Two-Span Floor Beam per NDS 2024

Summary: Design a two-span sawn lumber beam with uniform and point loads per NDS 2024 §3.3 (flexure), §3.4 (shear) and adjustment factors. Free wood beam…

Overview

Design a two-span sawn lumber beam with uniform and point loads per NDS 2024 §3.3 (flexure), §3.4 (shear) and adjustment factors. Free wood beam calculator NDS for multi-span beams, load duration, wet service, and deflection.

Problem statement

A 2×10 Douglas Fir-Larch #2 beam spans 10 ft + 10 ft (two spans, pinned interior support). Uniform dead 15 plf, live 60 plf. Check capacity per NDS 2024. CD = 1.0 for D+L. L/360 deflection.

Workflow in StructSuite

Use StructSuite's free beam design calculator: open the Wood Beam module. Enter spans [10, 10], supports (pinned-pinned-pinned). Add uniform load segments, assign D and L. StructSuite runs beam analysis, applies NDS 2024 Eq 3.3-1, 3.4-2, size factor CF, deflection check. Two-span reduces midspan moment vs simple span.

Design considerations (excerpt)

Two-span continuous reduces midspan moment vs simple span (M = wL²/8 vs wL²/24 at interior for equal spans). Negative moment at interior support often governs. Beam/girder carrying joists—single member, no Cr. Two 10 ft spans: interior support critical for negative moment. Longer interior span increases negative moment. Pinned interior = no moment restraint; fixed would reduce moment but uncommon for wood. Adding third span changes distribution. NDS for multi-span, point loads, or when IBC tables don't apply. Equal spans: interior support gets 1.25× simple-span moment. Unequal spans: longer span drives design. CD from load type.

75 plf total (15+60) on 10 ft: M_positive ≈ 470 ft-lb;…

Related terms

• StructSuite
• structural engineering
• design example
• wood beam
• NDS 2024
• nds multi span beam

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