Barwon Heads Bridge Redevelopment.

Introduction.
I object to the proposed demolition of the Barwon Heads Bridge (BHB). The bridge is a local and State icon with significant heritage value.

I am not going to put my opinion about the heritage value of the bridge; this has already been done by others, for example David Beauchamp in a report to Vic Roads March 2006. My concern is with the lack of quality and accuracy of much of the technical data used to condemn the bridge in report to Vic Roads. I am a practicing structural engineer with experience in the design, evaluation and rehabilitation of timber bridges.

My credentials in the field of timber bridges are demonstrated by the attached list of published papers, which I have authored or co-authored. My experience with timber bridges is as a practicing engineer and also an academic. I am currently involved in the structural evaluation of historic bridges, design of new timber bridges and load rating/inspection projects in Victoria, NSW, Queensland and Tasmania.

Culture of Timber Bridge Design and Maintenance.
Australia has a relatively short history of timber bridge building with the art reaching its peak in the early 1900’s. The design and detailing of timber bridges evolved to allow fairly convenient replacement of elements with damage from decay of wear or damage from traffic.

The use of paired headstocks, for example, allows replacement of one or both headstock elements without taking the bridge out of service or having to do major temporary support works. The same is true for the many large timber truss bridges in NSW where the compression elements are also generally paired.

Because of the ability to remove and replace damaged elements timber bridges are able to “live forever”. This timber bridge culture was used in the design of the Barwon Heads Bridge.

The construction of a concrete overlay on the timber deck of the BHB in 1980 prevented access to most timber elements from above or through the deck. This modification to the bridge made inspection and maintenance of the bridge very difficult, and is in effect a “death sentence” for a timber bridge. It is true that an concrete deck overlay increases the life of some bridges, but destroys the ability to replace elements needed for the bridge to live on.

Because of the above bridge building culture most of our stock of historic timber bridges do not contain much, if any, of the original timber used to construct the original bridge. Replacement of elements is an important part of the life cycle of the Australian timber bridge and this does not reduce their heritage value.

Report to Vic Roads, such as SW Engineers, argue that the BHB is not the original structure because many elements have been replaced and therefore not the original material. This is not the case. The Customs House in Geelong had its deteriorating stone work replaced with new but similar stone, this did not compromise the heritage value of this beautiful building. Bringing back to safe service the BHB by element replacement will not damage the heritage value of the bridge.

Condition of Existing Bridge.
The BHB is 79 years old, quite amazing considering the very poor maintenance it received for most of its life. It is true to say that a 1927 reinforced concrete bridge at the Barwon Heads location would not have survived for 79 years and would have needed replacement after probably 50 years. The performance of the BHB has been very good in relative terms.

The bridge is now very tired and undoubtedly due for some well designed rehabilitation work. None-the-less the report by Vic Roads consultants has damned the BHB without a thorough and proper investigation of its current structural condition. For example, by removing the concrete overlay a load reduction of 18 tones per span is achieved and access to allow replacement of deck elements is created. Why was this simple option to gain extra capacity not investigated?

I have investigated many timber bridges at the end of their safe working life. These old structures typically have cues indicating structural problems, such as sagging span; the BHB has a remarkably good form for a bridge reported to be in a very poor state.

It appears to me that the BHB has been condemned by technical reports and claims without proper investigation of the condition of the historic structure. Much of the recent maintenance costs at the BHB are due to deterioration of the steel beams installed in 1980. These steel beams were not provided with adequate lateral restraint, the recently installed bracing frames were required due to a design error in the 1980 rehabilitation works. That is, much of the recent costs are not due to timber but steel and design problems.

I am not claiming that the BHB is in a good condition, which it is not, but I do claim that it could be rehabilitated to continue in service for full traffic loading or as a pedestrian and recreational structure. With rehabilitation works the bridge could again deliver 80 years of service.

Cost of Rehabilitation Works.
Current cost of building new timber beam bridges (i.e. similar to the BHB) in Tasmania is $1,100.00 per sq. meter. This is a current figure as timber bridges are still being built in that State. The replacement cost for the BHB would be about $4 M with the 35% on-cost for design etc. used in the Vic Roads reports.

To systematically replace all timber elements in the BHB is possible if the 1980 concrete overlay is removed giving access for the timber elements throughout the bridge. I estimate this would be able to be achieved for less than $10 M, and the service life would be similar to that achieved by the current BHB. This is considerable less than the inflated $23 M provided by Vic Roads to achieve a service life of only 25 years, where does this come from?

If the cost of the rehabilitation of the BHB is important in the decision to approve or not approve the Vic Roads application to demolish the bridge, then the costs should at least be realistic.

Recommendations:
The heritage value of the BHB is well established by the National Trust, Heritage Victoria and the Institution of Engineers Australia. The bridge can be completely rehabilitated to maintain its heritage value and support normal traffic loading or be used as a recreational structure.

The claims in Vic Roads reports that the timber required to rehabilitate the bridge can not be sourced and skills to conduct the works are not available, are simply not true.

The costs to rehabilitate the BHB are of the order of $10 M for full vehicle loading and a service life similar to that achieved by the existing bridge. This is very different to the Vic Roads figure of $23 M and a service life of only 15 to 25 years. The simple fact is Vic Roads do not want an old world bridge structure in their system nor be responsible for it and have biased their figures accordingly.

The Barwon Heads Bridge is much loved by the local residents of Barwon Heads and also Ocean Grove and the tens of thousand regular holiday visitors; it is iconic and integral with the Village By The Sea. It preservation is technically and economically possible.

Peter J Yttrup
Chartered Professional Engineer, FIE Aust
BE(Civil), Melb.Uni. 1st Hon., M Eng Sc, Melb Uni., DipCE

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Published Technical Papers on Timber Bridges, By Peter Yttrup:

Yttrup P.J., Law P.W., (1991) “The Durability and Structural Performance of Timber Railway and Highway Bridges in Eastern Australia”. Int. Timber Eng. Conf. London UK

Yttrup P.J., Law P.W., Audova H., (1991) “The Mechanics of Timber Beam Bridges”. Austroads Bridge Conf. Brisbane.

Yttrup P.J., Law P.W., Subramaniam H., (1991) “Analysis and Determination of Safe Load Limits for Timber Beam Bridges”. Austroads Bridge Conf. Brisbane.

Law P.W., Yttrup P.J., McTackett P., McNaught A. (1991) “ The Testing of Old and New Timber Bridge Girder Elements”. Austroads Bridge Conf. Brisbane.

Yttrup P.J., Law P.W., Audova H. (1992) “Draft Manual for the Load Capacity Assessment of Timber Beam Bridges”. Proceedings of the Timber Bridges Conference, The University of Melbourne.

Yttrup P.J., Evans T.D., (1992) “The Development of a Computer Model for a Corbelled Timber Beam Road Bridge”. Proc. Timber Bridge Conf. Uni. Melb.

Yttrup P.J., (1992) “Rating of Timber Beam Bridges” . Proc. Timber Bridge Conf., Uni. Melb.

Yttrup P.J., Nolan G. (1996) “ Performance of Timber Beam Bridges in Tasmania, Australia”. International Wood Engineering Conference, New Orleans, USA.