Tributary Area & Load Takedown
Find the floor area a column supports and the load it carries, from your bay spacings and a live-load intensity.
- Interior column collects one full bay (×1).
- Tributary area = bay X × bay Y × 1.
- Live load only — add dead load and verify against your code (ASCE 7-22 T.4.3-1).
How load takedown works
Every column carries the slab area that drains to it — its tributary area — bounded by the midlines to the neighbouring columns. On a regular grid an interior column collects a quarter of each of its four surrounding bays, which adds up to one full bay; an edge column collects half a bay; a corner column a quarter.
The load that member carries is just tributary area × load intensity.
The presets are minimum live loads from ASCE 7-22 Table 4.3-1 — pick your
occupancy or enter a custom value. Remember this is live load only:
add the dead load (and snow or other loads as applicable) and verify against your
adopted code. It's a takedown estimate, not a structural design.
This is the practical companion to the load-paths idea — loads accumulate down the path, and tributary area is how you size each link.