Beam input form
Enter service loads, timber properties, adjustment factors, and section size. Results appear above this form after submission.
Example data table
Sample design case for a simply supported rectangular timber beam.
| Parameter | Value | Unit | Comment |
|---|---|---|---|
| Span | 4.2 | m | Simply supported beam |
| Section size | 90 × 300 | mm | Rectangular solid timber section |
| Dead load UDL | 1.2 | kN/m | Service load |
| Live load UDL | 2.4 | kN/m | Service load |
| Centered point load | 3.5 | kN | Additional concentrated load |
| Elastic modulus E | 11000 | MPa | Typical structural timber input |
| Allowable Fb / Fv / Fc⊥ | 14 / 2.0 / 6.0 | MPa | Entered base allowable stresses |
| Self-weight included | 0.146 | kN/m | Based on density 550 kg/m³ |
| Total service UDL | 3.746 | kN/m | Dead + live + self-weight |
| Maximum moment | 11.934 | kN·m | Passes with adjusted bending capacity |
| Maximum shear | 9.616 | kN | Support reaction |
| Bending stress | 8.840 | MPa | Below adjusted allowable stress |
| Shear stress | 0.534 | MPa | Below adjusted allowable shear |
| Deflection | 9.238 | mm | Less than L/360 limit |
| Overall result | PASS | - | All major checks satisfied |
Formula used
Area, A = b × d
Section modulus, S = b × d2 / 6
Moment of inertia, I = b × d3 / 12
R = (wL + P) / 2
Vmax = R
Mmax = wL2 / 8 + PL / 4
Bending stress, fb = M / S
Rectangular shear stress, fv = 1.5V / A
Bearing stress, fc⊥ = R / (b × bearing length)
Δ = 5wL4 / (384EI) + PL3 / (48EI)
Allowable deflection = L / chosen ratio
Fb,adj = Fb × Cd × Cm × Ct × Cr × Cf
Fv,adj = Fv × Cd × Cm × Ct
Fc⊥,adj = Fc⊥ × Cm × Ct
This calculator uses elastic analysis for a simply supported beam with a full-span uniform load and a single centered point load.
How to use this calculator
- Enter the clear span in meters.
- Input beam width and depth in millimeters.
- Fill in dead load, live load, and any centered point load.
- Enter timber stiffness and allowable stress values.
- Adjust modification factors for service condition assumptions.
- Choose the deflection ratio and support bearing length.
- Decide whether self-weight should be included automatically.
- Press the calculation button to see stresses, capacities, checks, and the Plotly graph.
- Use CSV or PDF export to save the design summary.
Frequently asked questions
1) What beam condition does this calculator model?
It models a simply supported rectangular timber beam carrying a full-span uniform load and one point load placed at midspan. That keeps the design logic clear and practical for common framing checks.
2) Which checks are included?
The calculator checks bending stress, shear stress, support bearing stress, and vertical deflection. It also reports reactions, moment capacity, shear capacity, required section modulus, required inertia, and governing utilization.
3) Are timber adjustment factors included?
Yes. You can enter load duration, moisture, temperature, repetitive member, and size factors. These modify allowable stresses so the output better reflects your project assumptions and timber grading data.
4) Does this replace a final engineered design?
No. It is a fast design aid and screening tool. Local code provisions, connection design, fire requirements, stability, lateral restraint, notching limits, and detailed engineering review still matter before construction.
5) Why does beam depth affect performance strongly?
Depth has a large influence because section modulus depends on depth squared, while inertia depends on depth cubed. Increasing depth usually improves bending resistance and stiffness much faster than increasing width alone.
6) Should I include timber self-weight?
Usually yes, especially for longer spans or larger sections. The calculator can estimate self-weight from density and section size, then add it to the service uniform load automatically.
7) What units should I use?
Use meters for span, millimeters for section size and bearing length, kilonewtons per meter for uniform loads, kilonewtons for point load, and megapascals for stiffness and allowable stresses.
8) What should I change if a check fails?
Start by increasing beam depth, reducing span, lowering applied loads, improving bearing length, or selecting timber with better allowable stresses and stiffness. The required section modulus and inertia values help guide revisions.