Extrapolation of Live Load Effects to 75 Years Return Period for Highway Bridges

Design of bridges is primarily governed by the live load models representing truck traffic. In Pakistan, bridges are designed as per live load models of Pakistan Code of Practice for Highway Bridges 1967 (called herein as CPHB ) and American Associations for State Highway and Transportation officials AASHTO LRFD Bridge Design Specifications (called herein as AASHTO ). CPHB is based on 1961 American Association of State Highways and Transport Officials (AASHTO) Bridge Design Specifications.Further, National Highway Authority (NHA) has specified legal limits on the live loads to prevent overstressing of bridges. Live load models are usually developed from existing truck data. Load model for highway bridges are primarily based on truck load, dead load and dynamic load. Live load data required for bridge design includes the Gross vehicle weight (GVW), axle weight, axle spacing and truck configuration.Correct estimation of data plays a vital role in designing of the bridge for intended design period which is 75 years as per AASHTO LRFD code. Estimating the traffic data is nearly impossible for 75 years as data recording for such a long time is not possible.However a reasonable result can be achieved by projectingthe collected data to 75 years. Data which is to be projected is usually collected over a short period ranging from 3 months to one year.Various techniques are used for extrapolation to 75 years but this paper aims at describing and comparing the test results using non-parametric fit method as was used by (Kozikowski and Nowak, 2009), Convolution method (NCHRP 683, 2012)and CDF (Cumulative Distribution Function)projection method adopted by MDOT(Michigan Department of Transportation) for investigation of current design/truck load to calculate maximum 75 years load effect on the bridge (RC-1413, 2002).

کلیدواژه ها:

Highway Bridge ، truck load ، Live Load ، Weigh in Motion ، Non-parametric fit