Distress Diagnosis, Repair and Retrofitting of Bridges
Dr. A.K.Pandey, Scientist and Dr. Rajesh Deoliya, Scientist, Structural Engg. Division, Central Building Research Institute, Roorkee, Uttaranchal
Introduction
Rapid industrialization in India after independence required infrastructure for transport of goods and raw materials and that has led to construction of wide network of roads with inbuilt bridges and flyovers. A number of existing bridges are showing sign of distress within their designed service life in many cases as early as 10-20 years of construction in India and in several other countries. Collapse of I-35W bridge at Mississippi river in United States of America in the month of August 2007 has drawn attention of international media. In India, collapse of Mandovi Bridge at Goa in 1986 (after 16 years of service life) and serious distress in Zuari bridge (rehabilitated in 2000 with the held of international consultant) at Goa and several other bridges like Khalghat and Borad Bridge on NH3 (Agra to Mumbai route) due to environmental loads is drawing the attention of transport authorities and scientific community to evolve an efficient bridge management system. Identification of the cause of distress, level of distress and reduction in load carrying capacity of the bridge may be ascertained in order to proceed with necessary repair to ensure safety of the bridge during their service life. The evaluation of state of stress and load carrying capacity of the existing bridges and enhancement of the load carrying capacity is required during upgradation of the highways. India has already implemented strengthening and four lanning of 7000 Km of highways under Golden Quadrilateral scheme where strengthening/retrofitting of many existing bridges was required. The various causes of distress of reinforced concrete bridges are poor quality of construction, corrosion of steel in reinforced concrete bridges and pre-stressing cables in prestressed concrete bridges, improper design and detailing for normal loads and seismic forces, improper functioning of bearings etc. A number of case studies have been reported in literature on damage of reinforced concrete and prestressed concrete bridges during earthquake [1-6] and distress of reinforced and prestressed concrete bridges [7-10] because of environmental and other loads.