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日本語

Following its successful application in the reinforcement of concrete in the civil engineering field, CFRP has now been developed as a means for strengthening steel members instead of conventional steel plates being used. CFRP is preferred because it offers several advantages such as being light weight, and having a high strength-to-weight ratio and excellent fatigue and corrosion resistances. To date, however, research and development on strengthening steel using CFRP has focused primarily on bonding techniques involving CFRP being attached to steel surfaces using an adhesive.

Bonded strengthening presents disadvantages as complex and time-consuming surface treatments are required prior to CFRP installation. Moreover, the bonding strength performance between steel and CFRP, which is the key aspect of this strengthening technique, can also decrease significantly owing to environmental exposure throughout the service life. Replacing this approach with another new bonded-CFRP technique may not provide an appropriate solution because it is unlikely to be cost-effective.

The research team developed its method for strengthening steel using CFRP without bonding it to the steel surface. This method has been shown to delay buckling and increase the compression capacity of steel bars, where the capacity gain is affected by the number of carbon fiber layers used.

"As an alternative to the steel strengthening method using CFRP which is bonded to the steel surface, we developed this unbonded-CFRP method," explained the primary author, Fengky Satria Yoresta. "The major advantages of this method are that it is easier and less time-consuming to implement, especially when it is applied to the existing elements of building structures. No more troublesome steel surface treatments are needed, such as sand blasting, grit blasting, or hand grinding, and this leads to significant cost savings," said the research team leder, Associate Professor Yukihiro Matsumoto.

Associate Professor Yukihiro Matsumoto also saids, "Nearly all previous studies used adhesively-bonded joints to strengthen steel members with CFRP. This method is quite complex because appropriate steel surface treatments are required before the application of the CFRP to obtain an acceptable bond between the CFRP and the steel surface. The surface treatment conditions also affect bonding strengths."

"Moreover, we cannot perfectly estimate the effects of environmental exposure during the service life on the bonding performance between the CFRP and the steel. As such, we sought to improve on conventional methods by developing our own bond-free strengthening method. The unbonded strengthening method is useful, easy to apply, and manageable," he said. "However, our method does not transfer stress smoothly, so an appropriate mechanical model needed to be established. Consequently, we performed mechanical simulations and experiments to demonstrate this," he added.

The findings of their work make the research team members believe that the bond-free CFRP method can be applied not only in civil engineering, but also to other fields such as those in the aerospace, automotive, and marine industries. This promising new method is expected to be adopted to rapidly produce innovative, high-quality products.