In this first part of a two-part paper, a general methodology for lifetime performance analysis of existing reinforced concrete bridges is presented. The framework for the methodology is established by identifying four distinct categories: limit state equations, random variables, deterministic parameters, and constant coefficients. The limit state equations are derived by strictly adhering to the load and capacity formulas and requirements set forth in AASHTO specifications. Generality is pursued by establishing parametric limit state equations such that the formulas are applicable to any type of reinforced concrete bridge having similar superstructure components. The methods presented in this paper for reinforced concrete bridges are part of a larger study focusing on lifetime performance evaluation of multiple bridge types in an existing bridge network. For time-variant performance analysis, special emphasis is placed on the chloride penetration modeling in slab and girders. In the companion paper, the lifetime performance of reinforced concrete slabs and girders in an existing bridge network is investigated and results are presented for three bridges located in Colorado.