Analysing and predicting falsework failure in Hong Kong

Falsework is a temporary structure supporting the permanent structure while it is not self-supporting. Falsework is commonly required in concrete construction which involves a number of parties such as the design engineer, contractor, subcontractor, supplier and checking engineer. In the past, many failures occurred due to procedural inadequacy such as confusion in responsibility delineation and communication. In Hong Kong, during the last six years, at least eight major falsework collapses have been reported. Researchers studying falsework failures have devised models for analysis and prediction. However, procedural inadequacy has not been adequately considered and assessed in these models. Further, these models were mainly used to predict the likelihood of eventual failure at loading stage without evaluating the safety condition at various stages of falsework construction. The overall aim of this thesis was to develop a procedural framework that can be used to assess the proneness to failure at different stages of constructing falsework in Hong Kong, thus, warning can be given promptly. The objectives of the research were: to review the practices of falsework scaffolding; to compare the different control systems on the design and construction of falsework; to analyse the causes of falsework failures; and to develop a procedural framework for assessing the safety of falsework at various stages. To identify the causes, 50 failure cases were analysed. Nine site visits to Hong Kong, Macao, China, Taiwan and Singapore, where falsework failures occurred, were made. A total of 33 tests of falsework scaffolding materials were performed in the laboratory. A procedural framework based on balloon theory was developed to assess the procedural errors for analysing and predicting falsework failure. The research yielded the following outcomes: the identification of causes, frequency and impacts of falsework failures; the classification of the key and critical activities of falsework under the five essential stages, i.e. design, erecting, loading, dismantling and anew; recommendations on the loadbearing capacity of the new and used falsework scaffolding material; the graphical presentation and assessment of the procedural errors accumulated throughout various stages; the flowchart, showing the role of various parties and the impact due to changes in the construction method of the permanent works and falsework, for analysing and predicting failures; and a procedural framework to analyse and predict falsework failures. Fifteen construction professionals confirmed that the procedural framework would be very useful in monitoring the performance of falsework as required under the latest Code of Practice for Metal Scaffolding Safety issued by the Labour Department of Hong Kong.