Mass timber: Improving on-site productivity for multi-storey construction

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Mass timber is a prefabricated, panelised form of building with many benefits such as faster construction and a reduction in both process waste and environmental impact. With worldwide population forecast to increase to 10 billion by 2055 and buildings using 40% of global energy and contributing over 33% of greenhouse gas emissions, mass timber can improve construction and increase industry’s productivity. However, the uptake of mass timber by Australia’s general construction industry has been slow, partly because insufficient quantitative productivity data is available to help contractors and developers forecast cost, time or resources for timber projects. The knowledge gap results in risk-averse pricing by contractors and clients and increased contingency pricing behaviour, which penalises mass timber’s uptake. This study focuses on mass timber on-site productivity in multi-storey construction to develop a method to forecast and identify the significant factors affecting its on-site productivity. A quantitative research case study approach was adopted. A method to measure installation data in multi-storey construction was designed to develop an indicative baseline productivity matrix and identify significant determinants, including materials handling and resourcing. Mass timber installation time and motion studies using a time-lapse digital video recording camera were conducted on three multi-storey residential buildings to understand on-site mass timber installation processes. This study included an analysis of repetitive work cycles and productivity factors, including crane cycle times and installation crew sizes. A mass timber productivity baseline matrix was established to categorise panel type and size for productivity improvement potential and identify a leading input resource. Five potential areas of process improvement, both in construction and design, were assessed. Larger size panels were found to provide significantly improved productivity over smaller panels. The crane, not labour, was found to be the primary input resource. Wind had the most significant adverse inclement weather effect on productivity. Floor level height did not statistically significantly affect productivity. Mass timber productivity models were developed from the above factors to forecast CLT panels’ and mean daily productivity. A merged model is presented with the relevant steps in the design and pre-construction stages to provide maximum efficiencies in mass timber projects. The model identifies the critical factors to address during the design and pre-construction stages. The findings and the empirical and quantitative models presented extend current theoretical knowledge. It provides tools to improve and forecast on-site productivity for mass timber multi-storey construction and enhance overall productivity for the construction industry.
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