Study of Old Bridges for Widening and Retrofitting on the Basis of Widening of Nulllah Lei Bridge near Chaklala

Abstract

Many highway bridges become functionally obsolete due to inadequate width long before they become structurally deficient. Since widening almost always is more economical than complete replacement, there is a need to make available the results of research and field experience pertaining to the widening of bridges. The objective is to enable widening of functionally obsolete bridges as needed to eliminate traffic operation and safety problems. Where ever an existing bridge was designed for a specific traffic load and has not deteriorated appreciably, widening is likely to be more cost-effective than complete replacement to accommodate increased traffic load. Guidelines need to be provided for widening/rehabilitation of such bridges. A two lane bridge constructed in 1906 existed on Nullah Lei on Airport road joining Rawalpindi with the Islamabad International Airport. Due to increase in traffic over the period of time the bridge became a bottle-neck to smooth flow of traffic especially during rush hours. The road way of the bridge was extended from 24 ft to 36 ft during 1996. Techniques adopted were studied in detail for extension of other (similar) bridges. It not only eliminates hazards caused by narrow bridges also gives saving of resources/funds along with saving of time. The technique can be applied to existing narrow bridges designed for current traffic loads and having pier/abutment projections in transverse direction.