Precast Concrete Spiral Stairs ~ this form of stair is usually
constructed with an open riser format using tapered treads which
have a keyhole plan shape. Each tread has a hollow cylinder at the
narrow end equal to the rise which is fitted over a central steel
column usually filled with in-situ concrete. The outer end of the
tread has holes through which the balusters pass to be fixed on
the underside of the tread below, a hollow spacer being used to
maintain the distance between consecutive treads.Precast Concrete Stairs