week 7 Constructing Environments India McKenzie 639 234
Site Overview Located at 587-589 Elizabeth St, this 11 storey buidling comprises 55 apartments over 9 residential levels and two commerical levels that open up onto the street. The illuminated light weight exterior finish is deceptive in that it conceals the heavy mass construction method that uses predominantly concrete slabs. The timeline for construction was one year, and given that we visited in september, there is only three months left until the expected completion date. The site manager estimated that they had progressed approximately 65-70% of the way in the nine months since the beginnign of construction. This proved to be an excellent time for us to investigate the site as there was works going on in various areas of the site that ranged from structural (metal stud walls), functional (ventilation ducts and bathroom fittings), technological (electrical wiring, heating & cooling) and aesthetic (windows, railings doorways etc). Construction Value: $11,985,000 Client: Austgroup Holdings Pty Ltd Builder: Maxstra Constructions Consultant/Architects: Architects EAT Completion Date: December 2013
Computer modelling pictures for advertising purposes. Images sourced from: http://www.e589.com.au/
WK 7_JOURNAL Mass Construction
This image shows the ground floor of the building and provided an excellent starting point for a discussion of the main construction system being mass construction. The floor levels are insitu concrete slabs and are bidirectionally post-tensioned after 1-2 days of curing. Given the sheer volume of concrete used in this site, this is cheaper than standard reinforced concrete and is more suitable to the site. Each of these slabs is 200mm thick.
The first aspect we must address is the foundations that the building sits upon. In this instance, bored pile foundations are used as the soil in the area is compressible and thus requires these deep foundations to penetrate the instable shallow soils to the rock bed below. These are described as endbearing piles as seen in the diagram below.
External walls = 12 metre pre-cast concrete panels Internal wall = steel reinforced concrete blockwork Floor levels = in situ concrete
Concrete Slabs Lightweight Construction From level 8, the construction method transitions into a lightweight steel member structure seen here with the truss system observed on level 11. The combination of the two main construction types (mass & lightweight) is common for commercial/residential buildings of this scale as it maximises material and construction efficicency.
In the upper levels of the bulding, the construction method transititons from mass to lightweight construction and uses steel beams as the main structure. The image above shows the connection between a concrete wall system and a steem floor beam, that supports the floor level above it. This transition uses a casting plat that is imbedded into the concrete slab during the casting process and then bolted and welded onto the steel connection.
The slab dimensions are limited to a maximum of 12metres which is occassionaly supported by mid-span vertical colmuns that join the floor and roof systems. This image shows the joining of two different panels to form a solid wall. From here the walls are complemented with steel stud rails that provide access for services and amenities and then covered with a fireproofed plaster sheeting as the finished material.
The image on far right shows a hold for the crane used to place the pre-case concrete slabs into place. Each slab section is up to 12 metres in span and this is largely due to the strength required of each segment for the construction process. The load stress placed on the slabs once theyre installed is considerably larger than the stress placed on it throughout construction as they are winched into place with cranes. These hole are then filled with grout/putty and covered by the wall finish.
Roof Structure The image to the right shows the gentle 3 degree slope of the roof which uses a thin 3mm steel sheathing. This is classified a a â€œlow slope roofâ€? and therefore facilitates the use of an internal drainage system using the box gutter as seen in the left image. The roof also provides an appropriate surface for duct work and solar panels on the roof to offset some of the energy required for this multi-residential building.
Accesibility The building has two internal staircase units through the centre of the building that are constructed of solid concrete formwork. The image above shows how the sacrificial formwork is used to mould the shape of the stairs and will remain part of the design. The choice of this material also assists in fireproofing the stairwell which is an essential factor as this would be the primary exit route in the case of a fire. However, there is of course a lift shaft installed which is practical for a building of this scale and expected in terms of resident satisfaction and accessibility. Windows & Ventilation The outward facing apartments make full use of the natural light available with large expanses of windows. The window frames use a lightweight extruded aliminium which is commonly used in this context as it is easily mass produced and fitted into the space which is likely to be replicated in most of the other apartments. This simplifies construction. The left image also shows the use of louvre windows as well to maximise natural ventilation of the space and provide some degree of interaction with the natural world.
The image to the right also shows the use of an internal courtyard to provide natural lighting to apartments in the inner column of the building. Whilst the outer facing apartments are rewarded with excellent city and port side views, the internal rooms are likely to depend on this light shaft to provide sufficient connection with the outside world. The aspect of each unit is likely to be a significant factor in asssessing the market value of the rooms.
Bathroom fitout These two images show details of the bathroom fixtures. The left image shows the use of timber to support the bathroom fixtures such as the brass tap fitting you can see here. Whilst the majority of the internal walls are steel stud, some timber work is needed for such fixtures. The right hand image illustrates the depression in the concrete slab which marks out the bathroom area which will be covered with a screed before laying the tiles. This set down would have been formed when the floor slab was fabricated off-site.
WK 7_JOURNAL Internal Walls
The bottom floor is the area in which all the service mains reside. With a plethora of tubes, wires and cords, the service tray (see image on right) provides a safe and clear rail to maintain order. The PVC pipe shown links to the stormwater detention centre which is enabled to filter grey water whilst a seperate pipe channel is used for sewerage waste. The ground floor houses the controllers for all the gas, water and electricity for the buidling.
The division between apartments requires multiple materials to make them acoustically private and also achieve the prescribed fire-rating for a residential apartment building. The internal walls are steel stud walls. Steel is preferential over timber in this instance given the large scale of construction. The stud wall also facilities the installation of services. The wall is then finished with a firecheck plaster board with a fire rating of 90:90:90. The walls are also offset with a 20mm acoustic gap between the apartments for added privacy. The top image shows a section detail of the width and density of the plasted used whilst the bottom photo shows the ventilation facilities extruding from the plasterboard. The roof is similarly plastered however with a thinner plaster. This is because the concrete floor slab is noncombustible and therefore sufficient for achieving the fire-rating.
The left image shows the transistion from mass construction to lightweight construction on the 9th floor as the roof structure above used the steel beams attached to the concrete wall. The silver ducts also provide insight into the order of construction as the amnetitie such as plumbing, lighting, heat and cooling are installed in the intermediate stages before any finishes. The combination of flexiduct and solid duct is due to the fact that flexi-duct can span a maximum of 5m. This stage of construction was particularly useful for identifying the extent of these services in the construction of the building as they were left exposed. The image to the left shows the joint details of the steel columns and beams used in the upper two levels of the structure. Using semi-rigid joints, the beams allow for a certain degree of controlled movement to as seen by the unconventional angles in this junction. The cross bracing is also evident here as it intersects with the steel roof/floor beams.
As mentioned above, the floor system transitions from the cement slabs to a lightweight steel structure that uses beams and colmumns to support the weight as well as steel stud internal walls. Noticeably, no noggings were used as the steel was more resistant to torsion and warping than timber is over time. They also uses cross bracing between spans to stabilise the supporting structure as seen by the thin metal cross-tubings in the image on the left.