Resistance to Debonding in the Ultimate Limit State

In the case of a debonding involving the first layers of the masonry and with anchor lengths equal to or larger than the optimum length, the factored tensile stress within the reinforcement, that is, the value of the maximum tensile stress at which the reinforcement can work on the ends of the anchor section, once the transfer of stresses from the masonry to the FRP reinforcement has taken place, is as follows  

The maximum factored deformation, Cfdd, which can be allowed on the FRP reinforcement without leading to decohesion problems has a value given by the ratio between the factored tensile stress, /fdd, and the normal elasticity modulus of the reinforcement, Ef. 

In the case of anchor lengths, k, smaller than the optimum length, 4, the factored tensile stress has to be proportionally reduced according to the ratio  

If the decohesion mechanism between the reinforcement and the masomy takes place in the form of the detachment of a surface layer of the brick or stone block, with a view for the actual availability of the lengths h and 4, the length of each of the elements forming the adherence surface (bricks or stone blocks) has to be assumed to contribute to a maximum value of 80 % to the formation of the above said lengths. 

When employing special anchor devices (composite intermediate bars, end binding by fabrics), the maximum anchor strength has to be assessed by special experimental investigations. 

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