What the Load Capacity Calculator Does
The Load Capacity Calculator checks how much weight a specific RSJ beam can safely support over a given span. It evaluates two critical engineering checks: bending strength (whether the steel itself will yield) and deflection (how much the beam will sag under load). By entering your beam section, span and expected uniformly distributed load, you can see at a glance whether the beam is adequate or whether you need to step up to a larger section.
How to Use the Calculator
- Pick your beam section – Select the RSJ size from the dropdown, for example 203×133×25 or 254×146×37. Each option includes the section modulus and second moment of area needed for the calculation.
- Enter the span – Input the clear distance between supports in metres. Deflection increases dramatically with span, so accuracy matters.
- Input the total load – Add the dead load (permanent structure) and live load (people, furniture, snow). The calculator will also add the self-weight of the beam automatically.
- Review the results – The tool shows the utilisation ratio for bending and the predicted deflection compared with the Building Regulations limit.
Why Load Capacity Matters for Safety and Building Control
Every structural beam must satisfy two independent limits: it must be strong enough to resist failure, and stiff enough to prevent excessive sag. A beam that passes the strength check can still fail the deflection check, leading to cracked plaster, bouncy floors or sticking doors. UK Building Regulations Part A requires both checks to be demonstrated for any load-bearing alteration. This calculator helps you understand the principles, but final sign-off must always come from a chartered structural engineer and Building Control.