William Stewart Bridge Update

Latest update - 17 December 2018

CONTRACTOR ON TRACK FOR COMPLETION OF REPAIRS TO WORST TRUSSES ON WILLIAM STEWART BRIDGE BY CHRISTMAS

Following the discovery of significant corrosion in some of the wrought iron and steel members on the William Stewart Bridge, Kumara-Inchbonnie Road, Grey District, in October, speed and weight restrictions were immediately put in place for the safety of users.

A full bridge inspection was carried out and work commenced on repairing the worst affected trusses (four out of 12), with the intention being that this work would be finished by Christmas. Council is pleased to advise that the Contractor has confirmed that they are on track for completion of the repairs by Friday 21 December 2018.

The bridge capacity will be increased to 50% Class 1 after Friday 21 December 2018 from the current restriction of 20% Class 1. This change will be advertised in the local newspaper and published on Council’s website, as well as circulated to emergency services and area representatives for the heavy transport industry and primary industries. The current road closures which have been in place during the repair works will be lifted from Saturday 22 December 2018.

It will also mean that transport operators can apply for a Special Permit to cross the bridge for up to Class 1 loads. Special Permit applications can be made from Tuesday 18 December 2018 - Council will be circulating application forms to representatives of transport operators, West Coast Federated Framers and Westland Milk Products and they can be approved on application to Council.

The above requirements are likely to remain in place for some time until Council assesses if it is cost effective to carry out further repairs to the existing bridge.

Council apologises for the inconvenience this service disruption has caused to normal traffic use of the bridge and thanks road users and businesses for their ongoing cooperation through this period of bridge load restrictions.

Previous update as at 23 November 2018

Following the discovery of significant corrosion in some of the wrought iron and steel members on the William Stewart Bridge, Kumara-Inchbonnie Road, Grey District, last month, speed and weight restrictions were immediately put in place for the safety of users pending an inspection of the entire bridge. These restrictions are 20% Class 1, 2000kg per axle and 10kph and will remain in force until further notice (see here for details).

A full bridge inspection has now been completed. Four of the 12 trusses (the ones that span over the main river flow) are worst affected by corrosion, however the bolts which link the trusses together have been confirmed as being in good condition. It should be noted that the existing trusses are about 100 years old. The detailed analysis of the bridge indicates that even if it was in good ‘as new’ condition, it is would not reach compliance with current design codes for traffic loading. In addition to this, initial assessment of the piers indicate that they would not comply with current seismic design requirements.

Engineering assessments have been carried out on the options to bring the bridge back up to Class 1 load capacity. Detailed analysis had to be carried out to assess the capacity of the bridge under different load conditions. This work has identified some possible options for longer term replacement of components of the bridge. More importantly, it has enabled an informed assessment of what needs to be done now to improve the load capacity of the bridge. Note that design checks and steel strength testing are still on-going, so estimates of improved capacity may change depending on the final results.

Council is pleased to advise that the aim is to have the worst corrosion in the trusses repaired by Christmas, severe weather and other circumstances permitting. The bridge will remain open to light vehicles while the repair work is progressing but to allow the most efficient means of repair, there will be closures of up to an hour each hour with the bridge opened on the hour to allow traffic to pass, Monday to Saturday. If motorists need the bridge to be open at certain times, please contact Council on 03 769 8611 or email infrastructure@greydc.govt.nz and this information will be passed onto the contractor on site.

Once the repair work is done:

  • We have preliminary indications that the bridge can be posted at or close to 50% Class 1 without a speed restriction.
  • Preliminary results also indicate that trucks that want to travel over the bridge at 100% Class 1 can apply to Council for a special permit. This permit will require trucks to travel across the bridge at crawl speed (4kph) and central on the deck.
  • Further analysis of the bridge is still pending, however, we are aiming to minimise the above restrictions as much as possible, while staying within safe and practical limits.
  • It is highly unlikely that permits can be issued for loads in excess of Class 1.
  • If severe weather and other circumstances means the target date cannot be achieved, a review of progress will be done prior to Christmas and, if possible, the allowable loadings on the bridge will be increased but to lower levels, for instance 40% Class 1 with no speed restriction and 80% Class 1 for trucks.
  • All changes to the allowable loads on the bridge will be advertised in the local newspaper, published on Council’s website, circulated to emergency services and area representatives for the heavy transport industry and primary industries.

These requirements are likely to remain in place for some time as Council assesses if it is cost effective to carry out further repairs to the existing bridge.

The restrictions that had to be imposed and the disruption to many industries and the community have emphasised the importance of this bridge to the economy of the West Coast. Council apologises for the inconvenience this service disruption has caused to normal traffic use of the bridge.

Page reviewed: 17 Dec 2018 5:40pm