Seismic rocking retrofit of Christchurch’s Triumphal Arch: validation of design concepts through numerical analyses

In the last two years the region around Christchurch was subjected to several seismic events and aftershocks that damaged buildings and infrastructures. Among them there were also historically relevant heritage structures such as the Triumphal Arch, which stands on the Bridge of Remembrance in the Christchurch CBD. The structure, built in 1924, consists of a central major arch and two lateral minor arches made of lightly reinforced concrete and architectural stone. Although the Triumphal Arch did not suffer damage after 4th September 2010 event, it required strengthening works after the 22 February 2011 earthquake. In this paper, the authors present different solutions to assess the seismic performance of for Triumphal Arch which incorporates rocking concepts. Three retrofit designs are herein shown: a pure-rocking mechanism of the arches’ columns designed by SCIRT and two dissipative rocking concepts developed by the authors. The dissipative rocking solutions are based on the hybrid PRESSS technology and one aims to create a sort of frame system while the second one a coupling rocking wall system. The former uses axial external elasto-plastic dissipaters while the latter steel U-shaped flexural plates. Numerical lumped plasticity models are developed and, by using RUAUMOKO 3D, time-history analyses are carried out as validation of the three design concepts. The three solutions are subjected to a set of ground motions which includes the Christchurch sequence. The results prove that the dissipative rocking solution reduces the displacements of the structure without inducing higher loads on foundations and limits post-earthquake damage to the replacement of the dissipaters. Accordingly it is a robust technology for seismic retrofit of heritage structures.