Over 150,000 highway bridges exist in Japan and about 47 percent of the bridges will be over 50 years old in 2026. The Ministry of Land, Infrastructure, Transport and Tourism (MLIT) launched nation-wide projects to inspect and to establish maintenance plans. About one half of the highway bridges were steel bridges with concrete slabs. Due to heavy truck traffics being operated in or between industrial cities, some of which were illegally overloaded, severe deteriorations to concrete slabs and fatigue cracks in steel girders have been observed. Fatigue cracks in orthotropic steel decks were also found. It is urgent to tackle such fatigue cracks observed in welded joints of steel bridges. Various attempts have been made in Japan to repair and rehabilitate such fatigue cracked members. One is to improve fatigue strength of welded joints in existing bridges, and the other is to repair and rehabilitate cracked members. The latter were, for example, re-welding cracked joints, strengthening by using high strength bolted splices, adding glue to cracks, rehabilitating by gluing CFRP. The authors developed a technique, so-called ICR Treatment, or Impact Crack Closure Retrofit treatment, where fatigue cracks was closed by giving plastic yielding at plate surface near fatigue cracks. Since fatigue cracks do not open due to applied stress ranges, the cracks either do not propagate, or propagate much slower, to prolong remaining fatigue life of the bridges. Fatigue tests were carried out on various welded joints to show how fatigue life was improved by applying the ICR treatment to the cracked welded joints.

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(Former student of Nagoya University) (7-3-1 Hongo, Japan) Various types of fatigue cracks have been found in steel bridges. To maintain steel bridges, repair and retrofit methods of such fatigue cracks have been developed. The authors developed a technique which generates plastic deformation of steel surface near the crack in order to close crack opening by an impact air tool. This method is called Impact Crack Closure Retrofit treatment (ICR treatment). Plate bending fatigue tests of out-of-plane gusset specimens were carried out. Fatigue cracks at turn-around welds and those which have propagated 10 and 20 mm were ICR-treated. Fatigue test results showed significant improvement in the fatigue life of specimens due to ICR treatment.