ANATOMY OF A STEEL HALL

Eleven parts in four layers

The groundworks sit in the soil and carry everything. The frame is the steel that holds up the roof and takes the wind. The envelope keeps out rain, wind and cold. The floor is a separate slab inside the hall. This is how the price of the example hall divides:

1. 01Foundation
2. 02Anchors
3. 03Column
4. 04Truss
5. 05Joint
6. 06Bracing
7. 07Purlins and rails
8. 08Roof panel
9. 09Wall panel
10. 10Flashings and gutter
11. 11Floor

The foundation

Each column stands on its own pad foundation. The wide pad at the bottom spreads the load into the soil. The pedestal on top carries the column. The reinforcement inside takes the tension. A concrete plinth runs along the walls, and the panels stand on it.

The dimensions come from the design and from the soil on site.

The anchors

Four anchor bolts per column, hooked at the bottom end. They are set into the pedestal before the concrete is poured. The column stands on them with its base plate and is tightened down with nuts. Under the plate is a layer of grout that fills any unevenness in the concrete.

Before the concrete, the bolts are checked for height and spacing.

The column

An I-section in hot-rolled steel. In the workshop it is cut to length, the base plate is welded on and it is primed. On site it is lifted by crane and bolted down. The column carries the roof and takes the wind that presses on the wall.

Each column is checked for plumb before it is tightened.

The truss

A lattice truss made of box sections. The top chord is in compression, the bottom chord in tension, and the diagonals and posts hold them together. That is how 20 metres are spanned with no column in the middle.

Every element leaves the workshop marked with its number from the erection drawing.

The joint

This is where the truss sits on the column. The end plate of the truss rests on the column cap and the two are clamped together with four bolts. There are washers under the bolt head and under the nut.

The bolts are tightened to the torque given in the design.

The bracing

Cross bracing keeps the wind from pushing the frame out of square. It goes in the end bays, on the wall and on the roof. Each rod has a turnbuckle, which tensions it until the frame stands plumb.

Before the panels go on, the frame is measured once more for lines and levels.

Purlins and rails

Purlins run along the roof from truss to truss. Rails run across the gable wall. The panels are fixed to them. They are cold-formed from galvanised sheet, so they are light, and the zinc protects them from rust.

Before the panels go on, the purlins are checked to lie in one plane.

The roof panel

A sandwich panel: two steel sheets with foam between them. The top sheet has ribs that the water runs down. The foam keeps the heat in and makes the panel stiff. The panel is fixed to the purlins with screws that have rubber washers.

The panels are laid from the eaves up to the ridge, overlapped and sealed.

The wall panel

The same type of panel, with a flat face. On the long walls the panels run horizontally, from column to column. On the gable walls they stand vertically and are fixed to the rails. The colour is chosen from the RAL chart.

The joints between the panels are checked from outside and inside.

Flashings and gutter

Flashings close off the corners, the eaves and the roof edge so that no water gets into the panels. The drip flashing above the plinth sheds water away from the concrete. The gutter collects water from the roof, and the downpipe takes it to the ground.

Water from the roof is carried away from the foundations.

The floor

The floor is a separate slab and does not carry the columns. Underneath is compacted gravel and a membrane. On top is reinforced concrete, power-trowelled smooth. A diamond-shaped joint is left around each column so that the slab does not crack.

The floor is trowelled as soon as the concrete is hard enough to carry the machine.

The load path

Snow weighs on the roof. The panels pass the load to the purlins, the purlins to the trusses, the trusses to the columns, the columns to the foundations and the foundations to the soil. That is why every part is designed for the load that comes from above.

1. Panel
2. Purlin
3. Truss
4. Column
5. Foundation
6. Soil

The frame is designed for the snow and wind at the place where it will stand.

Everything in its place

This is how the corner looks when the hall is finished. From outside you see the panels, the flashings and the gutter. Everything else you have seen so far is inside or underneath them.