Bond-slip relations for PBO-FRCM materials externally bonded to concrete

Existing reinforced concrete (RC) structures often need to be repaired, strengthened and upgraded to sat- 22
isfy current code requirements. In recent years many interventions have been done bonding composite 23
materials to the surface of existing RC elements. The structural effectiveness of these interventions 24
strongly depends on the bond between the strengthening material and the concrete and on the mechan- 25
ical properties of the concrete cover. In this paper the bond between fiber reinforced cementitious matrix 26
(FRCM) materials made out of a poliparafenilenbenzobisoxazole (PBO) net embedded in a cement based 27
matrix and the concrete is analytically analyzed with reference to the approach generally adopted for the 28
fiber reinforced polymers (FRP) materials, which is based on the local bond-slip relation between the 29
strengthening fibers and the supporting concrete. A local bond-slip relation is calibrated on the base of 30
the results of an experimental investigation previously performed by the authors. The bond-slip relation 31
is essential in the modeling of the structural behavior of RC elements strengthened with PBO-FRCM, in 32
that it allows to calculate the force that can be transferred to the concrete, the effective anchorage length, 33
the concrete cracks distance and opening.