Innovative seismic upgrade of Left Bank Art Gallery, Greymouth.

Abstract

The Grey District Council commissioned the strengthening of the C1910 Left Bank Art Galley building in 2018 to preserve its historical value and improve the building’s seismic safety rating. Formally the Bank of New Zealand and situated in the Greymouth’s new town square, the building was an entirely unreinforced masonry and heavy timber trussed construction. The building is approximately 240 metres square in plan, with a five metre floor to ceiling height for two-thirds of the building, the remaining being two storied. The strengthening methodology chosen increased seismic rating from approximately 20% NBS IL2 (earthquake prone) to 70% NBS IL3 (low risk), while preserving the full aesthetic character of the building. The seismic upgrades are not visible from either the exterior or the interior. Stage One prioritised making safe the unreinforced masonry parapet with the addition of steel angles and horizontal steel stays to the roof structure. Stage Two involved reinforced concrete foundation beams and columns cut into the brick walls in such a way that they did not protrude, which formed inverted portal frames. The masonry walls were also strengthened with closely-centred “Helifix” ties. The Stage Two structural work was completed on budget at a final cost $350,000. Other improvements include the strengthening of the rear two-storey section using steel girts and mullions in order to robustly connect all walls together with the roof structure.