A load takedown is the bookkeeping that turns a floor plan into a number at the bottom of a column. You work out what each square metre of floor weighs, decide how much of that floor each column carries, and then add it up storey by storey until you reach the foundation.
It is the first thing you do on any building and the thing most often got wrong — not because the arithmetic is hard, but because it is long, and one missed partition allowance propagates all the way down.
Step 1 — Dead load (Gk)
Everything permanent: the structure's own weight, screed, tiles, ceiling, and an allowance for partitions that may move. Reinforced concrete is taken as 24 kN/m³, so a slab's self-weight is simply its thickness times 24.
| Item | Working | kN/m² |
|---|---|---|
| 160 mm slab | 0.16 × 24 | 3.84 |
| Screed, tiles, ceiling | typical finishes | 1.20 |
| Partition allowance | lightweight, movable | 1.00 |
| Gk | 6.04 |
Finishes and partition allowances are office conventions, not code values. Use the ones your office uses, and write them on the sheet so the next person can see what you assumed.
Step 2 — Imposed load (Qk)
People, furniture and anything else that comes and goes. Taken from BS 6399-1 by occupancy — 1.5 kN/m² for self-contained dwellings, 2.5 for offices and classrooms, 4.0 for assembly areas and corridors in public buildings. This example is a residential floor, so Qk = 1.5 kN/m².
Step 3 — Combine them
At ultimate limit state BS 8110 factors dead load by 1.4 and imposed by 1.6. The two factors differ because we are less sure about the imposed load than the concrete.
= 1.4(6.04) + 1.6(1.5)
= 8.46 + 2.40 = 10.86 kN/m²
Step 4 — Tributary area
Each column carries the floor halfway to its neighbours in every direction. On a regular 4 m × 4 m grid, an interior column's tributary area is 4 × 4 = 16 m² — half a bay each way. An edge column carries half of that, and a corner column a quarter.
= n × tributary area = 10.86 × 16 = 173.7 kN
Tributary area is an approximation that assumes the panels are similar and regularly spaced. Where spans differ a lot, or a beam is continuous over an unequal pair, the real reaction is not the halfway split — that is when you analyse the beam properly instead.
Step 5 — Add the members' own weight
The beams framing into the column and the column itself are not in the slab load. Only the beam web below the slab counts, or you are weighing the same concrete twice.
self wt = 0.225 x 0.29 x 24 = 1.57 kN/m
8 m of beam framing in (half of four 4 m spans)
= 1.4 x 8 x 1.57 = 17.5 kN
Column 225 x 225 x 3.0 m storey
= 1.4 x 0.225² x 24 x 3.0 = 5.1 kN
Per storey 173.7 + 17.5 + 5.1 = 196.3 kN
Step 6 — Carry it down
Now repeat, adding each storey to the total as you go down. Taking every floor as a typical floor (conservative for the roof, which is lighter):
| Level | This storey | Cumulative N |
|---|---|---|
| 2nd floor column | 196 kN | 196 kN |
| 1st floor column | 196 kN | 393 kN |
| Ground floor column | 196 kN | 589 kN |
That 589 kN is what the ground-floor column is designed for, and what the foundation under it must spread into the soil. At an allowable bearing pressure of 150 kN/m² and a service load of about 410 kN, the pad needs roughly 2.7 m² — a 1.65 m square, before the footing's own weight is allowed for. Designing that pad properly takes it to 1.8 m.
One refinement: imposed load reduction
Every floor of a building is very unlikely to be fully loaded at the same moment, so BS 6399-1 Table 2 lets you reduce the imposed load carried by columns and foundations as the number of floors above increases — 10% for two floors, 20% for three, and so on.
The reduction applies to columns and foundations only. A slab or a beam is designed for the full unreduced imposed load, because that floor really can be fully loaded even if all of them cannot.
Try it on your own building
Structura does exactly this takedown — slab to beam to column to footing, with the loads accumulating storey by storey and the BS 6399-1 reduction applied where it belongs. Every step is shown the way it is above, so you can check it by hand.
Single members — slab, beam, column, footing, stair, lintel — are free to run, as many as you like.
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