With the world experiencing a mass increase in population, construction today is naturally growing upwards rather than outwards. As a result, there is an increasing need for multi-story and high-rise buildings to meet this demand. For these structures to be sound and cost-effective, construction needs to be strategic by focusing on factors that increase structural strength and reduce costs.
The type of multi-story and high-rise buildings that are growing in numbers include commercial developments, hotels, apartments, private housings, and student accommodation. For these repetitive structures to be sound and cost-effective, contractors make use of tunnel formwork which is a technique that was invented over 50 years ago. Tunnel formwork produces high quality structures and reduces the need for subsequent wet trades such as plastering.
What is tunnel formwork?
Tunnel formwork is a box sized steel fabricated form which allows the wall and the slab to be casted in a single operation. Once reinforcement is placed, concrete for slabs and walls can be achieved in a single continuous pour. A team of 10 workers can achieve a daily cycle of casting 1-2 apartments per day depending on the type of structure. A 10 storied building can be completed in a timeframe of between 20 and 30 days. For highly repetitive and cellular construction projects, tunnel formwork is extremely effective.
Tunnel formwork is highly systematic, earthquake resistant, and offers an ideal solution to the vital issue of sound transmission (providing a reduction of 50 decibels). Furthermore, this technique reduces heating costs by providing thermal mass and also speeds up the construction process. In order to achieve a design that is sound and cost-effective, it’s highly recommended that qualified contractors with experience in tunnel formwork are employed.
Each cell (or unit) in the structure is called a ‘tunnel’ and the formwork comes in half units in the form of an inverted ‘L’. Both halves are then bolted together at the top of each tunnel to form the cell. The inbuilt wheels and the jacks allow the formwork to be moved in and out of the position, along with being easily adjusted to the final height. Tunnel formwork is factory-made and manufactured from steel, allowing it to be reused up to 600 times in different sizes and measurements. For this reason, tunnel formwork is extremely versatile and economical.
The casting process of tunnel formwork
The buildability of in-situ concrete is significantly enhanced by choosing tunnel formwork as it allows for a 24-hour construction cycle to be achieved. The casting process of tunnel formwork include 7 stages as outlined in the following:
Stage 1: Prefabricated wall reinforcement is positioned by a crane along the entire wing of the structure prior to casting the kickers (used to position wall formwork).
Stage 2: Two-and-a-half tunnels are craned into position and then bolted together and ties are added.
Stage 3: The wall concrete is poured.
Stage 4: The slab reinforcements are fixed.
Stage 5: The slab concrete is placed. At this point, the formwork system provides for a pour to be wrapped in tarps and for the use of butane heaters to sustain a relatively high temperature for the concrete to reach its striking strength overnight.
Stage 6: The tunnel-forms are removed the following day.
Stage 7: This same process is repeated for the next two bays.
Tunnel formwork offers contractors the ability to produce durable in-situ cellular structures. Considering that the concrete finish is of high quality, there is little need for post-construction trades such as electricians and plasters. Generally speaking, structures that utilise tunnel formwork can achieve cost savings of 15% and time savings up to 25%.
Employing contractors that are experienced in dealing with tunnel formwork is vital to the success of the project, so if you are interested in using tunnel formwork, get in touch with the formwork specialists at Uni-Span by phoning 1300 882 825.