What are the issues?
The timber bridge network within Dungog Shire is rapidly reaching the end of its useful life. The majority of these bridges are in excess of 60 years old and, in some cases, much older. These bridges vary from single span 6m long structures to 6 span 60m long structures.
Whilst usual maintenance works such as redecking, girder replacement, etc have been ongoing over many years, the issue that Council will be facing in the short to medium term is that the substructure of these bridges (piers, piles, abutments, etc) are now also getting beyond their useful lives. These components are much more difficult to replace and therefore much more expensive.
Age, climatic and other naturally occurring matters when coupled with water penetration causing decay in critical elements, do account for some of the issues facing these structures. However, increased loadings, well above that for which the bridge was originally designed, are also having detrimental effects on these structures.
Whilst maintenance programs have not changed significantly over many years, anecdotal evidence has shown an increase in abutment, girder and deck distress or failure over recent years. It is therefore fair to assume, it is a combination of age, these naturally occurring distress triggers and the heavier vehicle loadings that are creating this increase in bridge degradation.
What has Council been doing?
Inspection - Council staff have used both visual and traditional invasive test-boring methods to identify timber component condition during inspections. These methods have been standard throughout Council’s and other Roads Authorities for a long period of time. However, these methods certainly do not allow for a full understanding of the condition of the timber components nor do they identify isolated weaknesses in the structure.
Replacement - In 1996, Council had a total of 81 timber bridges across the Local and Regional Road networks. Consistent application of Council’s own funds and successful applications under various grants have resulted in Council replacing a total of 47 of these timber bridges over the past 21 years. Of the remaining bridges, 33 are on the Local Road network totalling 920m in length.
Maintenance - Whilst our inventory has reduced, Council’s maintenance budget has been maintained at nearly 6% of general rates revenue per annum. So whilst the number of bridges has reduced, the maintenance cost of the remaining bridges has increased at a similar rate.
What is the current situation?
A report was presented to the Ordinary Meeting of Council on 21 March 2017, advising of the issues facing the community with respect to the age and condition of the Timber Bridge network and the load capacity of these structures.
Research into the history of the load designs when these structures were built and recent inspections of two (2) structures by Bridge Structural Consultants has identified that, based on the information available, only some of Council’s Timber Bridge network would have a maximum capacity of 44 tonne loadings in as new condition with some structures likely to be less than that amount.
In addition to this, changes administered by the National Heavy Vehicle Regulator (NHVR) now allow for General Access vehicles (ie those not requiring permits) to have a Gross Vehicle Mass of 50.5 tonnes and a length of 19.0m. When compared to vehicles even 40 years ago, this equates to articulated trucks now being allowed to be 24% longer, 58% heavier and 25% faster.
What is the Risk?
There is no doubt that there is a significant risk to all road users and Council to allow for 50.5t loadings to continue to utilise Council’s timber bridge network.
The effect of speed of the vehicle and vertical alignment of the structure also contributes to the damaging effect these vehicles have on the timber bridge structure. Low level bridges with steep approaches tend to suffer abutment degradation due to the size of the load, the speed at which that load comes into contact with the bridge and the “pounding effect” due to the sudden change in vertical alignment.
Council cannot rely upon “nonfeasance” as a defence if a bridge was to fail, if a Council can demonstrate that it was attempting to address the issue within the Councils financial means then the Council may have a chance to defend a case if something unfortunate did occur.
What Community Consultation is Council undertaking?
In addition to this letter which is being forwarded to all Rural and Business Property Owners, Council will be conducting two (2) community meetings to be held as follows:-
- Monday 10 April 2017 - School Of Arts Building, Gresford - 6.00pm; and
- Tuesday 11 April 2017 - Doug Walters Pavilion, Dungog - 6.00pm.
What is Council proposing?
In the short term, Council must mitigate this risk. Further review of Council data including recent inspection reports, maintenance history, bridge configuration (number of girders, girder lengths, deck arrangements, etc) and assumed design standards have resulted in the following load limits being proposed for the various structures:-
|Bridge Name||Road Name||Length (m)||Width (m)||Area (m2)||CurrentSignposted Load Limit (t)||Proposed
Load Limit (t)
|Thalaba Bridge||Alison Road||34||5.5||187.0||5||5|
|Bullockeys Bridge||Allyn River Road||46.5||4.8||223.2||-||44|
|Wheelabout Bridge||Allyn River Road||39||5||195.0||-||44|
|Archinals Bridge||Allyn River Road||32.5||3.1||100.8||-||40|
|Packhams Bridge||Chads Creek Road||6||4.7||28.2||-||40|
|Chesworth's Bridge||Chesworth’s Road||8.7||3.6||31.3||20||20|
|Simmons Bridge||Chichester Road||20.2||2.7||54.5||5||5|
|Dusodie Bridge||Chichester Dam Road||46||4.4||202.4||-||44|
|Saxby's Bridge||Clements Road||11.7||3.2||37.4||-||40|
|Dowlings Bridge||Dowlings Road||30||3||90.0||-||40|
|Fosterton Bridge||Fosterton Road||35||5.7||199.5||-||40|
|Suspension Bridge||Gabulah Road||70||3||210.0||3||3|
|Mary Carlton's Bridge||Glen William Road||19||6.1||115.9||16||16|
|James Rd Bridge||James Road||8.4||3.3||27.7||12||12|
|Kingfisher Ck Bridge||Kingfisher Ck Road||16.5||3.4||56.1||12||3|
|Longbottoms Rd Bge||Longbottoms Road||10||2.6||26.0||15||15|
|Gam's Bridge||Main Creek Road||10.6||4.5||47.7||-||44|
|Mate's Bridge||Main Creek Road||12||6.5||78.0||-||44|
|Reeves Bridge||Majors Creek Road||8.7||3||26.1||-||40|
|Hopson's Bridge||Masseys Creek Road||38.4||3.9||149.8||-||40|
|Ashards Bridge||Masseys Creek Road||12.6||4.2||52.9||-||40|
|Ryans Bridge||Myall Creek Road||12.8||3.6||46.1||-||40|
|Middlebrooks Bridge||Myall Creek Road||9||3.2||28.8||-||40|
|Hick's Bridge||Orange Grove Road||12.5||3.5||43.8||-||40|
|Osmond's Bridge||Osmonds Road||9.1||3.1||28.2||-||40|
|Coulston Bridge||Paterson River Road||59||4||236.0||-||44|
|Spooner Bridge||Paterson River Road||60||4.5||270.0||-||44|
|Banfield Bridge||Pine Brush Road||48.5||3.4||164.9||10||10|
|Weldon Rumbels Bge||Rumbels Road||9.1||3.5||31.9||-||40|
|Tillegra Bridge||Salisbury Road||57.5||4.6||264.5||-||44|
|Bruxner Bridge||Summerhill Road||30||5||150.0||-||44|
|Jordans Bridge||Summerhill Road||9||3.6||32.4||-||40|
|Summerhill - 3rd Bge||Summerhill Road||16||3.7||59.2||-||44|
In addition to this, speed limit and other appropriate signage will be installed on the approaches to these structures.
Council has also re-allocated funding to undertake inspections and load testing on five (5) critical bridges being:-
- Coulston Bridge - Paterson River Road
- Spooner Bridge - Paterson River Road
- Bullockeys Bridge - Allyn River Road
- Tillegra Bridge - Salisbury Road
- Wheelabout Bridge - Allyn River Road
The results of these inspections will form the basis of a report to Council and further consultation with the community.
Medium to Long Term
The financial and risk considerations of this matter are significant. Without Government Grants the only means that this Council has available to address the timber bridge issue is by way of significant loan borrowings.
Council will continue to pursue funding through all levels of Government to assist with funding the replacement of these structures. As a first step, Council will be making application under the current round of the Bridges Renewal Program with applications closing on 15 May 2017.
How can you assist?
Council needs the support of the community to:-
- Assist in identifying your requirements for transport access;
- Identification of Key Strategic Bridges;
- Provide support for funding applications.
Council therefore requests that you come along to the community meetings to make your requirements known.
If you cannot attend the meetings, enclosed within this envelope is a form that can be returned to Council to identify your needs and to provide Council with acknowledgement of your interest in this matter for future distribution of information. I therefore encourage you to fill in that form and return it to Council.
If you can attend the meetings, you can also bring the completed form with you to register your interest.
If you require further information, please contact Council on 4995 7777 or visit here a map showing the location of the timber bridge network by clicking on the Dungog Mapping link.