Presentation on theme: "Monitoring of Suspension Bridge Main Cables: The Forth Road Bridge Presented by Alastair Andrew B.Sc, C.Eng, MICE. General Manager & Bridgemaster Cambridge."— Presentation transcript:
Monitoring of Suspension Bridge Main Cables: The Forth Road Bridge Presented by Alastair Andrew B.Sc, C.Eng, MICE. General Manager & Bridgemaster Cambridge 15th May 2007
Structural Challenges Design based on 22 ton lorries The 38 tonne lorry introduced from 1983 The 44 tonne lorry introduced from 2001 Traffic increase from 4 to 24 million Bridge presently carrying 5620 tonnes Design load 2880 tonnes
Original cast diameter of 1524mm (5 feet) still apparent Testing – Sample wires
Factor of Safety
Conclusions An excellent external inspection and maintenance regime was not sufficient to prevent deterioration A good external condition doesn’t mean it is good on the inside Widely varying levels of corrosion in different areas were difficult to explain Current strength loss estimated to be 8% to 10%
Way Ahead Fitted acoustic monitoring 2006 Fit de-humidification 2007/9 Inspect and re-evaluate 2009 and 2013 Cable augmentation/replacement feasibility study.
Side view of whole platform
Close up of travelling rail (turquoise) and main hanging strap that runs along this rail.
Acoustic Monitoring Commission West Cable Nov’ 08 East Cable Sept’ 09 Re-examine cables FORTH ROAD BRIDGE MAIN CABLE CRITICAL PROGRAMME Wrap cables and fit equipment Plan and construct new crossing If Dehumidification Unsuccessful Heavy Vehicles Barred De-humidification Replacement/Augmentation Study Dec 2006