Ultimate strength of externally strengthened prestressed beams

It is sometimes necessary to increase the load capacity of bridges to cope with increased traffic loads. This can be achieved using external prestressing which increases the load capacity of the bridge speedily with little traffic obstruction and without significant added weight. However, this method will be used widely only if its effect on the ultimate moment of resistance of the strengthened beams is understood. Furthermore, for design purposes, a simple method to determine the ultimate moment of the strengthened beams is required. In this paper six factors were studied to investigate their effect on the prestressed beams strengthened using type G Parafil rope. These factors are the value of the external prestressing force, number of deviators, effective depth of the external prestressing force, maximum load prior to strengthening, concrete strength and span/depth ratio. An analytical investigation has also been carried out to develop a simple general equation for the ultimate strength of the beams. The comparison between the experimental and the theoretical results show very good agreement.