Expansion joints in concrete structures — typical spacing trigger In general building practice, expansion (movement) joints are introduced if the overall length of a concrete structure exceeds approximately which value?

Introduction / Context:
Concrete expands and contracts with temperature and moisture changes. In long structures, restraint can lead to cracking unless movement joints are provided at suitable intervals. This question addresses the typical overall length beyond which expansion joints are commonly considered in ordinary buildings.

Given Data / Assumptions:

• General building construction (not pavements or bridges with specific jointing rules).
• Normal environmental exposure.
• Reinforced concrete or plain concrete walls/frames.

Concept / Approach:
Guidance in practice often suggests providing movement joints at intervals of roughly 30 m to 45 m for buildings, depending on exposure, detailing, and structural system. A conservative upper bound frequently cited is around 45 m. Designers may choose smaller spacings for severe climates or where differential movements are expected, but 45 m serves as a reasonable threshold in many specifications.

Step-by-Step Solution:

Verification / Alternative check:
Standard handbooks cite joint spacing ranges; many practitioners adopt 30–45 m, with 45 m as a recognizable rule of thumb in moderate climates.

Why Other Options Are Wrong:

• 10 m, 15 m: too short for most buildings and would be uneconomical.
• 35 m: sometimes used, but the question seeks the typical maximum trigger; 45 m is more representative.

Common Pitfalls:
Applying a single spacing to all structures; ignoring effects of plan shape, restraint, and façade materials; neglecting joint detailing for watertightness.

Final Answer:
45 m