Formwork is the backbone of reinforced concrete construction, shaping structural elements and temporarily supporting enormous loads. When properly designed and installed, it ensures safety, accuracy, and durability. However, poorly executed formwork can lead to costly defects, structural failures, and even collapse.
Formwork, the temporary mold that holds wet concrete together in the desired shape on construction projects, may look like a routine part of structural engineering but it is in fact a critical element that requires a good understanding of materials, purpose of the formwork as well as best practice in safety.
If not done right, a formwork system poses significant dangers, the most catastrophic of which may be collapse of the structure under construction. This can result in serious injuries and even fatalities. Beyond the safety risks, sloppy formwork leads to compromised structural integrity, major project delays and eventually cost overruns.
What Constitutes Quality Formwork?
Quality formwork must be designed and constructed to meet several critical requirements. First, it must possess sufficient strength to safely withstand both the dead load of freshly poured concrete and the live loads imposed by workers, tools and construction equipment during casting. In addition, the formwork should be watertight, with all joints properly sealed to prevent leakage of cement grout, as such leakage can lead to defects like honeycombing that compromise the durability and appearance of the concrete. Finally, the formwork should allow for ease of removal; it must be designed so that it can be struck or stripped efficiently once the concrete has gained adequate strength, without causing damage to the finished concrete surface.
Role of Structural Engineer
Structural engineers should play their rightful role in guiding the installation of formwork. On critical tasks such as suspended slabs, multi-storey buildings, long spans, transfer beams, cantilevers and post-tensioned or heavily reinforced elements, the structural engineer’s presence and supervision is vital. Such formwork may carry extremely heavy loads. The engineer must therefore ensure that the formwork has adequate bracing and propping and will not collapse, deflect excessively or shift during pouring. In such cases, formwork itself becomes a structural system, even if temporarily. The engineer ensures the formwork matches the structural intent, not just architectural dimensions.
Misaligned panels or inadequate support can lead to uneven concrete thickness or air pockets. These weak points can crack under load, compromising the final structure’s strength and longevity. Joints that leak allow cement to bleed out, degrading the surface finish and potentially exposing steel reinforcement to moisture, which causes rust. All these are issues that a diligent structural engineer should watch out for.
When Should Formwork be Removed?
Pressure to stay on schedule can lead to formwork being removed before the concrete reaches adequate strength. This can cause the concrete to sag, crack or completely fail. The structural engineer must never compromise regardless of pressure. It is his/her duty ensure that the contractor allows the prescribed time to elapse before stripping off the formwork.
Implementing robust design, proper supervision, inspections before concrete pours and ensuring a well-trained workforce are essential steps to avoid pitfalls.
