SCENARIO : A contractor planned to cast a 3.0 m-high concrete wall in one lift. During prepour inspection, the engineer discovered the formwork supplier’s lateral-pressure limit was 50 kPa. The pour plan set no maximum rise rate, and the crew intended to use a highly workable mix. The pour was held.
ROOT CAUSE: Formwork design assumptions had not been matched to the mix and placing sequence. Drawing approval was treated as approval for any pour rate.
SCREENING (CALCULATION): Let's assume fresh concrete behaves as a fluid with unit weight 24 kN/m³, base pressure is p = γh = 24 × 3.0 = 72 kPa. Against 50 kPa, the indicative excess is 22 kPa, or 44%. This is a conservative screen, not a prediction of peak pressure - stiffness gain, mix, temperature, vibration and rise rate need a designer’s review.
REFERENCE : BS 5975-1:2024 covers temporary works controls; BS 5975-2:2024 covers falsework and associated formwork design. ACI PRC-347-14(21) guides concrete formwork pressure. Apply the project’s adopted standards.
RISK: Formwork failure or uncontrolled concrete release :
(L) 3 × (S) 5 = 15/25 (high).
Following design review and site controls, target residual risk = 1 × 5 = 5/25.
Severity remains 5 because a formwork collapse could still cause serious injury.
CA: Suspend the pour : obtain a written pressure check and revised ties/bracing or a justified controlled rise rate. Brief the crew, mark maximum levels and hold points, monitor deflection and leakage, and stop if limits are exceeded. Record an independent inspection and permit to pour.
PREVENTION : specify mix, temperature, vibration and pour rate in every formwork design brief