Effect of FRP Spike Anchor Installation Quality and Concrete Repair on the Seismic Behavior of FRP-Strengthened RC Columns

The use of fiber-reinforced polymer (FRP) to repair and seismically strengthen existing deficient or damaged structural elements is now widespread. FRP anchors have become an important component of such FRP strengthening. However, while reasonable quality control and field quality assurance measures exist for FRP fabrics and plates, such attention has not yet been given to FRP anchors. It seems logical to expect that poor FRP anchor installation will adversely impact the performance of the repaired element. This experimental program was envisaged to assess the level of such an adverse impact. It consists of six RC columns subjected to axial load and quasi-static cyclic load. Of the six columns cast for the experimental work, three columns had good concrete placement, while the remaining three showed poor consolidation, with substantial honeycombing and segregation at the base. It was decided that the latter columns could be used as examples of damaged concrete and so they were repaired by a local contractor by removing the poor concrete and replacing it with a commercially available bagged concrete repair material. One column of each set of three was designated as a control column without any FRP strengthening, while the four remaining columns were strengthened using longitudinal FRP sheets for flexural strengthening, anchors to develop the FRP into the foundation, and transverse FRP sheets for confinement. It was observed that the concrete repair did not adversely affect the behavior of the columns or the interaction between the concrete and the FRP. The FRP anchors were installed to replicate poor installation in the field. Those with improperly placed fans, or splays, did not perform at all as intended and it is recommended that such anchors be removed and replaced without exception. Inadequately saturated anchors were able to achieve their design rupture capacity but failed in a more brittle manner than adequately saturated anchors. Based on the observations from the experimental program, several ideas and options are proposed to enhance the quality of FRP anchors. Accompanied with onsite testing and mockups, these suggestions will substantially contribute to the mitigation of the associated variability in the performance of the rehabilitation.