A correct diagram begins with a correct structural model. CourseLab Beam calculates the determinate case you enter, but the app cannot decide whether the support condition, load direction, coordinate, or unit system matches the engineering problem you intended to study.
Define the beam and support condition
Set the span and choose the support arrangement that matches the exercise. Confirm the geometry and units before adding loads. A simply supported beam, cantilever, and overhanging beam can respond very differently to the same loading.
Add point loads, distributed loads, and applied moments
Place each load at the intended coordinate and check its sign or direction as it is added. For a distributed load, verify both its intensity and loaded length. Keep one unit system throughout the case.
- Use exact positions instead of estimating visually.
- Confirm whether a load acts upward or downward.
- Check the start and end positions of distributed loads.
- Keep force, length, and moment units consistent.
Check the support reactions first
Before interpreting the diagrams, ask whether the reactions are plausible. For a vertical-load case, the reactions should satisfy vertical equilibrium, and their signs should make sense for the chosen support arrangement. An unexpected reaction often points to a mistaken coordinate, direction, or support setup.
Connect loading changes to the shear-force diagram
Read the shear diagram from left to right. A concentrated vertical load produces a jump in shear. A distributed load changes shear progressively over its loaded length. Support reactions also appear as changes in the shear value. Cursor values and calculation steps help inspect important coordinates instead of relying only on the overall shape.
Connect shear to the bending-moment diagram
The bending-moment diagram changes according to the shear. Where shear is constant, moment changes linearly. Where shear varies under distributed loading, the moment curve changes accordingly. Maximum or minimum moment commonly occurs where the shear crosses zero, but the model and sign convention still need to be checked.
Study one change at a time
Revise one load, dimension, or support condition at a time when comparing cases. This makes it easier to see which modelling choice caused a change in reactions, shear, or bending moment.
Common modelling mistakes
- Mixing units within one beam case.
- Placing a load at the wrong coordinate.
- Choosing a support condition that does not match the exercise.
- Reading only the diagram shape without checking equilibrium and cursor values.
- Treating an educational calculation as a sealed professional design.
Model determinate beams and inspect support reactions, shear-force diagrams, bending-moment diagrams, cursor values, and calculation steps on Windows or Android.