Earthquake research in New Zealand on damaged buildings

Assessment of the extent of earthquake damage and the residual capacity of buildings following the earthquakes proved to be a challenging task for building owners, insurers, and structural engineers throughout New Zealand. As a result of these decisions, a significant portion of modern reinforced concrete (RC) multi-story buildings were demolished. The demolition of these buildings provided a unique opportunity to extract and test components from such structures.

The Clarendon Tower was a twenty-story office building located in the city center of Christchurch. The tower was designed in 1987 and was constructed primarily of RC, using both precast and cast-in-place elements as was common in New Zealand at the time of construction. The September 4, 2010 and February 22, 2011 earthquakes subjected the Clarendon Tower to approximate peak ground accelerations of 0.22g and 0.43g, respectively. Maximum displacement ductility demand near mid-height of the building was estimated to be as high as 4.0 during the February 22, 2011 earthquake.

During the deconstruction of the Clarendon Tower, three precast RC moment-resisting frame components were extracted from the building for structural testing in order to assess the residual capacity and reparability of the frames. This research program, described in an upcoming article in the ACI Structural Journal, involved testing these full-scale components that are amongst the largest beam-column joint sub-assemblies that have been tested in New Zealand, and are thought to be amongst the largest components worldwide to be extracted and tested from an actual building and, in particular, from an earthquake-damaged building.

The extracted RC frames were repaired using various techniques based on the extent of damage and then subjected to simulated seismic loading. Due to the size of the test components, a custom-designed steel reaction frame was utilized. The experimental testing involved collaboration between researchers at the University of Auckland and practicing engineers at Compusoft Engineering Ltd.

The results of the experimental tests indicated that the frames could withstand significant inelastic deformations following repairs, consistent with the expected performance of comparable undamaged frames. Given the prototypical detailing of the some of the tested elements, the experimental tests also provided an opportunity to verify the expected seismic behavior of precast RC buildings constructed in New Zealand in the 1980s, as well as provide critical evidence to improve the assessment of post-earthquake residual capacity. The authors believe that these findings will help to reduce the uncertainty of post-earthquake assessments and lead to better informed decision-making following future earthquakes. The Clarendon Tower frame test program is one of a number of projects being conducted at the University of Auckland to understand and learn from buildings damaged during the Canterbury earthquake series in order to ultimately improve design standards for new buildings and assessment guidelines for existing buildings.