Tilt-Up Concrete Panels For Warehouses

Tilt-up construction casts the walls of a warehouse flat on the building's own floor slab, then lifts each panel upright with a crane, braces it, and ties it into the footings and the roof. It is fast and economical for large industrial walls, and the engineering has to cover four separate stages: casting, lifting, temporary bracing and the finished building.

Each of those stages loads the panel differently. A panel designed only for the finished building is a panel that cracks on the way up.

Why warehouses use it

Warehouses have large, plain, repetitive walls, and tilt-up turns that repetition into speed.

The panels are cast on site with no separate casting yard and no transport, they give a hard and durable wall, and concrete gives the fire resistance a boundary wall needs. The roof is usually steel, either portal frames with the panels as cladding or a roof that bears directly on load-bearing panels. The frame side is covered in [steel portal frames for warehouses](/blog/steel-portal-frames-for-warehouses).

The slab as a casting bed

The floor slab is poured first, and the panels are cast on top of it with a bond breaker between the two so they release cleanly.

That puts demands on the slab well before the building exists. It has to be flat, because every bump and joint in the slab shows on the face of the panel cast against it. It also has to carry the crane. A mobile crane lifting a heavy panel puts very large loads through its outriggers, so the crane positions are agreed with the builder before the slab is designed, and the slab and the ground under it are checked for those loads.

Lifting loads and reinforcement

A thin panel lifted from flat bends like a plank picked up at a few points. The face in tension has to resist that bending with concrete that is only days old.

For thin panels with large door openings, the lift is often the case that sets the reinforcement. The number and position of lifting inserts, the rigging arrangement and the concrete strength needed at the lift are all part of the design. AS 3850, the standard for prefabricated concrete elements, treats the inserts, the handling and the bracing as engineering, not a site decision. The strength at lift is confirmed by test before the crane arrives, and what happens when a test comes back low is set out in [low concrete cylinder results and what happens next](/blog/low-concrete-cylinder-test-results-what-happens-next).

The panel in the finished building

Once standing, a panel is a tall slender wall. It carries wind pressure on its face, load from the roof, and has to resist buckling over its height.

Openings change everything around them. Roller door and dock door openings take wall away where the load still has to pass, so the panel either side carries more and is reinforced or thickened to suit. Where a panel is a fire wall on a boundary, its fire resistance level comes from the fire engineer, and the connections to the roof are detailed with that requirement in mind.

Temporary bracing until the roof is on

Between the lift and the completion of the roof, each panel stands on temporary braces fixed to the slab.

Wind during that period is the governing load. The braces stay until the engineer confirms the permanent structure is complete and connected, and the detail is covered in [temporary bracing of precast panels](/blog/temporary-bracing-of-precast-panels).

Connections and tolerances

At the base, panels sit on shims over starter bars or dowels from the footing and are grouted solid. At the top, they connect to the roof structure that ties the building together. Between panels, joints are sealed for weather.

None of that works if the panels and the footings disagree on where they are. Tolerances are part of the design, as discussed in [precast connections and site tolerances](/blog/precast-connections-and-site-tolerances).

Panel drawings

Each panel gets a drawing showing its size, reinforcement, openings, cast-in plates, lifting inserts, rigging arrangement and brace points. An erection sequence drawing shows the order the panels go up and how the structure stays stable while it is part-built.

How we approach it

We design the slab, the panels, the footings and the roof connections together, because each one sets loads on the others. The crane positions are agreed before the slab is finished, the panel drawings carry the lift and the bracing, and we inspect the reinforcement before each casting. A tilt-up panel has to survive three temporary jobs before it settles into the one it was built for.

ACSES provides structural engineering for industrial buildings across Sydney. Talk to us about a project.

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