Concrete formwork is a vital component to the construction of any commercial building considering that it creates the foundationof the structure. If the structure’s foundation is weak, there can be a variety of problemsfrom structural damage to collapse. One of the most critical processes in creating strong and long-lasting foundations is the correct design and use of formwork. In fact, the success of any construction project is heavily dependent on formwork which accounts for roughly 35 – 40% of the overall concrete construction costs.
Formwork is essentially temporary or permanent moulds into which concrete is poured until the structure has gained enough strength to support itself. While formwork is used to create the foundations, formwork is also used to create almost every aspect of the structure including columns, staircases, walls, beams, and suspended slabs just to name a few. Concrete formwork is generally constructed from either steel, aluminium, wood, or pre-fabricated modules such as glass reinforced plastics (GRP).
In today’s construction, most of the formwork used is modular to increase speed, accuracy, and efficiency. The two primary advantages of using pre-fabricated formwork in comparison with traditional wood formwork is increased speed and lower costs. The need for skilled labour is dramatically reduced when erecting and stripping pre-fabricated formwork, and steel and aluminium formwork can be reused hundreds of times.
The success of any construction project in terms of quality, speed, costs, and worker safety requires formwork to meet the following requirements:
- Capable of supporting the weight of concrete during pouring and vibration along with any other loads such as workers or equipment.
- Effectively propped and braced both vertically and horizontally to ensure its shape is retained.
- Prevents any leakage through adequately tight joints.
- Allows for stripping without damaging any concrete.
- Stable in any kind of weather – it should not distort or warp when exposed to the elements.
- Capable of being handled safely using the available equipment.
- Has a secure base or foundation.
Most common causes of formwork failure
Formwork failure can be caused by a range of reasons, however most of the problems occur when the concrete is being poured. The following lists some of the most common causes of formwork failure.
- Flawed design – Most of the failures resulting from flawed design relate to the structure’s stability where the formwork collapses due to excessive loads. In addition, each time formwork is reused its load capacity is decreased and this factor is difficult tor engineers to measure.
- Improper inspections – A lack of inspections or inspections performed by inexperienced or unqualified personnel results in many formwork failures.
- Defective components – Where proper maintenance isn’t carried out on formwork components, they can easily become defective after several uses. Insufficient bolts, nails or splicing, poor weld quality, and faulty wedges can compromise formwork integrity.
- Premature removal – A common reason for formwork failure is when formwork is removed before the concrete has cured properly due to scheduling or budget requirements.
- Inadequate foundations–Where formwork foundations are placed on weak soil or when the foundations fail to transfer the load to the ground, formwork has a tendency to collapse as it has a reduction in carrying capacity.
In order to prevent formwork from failing and causing injuries, the following preventative measures should be implemented.
Before concrete pour
- The formwork design should be completed by a qualified person with experience in the type of formwork being used.
- The expected dynamic and static loads should be easily supported.
- If the formwork doesn’t comply with the original design, amendments should be made with the designer inspecting the formwork to verify its structural integrity.
- Always assemble formwork systems according to the manufacturer’s guidelines.
- Inspect all formwork components before use and replace or repair any defective components.
- A qualified person must verify that the formwork has been properly erected before any concrete is poured (and prior to other trades accessing the construction site).
During concrete pour
- A boundary zone should be created to prohibit workers from accessing areas under theformwork while the concrete is being poured, and until the concrete has acquired enough strength to self-support
- During the early stages of the concrete pour, monitor the formwork to establish any signs of failure. If workers require access to the area under the formwork, a risk assessment should be performed to ensure its safe to do so.
- During the concrete pour, ensure the formwork is never overloaded.
- Ensure the concrete is given enough curing time (as specified in the formwork design) before stripping.
Concrete formwork poses many dangers to workers on commercial construction sites and contractors must ensure that all health and safety measures have been followed to ensure their safety. If you have any questions about formwork or any processes used to prevent formwork failure, get in touch with the experts at Uni-Span by phoning 1300 882 825.