The Clock Tower is the most iconic building at the University of Auckland. Originally constructed between 1923 – 1926 it is listed by Heritage New Zealand as a Historic Place Category 1 (which is defined as “places of special or outstanding historical or cultural heritage, significance or value”).
A seismic risk review carried out in November 2013 identified several areas of the annex building that did not meet comply with current New Zealand seismic standards. The report identified key areas that need to be addressed to ensure that the building would perform as it should, in a significant earthquake.
The University’s key objectives were:
- To preserve the building’s heritage and protect its heritage status.
- To reinstate historical features that had been damaged or lost e.g. returning the roof to more durable clay tiles, paying attention to the cracks in the stone cladding to prevent further water ingress, reinstating and refurbishing the timber windows and the door joinery and visually reinstating the fireplaces on both the ground and first floors.
- To reconfigure the space to suit a modern University. This included providing four new 50-seat seminar rooms for teaching, crush space for group learning and associated bathroom facilities, thereby increasing the University’s ability to meet modern teaching demands.
From a seismic performance standpoint, the key drivers were:
- Upgrade the building so that as far as possible the building would comply with current codes for seismic performance. This included upgrading the southern cloisters of the Clock Tower and to separate these from the Annex Building with a new joint.
- Strengthen local features such as parapets and balustrades so that they did not present a risk of toppling.
- The refurbishment provided an opportunity to restore some of the building’s significant historical features and the new revised layout aligns more with the original design.
BENEFITS OF HAVING US ON THE TEAM:
- We carried out a 3D seismic analysis using ETABS. This showed that even though new masonry walls were added to the interior of the building, the exterior concrete piers attracted significant over turning forces which resulted in them failing in bending. The analysis showed that if the piers could resist the overturning forces calculated, the building would meet the seismic design criteria. Post tensioning allowed us to pre-compress the piers so that there was no nett tension under the applied bending moment.
- Because the client’s overriding objective was to preserve the building’s heritage, we needed to strengthen the building in a manner that hid our work. We didn’t want to leave any sign we’d been there, with the exception of architectural features designed to provide future generations with a permanent record of the work. Post-tensioning also allowed us to do this.
- We adapted a technique used in masonry buildings, to deal with the tight tolerances we faced within a narrow wall with a fragile exterior face. This involved both vertical and horizontal drilling to strengthen the building with post tensioned bars. We were able to get the vertical bars perfectly straight via an innovative solution, and limit noise and dust – important as it was exam season and there were a number of classrooms nearby.
- Because this is an old building, the limestone façade was cracked and porous so, when we’d installed a bar and needed to grout, we knew there’d be leakage. To prevent this, we used geo socks as a grout retainer. However, there was no information available about how a geo sock would perform under pull out capacity and so we had to test it with a jack to assess this.
- The building strengthening work means the building now meets current earthquake standards. The work is not visible and does not adversely affect the heritage value of the building.
- The space that is provided is flexible and meets the current needs of the University.