Case Study for Seismic Assessment of an Existing Asymmetric non-prismatic Unique Reinforced Concrete- encased Steel Plate Column in Wellington

Abstract

This case study presents a tailored approach to assessing a high-rise building in the Wellington CBD constructed primarily from reinforced concrete encased steel frames. This construction is rare in New Zealand, and it is fascinating the way the building has been designed. Due to the singular nature of the building, traditional seismic assessment guidance is difficult to employ and a unique approach to the analysis is required. The structure is a 16-storey tower building on a 6-storey podium designed and constructed in the mid-1960s. The main structure at the perimeter consists of steel truss beams and flanged steel columns all encased in concrete. The podium perimeter structure consists of concrete encased steel braced frames and shear walls. This paper presents the assessment approach for this unique building, including the development of finite-element analysis models to capture the composite behaviour of the reinforced concrete and steel frame structures. Through combining complex modelling founded in fundamental engineering principles, we are able to assess more accurate building performance, likely behaviour mechanisms and seismic risk to guide the design for a safe and resilient building retrofit.