Formwork MCQ with answer and solution

Concept

IS 456 gives minimum stripping times for formwork when OPC is used at normal temperature. For soffit formwork to slabs, with props refixed immediately after removal, the time is 3 days.

Step-by-step solution

1. Recall the IS 456 table for stripping time of formwork (OPC, normal temperature). 2. Vertical formwork to columns, walls and beams: 16-24 hours. 3. Soffit formwork to slabs (props refixed immediately): 3 days. 4. Soffit formwork to beams (props refixed immediately): 7 days. 5. Props to slabs: 7 days for span up to 4.5 m, 14 days for span over 4.5 m. 6. Props to beams and arches: 14 days for span up to 6 m, 21 days for span over 6 m. 7. So the answer is 3 days, option (B).

Explanation

As per IS 456, the soffit formwork of slabs can be removed after 3 days if props are refixed immediately. This applies for OPC at normal temperature. Longer times are needed for beam soffits and for props.

Why the other options are wrong

A: 28 hours is not in the IS 456 table. Vertical formwork is 16-24 hours. C: 1 day is close to the time for vertical formwork, not slab soffits. D: 2 days is not the value given in IS 456.

Shortcut

Remember the sequence: vertical 16-24 h, slab soffit 3 d, beam soffit 7 d, slab props 7/14 d, beam props 14/21 d.

Common mistake

Confusing slab soffit (3 days) with beam soffit (7 days) or with vertical formwork (16-24 h).