|Budget Amount *help
¥1,480,000 (Direct Cost: ¥1,300,000、Indirect Cost: ¥180,000)
Fiscal Year 2007: ¥780,000 (Direct Cost: ¥600,000、Indirect Cost: ¥180,000)
Fiscal Year 2006: ¥700,000 (Direct Cost: ¥700,000)
This project is an experimental study on application of CFRP strips to repair and strengthening of fatigue cracks initiated in welded joints in steel structures in service condition, namely whether the CFRP strips can be delayed or stopped propagation of the fatigue cracks. Target welded joint in this project is out-of-plane gusset welded joints in which lots of fatigue crack initiation are reported.
In 2006, applicability of the CFRP strips to the repair and the strengthening in actual structures was examined experimentally. The specimen is a girder type ; 800mm in web height and 6,000mm in span. As the specimen is relatively large, it is considered that residual stress distribution, metallurgical character, etc. are nearly equal to actual structures. Static and cyclic loading tests were done using the girder type specimen. The CFRP strips were pasted on the welded joint initiated a fatigue crack in the cyclic loading test, and re-initiation of a crack was investigated.
In 2007, fatigue tests were performed to get the S-N curves using a model specimen of the out-of-plane gusset welded joints ; 250mm in width, 1,040mm in length. A part of the results is shown as follows.
(1) In the repair method pasting the CFRP strips in front of the crack, the strips came off steel member shortly and did not had an effect. However, in the repair method covering the crack with the CFRP strips with a slit on the central part, the strips did not come off steel member and had an effect.
(2) In the repair method covering the crack with the CFRP strips with a slit on the central part, fatigue life was greatly improved according to increase of the number of layer of the CFRP strips.
(3) Fatigue limit was not obtained through the experiment. Therefore, it is concluded that the repair method covering the crack with the CFRP strips with a slit on the central part is a temporary method.