Formwork Failures and Prevention

Formwork failure during concrete construction usually occurs when the concrete is being poured. Some unexpected event causes one portion of the formwork to fail, thereby overloading or misaligning the entire formwork structure until it ultimately collapses. One or more of the following can cause formwork failure:

1) Lack of inspection/attention during formwork placement and construction.Many failures occur due to lack of inspection, or the inspector/crew is inexperienced or unqualified.

2) Inadequate design. Most failures due to design flaws are related to lateral forces and the temporary structure's stability. The lack of a bracing system to deal with lateral forces, like wind and construction loads, causes the formwork system to collapse when an excessive load is applied. Also, as formwork is reused, its capacity to hold a load over time is reduced. Unfortunately, the formwork designer often omits the safety factor and calculates the load using original capacity data. The design of formwork should be approved by a licensed engineer before installation.

3) Defective components. Some cases of formwork system failure have been the result of the improper maintenance of formwork components, which then become defective after being reused several times. The capacity of these formwork components has been reduced due to corrosion and damages, yet is seldom taken into consideration during the erection.

4) Improper connections. Formwork components are sometimes inadequately connected to enable easier and faster dismantling. But lack of proper connection can result in progressive collapses. Insufficient bolts, nails or splicing, poor weld quality, and faulty wedges can readily compromise formwork integrity. Incredibly, sometimes there is no connection at all between two components.

5) Premature removal. Untimely removal of formwork prior to proper concrete curing usually happens because workers are in a hurry to reuse the form quickly because of tight scheduling requirements or budget pressures.

6) Improper shoring. Inadequate shoring is a significant cause of formwork failure, where impact loads from concrete debris and other effects trigger the collapse of vertical shores during concreting. Additionally, shoring must be installed to provide a continuous load path from the formwork to the foundation or other structural component capable to supporting the formwork and new concrete.

7) Insufficient foundation. Many formwork foundations fail to transfer the load to the ground, or are positioned on weak subsoil. These foundations are often constructed from sill plates, concrete pads, and piles, which can cause differential settlement of formwork and overloading of shores, ultimately resulting in collapse. In addition, insufficient foundation capacity can reduce the carrying capacity of the formwork.