Determination of Dynamic Load Allowance Factor for Reinforced Concrete Highway Bridges

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Addis Ababa University


Accounting the dynamic effect of vehicles using the dynamic load allowance factor has been widely accepted in bridge engineering. However, consensus on the evaluation of the dynamic load allowance factor is yet to be reached and this is because large number of parameters affects the dynamic load allowance factor. Bridge span length, fundamental frequency of the bridge and vehicle, bridge type, bridge material, damping, vehicle speed, vehicle weight, number of axles, number of vehicles and vehicle loading position are the parameters used to study the dynamic load allowance factor by different researchers and national bridge codes. Many national bridge codes have stated different provisions for the dynamic load allowance (DLA) factor. The different codes have specified the DLA factor in terms of bridge span length, as a function of road surface condition, based on different limit states, bridge fundamental frequency and design loading configurations. This indicates significant variation in bridge code provisions for dynamic load allowance factor exists and this thesis paper tries to asses and determine new appropriate dynamic load allowance formula for reinforced concrete Slab and Girder highway bridges. In this study, a complex finite element software called CSI Bridge 20 is used. In modelling; standard bridge lane width, different span length for both Slab and Girder bridges, design loading configurations and vehicle speeds used to determine the appropriate dynamic load allowance factor. Moving load analysis is done to get the static response and time history analysis is done to get the dynamic response. The static analysis using the finite element software is validated using influence line method and the dynamic analysis is validated using analytical solution and field investigation conducted on KOKA bridge. Finally, new dynamic load allowance formula is set as a function of bridge span length and vehicle speed using regression analysis. Conclusions and recommendations drawn based on the research findings.



ynamic Load, Highway Bridges, Reinforced Concrete