Determination of Dynamic Load Allowance Factor for Reinforced Concrete Highway Bridges
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Date
2019-07
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Addis Ababa University
Abstract
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.
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Keywords
ynamic Load, Highway Bridges, Reinforced Concrete