Pre-stressed CFRP Straps
Time-dependent shear behaviour of RC beams strengthened with pre-stressed CFRP straps
Shear failures in reinforced concrete (RC) beams often occur suddenly and without advance warning so it is important to prevent this brittle failure mode. To enhance the shear capacity of existing RC structures, an innovative shear strengthening technique using pre-stressed carbon fibre reinforced polymer (CFRP) straps was developed by Winistoerfer and Meier at EMPA in 1999. In this system, layers of thin CFRP tape are wrapped around a beam and the outer tape layers are fusion bonded to form a closed loop.
Experiments on RC beams strengthened with CFRP straps were previously conducted at the University of Cambridge, EMPA and ETH Zurich. Different parameters have been studied including the CFRP strap spacing, number of strap layers, and the pre-stress level in the strap (e.g. Kesse and Lees, 2007).
The long term shear behaviour of RC beams strengthened with pre-stressed CFRP straps depends on the shear deformation, load distribution and the strap behaviour. Ongoing experiments and theoretical modelling are helping to improve the understanding of the time-dependent shear behaviour of CFRP strap strengthened RC beams.
Collaborators
The use of prestressed CFRP straps to strengthen reinforced concrete has been the subject of a longstanding collaboration with Professor U. Meier from EMPA and Dr A. Winistoerfer from Carbolink.
Selected references/Further reading
Jin, F. and Lees, J.M. (forthcoming) "Experimental Behaviour of CFRP Strap Strengthened RC Beams Subjected to Sustained Loads". ASCE Journal of Composites for Construction (accepted) (doi)
Jin, F. and Lees, J.M. (2017) "Experimental investigation of time-dependent shear deformation in RC beams strengthened with CFRP straps" SMAR 2017 Switzerland, Sept 13-15, 2017
Hoult, N.A. and Lees, J.M. (2011) "Time-dependent Behaviour of RC beams Retrofitted with CFRP Straps" ASCE Journal of Composites for Constructionv. 15 (1) pp. 75-84 Jan 2011 (postprint) (doi)
Lees, J.M., Winistoerfer, A.U. and Meier, U. (2002) "External Prestressed CFRP Straps for the Shear Enhancement of Concrete", ASCE Journal of Composites for Construction,v. 6(4) pp. 249-256. (postprint) (doi)
Kesse, G.K. and Lees, J.M. (2007) "Experimental Behaviour of Reinforced Concrete Beams Strengthened with Prestressed CFRP Shear Straps", ASCE Journal of Composites for Constructionv. 11 (4) pp. 375-383 (postprint) (doi)