TWK/Specific/TBT-TWK-003

Propping and Backpropping

Temporary Works › Specific › Propping and Backpropping

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Propping supports newly poured concrete slabs until they reach the required strength to carry their own weight and imposed loads.
Backpropping transfers construction loads through completed floors to the foundations during multi-storey concrete frame construction.
Premature removal of props before concrete reaches the required strength causes slab failure, collapse, and fatalities.
A propping and backpropping schedule must be designed by a structural engineer and followed precisely on site.
Props must be positioned at the exact locations shown on the propping layout drawing — moving them changes the load distribution.
Prop bases must be on firm, level surfaces with sole plates and base plates to prevent sinking and load eccentricity.
The number of floors requiring backpropping depends on the structural design, concrete strength gain, and construction loading.
Propping must not be removed without written authorisation from the temporary works coordinator, based on cube test results.
Striking of props must follow the designed sequence — random removal creates dangerous load concentrations on the remaining supports.
Inspection of propping must take place before loading, during the concrete pour, and regularly until removal is authorised.

Prevent slab collapse	Removing props before concrete is strong enough causes immediate slab failure — the entire floor can collapse without warning.
Load transfer	Backpropping transfers construction loads through multiple floors — inadequate propping overloads lower slabs that are still gaining strength.
Sequence matters	Removing props in the wrong order concentrates loads on remaining supports, exceeding their capacity and causing progressive collapse.

Don't

Follow the engineered propping and backpropping schedule exactly as designed.
Position props at the precise locations shown on the approved layout drawing.
Place prop bases on firm, level ground with sole plates and base plates.
Maintain backpropping on the required number of floors during multi-storey construction.
Obtain written authorisation before removing any props, based on cube test results.
Follow the designed striking sequence — do not remove props in random order.
Inspect propping before loading, during the pour, and regularly until removal.
Report any damaged, leaning, or displaced props to the supervisor immediately.
Confirm concrete cube results meet the required strength before requesting prop removal.
Brief the team on propping requirements and the prohibition on unauthorised removal.

DON'T deviate from the engineered propping schedule under any circumstances.
DON'T move props from their designed positions to create access or working space.
DON'T place prop bases on soft ground without adequate sole plates for load spreading.
DON'T remove backpropping from lower floors before the schedule permits.
DON'T remove any props without written authorisation from the temporary works coordinator.
DON'T strike props out of the approved sequence — it causes dangerous load concentrations.
DON'T skip propping inspections — undetected problems lead to sudden collapse.
DON'T ignore leaning, bent, or displaced props — they indicate overloading or failure.
DON'T assume concrete is strong enough — only cube test results confirm readiness.
DON'T treat propping as a minor issue — it is a critical structural safety control.

See also: Formwork and Falsework | Temporary Works Awareness

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