N. Ismail ¹, H. Mahmood ², H. Derakhshan ³, W. Clark ⁴ and J. M. Ingham ⁵

1. PhD Student, Department of Civil & Environmental Engineering, The University of Auckland, New Zealand, nism009@aucklanduni.ac.nz
2. PhD Student, Department of Civil & Environmental Engineering, The University of Auckland, New Zealand, hmah012@aucklanduni.ac.nz
3. PhD Student, Department of Civil & Environmental Engineering, The University of Auckland, New Zealand, hder004@aucklanduni.ac.nz
4. Executive Officer, New Zealand Society for Earthquake Engineering, New Zealand, kksw.clark@clear.net.nz
5. Associate Professor, Deputy Head of Research, Department of Civil & Environmental Engineering, The University of Auckland, New Zealand, j.ingham@auckland.ac.nz

ABSTRACT

Numerous unreinforced masonry (URM) buildings in New Zealand have been declared earthquake prone but have heritage value that restricts changes to their original architecture during seismic retrofit. The earthquake prone building considered in this case study was constructed with cavity walls in the outer periphery, single leaf thick partition walls and two leaves thick interior bearing walls. The materials used in construction were solid clay burnt bricks and a lime mortar, with the masonry laid in a common bond pattern and plastered on the outer and inner faces. The roof consisted of corrugated iron sheets resting over wooden trusses. An initial evaluation of the building structure was performed with procedure suggested by New Zealand Society of Earthquake Engineering (NZSEE) guidelines. The building structure was found earthquake-prone in the transverse direction and earthquake-risk in the longitudinal direction, therefore a detailed evaluation was performed by using a homogenised finite element (HFE) computer model of the as-built structure and also the critically loaded walls were analysed for in-plane strength and out-of-plane stability using NZSEE guidelines. The results showed that the walls were unstable when subjected to out-of-plane loading and it was concluded that the building requires a retrofit. A literature review of existing viable retrofit solutions was performed and on the basis of relative merits and demerits the most suitable seismic retrofit solution (i.e., post-tensioning) was selected. The out-of-plane stability of post-tensioned URM wall was checked with an existing conceptual model and an appropriate seismic retrofit solution to satisfy strength and heritage conservation requirements was recommended.

KEYWORDS: retrofit, unreinforced masonry, strengthening, post-tensioning, earthquake

C5-5