ABSTRACT
GENERAL SESSION
1 INTRODUCTION In Japan, the construction of new steel bridges has been decreasing. On the contrary, old bridges have been increasing rapidly, and it has been reported that in 20 years, a half or even more of the existing bridges with a span exceeding 15 meters were predicted to be over 50 years old. It was also reported that more than 60% of the railway bridge stock in Europe was over 50 years old and more than 30% was over 100 years old. These bridges are subjected to higher loads and speeds than those for which they were designed. To satisfy the present and future demands, some bridges are in need of strengthening or replacement. Meanwhile, due to their high transport capacity and effective use of energy with lowest damage to the environment, railways are one of the most important means of transportation in Japan, in which steel bridges have been widely used and more and more bridges become old and need to be repaired or strengthened. For strategic railway, new constructions are usually performed to replace the old steel bridges, but for local or branch railways, maintenance is often undertaken to reduce the cost. Consequently, maintenance of existing steel railway bridges is of great importance in current civil engineering practice for Japan. However, old steel bridge strengthening generally faces a lot of difficulties.
