Yosuke Nakamura

CFRP reinforcement of steel chimney

Takeshi MIYASHITA

Seismic design methods for structures have been developed based on damage done by earthquakes. This is also for steel chimney structures. After reconsidering the seismic standards there are steel chimneys with insufficient seismic resistance. In addition, due to aging of materials, inspection and repair are also required. The conventional repair method requires welding or additional holes and plates; but these construction methods are complicated, also have problems such as cross-sectional defects, concerns about thermal effects, and increase in dead load. Steel chimneyfs diameter to thickness ratio is large, so these are designed to be lightweight, and their base is designed to correspond this ratio.  Therefore, a significant increase in dead load can affect the base.
The main purpose of this study is to investigate the improvement of the seismic resistance of existing steel chimneys in using carbon fiber sheet bonding method. This method permits a simple and lightweight reinforcement of the structure. In this research, a steel pipe simulating a steel chimney is reinforced with carbon fiber sheet. Horizontal positive and negative alternating loading is performed to obtain load capacity and deformation performance data. Three experimental cases are conducted, a non-reinforced specimen and two specimens with carbon fiber sheet reinforced (with or without putty). In addition, using two types of carbon fiber sheets, the reinforcing effect in the axial direction and circumferential direction of the steel pipe are examined.
Regarding to the horizontal load tests, the effect of reinforcing the carbon fiber sheet was confirmed in the two specimens with the carbon fiber sheet based on the maximum load. Furthermore, the energy absorption capacity, can be improved by carbon fiber sheet reinforce, and the amount of out-of-plane deformation can be kept small and the energy absorption can be increased from the viewpoint of the failure of the base. In addition, from the load-strain relationship of each specimen, it was confirmed that the effect of stress reduction and restraint was achieved by the carbon fiber sheet reinforce.