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Investigation of Dynamic Behavior of Beams with Different Supports under Moving Vehicles

Samanipour, Kianoosh | 2015

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 47787 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Vafai, Abolhassan; Esmaeil Pourestekanchi, Homayun
  7. Abstract:
  8. With the transportation progress and appearance of transit industry, necessity of modern vehicles redounded to appearance of heavier trucks with higher speeds, moving on the roads. In addition, with the progress in mechanical engineering and automobile industry, appearance of such trucks is growing increasingly. So, bridges as one of the structures that civil engineers design and construct, nowadays are subjected to higher moving dynamic loads in comparison with the past. As a result, lots of investigation and researches in the universities and institutions all over the world are being conducting on the effects of the vehicle speeds on the dynamic stresses of the bridges. Bridge codes approach is using an amplification factor which applies to the results of the static analysis. In the most of modeling, simplification such as "moving load problem" or "moving mass problem" is used, but in this dissertation a more realistic multi degrees of freedom model will be used. This dissertation presents how to model an actual truck on bridges and, by using finite difference method, how the maximum dynamic stresses of bridges change during the passing of the moving vehicles with different speeds. Then critical speeds which cause more dynamic amplification factor, will be obtained. Furthermore, different end conditions such as hinged-hinged, fixed-fixed and hinged-fixed are modeled and the influences are discussed. It will be shown that where vehicle speeds are considerably higher, current designing codes may predict dynamic stresses lower than actual stresses; therefore, the consequences of a full length analysis must be utilized, like this dissertation, to design safe high-speed bridges. The next section of this dissertation presents how to model passing two trucks simultaneously (congestion effect) and an algorithm to solve the dynamic governing equation of the bridge will be presented to calculate the dynamic load allowance with an example. By finite difference method and calculating the maximum dynamic stresses of a bridge passing two trucks simultaneously, for example in the case of railway bridges which have more than one high-speed railway line or in the case of multiple lane highway bridges where vehicle speeds are considerably higher, current designing codes may predict dynamic stresses lower than actual stresses. At the end, this dissertation presents how to model a bridge with viscoelastic supports and how the maximum dynamic stress of bridges change during the passing of moving vehicles in several case studies. Using viscoelastic supports with appropriate characteristic under the bridges can make a significant difference in the magnitude on the maximum dynamic stress of bridges. By finite difference method, it will be shown that how much the stiffness 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%
  9. Keywords:
  10. Dynamic Analysis ; Congestion ; Finite Difference Method ; Dynamic Amplification Factor ; Maximum Dynamic Stress ; End Conditions ; Viscoelastic Supports

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