ABSTRACT
Reinforced concrete bridge girders are increasingly being strengthened in torsion using fiber reinforced polymer composites (FRP) as externally bonded reinforcement. In recent years, the near surface mounted (NSM) technique has been successfully used to strengthen reinforced concrete (RC) members in flexure and possesses some advantages over the externally bonded method such as prevention of premature debonding. However, the use of the NSM technique when applied to shear strengthened members has been limited. Furthermore, no studies have been conducted on the application of the NSM technique on girders strengthened in torsion. The following research outlines an experimental study involving the strengthening of RC rectangular beams in torsion using the NSM technique. Six beams have been tested comprising of two control beams and an additional four beams strengthened in torsion using alternative groove spacings. FRP laminates are applied to all four faces of the beam and embedded into precut grooves and compared with an unstrengthend control specimens. The beams were tested using a specialized torsional rig system (Figure 1), and the results expressed in terms of the maximum torsional capacity with respect to the peak angle of twist (Figure 2). The torsional test systems. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig52_1.tif"/> Torque-angle of twist curves. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig52_2.tif"/>
Linear elastic response was displayed for all beams until the crack load was reached which was followed by a large increase in the angle of twist with gradual increase in load until failure.
The ultimate loads of the beams have been significantly improved by an average of 28.22% and 35.93%. It appears that using the same FRP percentage in each groove with a lower spacing between the grooves provides a higher torsional strength. However, as the failure mode of the beams has been changed, it is an indication that the number of grooves (spacing between the grooves) may limit the degree of strengthening that may be achieved using the NSM technique.
