Wood Beam Design Step by Step — Two-Span Continuous Worked Example (NDS 2024, ASCE 7-22)
3:45Published July 8, 2026Narrated, with captions and a full transcriptAlso on YouTube
Design a two-span continuous wood floor girder start to finish in StructSuite, per NDS 2024, with ASCE 7-22 load combinations and IBC 2024 deflection limits. Geometry and support restraints, loads entered from a tributary width, species and grade off NDS Supplement Table 4A, every NDS adjustment factor, an optional Simpson Strong-Tie hanger, and trial-and-error to the optimum section. The first two sections fail on screen, and each failure is read off its demand-capacity ratio and fixed.
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About this video
What you will see
- The restraint set at each support — Pinned, Roller, Fixed or Free — and a second span added so the beam runs continuous over three supports
- Loads defined per ASCE 7-22: each load carries an ASCE load type, a distribution (uniform, point or triangular) and an input method
- A uniform load entered two ways — directly in plf, or as a pressure in psf times a tributary width: 15 psf over a 10 ft tributary is 150 plf
- Member self-weight added automatically as dead load once a section is picked
- All six product categories inside one module — Sawn Lumber, Glulam, LVL, LSL, PSL and I-Joist — each loading its own NDS or manufacturer tables
- Species and grade picked straight off NDS 2024 Supplement Table 4A: Douglas Fir-Larch No. 2 at Fb = 900 psi, Ft = 575 psi
- The section chosen from NDS Supplement Table 1B, with b, d, A, Sx and Ix
- The Step 4 NDS adjustment factors, each tagged Calculated or User-defined: wet service CM (NDS Table 4.3.1), temperature Ct (NDS 2.3.3, Table 2.3.3), incising Ci (NDS 4.3.8, Table 4.3.8), repetitive member Cr, size factor CF, load duration CD (combination-specific, NDS 2.3.2, Table 2.3.2) and the deflection limit — floors default to L/360 live and L/240 total per IBC 2024 Table 1604.3
- An optional Simpson Strong-Tie hanger sized for the beam's end reaction
- Step 6 checking the beam against every ASD load combination (ASCE 7-22 Section 2.4.1): flexure fb = M/S (NDS 3.3.1, Eq. 3.3-1), shear fv = 1.5V/A (NDS 3.4.2, Eq. 3.4-2) and deflection (NDS 3.5, IBC 2024 Table 1604.3)
- Any combination opened into the full, code-referenced calculation, step by step
- Trial and error to the optimum section: 4x12 at D/C 1.36, 4x14 at 1.08, 4x16 at 0.82
- Shear, moment and deflection diagrams for the continuous beam
The beam in this example
Two 12 ft spans, continuous, pinned at all three supports. Dead load 15 psf over a 10 ft tributary width = 150 plf; live load 30 psf over 10 ft = 300 plf; self-weight added automatically. Douglas Fir-Larch No. 2 from NDS Supplement Table 4A: Fb = 900 psi, Ft = 575 psi, Fv = 180 psi, Fc = 1,350 psi, E = 1,600,000 psi. Sections tried from Table 1B: 4x12 (Sx = 73.83 in3) fails at D/C 1.36; 4x14 (Sx = 102.41 in3) still fails at 1.08; 4x16 (Sx = 135.66 in3) passes at 0.82.
Codes referenced: NDS 2024 Sections 2.3.2, 2.3.3, 3.3, 3.4, 3.5 and 4.3, with Tables 2.3.2, 2.3.3, 4.3.1 and 4.3.8; NDS 2024 Supplement Tables 1B and 4A; ASCE 7-22 Section 2.4.1; IBC 2024 Table 1604.3.
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Transcript
The narration word for word, 425 words, from the video's own captions. Select a time to play from there.
Wood Beam — the complete NDS 2024 designer
0:05The Wood Beam module is StructSuite's most complete designer. It handles sawn lumber, glulam, LVL, LSL, PSL, and I-joists, single or multi-span, with the full NDS 2024 adjustment factors, hanger selection, and shear, moment, and deflection diagrams. Let's design a two-span floor girder.
Add the Wood Beam module
0:23From the dashboard, add the Wood Beam module. It opens empty. Step one, geometry. At each support you choose the restraint — pinned, roller, fixed, or free. We set the first support pinned, enter a twelve-foot span, then add a second span to make the beam continuous, pinned over all three supports.
Step 2 — enter loads by tributary width
0:53Step two, loads. Each load has an ASCE load type, a distribution — uniform, point, or triangular — and an input method. For a uniform load you can enter it directly in plf, or from a tributary width in psf. We'll use tributary: fifteen psf of dead load over a ten-foot tributary — a hundred fifty plf.
Live load + self-weight is automatic
1:15The live load the same way — thirty psf over ten feet, three hundred plf. Member self-weight is added automatically once we pick a section.
Step 3 — every wood product category
1:30Step three, material and section — where the module shines. Choose the product category: sawn lumber, glulam, LVL, LSL, PSL, or I-joists — each loads its own manufacturer or NDS tables.
Douglas Fir-Larch No. 2 from Table 4A
1:50For sawn lumber we pick the species and grade straight from NDS Table 4A: Douglas Fir-Larch, Number 2. Then the section, from Table 1B. Let's start modest — a four-by-twelve — and size up if it doesn't work.
Step 4 — NDS adjustment factors
2:10Step four, the NDS adjustment factors. Each is tagged Calculated by the program or User-defined: moisture CM, temperature Ct, incising Ci, repetitive-member Cr, the size factor CF, load duration CD, and the deflection limit. Open any one — like moisture — to change it.
Step 5 — optional Simpson hanger
2:27Step five is optional — a Simpson Strong-Tie hanger. Enable it, and it sizes a hanger for the beam's end reaction; you choose the connection, hanger, and fastener type.
Step 6 — the 4x12 fails (D/C 1.36)
2:38Step six checks it against every load combination. The four-by-twelve is overstressed in bending — demand-capacity one-point-three-six. It fails.
Trial & error — 4x14 still just fails (1.08)
2:57So we iterate. A four-by-fourteen is closer, but still just over, at one-point-oh-eight.
The 4x16 is the optimum — it passes (0.82)
3:11A four-by-sixteen brings it to zero-point-eight-two — the optimum, the shallowest section that passes. Open any combination for the full, code-referenced calculation, step by step.
Step 7 — shear, moment & deflection diagrams
3:25And step seven draws the shear, moment, and deflection diagrams for the continuous beam, so you can see exactly where the demands peak. From geometry and loads to the optimum section, the adjustment factors, the hanger, and the diagrams — that's the complete Wood Beam design, StructSuite's flagship module.