Rating of Bridges incorporating Dynamic Effect of Moving Loads

Rating of existing bridges is necessary to ensure safety to the public as well as to take appropriate decision for the repair, rehabilitation or reconstruction. In the present work, the capacity ratings of bridges have been outlined incorporating dynamic effect of moving vehicles. Dynamic effect has been considered in the rating procedure making use of impact factors obtained from simulation studies as well as from codal guidelines. The case study of six reinforced girder bridge located in a hilly region of India has been presented. Two levels of capacity ratings- the upper load level capacity rating (called operating rating) and the lower load level capacity rating (called inventory rating) were found out using Allowable Stress Design (ASD) method and Load factor Design (LFD) method. Loading standard adopted are IRC loads and one of the heaviest loads of AASHTO. Simulation studies with vehicle moving eccentrically at different speeds were performed using Finite Element package. Regressions of rating factor versus span have been obtained. Results show that rating factor decreases when the impact factor other than those in the codal provisions are considered. The ASD method always gives a lower value of rating factor than LFD method. In addition to this, the study reveals that rating factor decreases when the span of the bridges is increased.