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

Concrete-encased steel columns are widely used in high-rise building all over the world due to the high performance level under seismic and gravity loads. There are many types of composite columns, classified according to the position of the steel plate, longitudinal profiles and the column shape as shown in Figure 1. Many experimental tests have been performed to obtain the lateral response of concrete-encased steel columns.

by many researchers (Suzuki et al. 1984) (Viest et al. 1997) (Chen 2007) (Chen et al 2014). The experimental tests results revealed that encasing the steel section in concrete provides high shear capacity, stiffness and ductility and large energy absorption, while the surrounding concrete protects the steel elements from fire damage and delays the buckling failure. There are many factors that control the seismic response of composite column such as the axial load ratio, aspect ratio, steel ratio and reinforcement ratio. To deeply understand the modes of failure and the key parameters that influence the composite column behaviour, a comprehensive parametric study using FE analyses was conducted by Ellobody and Young (Ellobody and Young 2011).

Additionally, a comparative numerical study on the encased steel composite columns and steel columns was performed by Lacki et al. (Lacki 2018). The previous studies focused on the performance of the rectangular or circular concrete-encased columns with steel profiles distributed in symmetric manner across the column section. In some old high-rise building, it was noticed that a prismatic concrete-encased steel column was used in some cases, such as the Morrison Kent House building designed and constructed in the mid-1960s.

In such cases, the composite column may behave with a different response in comparison with the conventional concrete-encased steel column. In this study, a proved-reliable finite element model for assessment the seismic response of prismatic concrete-encased steel columnsis provided using DIANA software (DIANA FEA 2016). Non-linear static pushover analyses were performed to obtain the column behaviour under lateral and gravity loads. To this end, the gravity load level was varied to cover the axial load variations under earthquake load case.