The Hanshin Expressway serves as an economic and industrial artery in Osaka, Japan. The 250 km long expressway network forms an important part of the infrastructure, being travelled by about 700,000 vehicles per day. After over 50 years in service since 1964, most of the structures are in need of large-scale reconstruction or rehabilitation. However, many challenges must be addressed to implement the renewal project efficiently. There are various types of works required, ranging from repair and strengthening to reconstruction of steel and concrete bridges. Other problems include considerably long work periods for the large-scale project, very limited space available for the work in a highly dense area, and adverse influence to the road traffic during the work. It is important to adopt methods and techniques that provide efficient cost reduction with minimum impacts to the public. Many of the reinforced concrete slabs on the Hanshin Expressway had been retrofitted with steel plates on the bottom surfaces to improve load carrying capacity and durability. In this study inspection and evaluation methods were developed for evaluating internal concrete damage without removing the existing steel plates.
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