Mangatangi Dam Spillway Shaft Seismic Assessment, Kaiaua, Franklin, NZ

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Compusoft Engineering Ltd. (CEL) was engaged by Damwatch Services Ltd. (DSL) to undertake a detailed seismic assessment of the Mangatangi Dam spillway shaft.

The assessment was a continuation of a previous study that had shown that the spillway shaft was likely to exhibit inelastic behaviour when subjected to ground motions corresponding to return periods of 2,500 years and 10,000 years for the site.

The primary foci of the analysis was to:

  1. Develop a better understanding of the likely inelastic demands during seismic events to allow a more rigorous assessment of the reinforcing details identified as potentially deficient in the previous study and,
  2. Provide estimates of (horizontal) crack widths likely to be present during and following each of the seismic events to allow determination of whether cracking is likely to induce significant leakage. This was achieved by the use of inelastic time history analyses utilising the advanced finite element analysis package SAP2000 for the spillway shaft.