Comprehensive Detailed Explanation with all NCARB ARE 5.0 Project Development and
Documentation (PDD) Study Guide Reference:
The question is about the relative section modulus (S) required for a glue-laminated beam vs. a sawn
timber beam to resist the same bending moment. The formula relating bending stress (Fb), moment
(M), and section modulus (S) is:
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For the same bending moment M, the section modulus is inversely proportional to the allowable
bending stress
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Therefore, the glue-laminated beam requires half the section modulus compared to the sawn timber
beam.
Supporting Reference:
NCARB ARE 5.0 Review Manual, Structural Systems chapter
Basic bending stress and beam design equations from structural design texts
