Retrofits in Twin Tub Girder Bridges for System-Level Redundancy

Abstract

Because of the perceived risk of fracture critical members (FCMs) in steel bridges, hands-on inspection cycles are mandated, resulting in high maintenance costs. This paper describes the redundancy evaluation of three twin tub girder bridges with FCM designations. Several failure scenarios of primary members are considered using refined finite element analysis of each structure to determine whether fractures result in collapse or loss of serviceability of the bridge. The analysis follows the American Association of State Highway and Transportation Officials Guide Specifications for Analysis and Identification of Fracture Critical Members and System Redundant Members. Based on the outcomes of these analyses, the feasibility of retrofit alternatives is assessed with the purpose of reclassifying FCMs as system redundant members and precluding hands-on inspection requirements.