Miyamoto New Zealand provided structural and geotechnical engineering services to support the seismic assessment and strengthening of a 1960’s high-rise building in central Wellington. The objective was to complete a detailed seismic assessment of a building previously identified as an earthquake risk.
The key challenge was the absence of established guidelines for the building’s unique construction type—reinforced concrete-encased steel lattice frames. The composite behaviour between steel and concrete is inherently complex, and conventional assessment methods produced overly conservative performance predictions. As a result, all proposed strengthening schemes were deemed economically unviable.
To address this issue, Miyamoto developed a complex, performance-based assessment methodology including detailed finite element modelling of critical structural components, validated through experimental testing, and incorporated into a global building model. This approach enabled a realistic understanding of the composite behaviour of the frames and the expected seismic performance of the building.
The outcome was a targeted retrofit scheme focused on key vulnerabilities, avoiding unnecessary intervention and cost. The methodology and findings are in the process of being published, contributing to industry knowledge on the seismic assessment of reinforced concrete-encased steel lattice frames. This approach resulted in a dramatic reduction in retrofit costs from 20 million to 5 million NZD, representing a 75% savings.
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