An Innovative Procedure for Load Rating of Suspension Bridges

Over two hundred million trips are taken daily across structurally deficient bridges in the nation’s 102 largest metropolitan regions, per 2013 ASCE Report Card for America’s Infrastructure. The average age of the nation’s 607,380 bridges is currently 42 years. The nation has an entire generation of bridges, constructed in the 1950s and 1960s, that need major repair or replacement. To address this problem, National Bridge Inspection Standards (NBIS) mandates bi-annual inspection. Load rating of bridges is required by the Department of Transportations (DOTs) across the Nation. While general guidance is available in the American Association of State Highway and Transportation Officials (AASHTO) manual for typical and simple bridges, no general guidance for load rating of complex bridges is available in current civil engineering practice. Therefore, more complex procedures must be developed and used for the actual determination of the load rating of these bridges. In this paper an innovative procedure for load rating of suspension bridges is presented, which provides a framework for the rating of complex bridges. It eliminates the uncertainties in the calculation of dead load, live load or unknown overweight vehicles, distribution factor, increase in traffic volume, impact loads, and vehicular speed. The component-specific demands will be obtained from measured displacements at limited selected locations, and will be compared with the resistance or state of structure in its healthy condition (baseline). The proposed procedure will be applied to the Alfred Zampa Memorial Bridge, also known as the New Carquinez Bridge, which connects the cities of Vallejo and Crockett in California.