Bridge Inspections - RSI

Scottish Water

The Lanner Hill Reservoir Incident
On the 6 th December 1999 the Lanner Hill Reservoir operated by SWW, suffered a collapse of its pre-stressed concrete shell roof and ring beam. Lanner Hill is a reservoir which was built using the Preload system. This process used a self propelled wire winder to apply cold draw high tensile steel to the walls and ring beam of the structure whilst simultaneously pre-stressing the wire. The walls of the structure had then been sprayed with a coat of gunite to approximately 38mm.

Investigations into the cause of the collapse indicated no weakness in the roof structure itself or any sign of overloading. The load capacity of such structures are high in relation to their span (in this case 43m).

However there had been clear evidence of
corrosion to the pre-stressing wires of the ring
beam. The roof structure relies largely upon the
integrity of the monolithic concrete ring beam
for its stability.

Due to the corrosion of the pre-stressing wires,
the ring beam had lost a significant degree of its
strength resulting in a transference of tension to
the roof structure. There was evidence of failure
of the bond between the ring beam and collar. On December 6th the ring beam collar was cut as part
of an investigative action plan. This resulted in the
roof becoming unstable and collapsing into the
reservoir.

Back to Project list