Example
A sawn lumber floor beam supports floor joists in a residential application. Given: beam size 2×10; species Douglas Fir-Larch (DF-L); grade No. 2; span 12 ft simple (pinned at both ends); uniform dead load 20 plf; uniform live load 80 plf. Load combination D+L governs (CD = 1.0 per NDS Table 2.3.2). Check flexural and shear capacity per NDS 2024 §3.3 and §3.4. Verify deflection L/360 for live load (IBC Table 1604.3). Sawn lumber is the most common product for headers, girders, and beams within residential construction.
How StructSuite solves this
StructSuite's free structural design software provides NDS design: Select Floor Joist, then Design per 2024 NDS. In Geometry: enter span 12 ft; set both supports to Pinned. In Loads: add two uniform load items—Type D, 20 plf; Type L, 80 plf. In Materials: select Sawn Lumber, Species Douglas Fir-Larch, Grade No. 2, Size 2×10. In Design Parameters: deflection limit L/360. StructSuite runs beam analysis, applies NDS 2024 Eq 3.3-1 (flexure), Eq 3.4-2 (shear), size factor CF from Table 4A. Simple span maximum moment M = wL²/8 at midspan.
Steps
- Step 1: Select member type
Design consideration: Beams/headers carry joist loads. Moment M = wL²/8 for simple span—span length dominates. 12 ft is common for residential headers; 14–16 ft may need LVL. Single beam (not repetitive) gets no Cr factor.
In StructSuite: In the "Select member type" section at the top, click the Floor Joist card.
- Step 2: Select design method
Design consideration: NDS flexure and shear; deflection often governs long spans. CD: D+L=1.0, snow/roof live=1.15, wind/seismic=1.6. Short-duration loads (W, E) get higher allowable stress. Governing combo has highest D/C ratio.
In StructSuite: In the "Select design method" section, click the "Design per 2024 NDS (National Design Specification for Wood Construction)" card.
- Step 1: Geometry & Configuration
Design consideration: Span length affects moment (∝ L²) and deflection (∝ L⁴). 12 ft vs 14 ft: 36% more moment, 95% more deflection. Pinned ends = simple support; fixed ends reduce moment but rarely used for wood. Slope length for rafters > horizontal projection.
In StructSuite: Open the Geometry section. In the beam schematic, enter span lengths: 12. For each support, use the support type dropdown to select: Pinned, Pinned. NDS 2024 Eq 3.3-1, 3.4-2 for flexure and shear.
- Step 2: Load Definition (ASCE 7-22 / NDS 2024)
Design consideration: 100 plf total (20 D + 80 L) on 12 ft: M = 1,800 ft-lb. Tributary width from joist spacing: 16 in. o.c. → 1.33 ft. Point loads from columns, beams: add at position; moment diagram changes. D+L governs for floor; add Lr or S if roof.
In StructSuite: Open the Loads section. Add load items with these exact values: D 20 plf; L 80 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.
- Step 3: Material & Section
Design consideration: DF-L #2: Fb ~875 psi (2×10); CF from Table 4A. No Cr (single beam). Wet service: CM reduces Fb, Fv ~0.85 for most species. L/360 floor; L/240 if bouncy floor acceptable. Larger depth improves both moment and deflection.
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.
Select member type
Select design method
Floor Joist — Design per 2024 NDS
National Design Specification for Wood Construction