The Old Municipal Chambers Building – Damaged But Not Destroyed – Will It Be There In Another 125 Years?

The Old Municipal Chambers is a Category I heritage building situated in Worcester Street, Christchurch. It was designed by architect Samuel Hurst Seager in the Queen Anne Arts and Crafts Style and was opened in 1887. The two-story building is constructed in solid brick and incorporates several decorative features, and it is an important part of the cultural heritage fabric of Christchurch. Some securing works were undertaken in 1989 to improve its performance under seismic loads. This paper will outline damage during the earthquake on 4 September 2010, subsequent aftershocks and the 22 February 2011 earthquake which resulted in some localized zones of collapse. The structure of the building has been stabilized externally, to secure or allow retrieval of very significant heritage features. The high cost to repair the building makes the future of the building uncertain despite its very significant heritage value. In response to the building’s seismic vulnerability and possible retrofitting, finite element and simplified equivalent frame models were used for pushover analysis, enabling a complementary seismic evaluation from both approaches. The predictions identify the weak parts of the building and its expected failure modes, which are in agreement with the observed damage. The computations appear conservative, because the computed capacity curves provide insufficient capacity of the building to survive the recorded earthquakes. Given that there was uncertainty on the constitution of the floors, they were assumed as unidirectional by default, bidirectional diaphragm floors were also simulated in the simplified model, reflecting the securing works undertaken in 1990. In this case, a significantly better behavior is observed. This paper will examine the seismic performance of the building, comparing results of analysis including both in-plane and out-of-plane behavior, with actual damage. It will then consider conceptual scenarios for the future of the building, including comparison of performance and cost of both conventional and base isolation retrofit.

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