Rogers Structural Investigations Ltd RSI | Bridge Inspection, Bridge Testing, Bridge Repair

Scottish Water
Rogers Structural Investigations Ltd were instructed by Concrete Repairs Ltd to undertake a specialised intrusive investigation into the condition of the pre-stressing systems of 7 No. preload water tanks.

These works were completed in response to a structural failure of a tank of similar construction in 1999 as detailed in the subsequent HSE report reproduced below.

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.

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