Concrete construction — safe stripping time for beam formwork (including props) According to standard building practice for cast-in-place reinforced concrete, the formwork to beams — including the supporting props — should be removed only after approximately how many days under normal curing and ambient conditions (no special accelerators, typical cement)?

Introduction / Context:
Correct formwork striking (removal) times are crucial for structural safety and surface quality in reinforced concrete construction. Beams carry significant bending and shear, and their soffit formwork and props support fresh concrete until adequate strength develops. This question checks recognition of the conservative, widely taught timeframe for removing beam formwork including props.

Given Data / Assumptions:

• Ordinary Portland cement, normal ambient temperature, and curing.
• No accelerators or steam curing; no special high-early-strength mixes.
• General site practice for typical spans (if spans are large, even longer times may be adopted).

Concept / Approach:

Codes and textbooks provide indicative stripping periods: sides of beams and columns can be struck early (when concrete can support its own edges), slabs with props are commonly kept for 7–14 days depending on span, and beams/arches require the longest duration because the soffit and props carry flexural loads until the concrete gains sufficient strength. A conservative classroom value often cited for beam formwork including props is about 21 days under normal conditions.

Step-by-Step Solution:

Verification / Alternative check:

Many syllabi and handbooks tabulate indicative periods: sides of beams ~1–2 days; slab props ~7–14 days (span dependent); beam props ~14–21 days (span dependent). In the absence of span data, the safer answer is 21 days.

Why Other Options Are Wrong:

• 3 or 7 days are too early for beam soffit props in ordinary conditions.
• 14 days may suffice for shorter spans, but 21 days is the safer, commonly taught value when span is unspecified.

Common Pitfalls:

• Ignoring span length and temperature effects on stripping time.
• Removing props early because side shutters were removed without distress.

Final Answer:

21 days.