The efficiency of mechanical anchors in CFRP strengthening of masonry: an experimental analysis

Fiber reinforced composite materials are widely used for structural rehabilitation and retrofitting of existing buildings. Failure of not anchored CFRP reinforcements, applied to both concrete and masonry, mainly occurs in the substrate or at the bonding surface, for load values lower than the tensile strength of the composite. Mechanical anchors can effectively increase the maximum load of this type of rein- forcements. Particular attention should be paid to the design and sizing of mechanical anchors so that these can produce adequate increments of both strength and ductility of the reinforcement. At the moment there are no specific rules or reliable predictive formulas that adequately support designers in the design choices and sizing of anchors. Of course, these can be defined only after collection of an extensive experimental database that highlights the peculiar characteristics of these reinforcements also with reference to the substrate material. In this context, the present work describes the results of an experimental campaign carried out on brick specimens reinforced with CFRP strips, anchored to the sub- strate by CFRP spike anchors. Almost all research in the literature about this topic refers to the use of this reinforcement technique for concrete structural elements. Studies concerning masonry are limited: this work contributes to bridge part of this gap. Plane CFRP reinforcement strips generally exhibit brittle fail- ure mode. The experimental campaign reported in this paper shows that properly designed mechanical anchors increase both the failure load and the ductility of the reinforcement.