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

for 50% reduction in strength of the pilecap bottom reinforcement, this means the
pilecaps could have no safety factor, when two fully loaded semi-trailers pass each other.

The current risk to Council is this: if someone drives anything a vehicle(s) across that
imposes higher stresses on the bridge:
   • A pilecap beam could fail, and
   • The loads would become concentrated on 4 to 6 of the piles, and
   • These (cracked) piles are likely to buckle, and then
   • Partial bridge collapse would occur
   • Without action, partial collapse is likely to occur sometime within 1-3 years (by
       2015-2018).
   • Using the risk assessment methodology in Appendix D, the overall risk is HIGH,
       and it is imperative to reduce the risk.

The stresses in the pilecap beams need to be alleviated NOW. Fortunately, for a
relatively low cost within the available FY2013/14 budget, these new columns would
reduce stresses to safer levels, and give NSC more time to prepare for the main repairs,
which need to be staged and completed over the next 3-5 years.

The recommended new columns can also be viewed as a low-cost risk management
tool. This is because they are likely to prevent catastrophic collapse, if future
maintenance/repairs of the pilecap beams and piles were not carried out for some
reason. There are constructability and cost benefits too – see item 2 below.

OTHER REPAIRS (BETWEEN FY 2014/2015 to 2018/2019):

2. (FY 2014-15): Pilecap beams 3, 4 & 5 (worst condition) - remove cracked concrete
   around perimeter of pilecap beams and clean up corroded reinforcement. Arrange for
   RPEQ engineer to judge if remaining reo is sufficient to carry loads and renew reo if
   necessary (10-30% chance of being required). Ensure electrical connectivity between
   bars. Replace removed concrete with use cement based repair grouts or shotcretes
   that contain 25% flyash or an pre-approved pozzolanic alternative, to prevent
   introducing more alkalis to the existing concrete (which is ASR prone). Coat full
   exterior of pilecap beams with silane to exclude water and minimise ASR reaction.
   Install impressed-current cathodic protection system to pilecap beams to achieve 50-
   year protection of the pilecap reinforcement.

   •   This operation can be carried out while the bridge is open to road and boat traffic,
       if the Stage 1 columns have been installed. Stage 1 columns reduce the risks to
       the Contractor’s team, the public and Council.
   •   If the Stage 1 columns have been installed, some of the reinforcement in the
       pilecap beams can be treated as sacrificial. In our opinion, based on our spot
       visual checks of reinforcement condition, it is likely that there will be sufficient
       good reinforcement to safely support the bridge loads, but this will need to be fully
       checked when the cracked concrete is removed. We anticipate a construction



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