Apply a point load and a distributed load to a simply supported beam. Reactions, shear, and moment update instantly from equilibrium.
Loads in a model must represent real conditions. A point load represents a concentrated force (e.g., beam reaction landing on a girder). A distributed load represents weight spread along a member (floor dead load via tributary width). Load cases group loads by source — Dead, Live, Wind, etc. — so they can be factored and combined per code requirements. Getting loads wrong is the most common modeling mistake.
The most common modeling mistake isn’t wrong member sizes or wrong supports — it’s wrong loads. Loads must represent the real conditions the structure will see. Miss a load and the member is undersized. Apply a load to the wrong location and forces flow through the wrong path. Every load must have a clear physical source (what weight? what pressure? what occupancy?).
A point load (P, in kips) represents a concentrated force — a column reaction landing on a girder, a hanger rod pulling on a beam, a heavy machine bolted to the floor. A distributed load (w, in kip/ft) represents weight spread along a member — floor dead load × tributary width, a wall sitting on a beam, wind pressure across a surface. Most real loads start as distributed and become point loads at connections.
For linear elastic structures, you can analyze each load separately and add the results. A beam carrying both a uniform load w and a point load P at midspan has reactions, shear, and moment equal to the sum of the two individual cases. This is the principle of superposition — it’s why beam formula tables are so useful. The tool above shows this directly.
Once loads are applied, the first thing to check is reactions: ΣFy = 0 and ΣM = 0. The sum of all vertical reactions must equal the total applied vertical load. If they don’t balance, something is wrong with the model. Reactions also tell you what the supports and foundations must be designed for — they’re the starting point for everything downstream.