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.
Frequently asked questions
What is tributary area?
The floor or roof area that drains its load to a single column or beam, bounded by the midlines to the neighboring supports. It's the area that one member is responsible for carrying.
How do I find the load a column carries?
Multiply its tributary area by the load intensity — area in square feet times pounds per square foot. On a regular grid an interior column's tributary area is one full bay, an edge column's is half a bay, and a corner column's is a quarter bay.
What is the difference between interior, edge, and corner columns?
It's how much of the surrounding bays each collects: an interior column gathers a quarter of each of its four bays (one full bay total), an edge column half a bay, and a corner column a quarter bay — so interior columns carry the most.