Steel: The faster, easier and lighter choice
(First published in 2015)
A multi storey commercial office development, 35 Dalmore Drive comprises two four storey building blocks (North and South) over two basement carpark levels. The total net lettable area (NLA) of the development is 15,520sqm divided evenly between the two buildings, with typical open floor plates of 1,940sqm NLA, which include an offset core. A secure underground carpark across the whole site covers an area of 22,000sqm and includes cycle spaces and bathroom amenities.
A landscaped intensive roof garden will be situated on a podium area between the two building blocks and on the eastern side a café will be integrated into the landscaping which features views of the nearby Dandenong ranges.
The Project’s structural engineer Ian Naismith from Davis Naismith & McGovern used Liberty OneSteel’s composite software CompPanel® and CompPen® for the composite floor design. The structure, he said, is braced by a precast concrete offset core and the steel tenancy stairs which feature in the glass façade. The carpark and office floors are constructed from composite steel beams and 130mm thick slab supported on un-propped structural steel decking. The composite steel floor slab forming the open courtyard, which incorporates a waterproof membrane, varies in thickness from 150-210mm to allow drainage to the centre of an 8.3 x 8.3 metre grid.
Un-propped construction was a big contributing factor to the rapid speed of construction, allowing follow-on trades to work underneath a slab the morning after it was poured, explained Brían Buckley project engineer with Caribbean Park. Brían said the construction cycle was more efficient by staging the steel erection on both building blocks two storeys at a time as this allowed the preparation and placement of the concrete slab concurrently. Once the first suspended level was poured the next day decking placement could commence on the second suspended level directly above.
Brían said offsite fabrication was a major benefit of structural steel construction as fewer people are involved in manual labour onsite, there are fewer clashes between trades and as a consequence a much safer site is created.
The building is designed to achieve a Property Council of Australia (PCA) “A” Grade standard with a minimum 5 Star Green Star and 5 Star NABERS rating. It’s also designed for disassembly, which means when the building has served its useful life the façade, roof and steel structure can be easily disassembled and materials reused or recycled.
According to the Building Code of Australia (BCA) the office building is of Type A construction and considered a large isolated building, due to the interconnected floor area exceeding 8,000sqm, and hence sprinkler protection is required. Using the deemed-to-satisfy (DTS) provisions meant that a two hour fire resistance level (FRL) would be required for the steel beams and columns in the office area, whilst at the basement the columns require one hour FRL (which was applied with a coat of intumescent paint on site) and unprotected beams with exposed surface area to mass ratio ESA/M less than 30sqm/t.
For the office part of the building an alternative fire safety engineering solution developed by Dr Weng Poh from Umow Lai meant that most of the steel members did not require the application of any passive fire protection material. The alternative design assessed the inherent fire resistance of 300PLUS® steels and an enhanced automatic fire sprinkler system from light hazard to ordinary hazard with fast response head as part of this solution.
Only the internal columns up to Level 2 are to be protected as required by the BCA, as shown in Figure 1.
EFFICIENT, FLEXIBLE, FUTURE-PROOFED:
Each floor plate has been designed with adaptability in mind. Floors can be easily altered to accommodate up to four tenants, and connections between floors, via new stairs, can be added simply by cutting out the slab between the 2800mm spaced structural steel beams.
According to Caribbean Park the first stage which is nearing completion was a success and has seen an increase in the construction team’s confidence in structural steel. Excavation has commenced on the second stage which will be a similar construction process to the first.
|Structural Engineer||Davis Naismith & McGovern|
|Fire Safety Engineer||Umow Lai|