Seismic Retrofit of Square RC Columns Using Prestressed Non-Laminated CFRP Straps

Abstract eng:
Many existing columns have insufficient transverse reinforcement leading to premature collapse during an earthquake. One solution that has become very popular in the last couple of years is confinement with fibre reinforced polymer (FRP) wraps or jackets. Whereas confinement is most efficient when applied to circular columns, it is usually much less effective when applied to columns having a square or rectangular cross section because a significant portion of the cross section remains unconfined. In this paper, an innovative method is presented to confine rectangular reinforced concrete columns using non-laminated CFRP straps. The CFRP straps can be either unstressed at the beginning or prestressed. Tests were carried out at the Swiss Federal Laboratories for Materials Testing and Research (Empa) on three large scale columns (2.0 m high with a cross section of 0.4 m x 0.4 m). The first column was the unconfined reference column, the second column was confined with prestressed non-laminated CFRP straps and the third column was confined with non prestressed non-laminated CFRP straps. The test results show no or only a small increase in strength but a significant increase in the deformation capacity of the confined columns with respect to the unconfined column. This behaviour is in fact desired for seismic loading to ensure life safety of the structure. Finally, a simple analytical model is introduced to predict the axial stress-strain relationship.

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