Load-Bearing Precast Concrete Panel System

Units arrive finished. They are cured, faced, and already carry their lifting points, cast-in fixings, service voids and connection preparation, so nothing about a unit can be adjusted once it is delivered. Everything the structure needs to accommodate - deviation, movement, continuity, weather - has to be accommodated in the joints between units.

The common arrangement runs load-bearing walls across the building with floor units bearing between them, which gives a plan that repeats from bay to bay and from storey to storey. That repetition is what makes the method work and also what makes it inflexible: a plan change is a change to the manufacturing schedule, not a change to a drawing.

Because the structure is a stack of separate pieces, the ties that link them do work that has no visible equivalent in a cast frame. They make the assembly behave as one and give it a route around a locally damaged unit, and that arrangement is designed deliberately rather than arising from the way the pieces sit together.

The nearest relative is precast-concrete-facade-panel-system, and the panels can look identical. The test is what is above. A load-bearing panel has floor units bearing on it and building continuing over it; a facade panel has a structure standing behind it and carries only itself and the wind on its face. Remove the first and the floors above come down; remove the second and the structure is untouched. Neither is the materials-library entry precast-concrete-panels, which is the manufactured unit rather than the assembly.

Every unit is made to a manufacturing deviation and placed to a construction deviation, and the joint has to absorb both at once. A joint dimensioned for the drawn gap rather than for that accumulation will either refuse to close at one position or open too far at another, and by then the units either side of it have already been made.

Bearing is created, not inherited. A unit lands on packs, which carry it locally until the joint is filled, and the filling is what spreads the load of the storey above across the whole joint. Where a joint is left partly filled or filled unevenly, the load stays concentrated on the packs, which is a condition the units were not designed around.

Ties are what make a heap of pieces into a structure. They pass through joints, link floors to walls and carry around the perimeter, so a tie omitted, mislocated or interrupted by a later opening does not announce itself. The consequence is not that the building is immediately unstable but that the alternative route the design relied on has quietly gone.

Where a load-bearing unit is also the external face, structure and weather share one line. A profiled joint that relies on an outer barrier being deliberately open, a drained chamber behind it and a continuous inner seal is doing three things in the same gap that a connection also passes through. Sealing, drainage and connection are therefore one detail rather than three trades.

Manufacture closes the options early. A hole cast into a unit is a hole in a piece designed with it; a hole cut later is cut into a thin element with reinforcement near both faces. The design has to know what will pass through before the mould is set, which means service and fit-out coordination precedes production rather than following the frame.