Formwork Tolerances – Columns and Beams Within what tolerance band are the dimensions of formwork for columns and beams typically permitted (negative to positive)?

Introduction / Context:
Formwork tolerances control the dimensional accuracy of reinforced concrete members. Excessive deviation can alter cover, stiffness, and load-carrying capacity, as well as affect architectural alignment. The question tests awareness of the typical tolerance window used for columns and beams.

Given Data / Assumptions:

• Member types: cast-in-situ columns and beams.
• Context: general building construction with competent formwork.
• Measure: dimensional tolerance range (negative to positive).

Concept / Approach:

Practical tolerances strike a balance between constructability and performance. A modest negative tolerance ensures sections are not undersized significantly (which would reduce capacity), while a positive tolerance compensates for buildability and stripping effects without creating excessive oversizing.

Step-by-Step Solution:

Verification / Alternative check:

Project specifications often echo the −6/+12 mm tolerance for typical member dimensions unless special finishes or precast standards demand tighter control.

Why Other Options Are Wrong:

• −3/+6 and −4/+8: Too tight for routine site conditions; may be reserved for special finishes.
• −8/+12: The negative side is overly permissive, risking section undersizing.

Common Pitfalls:

Measuring tolerances at incorrect reference points; neglecting that cover tolerances and alignment tolerances are checked separately.

Final Answer:

- 6 mm to + 12 mm