The Centre City shopping complex at 11 Gill Street, New Plymouth is comprised of four seismically separate structures built in in 1986 and is used for retail and parking purposes. The four buildings are predominantly constructed with precast concrete floors supported by reinforced concrete gravity frames with full height shear walls providing lateral resistance. Miyamoto was engaged to provide Due Diligence prior to the purchase of the site. A Detailed Seismic Assessment (DSA) was subsequently undertaken to determine the current %NBS rating under the New Building Standard, and to design a strengthening solution to improve the rating to 80%NBS.
Following the DSA, it was determined that the structural limitations governing the buildings global capacity were diaphragm capacity and the connections between the shear walls and perimeter beams. Miyamoto has proposed a retrofit solution that utilises a combination of post-tensioning systems and Fibre Reinforced Polymer (FRP) to strengthen the existing connection concrete frame and diaphragms. This approach has been selected as it is non-intrusive and cost-effective compared to traditional strengthening techniques. FRP also has the added benefit of being resistant to corrosion which valuable for this project as the structure is located 80m from the sea.
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