Review of recently constructed concrete wall-steel frame hybrid buildings

Around New Zealand there has been an increasing trend of ‘hybrid’ multi-storey buildings that combine reinforced concrete walls with structural steel framing systems. This study aims to characterise and understand this type of building, focusing on buildings constructed in Auckland and Christchurch from 2014 onwards. Drawings from a total of 50 buildings were reviewed, and their structural features were documented, including building use, building height, lateral load resisting system, ductility, wall configuration, wall construction method, steel framing system and suspended floor system. Meetings with structural engineers were conducted to validate the review findings and to further understand design principles and decisions that lead to these outcomes. A typology comprising five building types with distinct lateral load-resisting systems was proposed based on the building review. Results showed regional differences between Auckland and Christchurch, owing to building use and seismic hazard in the respective cities. Auckland buildings surveyed tended to be residential buildings five storeys or higher made of precast walls connected with steel beams. Christchurch buildings, on the other hand, were primarily commercial buildings three to seven storeys high with dual frame-wall systems. Structural connections between steel frames and concrete walls were also documented, showing that bolted connections with headed stud embedment were most common. The results can be used to identify critical aspects of these mixed structural systems for further investigation and to develop archetype building designs that can be used for modelling and testing.