Bridge falsework systems are one of the most common temporary structures used in the construction industry, namely to support the formwork during the construction, rehabilitation or retrofit works of concrete bridges and viaducts. This Thesis presents new results and research that improve the available knowledge about the structural behaviour, reliability, robustness and risk of these structures. The main, internal and external, hazards are identified and detailed, including the procedural, enabling and triggering hazards. The use of reduction factors to determine the values of the applied loads to design bridge falsework, and other temporary structures, is critically analysed and it is recommended not to use them, unless supported by specific site data. The importance of implementing effective quality control, inspection and communication measures to manage human errors during planning, designing and operation is highlighted. From the 192 tests carried out during the experimental campaign, consisting of five different tests using three different joint types, new results are obtained concerning bridge falsework components, namely the bending behaviour and resistance of spigot joints and forkhead joints (falsework to formwork interface) from which no published research was found. Existing joint models are evaluated and improved alternative models are developed. The results of numerical studies of a selected structural system are presented using a novel joint finite element and information gathered from the experimental tests. This new finite element has features that the available elements in ABAQUS® program do not have, specifically the capability of simulating an analytical modelling of the cyclic behaviour of joints with allowance for stiffness and resistance degradation and joint failure. The accuracy and precision of the developed numerical models improves the existing numerical results of full-scale tests of bridge falsework systems, in respect to structural behaviour and resistance. It is recommended that formwork should be explicitly modelled and modelling of spigot joints should follow the model presented in this Thesis. From a sensitivity analysis of the bridge falsework systems to modelling hypothesis, it is found that the most important joints are the beam-to-column joint, followed by the forkhead joint and the spigot joint, with variations of up to 70% between the resistance of the system when the joints are modelled as continuous or as pinned. A key contribution of the Thesis is to introduce a novel risk management methodology based on newly developed robustness and fragility indices. This new methodology is applicable, in principle, to all structural analyses not only those concerning bridge falsework systems. Based on advanced deterministic studies, the main parameters affecting the performance of bridge falsework are identified, analysed and discussed. These studies involved a comprehensive set of external and internal hazards: (i) applied external actions of different nature and (ii) structural configurations to design bridge falsework. It is found that differential ground settlements are a critical action and that stiffer systems are more sensitive. Also, it is highlighted by use of plenty examples that bracing is an essential design requirement. Advanced stochastic investigations are also carried out, in which the key random variables that control the stochastic behaviour of bridge falsework systems are identified, namely joint looseness and initial stiffness after looseness. Possible strategies to increase robustness and decrease fragility are discussed and based on an application example the cost-benefit of alternative solutions is investigated. It is concluded that implementing quality control and quality assurance procedures to bridge falsework elements is an extremely effective and efficient way of reducing existing risks. The information gathered in this Thesis can be used to develop more rational and reliable bridge falsework structures thus safer and more design efficient.
Andre, J
School of the Built EnvironmentFaculty of Technology, Design and Environment
Year: 2014
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