A nonlinear deterioration model for the estimation of bridge design life

A comprehensive literature review was conducted, and a questionnaire was circulated, on the subjects of bridge deterioration and bridge life. Several relevant studies were identified, and selected methods were applied to Pennsylvania data. In general, the findings of the investigators were confirmed in the context of the Pennsylvania data. However, these studies were deficient in two significant ways: first, deterioration was assumed to occur linearly with time; second, no systematic effort was made to incorporate the effects of rehabilitation. A nonlinear deterioration model was developed that expresses condition rating as a function of age using an exponential decay function coupled with a rehabilitation "spike" to provide the sudden increase in rating that accompanies bridge rehabilitation. Several variations of the basic model were considered with the coefficients for each model determined through a nonlinear regression analysis. The model was applied to substructures, superstructures, and decks of steel girder-type, prestressed concrete, and reinforced concrete bridges. For each component of each bridge type, three separate ADT ranges were considered. The resulting deterioration models were assessed, limited conclusions were drawn regarding their applicability, and selected versions were applied to the problem of predicting bridge life (A).