KS
K. Sektani
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Mechanical bridge machineries
Phenomenological modelling and experiments
The reassessment of existing mechanical bridge machineries in The Netherlands has prompted the development of acceptance/rejection criteria for evaluating their structural safety. The current design code in The Netherlands [1, 2] establishes an ultimate limit state, primarily intended for the design of new machineries, employing a conservative approach with upper bounds on maximum loads. However, to reassess existing bridges and prevent unnecessary replacements, a more accurate prediction of the dynamic response is essential. The current code relies on a linear single degree of freedom (SDOF) dynamical system [3], which is found to inadequately predict the dynamic response of existing machineries across all load cases [4]. This discrepancy can be attributed to, for instance, the neglect of time-dependent and discontinuous model parameters of the machineries [5, 6, 7]. Given that each movable bridge possesses a unique set of fixed parameters, on-site measurements of a single bridge do not provide the generic information required for the design and/or reassessment of existing structures in general terms. In this paper, a novel experimental setup is presented which allows the investigation of a wide range of variations in order to capture the dynamics of the powertrain in a class of bridge machineries. Additionally, a modelling methodology is developed to overcome the limitations of existing calculation rules, by incorporating base excitations, damping, and other relevant variables of the physical system, which are currently neglected by the code. A subsequent comparison with measured data, demonstrating the accuracy of the proposed methodology for different driveline compositions, machinery configurations and braking systems is included in the thesis of this research, due to page limitations.
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The reassessment of existing mechanical bridge machineries in The Netherlands has prompted the development of acceptance/rejection criteria for evaluating their structural safety. The current design code in The Netherlands [1, 2] establishes an ultimate limit state, primarily intended for the design of new machineries, employing a conservative approach with upper bounds on maximum loads. However, to reassess existing bridges and prevent unnecessary replacements, a more accurate prediction of the dynamic response is essential. The current code relies on a linear single degree of freedom (SDOF) dynamical system [3], which is found to inadequately predict the dynamic response of existing machineries across all load cases [4]. This discrepancy can be attributed to, for instance, the neglect of time-dependent and discontinuous model parameters of the machineries [5, 6, 7]. Given that each movable bridge possesses a unique set of fixed parameters, on-site measurements of a single bridge do not provide the generic information required for the design and/or reassessment of existing structures in general terms. In this paper, a novel experimental setup is presented which allows the investigation of a wide range of variations in order to capture the dynamics of the powertrain in a class of bridge machineries. Additionally, a modelling methodology is developed to overcome the limitations of existing calculation rules, by incorporating base excitations, damping, and other relevant variables of the physical system, which are currently neglected by the code. A subsequent comparison with measured data, demonstrating the accuracy of the proposed methodology for different driveline compositions, machinery configurations and braking systems is included in the thesis of this research, due to page limitations.
The reassessment of existing movable bridges in The Netherlands has created the need for acceptance or rejection criteria to assess whether the machineries meet certain design demands. However, the existing design code NEN 6786:2001 Rules for the design of movable bridges defines a limit state design, meant for new machineries, which is based on simple linear spring-mass models. These models, as first proposed by Stroosma in 1980, are valid as long as damping is negligible and the externally applied loads, such as motor and braking torques, are assumed to be constant. However, observations show that these assumptions lead to a more stringent reassessment of existing bridges. As a result, existing bridge machineries do not confirm the model predictions and should unduly be replaced. In fact, the powertrain of movable bridges are nonlinear systems consisting of many mechanical components, such as, couplings, shafts, gears and push-pull rods, with significant damping. Besides, the excitation of externally applied torques by motors and brakes are time-dependent and smooth. In this paper, a model is developed that overcomes the limitations of the existing modelling approach. First, the classical semi-definite model is amended by an extra term which accounts for damping, using three load cases: opening from closed position, acceleration or deceleration and braking. The model gives an upper bound of the peak forces or torques occurring in the powertrain during normal operations and emergency braking. Subsequently, we discuss a novel nonlinear discrete model that allows one to deal with the time-dependency of the externally applied torques, such as, torque-speed characteristics of electric motors and braking torque characteristics.
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The reassessment of existing movable bridges in The Netherlands has created the need for acceptance or rejection criteria to assess whether the machineries meet certain design demands. However, the existing design code NEN 6786:2001 Rules for the design of movable bridges defines a limit state design, meant for new machineries, which is based on simple linear spring-mass models. These models, as first proposed by Stroosma in 1980, are valid as long as damping is negligible and the externally applied loads, such as motor and braking torques, are assumed to be constant. However, observations show that these assumptions lead to a more stringent reassessment of existing bridges. As a result, existing bridge machineries do not confirm the model predictions and should unduly be replaced. In fact, the powertrain of movable bridges are nonlinear systems consisting of many mechanical components, such as, couplings, shafts, gears and push-pull rods, with significant damping. Besides, the excitation of externally applied torques by motors and brakes are time-dependent and smooth. In this paper, a model is developed that overcomes the limitations of the existing modelling approach. First, the classical semi-definite model is amended by an extra term which accounts for damping, using three load cases: opening from closed position, acceleration or deceleration and braking. The model gives an upper bound of the peak forces or torques occurring in the powertrain during normal operations and emergency braking. Subsequently, we discuss a novel nonlinear discrete model that allows one to deal with the time-dependency of the externally applied torques, such as, torque-speed characteristics of electric motors and braking torque characteristics.