Effect Of Floods And Obsolescence On Bridge Life

The economics of the design of a bridge waterway opening is usually related to the return period of the design flood. A factor not usually considered in determining the frequency of replacement of a bridge is the effect of obsolescence which has a probability distribution just as floods do. A general formula is developed for a step function that defines the average replacement period where each year there is a constant probability of replacement because of destruction by flooding and a variable probability of replacement because of obsolescence. Examples are given for simple conditions. It is shown that obsolescence may have a large effect on increasing the frequency of replacement and hence on planning for future financing of bridges.