Structural strengthening for optimizing floor space during retrofitting of high-rise office buildings

Re-life of aged buildings is frequently more cost-effective and time efficient than re-building. In developing a strong business case for re-life, a major challenge to be addressed is that of maximizing the rentable floor space which often puts a re-life project at a disadvantage. In increasing usable floor space, options available to the client include removal or adding floors and partitions, relocating services, cutting openings or extending floors and relocating lift wells etc. In these situations, innovative structural strengthening schemes could be implemented to strengthen the existing structure. Whilst there are decision-support tools reported in literature to cover other parameters in relation to re-life of buildings, they do not include evaluation of the optimizing of rentable floor space and corresponding structural strengthening needs.The structural strengthening of existing buildings can be achieved using one of many upgrading techniques such as span shortening, externally bonded steel, fiber-reinforced polymer (FRP) composites, external post-tensioning systems, section enlargement, or hybrid strengthening systems. Each technique has specific advantages and disadvantages and the applicability to building materials such as concrete, steel, timber and masonry varies. This paper presents a decision support framework developed to compare and assess options available to the design team of a re-life project in optimizing rentable floor space. A matrix developed to map existing as well as innovative structural strengthening techniques to strengthening needs will also be presented with application examples from a case study in Melbourne