Bearing Up
Analysing Options
3 New reinforcing cages on the bases of the southerm columns prepared them to meet their lower counterparts (click to enlarge).
4 The props are designed to carry 1000 tonnes (click to enlarge).
The library is pivotal to the university's functioning. It didn't want to be put in the position of California University, where the library was out of action for about eight years after the 1994 Long Ridge earthquake. So although there was no legal requirement for seismic upgrading, the university engaged SKM to investigate strengthening options. SKM had access to the original construction photographs and drawings, as the designer – Jones, Adams, Kingston and Reynolds (later KRTA) – was incorporated into SKM after a series of mergers.
The university placed certain provisos on the work. First, the library could not be closed during the academic year, so the contractor had to seismically upgrade the building while it was in use – according to Robinson Seismic, the first time this has been done in New Zealand. Secondly, the boilers had to be operational by 1 April. And thirdly, the library's collections had to be protected.
Some compromise was needed between what the university wanted to achieve and what it could afford, says Mr Clark. Several options were quickly ruled out on the grounds of operational disruption and expense. One was strengthening the 1,760 hinge zones between the column heads over 10 floors and the concrete ribs of the waffle slabs, by confining the vulnerable sections with steel plates. The second option, to tie the building to four steel towers rising through the podium to the top of the building, was also judged more disruptive and marginally more expensive than base isolation. Base isolation also provided a higher level of protection to the contents of the building, as it would reduce horizontal accelerations and velocities.
