Council is acutely aware of the importance and significance of the bridge to the Katikati community and is doing its best to get repair work underway and the bridge reopened. Work will begin as soon as possible before Christmas.
Since the initial discovery that the bridge is bent sideways approximately 150mm, further investigation and review by a qualified Chartered Professional Engineer (and peer reviewed by another external consulting Chartered Professional Engineer) has revealed the following:
• The bridge construction is generally in keeping with the building consented drawings, but the construction drawings, and consequently the construction differs significantly from the design intent (the assumptions made by the designer in their design), and has resulted in a bridge which has inadequate strength for it’s purpose.
• The bridge is not restrained (laterally) sufficiently to design standards, which has resulted in the observed bend. The lack of restraint has the effect of significantly reducing the strength of the beams and loading that can be applied.
• The beams and splice joints are not of a sufficient size to support the full design live loading. For example, the main beam splice joints are assessed as capable of only 0.75Kpa live loading, well below the designed 3.48Kpa. Live loading is the weight caused by people on the bridge or from other loading such as from wind, earthquakes, etc.
Note: 1.0 Kpa is equivalent to 100Kg per square metre – or approximately 1 person per square metre.
• In summary, the bridge currently lacks the strength, stiffness and connectivity to transfer the design lateral loads to the abutments, which include loads created by users leaning on the handrail, wind and earthquake loading. Professional opinion is of the view that the bridge has not collapsed because it is unlikely to have reached a loading of say 30-40 persons on the bridge at the same time.
• The bridge is assessed as a “Dangerous Building” as defined in S121 of the NZ Building Act.
The Engineers report considered 3 main mitigation options to make the bridge safe for use:
a. Remove or replace the bridge. Not recommended - Replacing the bridge is the most expensive option and is not recommended.
b. Strengthen and restrict users. Not recommended - This involves the installation of cables extending from the river banks to tension the bridge laterally and improve the available live loading. However, the loading would remain restricted due to the weak beam splice joints. Enforcing restrictions would be very difficult and impractical and the cabling to the bridge from the embankments would ruin the aesthetic values of the bridge.
c. Strengthen to current code requirements. Recommended option: Strengthening to current code is the preferred option (current code is 3.2Kpa versus original design in 1999 was 3.48Kpa).
Council has agreed that the bridge be strengthened to the current building code requirements.
So what happens now?
The bridge remains closed until it’s repaired. Note that it has now been declared a “Dangerous Building” under the Building Act and Council as owner of the bridge must therefore take appropriate action to prevent use. Alternative pedestrian access is via the Main Street and SH2.
A qualified Chartered Professional Engineer has been engaged to:
• Design appropriate steel reinforcing repairs to strengthen the bridge to current code requirements (option c, above).
• Discuss repair methodology with potential contractors. Depending on preferred contractor / methodology, the bridge will either be dismantled and repaired off site or repaired in-situ.
• Prepare contract specifications and obtain prices (decision on price and awarding of the contract is expected on or around 6th December).
• Obtain all necessary consents.
• Oversee the physical works contract and certify repairs