2015-03-31 I&S Committee - Item 5 - Attachment 1 - Munna Pt Bridge Repairs Level 3 Bridge Report

have formed in the pilecap beams so that corroding reinforcement is (temporarily)
protecting the remaining good reinforcement. In the piles, it appears that the reduced
oxygen below tide level has resulted in slower than expected corrosion rates.

This has given more time than expected to complete repairs (commence now, complete
by FY2017/2018). Essentially, there are two options: Option 1 is to rebuild the
substructure and keep the existing deck; Option 2 is to repair the existing bridge. Either
needs to commence now. Complete replacement of the bridge is not a realistic option, as
the bridge crossing would need to be shut down for 18 months or more; or alternatively a
costly staged method of construction would be required.

Tod Consulting strongly recommends and urges Council to adopt Option 2 (repair the
existing bridge), so that:

   a) Public safety is maintained.
       (Right NOW, the pilecap beams of Piers 3, 4 & 5 are likely to be suffering very high
       stresses when two loaded semi-trailers pass each other)

   b) The repair cost and comparison-life costs are kept at reasonable levels, and able
      to be spread over a number of years, rather than being largely incurred in
      FY2013/14 & FY2014/15.
       A relatively small cost incurred in FY2013/14 for 6 new columns will give increased safety
       and time to take planned action over the next 3-5 years. Delaying any longer will only
       result in spiralling increases to repair/rebuild costs and risk.

   c) With impressed-current cathodic protection and protective paint-on coatings, the
      bridge life can be extended by an estimated 50 years to year 2064, if these
      protective measures are properly maintained.

       Notes:
       i) The cathodic protection system must include a modern internet-connected monitoring
       system. NSC or their nominated maintenance subcontractor can remotely check that the
       bridge is protected, and warning messages can be automatically sent to their mobile
       phones. The media and the public could find a 24-hour-internet-connected 1979-era
       bridge interesting.
       ii) The estimated life is based on the design conditions of today (2014), such as flood
       levels & velocities, sea levels, air temperatures, vehicle loads and the like. No allowance
       has been made for increased loads brought on by future climate change or vehicle type
       changes.
       iii) Life might be extended further by installing a replacement cathodic protection system, if
       a bridge engineer deems climate conditions, condition of reinforcement, and condition of
       high strength steel strand, satisfactory in the future. Special scour protection around piers
       and abutments, or even lengthening of the bridge might be required by that time.

Refer to the drawings S01-S04 in Appendix F for timing of each repair. Note these
timeframes are estimates. The actual timeframes could vary: the bridge should be
monitored regularly for any unexpected dilapidation or damage, and recommended
actions should be carried out earlier if necessary to maintain safe operation.


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