Re-engineering Old Foundations For A New Structure – Greenland Centre

The concept of reusing existing building elements during site redevelopment within urban environments is gaining momentum. With ever-increasing pressure from modern society for engineers to focus on sustainable solutions, the industry is also beginning to recognise other benefits from maintaining, improving or re-engineering existing structures. These include fast tracking decommissioning and construction programs while at the same time saving on demolition and waste disposal costs. Along with the various challenges, such as testing, confirming the integrity of older structures and understanding foundation conditions, one of the major obstacles to effectively reusing existing building elements is the often complex re-engineering required to design and prove a solution is viable. In urban areas where space is at a premium, usually the ‘bigger is better’ approach prevails, and existing columns and footings will be required to support higher applied loads than they were originally designed to carry.

The Greenland Centre in Sydney’s CBD is an example where the re-use of existing structural elements has been successfully adopted, by re-engineering of footing arrangements. The steel portal frame and piled footings of an old 27 storey building were retained, with the piles augmented with new pad footings to increase the footing bearing capacity to support a significantly higher 67 storey building. Finite element analysis was conducted to assess various footing arrangements to optimise the final design so that serviceability limits for the new structure could be achieved. Settlement monitoring and stress, strain measurements have been conducted through construction, with results so far shown to be within the limits predicted in the initial modelling process.

The paper discusses the general issues involved in the reuse of foundations and present results from the Greenland Centre to illustrate the advantages and challenges of reusing existing foundation elements.