A moving vehicle, owing to its vibration and mass inertia, has significant effects on the dynamic response of structures. Most bridge codes define a factor called the dynamic load allowance, which is applied to the maximum static moment under static loading due to traffic load. This paper presents how to model an actual truck on bridges and how the maximum dynamic stresses of bridges change during the passage of moving vehicles. Furthermore, an algorithm to solve the governing equation of the bridge simultaneous with the equations of motion of an actual European truck is presented. Subsequently, 32 dynamic analyses of different bridges with different spans, road profiles and boundary conditions are performed and critical influential speeds are obtained. Results, based on these analyses, illustrate that, depending on the bridge boundary conditions, the speed of the moving truck has a significant influence on the entire structural dynamic response. Using the finite-difference method, it is shown that, when vehicle speeds are considerably higher, for example in the case of high-speed railway bridges, current design codes may predict dynamic stresses lower than actual stresses; therefore, the consequences of a full-length analysis must be utilised to design safe high-speed train bridges.
Abstract. One of the most important problems facing structural engineers is the analysis of dynamic behavior of bridges subjected to moving vehicles. In addition, viscoelastic supports under bridges change their dynamic behavior under passing tra c loads. This paper presents how to model a bridge with viscoelastic supports and how the maximum dynamic stress of bridges changes during the passing of moving vehicles. Furthermore, this paper presents an algorithm to solve the governing equation of the bridge with viscoelastic supports as well as the equation of motion of a real European truck with di erent speeds, simultaneously. Using viscoelastic supports with appropriate characteristics can make a signi cant di erence in the magnitude on the maximum dynamic stress of bridges. By nite di erence method, it will be shown that how much the sti ness and damping of viscoelastic supports should be to have less impact and dynamic stresses in the bridges. It will be demonstrated that using viscoelastic supports can decrease the local maximum DAFs in the case of short and medium spans up to 5%. This study becomes more important where vehicle speeds are considerably high; therefore, the consequences of a full-length analysis with viscoelastic supports must be used to design safe bridges.
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