The same weight can be a pressure, a line load or a point load depending on what carries it. An area load sits on a slab as a pressure, a line load runs along a wall or beam, and a point load concentrates at a column. A load takedown is largely the job of converting between these three forms down the load path. StructLoads handles all three, and knowing the difference keeps the units and the method straight.
The three forms
A structural load is described by how it is distributed.
| Load type | Spread over | Units | Applied to |
|---|---|---|---|
| Area load | A surface | kN/m2 or psf | Slabs, floors, roofs |
| Line load | A length | kN/m or plf | Walls, beams |
| Point load | A point | kN or kips | Columns, equipment |
An area load is a pressure; a line load is force per length; a point load is a single force. The units follow directly, and keeping them straight matters because the takedown multiplies one by a dimension to get another. This is the same distributed-versus-concentrated classification used in Udoeyo’s Structural Analysis chapter on loading systems, the open Temple University textbook, so the takedown vocabulary matches what analysis courses teach.
Area loads
An area load is the floor pressure: dead, live, roof or snow, spread over the slab surface in kN per square metre. It is how occupancy loads are specified, as in published imposed load values by use. The area load only exists on the surface; the moment it reaches a support it is converted to a line or point load, which is the first step of any takedown.
Line loads
A line load runs along a one-dimensional element, a wall or a beam, in kN per metre. A beam gets its line load by multiplying the area load by its tributary width, and a wall carries its own self-weight as a line load plus any floor it supports. So a line load is usually an area load collected along a strip, the conversion set out in tributary width for a beam.
Point loads
A point load is concentrated at one location, in kN: a column reaction, a beam reaction landing on a column, or a heavy item of equipment. A column collects an area load over its tributary area into a point load, and a beam converts its line load into point-load reactions at its ends. Point loads are where the load finally concentrates before going down to the foundation.
How they convert down the load path
A takedown is a chain of conversions. The slab area load becomes a beam line load by the tributary width, and a column point load by the tributary area. The beam line load becomes point-load reactions at its end columns. Those point loads accumulate down the columns to the footings, where they spread back into an area pressure on the soil. The whole sequence is the structural load takedown, and each step is one of these conversions. The split into dead, live and roof, from dead load vs live load, is carried through every conversion.
Key takeaways: area, line and point loads
Area loads are pressures on slabs in kN per square metre, line loads run along walls and beams in kN per metre, and point loads concentrate at columns in kN. A takedown converts between them: area times tributary width gives a line load, area times tributary area gives a point load, and beam reactions are point loads. StructLoads tracks all three as a preliminary model a qualified engineer confirms.
Quick answers
What is the difference between area, line and point loads?
An area load is a pressure over a surface, measured in kN per square metre, used for floor and roof slabs. A line load is spread along a length, measured in kN per metre, used for walls and beams. A point load is concentrated at one location, measured in kN, used at columns and for heavy equipment. They differ in how the load is distributed.
What units does each load type use?
An area load uses force per area, kN per square metre or psf. A line load uses force per length, kN per metre or plf. A point load uses force, kN or kips. Keeping the units straight is essential, because a load takedown multiplies an area load by a length to get a line load and by an area to get a point load.
How do area, line and point loads convert in a takedown?
An area load on a slab becomes a line load on a beam by multiplying by the tributary width, and a point load on a column by multiplying by the tributary area. A beam carrying a line load delivers point-load reactions to its end columns. So a takedown is largely a sequence of conversions between the three forms down the load path.
When does an area load not stay an area load?
It does not stay an area load as soon as it reaches a one-dimensional or point support. The floor pressure becomes a line load when collected by a beam or wall, and a point load when collected by a column or delivered as a beam reaction. The area load only exists on the surface; below that it is converted to line and point loads.