Cantilever Beam per NDS 2024

Example

A 2×8 Douglas Fir-Larch No. 2 cantilever extends 4 ft beyond the support (fixed at building, free at end). Uniform dead 8 plf, live 30 plf. CD = 1.0. Check capacity. Cantilever has maximum moment at fixed end; deflection often governs at free end.

How StructSuite solves this

StructSuite's free wood beam calculator NDS: select Floor Joist, Design per NDS. Enter span [4]. Set left support = Fixed, right support = Free (cantilever). Add uniform load D 8 plf, L 30 plf. StructSuite analyzes cantilever—Mmax at fixed end, Δmax at free end. Fixed-free is one of six support types in NDS Table G1 (though Table G1 is for columns; beam analysis uses support boundary conditions).

Steps

1. Step 1: Select member type

   Design consideration: Cantilever: M_max at fixed end = wL²/2 (vs wL²/8 for simple span). Same load, 4× moment—cantilevers are moment-critical. Common for deck overhangs (1–4 ft), balcony ledgers, roof overhangs. No IBC tables—NDS required.

   In StructSuite: In the "Select member type" section at the top, click the Floor Joist card.

2. Step 2: Select design method

   Design consideration: Fixed-free boundary. Reaction at support = wL; moment = wL²/2. Tip deflection Δ = wL⁴/(8EI)—deflection often governs for short cantilevers. L/240 for deck; L/360 if supporting rigid finish.

   In StructSuite: In the "Select design method" section, click the "Design per 2024 NDS (National Design Specification for Wood Construction)" card.

3. Step 1: Geometry & Configuration

   Design consideration: 4 ft cantilever: short, so shear rarely governs. Moment at fixed end = 38×4²/2 = 304 ft-lb for 38 plf. Doubling length quadruples moment. Connection at fixed end must transfer moment—often through ledger or joist hangers.

   In StructSuite: Open the Geometry section. In the beam schematic, enter span lengths: 4. For each support, use the support type dropdown to select: Fixed, Free. NDS 2024 Eq 3.3-1, 3.4-2 for flexure and shear.

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

   Design consideration: 38 plf (8 D + 30 L) typical deck: decking 2.5 psf, joist 1.5 plf, live 40 psf × tributary. Guardrail post at tip adds point load—often 200 lb. CD=1.0 for D+L; 1.6 for wind if exposed.

   In StructSuite: Open the Loads section. Add load items with these exact values: D 8 plf; L 30 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.

5. Step 3: Material & Section

   Design consideration: Exterior: wet service CM reduces capacity. 2×8 DF-L #2: Fb ~1,250 psi with CF. Deflection at tip—short cantilever, EI matters. PT lumber: incising reduces capacity; specify if used.

   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 2×8. 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.