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How to use the timber beam calculator

A solid, glulam or LVL beam: what each input means, how k_mod follows each load combination, and why lateral-torsional buckling and creep matter.

All guides Inputs Result Calc sheet Walk-through Mistakes

1. What the calculator does

The timber beam calculator designs a solid timber, glulam or LVL beam: simply supported, a cantilever or continuous. It builds the load combinations, takes the modification factor k_mod for each combination from its shortest-duration action, and checks bending with lateral-torsional buckling, shear, bearing and the instantaneous and final deflection with creep. Notches, connections and fire are options.

Two codes are chosen separately: the load combinations (SANS 10160-1, 1.2G + 1.6Q, or EN 1990, 1.35G + 1.5Q) and the resistance (EN 1995-1-1 with k_mod and γ_M, or SANS 10163-1:2003). The badge says it plainly: the characteristic grade stresses are inputs to check against SANS 10163-1, SANS 1783-2 or EN 338.

Timber beam calculator header with the PASS badge — The header: PASS 92 %, governed by bending with lateral-torsional buckling, EN 1995-1-1 6.3.3, 11.38 / 12.35 MPa.

2. The inputs, group by group

Input	What it means	Typical value
Member	Supports (simply supported, cantilever, continuous, or place them yourself) and the span.	simply supported, 4.0 m
Codes	Load combinations and resistance code.	SANS 10160-1, EN 1995-1-1
Section	Width, depth, plies, material (solid, glulam, LVL), grade and service class.	75 × 300, solid, C24, class 1
Loads	Characteristic permanent and imposed line loads, the duration of the imposed load, and wind (+ down, − up). Point loads under the link.	g_k 2.0, q_k 2.5 kN/m, medium-term
More inputs	Self-weight, load sharing, bearing, notches, connections, fire and floor vibration.	as needed

Timber beam inputs: member, codes, section and loads — The inputs. The grade fills the strength properties; check them against the grading standard of the timber you buy.

3. How to read the result

The loading and span sketch shows the design load, the moment and the reactions, with the final deflection under it.

Timber beam loading, span and section — Loading and span: w_d 6.40 kN/m, M_d 12.8 kNm, reactions 12.8 kN; section 75 × 300.

The load combination table is the heart of the page: each combination with its k_mod, the shortest action, the load, the moment, the compression edge, the LTB length and k_crit, and the utilisation in bending, shear and bearing. Under it are the deflection combinations: instantaneous, final with creep, and net final.

Load combination table and deflection combinations — Load combinations: C1 with k_mod 0.80 (medium-term), w 6.40 kN/m, M_d 12.8 kNm, k_crit 0.836, bending 92 %, shear 52 %; deflection S1, final 11.99 mm.

The badge names the governing check; here bending with lateral-torsional buckling at 92 %. A deep, narrow timber beam that is not restrained along its top edge loses strength to LTB (k_crit below 1). With no wind entered, one gravity combination applies, as the note under the table says. Anything the engine could not run shows as NOT CHECKED.

Design checks summary for the timber beam — Design checks: EN 1995-1-1 · 6 pass.

4. Calc sheet and take-off

The result (pass / fail and utilisation) stays free for everyone. Every check with its clause, the calc sheet and the bending schedule are open to signed-in users. Sign in free: 3 designs a month (one calculator, open for 24 hours). Unlimited with a calculator pack.

The detail drawings are part of the paid plan. The timber take-off collects every member in the project with its section, material, length, volume and mass.

Combined timber take-off — The timber take-off: one member, 0.09 m³, 37.8 kg.

5. A 2-minute walk-through

Open the calculator: a 75 × 300 C24 beam on a 4 m span, g_k 2.0 and q_k 2.5 kN/m, service class 1.
Read the badge: PASS 92 %, bending with LTB.
Enter a lateral restraint spacing under More inputs (joists or noggins at 0.6 m, say) and see k_crit rise.
Change the service class to 2 and see k_mod and the creep change.
Enter a wind uplift and see the extra combinations appear.
Switch the grade to SA pine S5 and compare.

6. Common mistakes

One k_mod for everything. Each combination takes k_mod from its shortest-duration action; let the engine do it.
Grade stresses that do not match the timber on site. Check the stamp on the timber against the grade you chose.
Service class 1 for a beam outside. Covered but humid is class 2; exposed is class 3, with lower strength and more creep.
No restraint to the compression edge. Under uplift the bottom edge is in compression, often with nothing holding it.
Instantaneous deflection only. Timber creeps; the final deflection is what the finishes see.

8. Learn more

Try it nowThe calculator opens with the walk-through inputs above. The result is free; sign in for the checks, calc sheet and schedule.
Open the timber beam calculator

A guide to using the calculator, not a design. Check every value against the current code and your own project, and have the design checked and signed by a registered professional engineer.

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