Design of the Ashburton District Council Civic Centre: A steel designers' learnings from an engineered timber building design

Abstract

This paper discusses the learnings from the structural engineering for the Ashburton District Council (ADC) Civic Centre. The building was initially steel but after consulting with the Ashburton community an alternative timber structural concept was selected. This revised approach led to a number of challenges in adapting a building originally conceived in steel, to timber. ADC Civic Centre is a 3-storey timber structure consisting Cross Laminated Timber (CLT) walls with post-tensioning (Pres-Lam) and dissipators, Laminated Veneer Limber (LVL) gravity beams and columns, Potius flooring and a concrete topping slab. Key challenges included designing the structure to allow for movement expected in the rocking walls without sacrificing robustness in the connections. The drive to show off the timber led to exposed structure and services meaning architectural, services and fire requirements drove key design decisions. As an industry we have had the opportunity to develop our earthquake design knowledge for steel and concrete buildings from learnings from the Christchurch Earthquakes and other events. Engineered timber structures are becoming more common, however there has not been as much practical application. Some approaches we use in steel design can be transferred, but in some areas the steel design thinking that most structural engineers are comfortable with needs to be turned on its head. This paper shares the learnings from the design process and highlights some of the key features of timber design. It is expected to be of interest to structural engineers interested in the practical realities of the growing field of timber design.