Two-Span Floor Beam per NDS 2024

Example

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.

How StructSuite solves this

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.

Steps

1. Step 1: Geometry & Configuration

   Design consideration: 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.

   In StructSuite: Open Step 1: Geometry & Configuration. In the beam schematic, enter span lengths: 10, 10. For each support, use the support type dropdown to select: Pinned, Roller, Pinned. For sloped rafters or pitched members, set Roof slope (rise : 12 run) as needed; use 0 for a horizontal beam or joist. NDS 2024 Eq 3.3-1, 3.4-2 for flexure and shear.

2. Step 2: Load Definition (ASCE 7-22 / NDS 2024)

   Design consideration: 75 plf total (15+60) on 10 ft: M_positive ≈ 470 ft-lb; M_negative ≈ 940 ft-lb at interior. Negative moment at support often 2× positive—design for it. Tributary from joists: 16 in. o.c. → 1.33 ft; 10 ft beam → ~7–8 joists.

   In StructSuite: Open the Loads section. Add load items with these exact values: D 15 plf; L 60 plf. For each uniform load: set Type (D, L, Lr, S), enter the plf value in Uniform (plf). For point loads: set category Point, enter magnitude (lb) and position (ft). Include self-weight. NDS 2024 Table 2.3.2 sets CD.

3. Step 3: Material & Section

   Design consideration: CF for 2×10 from NDS Table 4A. No Cr (single beam). Wet service if exposed. Deflection L/360; check both midspan and support. Larger depth improves negative-moment capacity; may need 2×12 for 14+ ft spans.

   In StructSuite: Open the Materials section. In Product category select the type; in Species select Douglas Fir-Larch; in Grade select No. 2; in Size select 2×10. Open Design Parameters: set Wet service (CM) to No; set Repetitive member to No; select Deflection limit. NDS 2024 §4.3.

Live design (pre-filled)

The form below is the real StructSuite module with example data loaded. Display only—values cannot be changed.