How is an outdoor amphitheatre built at a school?

Two things make a school amphitheatre: ground shaped into a slope, and stepped concrete seats formed into it. The structure is modest in size and leaves very little room for error, because every step stays on show for decades.

Levels and ground

A natural slope is a good start, because the seating can follow the ground. Where the site is flat or the fall is too steep, earthworks and retaining walls create the shape, and an engineer designs what holds the soil behind them.

Services under the area are found before any excavation. The structural side of a change in level is covered in retaining walls and level changes.

Formwork and steel

Every step needs its own form, set level and square to the one below it. A few millimetres out on one step is hard to see on a drawing and easy to see across a long row of seating.

Reinforcement goes in as designed and is checked before the pour, since nobody can inspect it afterwards.

The pour

Concrete does not wait once the truck arrives, so the sequence is settled in advance: which sections go first, where the joints fall and how the pump reaches each step. Joints stay visible for the life of the structure, so they are drawn as part of how it looks.

The finish has to suit people sitting on it and walking on it, and curing is left to run its full time before anyone uses it. On a school site, the pour days also have to fit around students, as described in concrete works on an occupied site.

Water

A set of steps collects a lot of rain. Each step needs a slight fall to shed water, and the bottom of the amphitheatre needs somewhere for it to go, or the stage ends up as a pond after every storm.

Stains and slime on a concrete seat usually trace back to this detail. Good falls cost very little on the day of the pour and are very hard to fix later.

Access

Steps shut out anyone who cannot climb them unless the design allows for it from the start. An accessible route to the stage and to a level viewing spot belongs in the first drawing, along with handrails where people need them and protection at any drop.

The wider approach is in pathways and accessible routes across a site.

Coogee Public School

Monument delivered an amphitheatre and sports court at Coogee Public School, a large concrete structure built with high precision and designed to last. It shows Monument's ability to construct substantial concrete structures, and it is intended to be enjoyed for generations. More on that project is in the Coogee Public School amphitheatre and sports court.

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