The building that decides a cooperative's harvest is not the mill. It is the receiving shed.
A mill can run all year and catch up. A receiving shed cannot. Every tonne the cooperative will handle in the next twelve months passes through one opening, in one harvest window, at the speed of a truck tipping. If that opening is too narrow, the queue forms on the road, the drivers wait, the samples are taken in the dark, and the whole intake record becomes an argument. Everything downstream — drying, cleaning, storage, milling, bagging — inherits that argument.
So the sequence I work through is not "how big is the mill". It is: how many trucks in the peak hour, where does the grain go in, and what has to be true about the floor before the first truck arrives.
1. Size the receiving shed by the peak hour, not the annual tonnage
Annual tonnage tells you almost nothing about the building. A cooperative taking in a large crop may still deliver ninety per cent of it across two or three weeks, and half of that between mid-morning and late afternoon.
The number that matters is a rate. Two receiving lanes, each truck carrying around 30 tonnes (about 33 short tons) and clearing the pit in twenty minutes, is roughly 180 tonnes an hour at the pit. That single figure sizes the hoist, the pre-cleaner, the conveyors, the dryer feed and the dust system — in that order, because the slowest link sets the rate for all of them.
Get this wrong in the generous direction and you pay for capacity that runs four weeks a year. Get it wrong in the tight direction and you cannot buy your way out of it later: a pit cannot be widened once the slab is poured around it.
2. The tipping pit sets the floor level for everything downstream
The pit is where the geometry of the whole building is fixed, and it is usually decided last.
A pit with a working depth of about 2.5 m (8 ft) needs an approach ramp long enough that a loaded truck can reverse down it without riding the brakes. In practice that is a ramp in the order of 18 to 22 m (60 to 70 ft), and that ramp is roofed area you are paying for whether or not you thought about it.
Three consequences follow immediately. The receiving floor has to fall toward the pit, not away from it, so surface water does not run into the grain. The pit itself needs a sump and a pump, because washdown water and rain off the truck beds both end up at the lowest point in the building. And the eaves height over the ramp is set by the tallest truck that will ever use it plus its raised body — not by the height of the shed behind it.
3. Dust is a load, fire risk and a cleaning problem at once
Grain dust does not stay in the air. It settles on every horizontal surface, and in a steel building the horizontal surfaces are the purlins, the tie beams and the top flange of every rafter.
That has two effects that get designed out cheaply and retrofitted expensively. First, an accessible roof structure — maintained access, no inaccessible pockets over the pit — matters more than a slightly deeper rafter. Second, dust that accumulates on a warm surface and is never removed is a fire load sitting above the intake; the answer is a roof and wall profile that sheds dust rather than traps it, and a cleaning route that a person can actually walk.
Where grain dust is generated hardest — at the pit, the elevator head and the cleaner discharge — the sensible move is to keep those points in a separate, better-ventilated bay rather than under the same roof volume as the bagging area.
4. Where the mill extension breaks the frame
Almost every cooperative I look at is not building one building. It is adding the third or fourth building to a site that grew.
The failure mode is consistent. The new mill hall is set out from the property line rather than from the existing gutter, and the new column line lands exactly where the old roof drained. Overnight, a gutter becomes an internal valley, a downpipe becomes a pipe running through a wall, and a free-draining roof becomes a place where water ponds against a new wall.
The fix is cheap on paper and expensive on site: decide the extension line before the first building is detailed, and keep one full bay of the original building clear of anything that cannot be moved — pits, plant rooms, buried drainage. A bay that costs a little extra now is the only thing that makes the next phase possible without stopping intake for a season.
5. The silo interface is the joint nobody draws
Silos and the receiving building settle differently, and they are designed by different people. The junction between them is where I see the most unfinished thinking.
Two things have to be settled early. What separates the silo battery from the shed — a movement joint, or a structural connection that assumes they move together — and how a person or a conveyor crosses that gap. A 200 mm (8 in) gap that nobody details becomes a place where water enters, grain accumulates and the conveyor support gets welded to whatever is nearest.
The second is the free span between the last silo and the shed wall. If that span is going to carry a conveyor gallery or a dryer, it needs to be a structural decision, not a length of purlin that happened to fit.
6. What I want before drawings
Six answers change this building more than its footprint does.
- The peak-hour truck rate, and the largest single load that will ever arrive.
- Whether intake is sampled and weighed before or after tipping — this alone can move the pit.
- What the site does with surface water today, and where it is allowed to go.
- Whether the mill, the dryer or the silos are planned within five years, and roughly where.
- Whether the same shed will later take a different crop, with different dust and different flow.
- The wind speed to be used, taken from the applicable code at the project site rather than a round number — on an exposed inland site with a short wet season, that figure and the roof's edge detail decide whether the intake stays usable during the storm that always comes at the worst moment.
None of these are steel questions. All of them change the steel drawing. That is the part of a grain project a quotation cannot fix later.