NASCLA Accredited Commercial General ContractorConcreteMedium
A concrete framing subcontractor is erecting formwork for a heavily reinforced concrete beam that will support significant loads. The structural engineer's drawings specify a maximum allowable deflection of the formwork during concrete placement as L/360, where L is the span length. What is the primary reason for strictly controlling formwork deflection?
- ATo prevent premature cracking of the fresh concrete during placement.
- BTo facilitate easier removal of the formwork after the concrete has cured.
- CTo ensure the final concrete element meets specified dimensional tolerances and aesthetic requirements.
- DTo minimize the amount of concrete required for the pour.
Show answer & explanationAnswer & explanation
Correct answer: C. To ensure the final concrete element meets specified dimensional tolerances and aesthetic requirements.
Controlling formwork deflection is critical to ensure that the final hardened concrete member accurately conforms to the specified dimensions, alignment, and surface flatness. Excessive deflection can lead to unsightly bulges, sags, or misalignments, impacting both structural integrity and aesthetic quality, and potentially requiring costly rework.
Why the other options are wrong
- A. Premature cracking of fresh concrete is more related to settlement, drying shrinkage, or rapid hydration, not directly formwork deflection.
- B. Easier formwork removal is primarily influenced by proper release agents and form design, not directly deflection limits.
- D. Deflection control is about shape and dimension, not concrete volume reduction.
Formwork Deflection
The temporary deformation or bending of formwork components under the weight and pressure of fresh concrete before it hardens.
- Must be limited to maintain dimensional accuracy.
- Affects aesthetics and structural alignment.
- Calculated based on material properties and load.
Memory trick: Deflection kept low, so the structure won't show a bow.