Inputs
This tool builds a load chart for a simply supported beam using combined area loads and optional point loads. Use it for quick checks; confirm with applicable codes and project details.
Example data table
Illustrative values only. Always verify with your project requirements.
| Use case | Dead load (kN/m²) | Live load (kN/m²) | Notes |
|---|---|---|---|
| Residential floor | 2.5 | 2.0 | Finishes + partitions included in dead load estimate. |
| Office floor | 3.0 | 3.0 | Higher live load reflects occupancy and layout changes. |
| Light roof | 0.8 | 0.6 | Add snow or wind where relevant. |
| Storage / archive | 4.0 | 5.0 | Use appropriate category for heavy storage areas. |
Formula used
- q = D + L + S + W + E (area load sum, service or factored).
- w = q × b (equivalent line load using tributary width b).
- UDL reactions: RL = RR = wL/2.
- Point load at a from left: RL += P(L−a)/L, RR += Pa/L.
- Shear at station x: V(x) = RL − wx − ΣP (for loads at positions ≤ x).
- Moment at station x: M(x) = RLx − wx²/2 − ΣP(x−a) (for loads at positions ≤ x).
How to use this calculator
- Select the unit system used on your drawings.
- Enter area loads for the supported slab or roof zone.
- Enter tributary width and the simply supported span length.
- Add point loads for concentrated equipment or reactions.
- Choose service-level or enter simple design factors if needed.
- Press Calculate to view charts and the load table.
- Download CSV for spreadsheets or PDF for quick sharing.
Practical guide to using load charts in construction
1) Why a load chart matters
Load charts turn scattered project inputs into one coherent view of demand along a span. By combining area loads, tributary width, and optional concentrated loads, you can quickly see reactions, shear peaks, and moment hot spots. This supports early sizing, cross‑checks, and clearer communication with your team.
2) Converting area load to line load
Many floor and roof requirements are specified as area loads, such as 2.0 kN/m² for residential live load or 3.0 kN/m² for office occupancy. The calculator converts the combined area load q to a uniform line load w using w = q × b, where b is tributary width.
3) Selecting tributary width correctly
Tributary width depends on framing layout and load paths. For a beam supporting joists at spacing s, a common approximation is b ≈ s for interior beams and b ≈ s/2 for edge beams, unless diaphragms or cantilevers change distribution. When unsure, check plans and framing notes.
4) Service versus factored inputs
Service-level charts help with deflection checks, vibration discussions, and load tracing. Factored charts are useful for strength screening. This calculator includes simple user-defined multipliers by load type so you can reflect your chosen method. Keep factors consistent with your project basis and ensure combinations match governing cases.
5) Point loads from equipment and framing
Mechanical units, stair landings, transfer posts, and beam-to-beam reactions often act as point loads. Enter magnitude and position measured from the left support. The reactions update automatically using statics, and the shear plot shows visible “steps” at each point load. This is a fast way to test alternate equipment locations.
6) Interpreting shear and moment shapes
For a uniform line load only, shear changes linearly while moment is parabolic, with the classic midspan maximum M = wL²/8. Point loads add jumps in shear and kinks in moment slope. If the moment diagram looks discontinuous, check that point-load positions lie within 0 to L.
7) Quality checks you should perform
Use the reaction balance as a quick sanity test: the sum of reactions should equal the total applied load (UDL over the span plus all point loads). Increase chart stations to refine peaks for closely spaced loads. If wind uplift is modeled as negative, confirm sign conventions and verify that support reactions remain realistic.
8) Reporting and coordination
The CSV export supports spreadsheet verification, while the PDF export provides a compact record for submittals and design logs. Capture assumptions alongside the report: span, tributary width, load components, and any equipment locations. This improves traceability and reduces rework when architectural grids or framing directions change.
FAQs
1) What does “chart stations” control?
Stations are the number of points sampled along the span. More stations create smoother plots and can better capture peaks near point loads. Typical values are 41 to 201 for quick checks.
2) Can I model uplift from wind?
Yes. Enter wind load as a negative area value to represent uplift. Review sign conventions and confirm that reactions and moments align with your intended direction of loading.
3) Does this handle cantilevers or continuous beams?
No. The chart is for a simply supported span. For cantilevers or continuous systems, internal moments and reactions differ and require a different structural model.
4) How are reactions computed with point loads?
Each point load is distributed to supports using statics: left reaction increases by P(L−a)/L and right reaction by Pa/L, where a is the distance from the left support.
5) Why do I see steps in the shear chart?
Steps occur at point-load locations because shear decreases instantly by the magnitude of the point load. This is expected and helps you identify concentrated load effects.
6) What units should I use for loads?
Use consistent units. In metric, area loads are kN/m² and lengths are meters. In imperial, area loads are psf and lengths are feet. The calculator converts area loads to line loads using tributary width.
7) Is the maximum moment always at midspan?
Only for pure uniform loading without point loads. With point loads or mixed loading, the maximum can shift. Use the moment plot and table to locate the governing position.