A STATISTICAL STUDY ON LIFE TIME OF BRIDGES

This study is to estimate statistically the life time of bridges and to analyse the reason of demolish and renewal. Data sources are the ledgers of bridge in Niigata prefecture, from which the numbers of remaining bridges and demolished ones were took out in order of newly built year. Total of remaining bridges are 4333 and demolished ones are 44 at 1986.Using terms of reliability theory, the “probability density function of failure” is supposed to follow a weibull distribution from graphic analysis, and by the presumed reliability function, the life expectancy of steel bridge are estimated at some 35 years and of reinforced concrete bridge are at some 54 years. Concerning reason of demolish, using information theory, the contributed ratio of information are calculated. Political or functional reason are superior to physical reason.