Japan’s Infrastructure Situation and Peening

Author:  Fukuoka University Koji Kinoshita, Gifu University Yuki Banno Yamada Infra Technos Co., Ltd. Shohei Yamada, Motohiko Tsuruta Toyoseiko Co., Ltd. Yoshihiro Watanabe
Source:  The Shot Peener magazine, Vol 39, Issue 3, Summer 2025
Doc ID:  2025016
Year of Publication:  2025
Abstract:  
1. Background The aging of infrastructure, particularly steel bridges constructed during Japan's period of rapid economic growth (1955-1973), is accelerating and has become a pressing social issue. According to infrastructure maintenance data published by the Ministry of Land, Infrastructure, Transport and Tourism (MLIT), of the approximately 730,000 road bridges (with a length of 2 meters or more) whose construction year is known, it is estimated that around 30% will be over 50 years old by March 2020, about 55% by March 2030, and approximately 75% by March 20401). MLIT’s estimates indicate that, for infrastructure under its jurisdiction, total maintenance costs over a 30-year period could be reduced by about 30%2). “Preventive maintenance” is projected to cost approximately $1.2 to $1.3 trillion, compared to $1.7 to $1.9 trillion for “post-defect maintenance.” In response to this situation, MLIT highlighted the importance of shifting toward preventive maintenance in their 2024 New Year’s address. This paper presents a case study involving both post-defect and preventive maintenance of fatigue cracks on an existing steel bridge under MLIT’s jurisdiction. Fatigue cracks identified during the repainting process were addressed through post-defect maintenance using needle peening, while shot peening was applied as a preventive measure in areas without cracks. Based on the results of this case study, a series of processes necessary for future infrastructure maintenance is proposed.