground floor walls 5 or 6 skins thick to provide the stability required for the high rise building. This reduced the amount of floor space available and not many openings or glass windows could be incorporated. But nowdays, with the use of steel framing, or reinforced precast concrete walls (shear walls) we are now able to provide thinner and stronger structures using hot rolling or cold rolling of steel to form efficient and strong shapes to take loads.

When materials are produced in smaller more efficient shapes, this allows the structure become lighter. Steel universal beams are designed so that the flanges prevent lateral buckling and the web provides a large depth and has good capacity in resisting shear and bending. To expedite the construction process, new systems have been introduced, such as permanent formwork systems like bondek where time is saved from not having to strip formwork. Back propping is only required for 3 days and at much larger span intervals.

Precast lift cores and columns are able to be fabricated off site, and delivered when needed. They can be produced at up to 3 storey heights at a time, and crane lifted onto site when needed. The tolerances for being square and quality of the finish is much higher compared to when produced on site, in-­‐situ.

Week 2: Structural Loads and Forces

Transfer of Loads In a building all the loads and forces that effect it are transferred down to the footings, which then transfer the load into the ground (foundation)

The loads acting on the building are dead loads and live loads. Dead loads are loads that are constant in magnitude and fixed in location, these include lift core, Slab, beam, capping beam, shotcrete walls, façade panels and columns. Live loads are occupancy loads and include students (or currently construction workers), computers, furniture and other equipment.

Lateral loads consist of wind and pressure of soil against the basement retention system.

Depending on how stable the soil is, effects the centre to centre spacing between the bored piles and the depth of excavation. When excavating the basement, the bored piles had post tensioned grouted anchors used to resist it from the pressure (lateral load) of the soil. Once the basement and ground floor slab is poured, the anchors will be de-­‐ tensioned and the slab will act to resist the lateral loads of the soil in the basement.

Wind loads are resisted by shear walls. The column and beam connections are rigid and can withstand wind loads.

The gravitational loads (live and dead loads) are placed on to the slab and are transferred to the beams which then transfers it to the columns. Depending on the span of the slab and beam, the loads transferred and depth will vary. For example, the basement lecture theatre spans 18m with its beams as compared to normally 8-­‐9m spans. Columns will take a larger gravitational load from a deeper beam. This load path from slab to beam to column occurs from level 5 down to level 1.

At level 1 (ground) the columns transfer the load down to a capping beam shown on the photo on the right. The capping beam is made from reinforced concrete and distributes the load evenly and then down to the bored piles into the ground. The bored pile is designed so the bottom surface, its bearing capacity is enough to support the whole 5 floors above it.

ESD

Passive

Material Selection

Thermal Mass

Active

Maximising Sunlight

Insulation

Orientation

Heating and cooling

Shading

Maximising fresh air and wind

Grey water treatment

stormwater collection

Reducing carbon emmisions

Minimising wastage

Night purging

Savings

recirculating air

Waste water recycling

Glazing

Cross`low ventilation

Plants and trees

Automated lighting controls

Solar Power

Thermal

Higher indoor air quality

Thermal mass: a material that is very good at storing heat. An example of this is brick or concrete. This property is used in buildings by giving a delay in the time it takes to gain the temperature. It can store day time heat and radiate it off later at night when it becomes cooler. Oppositely a thermal mass will keep a house cool during the day from the thermal mass being cooled during the night.

By applying this to ESD it can give savings in heating and cooling costs.

Insulation: This helps retain heat and is useful in winter for houses with timber framing walls and roof. With a efficient heating system, very little heat escapes if a house is well insulated in the floors, roof and windows. Even water pipes use insulation, to prevent hot water loosing heat when travelling between the tap and the tank.

With our Balsa wood tower that we built, our design was either a triangle base or square. Obviously the square imposed greater area to transfer the load to the foundation, 4 corners compared with 3 of a triangle base. However we went with using a triangle base as this allowed more gains to be made in height.

With the three studs acting to achieve the highest possible height, it experienced some buckling. By placing some struts at intermediate positions we were able to increase its structural integrity and allow it to be come more robust.

All in all it stood tall, but however with a roll of masking tape placed on top it would fall over.

Given we couldn’t change the strength of the material used, It needed to be wider at the base or the height to be reduced.