Difficulty: Easy
Correct Answer: less than 2.5
Explanation:
Introduction / Context:Deep beams behave differently from slender beams because plane sections do not remain plane, and load paths resemble strut-and-tie or arching action. Codes distinguish deep beams by span-to-depth ratios, with separate detailing and shear provisions. The limit varies for simply supported versus continuous members.
Given Data / Assumptions:
Concept / Approach:For continuous members, a commonly used threshold is stricter than for simply supported members due to continuity-induced stiffness and different moment distributions. Educational references typically adopt l/D < 2.5 as the deep-beam threshold for continuous spans, while simply supported spans use l/D < 2.0.
Step-by-Step Solution:
Identify classification rule for continuous beams: deep if l/D < 2.5.Compare with options and select the statement that captures the 'less than 2.5' criterion.Note: simply supported deep beams often use l/D < 2.0, hence the difference in the criterion.Verification / Alternative check:
This threshold aligns with deep-beam provisions that switch analysis to strut-and-tie or equivalent methods and adjust shear design accordingly.Why Other Options Are Wrong:
'2.0' and 'less than 2': describe simply supported deep-beam criteria, not continuous ones.'2.5' (exact equality): the conventional phrasing requires 'less than 2.5' for continuous deep beams.'less than 3': too lax; includes members that are not deep by standard definitions.Common Pitfalls:
Applying slender-beam flexural formulas to deep beams; deep beams require special shear and detailing rules.Final Answer:
less than 2.5
Discussion & Comments