Continuity requirement – approximately equal spans in continuous members In continuous structural members, spans are considered approximately equal if the longest span does not exceed the shortest span by more than:

Introduction / Context:
Simplified analysis and detailing rules for continuous beams/girders often assume “approximately equal spans.” This allows use of standard bending moment coefficients and distribution rules.

Given Data / Assumptions:

• We compare the extreme spans within a continuous series.
• Criterion is expressed as a percentage difference relative to the shortest span.

Concept / Approach:
When span variations are small, support moments and distribution factors do not deviate drastically from tabulated “equal-span” values. A widely adopted threshold is 10%, beyond which redistribution may be significant and specific analysis is recommended.

Step-by-Step Solution:

Verification / Alternative check:
Many handbooks stipulate 10% as a practical limit for using equal-span coefficients without notable error.

Why Other Options Are Wrong:
5% is unduly restrictive; 15–25% allow excessive variation, undermining equal-span assumptions.

Common Pitfalls:
Applying equal-span tables to irregular layouts with larger variations, leading to inaccurate moment distribution.

Final Answer:
10%