Experimental investigation on reinforced RC column with prestressed double helix FRP strip

Abstract

It is well-known that prestress strengthening technology can eliminate strain hysteresis of the fibre reinforced polymer (FRP) reinforced concrete column and improve the reinforcement effect significantly, but the technology is by far immature enough. This investigation proposed a new method of prestressing FRP strip by which we screwed the nuts to push out the steel strips previously wrapped inside the fibre strips. Then a tensile test was conducted to test the strength and strain of the tested fibre strips, the results revealed that the three superposed fibre strips worked well together. Additionally, the average bond strength was gained from the bonding test of the fibre with the concrete. Taking the level of prestress, the spacing of the fibres, and whether the columns chamfer as three main variable parameters, an axial compression test was furthermore proceeded of the six reinforced concrete columns with double-spiral FRP strips, and a comparison was made with that of unreinforced concrete column. The test results show that the new prestressed reinforcement method is effective. The bearing capacity of the reinforced prestressed specimens, the initial stiffness as well as the deformation properties was much higher than those of the unreinforced and non-prestressed reinforcement specimens. And the higher the prestress level was, the better the reinforcement effect would be. Meanwhile, it was found that the reinforcement effect only changed a little when the fibre spacing was reduced from 200 to 100 mm, and that the reinforcement effect of concrete column by fibre strips is insensitive to column chamfering. Due to the loss of prestress caused by the column axial compression, the stress of the fibre strips decreased slightly during the loading process, and the specimens damaged with no fibre fracture.

Keywords:

• FRP strip
• reinforcement
• prestress
• double helix wound
• RC column

Acknowledgements

The accomplishment of this paper, which is based on the sample fabrication and test process, has obtained great help from Xiaoquan Wu, from Nanjing Hongya Construction Company, and Jianning Chen, from Civil and Transportation Test Center of Hohai University, therefore, the authors of this paper would like to express their heartfelt thanks to them here. This study is funded by the central university research business fee under grant No. 2010B03514.