TIME-VARYING RELIABILITY MODEL OF STEEL GIRDER BRIDGES

The reliability of bridges depends on load and resistance parameters, which vary with time. The variation is due to natural causes (loads, s trength of material), time-related trends (growth in legal load limits ), and deterioration (corrosion, fatigue). A considerable research eff ort was focused on the development of reliability analysis procedures. A statistical database has been developed for various types of bridge (steel, reinforced concrete, prestressed concrete). The objective of this paper is to establish time-varying reliability profiles relating the reliability index to various rates of deterioration (corrosion and fatigue). A representative set of steel girder bridges was selected ( with regard to span, girder spacing, slab thickness, type of environme nt, and traffic parameters), and reliability indices and load capacity factors calculated. The effect of long-term exposure to corrosion was considered. The calculations were also performed for selected existin g bridges. The obtained reliability spectra will serve as a basis for the selection of target reliability level(s). The minimum acceptable r eliability is determined as the lower tail of the reliability spectrum .