# Load takedown, floor by floor: a worked example

> A column reaction is just every floor above it, added up in the right order. Here is a full three-storey gravity takedown worked by hand, from slab pressures to a factored foundation load.

**Category:** Load paths  
**Author:** Elena Marchetti (Structural engineer · Founder)  
**Published:** 2026-05-09

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A load takedown sounds intimidating until you realise it is just accumulation. You follow one support downward through the building, and at every floor you add what that floor hands it. By the time you reach the foundation you have the number you came for.

Let us actually do one. We will take a single interior column through three suspended floors and a roof, and stop at a factored foundation reaction.

## The building

A small three-storey building on a regular column grid of 6 m by 5 m. We are checking an interior column, so its tributary area is the full bay:

> tributary area = 6 m × 5 m = 30 m²

The same 30 m² applies at every level, because the grid does not change up the height. (If the grid stepped in, or a transfer beam picked up the column, the tributary area would change level by level, and you would simply use the right area at each.)

## Step 1: the floor pressures

Before any geometry, write down what each square metre weighs. These are service loads, unfactored, in kPa.

| Level | Dead (kPa) | Live (kPa) | Roof (kPa) |
| --- | --- | --- | --- |
| Roof | 3.8 | 0 | 1.0 |
| Level 3 floor | 4.5 | 3.0 | 0 |
| Level 2 floor | 4.5 | 3.0 | 0 |
| Level 1 floor | 4.5 | 3.0 | 0 |

The dead load of 4.5 kPa is a typical 150 mm concrete slab at about 3.6 kPa plus finishes, services and an allowance for partitions. The 3.0 kPa live load is a normal office or residential occupancy. Your real numbers come from the code and the project, but the method does not care what they are.

## Step 2: load per level

Multiply each pressure by the 30 m² tributary area to get the load that level delivers to our column.

| Level | Dead (kN) | Live (kN) | Roof (kN) |
| --- | --- | --- | --- |
| Roof | 114 | 0 | 30 |
| Level 3 | 135 | 90 | 0 |
| Level 2 | 135 | 90 | 0 |
| Level 1 | 135 | 90 | 0 |

Nothing subtle here. 4.5 × 30 = 135, 3.0 × 30 = 90, and so on. The arithmetic is the easy part, which is exactly why you want the tributary area and the pressures pinned down first.

## Step 3: accumulate top down

Now walk down the column, carrying a running total. The reaction at the base of each storey is everything above it.

| At the base of | Cumulative dead (kN) | Cumulative live (kN) | Cumulative roof (kN) |
| --- | --- | --- | --- |
| Level 3 column | 249 | 90 | 30 |
| Level 2 column | 384 | 180 | 30 |
| Level 1 column | 519 | 270 | 30 |

So just above the foundation, the column has gathered 519 kN of dead load, 270 kN of live load and 30 kN of roof load, all unfactored. (For clarity this example ignores the self-weight of the columns themselves, which you would add as a small dead load per storey.)

## Step 4: apply a gravity load combination

Service loads do not size members; factored loads do. For a gravity check, the usual ASCE 7 strength combinations to consider are:

- 1.4 D
- 1.2 D + 1.6 L + 0.5 (Lr or S or R)

Take the foundation level totals. The first combination gives:

> 1.4 × 519 = 727 kN

The second gives:

> 1.2 × 519 + 1.6 × 270 + 0.5 × 30 = 623 + 432 + 15 = 1070 kN

The second combination governs, so the factored design reaction at the foundation is about **1070 kN**. That is the number that sizes the footing.

## Step 5: do not forget live load reduction

There is one more move that matters as soon as the accumulated area gets large. Codes let you reduce the design live load on members that support a big tributary area, because it is statistically unlikely that every square metre is fully loaded at once.

Our column supports three floors of 30 m² each, an accumulated 90 m² of live-loaded floor. That is well past the threshold where ASCE 7 permits a reduction, and applying it can shave a meaningful slice off that 270 kN of live load before it is factored. The provision is written into the building code itself, in Section 1607.12 of [IBC Chapter 16 on structural design](https://codes.iccsafe.org/content/IBC2021P1/chapter-16-structural-design), which allows members whose live load element factor times tributary area reaches 37 m² (400 square feet) to be designed for the reduced value; an interior column with 90 m² accumulated clears that several times over. We work through exactly how that calculation goes in [ASCE 7 live load reduction, explained simply](/blogs/asce-7-live-load-reduction).

## The pattern, not the numbers

Strip away the specifics and every gravity takedown is the same five moves: set the pressures, find the tributary area, accumulate from the top, combine with the governing factors, and reduce live load where the code allows. Do that for every column and wall and you have a foundation load schedule.

The reason this is worth automating is not the multiplication, it is the bookkeeping. One mis-carried subtotal, one floor counted twice, one column that quietly uses the wrong tributary area, and the error rides all the way down to the footing. StructLoads keeps the running totals for every support at once and shows the dead, live and roof split at each level, so the takedown stays auditable rather than living in a spreadsheet only its author trusts.

If you would like to follow your own column down a building, [open the studio](/), stack a few levels, and read the reactions off directly. The mental model in [how tributary areas work](/blogs/tributary-areas-explained) is the foundation for all of it.