MS3.6 - Bridge Dynamics

Hazardous wind conditions can lead to vital safety problems for long-span bridges, either dynamic oscillations or overturning of high sided vehicles. Engineers need to understand the local wind effect to ensure the safety and acceptable performance of infrastructures. Traditionally, aerodynamic studies were carried out in wind tunnel facilities, however the opportunities of using computational fluid dynamics (CFD) modelling for wind assessments in place of wind tunnel tests are significant. To data, few studies of three-dimensional (3D) aerodynamic simulations of bridges with bridge tower and wind shields on them exist. Moreover, most of the existing studies are aimed at validation with wind tunnel tests and do not investigate full-scale effects. To the best of authors’ knowledge, there have not been any full-scale simulations with validation with field monitoring data done to date regarding to bridge aerodynamics. In this study, full-scale 3D CFD models are developed in OpenFOAM using the k-ω-SST turbulence model for the world longest three-tower cable-stayed bridge: the Queensferry Crossing Bridge, which located at Edinburgh in the United Kingdom. The 3D CFD model contains details such as wind shields. Atmospheric boundary layer inflows were created based on wind profiles provided by a full-scale Weather Research and Forecasting (WRF) model. The CFD predictions of the wind condition are compared with on-site data, which was provided by Transport Scotland, United Kingdom. The aerodynamic force conditions of the sample vehicle on the bridge are subsequently determined and analysed.

The reassessment of existing mechanical bridge machineries in The Netherlands has created the need for the development of acceptance/rejection criteria to assess their structural safety. The existing design code in The Netherlands [1] defines an ultimate limit state, meant for new torque regulated machineries, which is based on a linear single degree of freedom (SDoF) dynamical system [2]. Observations show that the SDoF model fails to predict the dynamic response of existing machineries during all load cases. Nowadays, movable bridge machineries are speed regulated and they are in fact nonlinear systems consisting of many mechanical components connected to each other while each movable bridge is characterized by a unique set of fixed parameters. Thus, on-site measurements of a single bridge do not always provide the generic information that one needs for design and/or reassessment of existing structures. In this paper, a novel experimental setup is presented which allows the investigation of a large number of variations in order to capture the dynamics of the powertrain in a class of bridge machineries. A model is also developed that overcomes the limitations of existing SDoF systems, i.e. it accounts for base excitations, damping, and some additional variables of the physical system which are neglected by the current code. A comparison of model predictions with measured data shows that the proposed model provides an upper bound of the peak torque occurring in the powertrain during an emergency braking. Keywords: Dynamics of movable bridges, bridge machinery, powertrains, torque measurements. REFERENCES [1] NEN 6786, Rules for the design of movable bridges, 2001. [2] K. Sektani, A. Tsouvalas, A. Metrikine, Heron Journal, Volume 67, Issue 1: Dynamics. A mathematical model to quantify dynamic forces in the powertrain of torque regulated movable bridge machineries, 2022.

The scissors mechanism, which consists of a chain of rotating discrete elements pin-connected to multiple framework members, can be deployed and retracted, making it highly functional and compact. This useful module can be used on bridges close to unmanned automated bridges. In order to use this useful module in bridges that are similar to unmanned automated bridges and meet various performance requirements, it is necessary to consider structural stability and optimal dimensional design for dead and active loads, buckling, and vibration. For the finite element method (FEM) of the scissors structure, the objective is to construct a program that updates the optimum cross-sectional dimensions from each cross-sectional stress of each member to achieve the minimum weight. Based on the analysis from the axial stress and bending moment stress states calculated using FEM, the cross-sectional dimensions b_i, c_i of each member were updated, and a new method was developed to modify the cross-sectional area and cross-sectional secondary moment of the member based on the sensitivity. In this study, the cross-sectional dimensions of each member unit were efficiently updated to the optimum by distinguishing each cross-section of each scissors member into axial stress and bending moment stress components. The optimal structural configuration obtained using this method is discussed. In this study, a deployable bridge with a series of 5 units was used as a model. The analysis was performed for different models with different loading conditions and different boundary conditions, and the optimal structural configurations were compared. The results showed that the optimal structural configuration for all models corresponded to the overall bending moment distribution. The stresses in each member also asymptotically approached the allowable stress. Therefore, the optimal structural configuration is considered to have been obtained. The optimal structural configuration corresponding to various conditions was obtained by combining the optimized members under different conditions. The method proposed in this paper is optimally updated for the stresses in each member, and the optimal dimensions of each member are determined. As a result, the overall structural form was determined and the weight was minimized.