30 November 1999
Auckland Harbour Bridge is the first bridge to benefit from a new maintenance policy introduced this year by its owner Transit New Zealand. The organisation has been using competitive pricing procedures since 1991 but until recently, they were implemented using short-term contracts.
The development of a new longer-term approach is expected to encourage more research and innovation by contractors. When competitive pricing policies were first introduced, the philosophy was for short duration and separate professional services and physical works contracts.
The former covered overall control of the bridge maintenance and was awarded to a consulting engineering company which would then prepare specifications for maintaining the protective coatings, among other things. The resulting contracts were then administered and supervised by the consultant. Specific areas of the structure were identified for maintenance by the consultant and scheduled rates for this work were priced by tenderers.
This resulted in minimal input from the physical works contractor in terms of systems development, innovation and technological advances and led to the client having less financial control, particularly with claims for variations. In addition, the consultant was responsible for inspections covering all aspects of the bridge - protective coatings, structural, mechanical and electrical systems and components, and the development of short and long term maintenance strategies. This included the development of options for protective coatings, deck surfacing materials, structural repairs and so on.
But over the past few years TNZ has been developing the concept of 'performance specified maintenance contracts', driven largely by a desire to encourage an innovative approach to the core maintenance activities. This has been made possible through the introduction of a long-term contract approach for the Auckland Harbour Bridge which gives the contractor an incentive to research and invest in new technologies.
Central to this new philosophy is the requirement that the contractor maintains the overall condition and level of service of the asset to a pre-determined standard. The methods by which this is achieved are largely at the discretion of the contractor and this is where the innovative approach is encouraged. Under this method of working, TNZ will have tighter control over expenditure and the contractor will find it more difficult to secure variations.
There will be a greater degree of flexibility in programming works as necessary and the contractor will have a greater responsibility to produce high quality work. Because it is a long-term contract, there will be more incentive for the contractor to adopt cost-effective maintenance practices, invest in plant and resources and research and develop innovative approaches to maintenance.
One of the key initiatives is the formation of a 'management board' which has the ability by agreement to alter the scope of the contract works, introduce new initiatives and actively encourage innovation. Client and contractor are equally represented on the management board, allowing a real sense of ownership to be fostered.
At the beginning of 1999 a condition survey of the structure was carried out to determine its handover condition. The data was used to estimate the mean remaining life of the protective coatings systems to provide a benchmark. This confirmed the mean remaining coating life as 4.7 years; based on an assumed ten year life for the alkyd system applied under the previous contracts. The criteria for selection of sample areas required that a minimum of 10% of the total surface area of exterior coatings must be inspected and that at least 10% of each microclimate was included within the selection.
The structure was divided into zones bounded by adjacent panel points and 10m2 areas were selected for detailed assessment. Inspection parameters were based on performance measures as specified in the contract documents; crevice corrosion, coating deterioration on flat faces, edges, bolts and rivets, and cracking of the existing coatings. The ASTM D5065 Standard Guide for Assessing the Condition of Aged Coatings on Steel Structures was used in this process. The benchmark survey confirmed that overall, the condition of the protective coatings systems was good and was offering a satisfactory level of protection to the steelwork. Some of the key areas of concern included the build-up of aged paint layers up to 1200mm thick in some areas.
Paint adhesion in these areas was fairly low, typically 2MPa. Areas of inter-coat adhesion failure were noted. This frequently occurs at the interface of subsequent coatings with batches of the No. 3 primer that had a high gloss finish. Also noted was a relatively high incidence of crevice corrosion in the over-arch spans and the southern-most spans close to the water level. The winning tender was submitted by Total Bridge Services, which offered three different maintenance systems; a 'budget' system based on copolymer vinyl, a preferred longer life system based on moisture cured urethane (MCU), and a very long life system based on thermal metal spray.