Kaitoke Flume Bridge Replacement: Using Seismic Resilient Ductile Iron Pipe
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Hayden Pipe (Stantec New Zealand), Todd Randell (Hynds Pipe Systems)
The Kaitoke Flume Bridge conveys raw water 20 metres above the Te Awa Kairangi River on its way to Te Mārua Water Treatment Plant. This plant provides the Wellington Region with up to 50% of its drinking water supply. The bridge is located in a geographically, geological and seismically challenging location and crosses numerous shear zones. It is therefore at risk to significant seismic forces.
The 50 metre long flume bridge is a 50-year old leaky concrete structure in poor condition. The bridge has poor seismic resilience and does not meet post-earthquake serviceability requirements for a critical supply.
A new network arch bridge with a DN1500 Seismic Resilient Ductile Iron Pipeline (SRDIP) has been designed to replace the existing flume bridge.
This paper outlines what SRDIP is, why SRDIP was selected as the pipe material for the bridge crossing, and how it is designed to behave in conjunction with the bridge in the design seismic events.
This paper also covers the pipe support system and restraint required to the pipeline due to seismic acceleration.
SRDIP originated in Japan and has been used there for many years. It suffered no documented failures in the 1995 Great Hanshin (Kobe) earthquake or the 2011 Great East Japan Earthquakes. The key aspects of the pipe that make it worth considering is the ability for every joint to deflect as well as contracting and expanding. This allows for a certain amount of differential movement between pipes without putting strain along the pipe barrel.
SRDIP was selected as it offers a robust system that allows for the differential movement along the pipeline that is expected in a large seismic event without the need for any other seismic or thermal joints. This was particularly important at the bridge ends where the superstructure is designed to slide on the abutmentsresulting in large deflections. These large deflections were allowed for by using the joint deflection as well as allowing the pipe to move transversely near the abutments.