A column’s load is every floor it carries, gathered over its tributary area and added from the roof down. To calculate it: find the column’s tributary area on each level, multiply by the floor loads to get the load per level, accumulate downward, then apply a load combination for the factored axial reaction. StructLoads does this for every column at once, but the steps below are the same by hand.
Step 1: the tributary area on each floor
The tributary area is the slice of floor closest to the column, set by the lines halfway to the neighbouring supports. On a regular grid it reads straight off the plan: an interior column takes the full bay, an edge column about half, and a corner about a quarter. For a six metre by five metre grid the interior tributary area is 30 square metres. The method, and where it gets harder on irregular floors, is in how tributary areas actually work.
Step 2: tributary area to load per floor
Multiply the tributary area by each floor pressure to get the load the column collects on that level. With a 30 square metre area, a 4.5 kN/m2 dead load gives 135 kN and a 3.0 kN/m2 live load gives 90 kN, per floor. Keep dead, live and roof separate so the load factors can act on each correctly later.
Step 3: accumulate from the top down
Walk down the column adding each floor to a running total. The reaction at the base of any storey is everything above it.
| At the base of | Cumulative dead (kN) | Cumulative live (kN) |
|---|---|---|
| Level 3 column | 249 | 90 |
| Level 2 column | 384 | 180 |
| Level 1 column | 519 | 270 |
By the foundation the column holds 519 kN of dead and 270 kN of live load, before any factors. The detailed version of this accumulation is in a floor-by-floor worked example. This top-down walk is what textbooks call load tracing: Anahita Khodadadi’s open chapter on load tracing follows the same hierarchy, roof to joists to beams to girders to columns to foundation, with the tributary area as the tool that keeps every kilonewton accounted for at each handoff.
Step 4: factor it for the design load
Apply the governing ASCE 7 combination. With 519 kN dead, 270 kN live and 30 kN roof, the combination 1.2 times dead plus 1.6 times live plus 0.5 times roof gives about 1070 kN, which governs over 1.4 times dead. That factored 1070 kN is the axial load that sizes the column and its footing.
Interior, edge and corner columns
Position sets how much floor a column draws, and the ratios are a fast sanity check.
| Column position | Share of a full bay | Rough load ratio |
|---|---|---|
| Interior | Full bay | 1.0 |
| Edge | About half a bay | About 0.5 |
| Corner | About a quarter bay | About 0.25 |
If your interior column is not close to twice the edge and four times the corner, something upstream in the geometry is wrong.
Key takeaways: calculating column loads
A column load is tributary area times floor pressure, accumulated down the building, then factored. The arithmetic is light once the tributary areas are right, which is why the geometry deserves the care. StructLoads draws the tributary partition, keeps the per floor and cumulative totals, and applies the load combinations, so the axial number is auditable. It is a preliminary gravity load; slenderness, moments and lateral effects, plus a qualified engineer’s review, finish the design. From here, the same reaction continues into a structural load takedown to the foundation.
Related guides
More in this series: the column load schedule and foundation reactions from a takedown.
Also: the fastest way to calculate column axial loads.
Quick answers
How do you calculate the load on a column?
Find the column’s tributary area on each floor it supports, multiply each area by that floor’s dead, live and roof loads to get the load per level, then add the levels from the roof down. Apply a load combination for the factored axial load. StructLoads computes the tributary areas and the running total for every column.
What is the tributary area of an interior column?
On a regular grid it is the full surrounding bay: half the distance to the neighbouring column on every side. For a six metre by five metre grid that is 30 square metres. An edge column draws about half a bay and a corner about a quarter, giving the rough 1, one half, one quarter ratio.
How do you turn a column load into a column size?
The factored axial load is the demand; a trial size comes from comparing it to the capacity of a candidate section. For a quick check, divide the load by an allowable stress to get a required area, then pick a practical section. This is preliminary sizing only, confirmed later with full code checks.
When do you need more than a hand column load?
A hand axial load is a gravity, preliminary number. You need a fuller analysis once moments, lateral loads, slenderness, continuity or unequal spans matter, or when the column carries a transfer beam. The hand takedown sets the early size, and a qualified engineer takes it through detailed design.