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Concrete In Australia : September 2013
Concrete in Australia VolVol 39 No 3 5 Saving Brisbane City Hall Aurecon has successfully helped to restore historic Brisbane City Hall, situated in the heart of the Queensland capital. Brisbane City Hall has been a hub of community activity for over 80 years and was of the most signi cant heritage buildings in Queensland-it has hosted both royalty and rock stars and holds a special place in the heart in many of its residents. Behind the sandstone façade is a reinforced concrete frame that was constructed over a 10-year period during the 1920 s and 1930 s and, although not readily visible to the public, this concrete frame has su ered serious structural problems. Aurecon was engaged as the structural engineers for the $215 million restoration of the building from August 2009 to December 2012, with the challenge of preserving the building and providing another 50 years of design life for a structure with a characteristic concrete strength of 3.4MPa. is required not only an innovative design and remedial approach, but also constant and continual dialogue with Brisbane City Council in order to communicate the challenges and intimately understand their needs in terms of outcomes. e nature of the existing concrete was such that it fell outside of the guidelines of AS 3600, or any other code of practice. e main structural challenge was to reconcile 80-year old concrete with modern analytical and design methods. e concrete frame has also su ered from a number of serious structural problems. e hand-batched concrete was highly variable in nature, beams which are heavily over-reinforced, and shear reinforcement which falls well below modern requirements. Aurecon used engineering science to derive an innovative conceptual solution for a signi cant structural design challenge and then followed through with old-fashioned on-site full scale load testing which con rmed the critical details of the concept. e team proceeded to deliver the structurally restored building. ere were several aspects to the strengthening works, each with di erent solutions. Wherever possible, design solutions were selected to minimise the damage to the original heritage fabric, which could be removed at a later date if required. As an example, for the beams, two alternative strengthening methods were developed. e rst was increasing the strength of the beams by adding additional bending and shear reinforcement in a concrete overlay along the a ected length of the beam. e strengthening reinforcement was then drilled and epoxied vertically into the existing beams. For the positive bending at midspan, the reinforced concrete overlay increases the e ective depth of the section. e vertical dowel bars between it and the original concrete resist the horizontal shear force. At the column positions the e ect of the overlay is to Brisbane City Hall, and the Museum of Brisbane which is housed inside the building, has again become the tourist attraction that it was in the past.