Bending Moment Calculator Formula
Understand the math behind the bending moment calculator. Each variable explained with a worked example.
Formulas Used
Maximum Bending Moment
max_moment = load_w * pow(span_l, 2) / 8Maximum Shear Force
max_shear = load_w * span_l / 2Variables
| Variable | Description | Default |
|---|---|---|
load_w | Distributed Load (w)(kN/m) | 10 |
span_l | Beam Span (L)(m) | 6 |
How It Works
Maximum Bending Moment for a Simply Supported Beam
Under a uniform load, the moment diagram is parabolic with its peak at midspan.
Formulas
M_max = w L^2 / 8 (at midspan)
V_max = w L / 2 (at the supports)
These are the most fundamental results in structural analysis and form the starting point for beam design.
Worked Example
A 6 m simply supported beam carrying 10 kN/m.
- 01M_max = 10 x 6^2 / 8 = 10 x 36 / 8 = 45 kN-m
- 02V_max = 10 x 6 / 2 = 30 kN
Frequently Asked Questions
What if the beam is fixed at both ends?
For a fixed-fixed beam with uniform load, M_max at midspan is w L^2 / 24 and the moment at each support is w L^2 / 12. Fixed ends reduce midspan moment significantly.
How do I combine dead and live loads?
Add the dead load and factored live load per unit length together to get the total w, then apply the formula. Use load factors from your governing design code.
Where does maximum moment occur for a point load?
For a single point load P at midspan of a simply supported beam, M_max = P L / 4, occurring directly under the load.
Ready to run the numbers?
Open Bending Moment Calculator