Rehabilitation of steel bridges through prestressing

Throughout the world, bridges are being newly built, repaired, strengthened, replaced to provide essential infrastructure facilities for the Development. Sri Lanka is no exception. The cost of bridging has become a heavy burden to the National Economy in Sri Lanka, due to the continuing demand for access and mobility to under developed or developed areas respectively. The bridge stock in Sri Lanka mainly comprises of small to medium span bridges, built using steel and/or concrete. Almost all the Medium Span Bridges are steel truss bridges. The Steel Bridges are generally more than 50 years old and are in need of repair/strengthening or replacement. Sri Lanka has successfully repaired/strengthened some of the Steel Bridges in the past, though now they are replaced due to their insufficient width, more often than not. This is primarily due to the fact that the steel truss bridges are not easily amenable to widening, economically. In this research, it is shown that the steel truss bridges could be widened to meet the current traffic demand, even without strengthening, due to the large factor of safety, used in the original designs, and the new knowledge gained in the material and structural behavior of these bridges. In bridges where such a large' factor of safety is not in-built, it is shown that prestressing could strengthen the bridge after the widening, economically. Further, it is shown that the life span of the widened bridge could be prolonged after the widening due to the application of the prestressing force. which reduces the probability of fatigue failure