The Effect of Increasing Heavy Vehicle Loads on a Steel Bridge with RC Deck Lifespan

Addressing the nation’s highway bridge retrofitting and replacement needs is one of the challenges faced by most of the state departments of transportation and other bridge owners. Under the current conditions of traffic volume and truck weight limits, more than 25% and 30% of the nation’s bridges are classified as structurally deficient or functionally obsolete and exceed 50-years of their design life. Nevertheless, national projections predict that freight shipments will double in the next 10 years. Meeting this increase by doubling the number of heavy vehicles or increasing the heavy vehicle weight limit will be detrimental to bridge longevity. Moreover, the total number of maintenance periods is directly affected by the estimated service life and the remaining life of the bridges. The study compared the effect of doubling the traffic volume and truck weight of the American Association of State Highway and Transportation Officials (AASHTO) fatigue truck and the site-specific fatigue truck, extracted from recorded weigh-in-motion (WIM) data, with different annual-traffic growth rates under the present limits on the service life of bridges. Five different practical spans (30, 60, 90, 120, and 140 ft) of a very common U.S. bridge with concrete deck over steel girders were analyzed utilizing two different specialized softwares, CSiBridge and AASHTOWare Bridge Rating programs. The bending moment induced by those two trucks along with the traffic-volume conditions were used to compute effective stress, finite fatigue life, and the remaining life following the AASHTO fatigue calculation procedures and the proposed National Cooperative Highway Research Program (NCHRP) equations for girders and deck as well.