FORTH ROAD Bridge contractor Monberg & Thorsen faces late completion penalties of £350,000 after problems replacing the crossing's 192 suspension hangars.
The five-month delay is due mainly to difficulties analysing the bridge's complex loading regime as vital temporary hangars are added to deck sides.
The £7.8M contract to renew the 26km of hangar cabling should have finished last month. But only 40 steel hangars have been replaced.
'We underestimated the complexity of determining additional loads on side beams where the temporary hangars must be fixed,' explained project manager Henning Schultz.
'We have started a night shift and have increased work fronts, but it is unlikely we can reduce the delay.'
The Danish contractor beat Kvaerner Cleveland Bridge and Laing with the lowest price and a promise to complete the contract 16 weeks more quickly
Deputy bridge master Barry Colford pointed out that the contract was the first of its kind in Europe involving vertical hangars.
As all temporary works are the sole responsibility of the contractor, no claims for time extensions are expected. But Schultz claimed that the weather, especially high wind, had been worse than anticipated. To date, the expected downtime has been doubled and a claim for at least one month has been lodged.
The need to replace the 35 year old hangars was triggered by the discovery four years ago that wires had snapped or frayed in nine of the 44mm diameter cables. The cause is attributed to fatigue loading, corrosion and a lack of protective lubricant between the 113 wires in each cable.
The four temporary cables, fixed around the original hangar assembly, are tensioned to take full bridge loading while the old cables are removed and replaced. The exact position of these temporary cables is crucial to avoid deck beams being overstressed.
(see feature page 34)