Indian Road Congress (IRC)-06 specifies consideration of impact factor for dynamic analysis of bridge loaded with Class A and Class B vehicles. As per IRC-06 specifications, the impact factor is estimated based only on the span length of the bridge. In the present study, the effect of vehicle speed, road surface roughness condition and span length of the bridge on the impact factor is investigated. The dynamic response of a simply supported bridge loaded with IRC Class A and Class B vehicle loads are considered for the study. For simplifications, the vehicles are idealized as a series of moving mass spring damper system. The interaction between the bridge and vehicle is accomplished by coupling the equation of motion using the interaction force at the contact point of the wheel and bridge. The coupled equation of motion is solved using Newmark's beta method. The model is validated using past available literature. The vehicle is considered to move at a consistent speed between 20 and 100 km/h. The excitation caused due to the presence of road surface roughness at various vehicle speeds on the bridge response with span lengths varying between 20 and 100 m is investigated. Parametric studies are also conducted using frequency ratio. From the studies, it is observed that the response of the bridge subjected to IRC Class A vehicle is 40% higher than the response of the bridge subjected to IRC Class B vehicle. It is also observed from the parametric study that, the bridge response becomes critical when the vehicle moves at resonance speed and the amplitude increases with deterioration of road surface condition. The results of the impact factor study show that IRC-06 specifications underestimate the response of the bridge for high speed moving vehicles under different road surface conditions. The findings of this study can be utilized to update the IRC specifications at the time of analysis and design of both short and as well as long-span highway bridges.
In this paper, a new ground-motion prediction model (GMPE) for North-eastern India (NEI) is developed based on the available recorded events. NEI has already faced several high magnitude earthquakes (moment magnitude [Mw
]>7.0) during the period 1200 to 2018. It is difficult to develop GMPE and estimating the seismic hazard of NEI, due to sparse recorded strong motion database. To date, seismic hazard maps for NEI have not been prepared. All developed countries have developed seismic hazard maps for their cities using region-specific GMPE. So, to prepare the seismic hazard maps of NEI, a ground motion prediction model will be required. The success of earthquake hazard mitigation depends to a large extent on how accurately the ground motion hazard can be estimated at a vulnerable site. The GMPE developed in this study has been compared with other ground-motion models as well as with the available limited recorded strong motion database. Based on the comparison, it is observed that the new model is reasonably correct as the model is unbiased with respect to both magnitude and hypocentral distance. This model needs to be upgraded as and when more recorded strong ground motion database is available for this region.
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