ETAG 001

With bonded anchors uncontrolled slip occurs when the mortar with the embedded part is pulled out of thedrilled hole (because then the load displacement behaviour depends significantly on irregularities of thedrilled hole). The corresponding load when uncontrolled slip starts is called load at loss of adhesion Nu,adh.Nu,adh shall be evaluated for every test from the measured load displacement curve. In general the load atloss of adhesion is characterised by a significant change of stiffness, see Figure 6.1a). If the change instiffness at a defined load is not so obvious, e.g. the stiffness is smoothly decreasing, the load at loss ofadhesion shall be evaluated as follows:1) Compute the tangent to the load-displacement curve at a load 0,3 Nu (Nu = peak load in test). Ingeneral the tangent stiffness can be taken as the secant stiffness between the points 0/0 and0,3 Nu/0,3 (0,3 = displacement at N = 0,3 Nu).2) Divide the tangent stiffness with a factor of 1,5.3) Draw a line through the point 0/0 with the stiffness as calculated in 2).4) The point of intersection between this line and the measured load-displacement curve gives the loadNu,adh where the adhesion fails, see Figure 6.1b).If there is a peak in the load-displacement curve, to the left side of this line, which is higher than the load atintersection, Nu,adh is taken as the peak load, see Figure 6.1c).If there is a very stiff load-displacement curve at the beginning (0,3 0,05mm) the drawing of the line forthe calculation can be shifted to the point (0,3 Nu/0,3 ), see Figure 6.1d).For all suitability tests factor 1 shall be calculated according to Equation (6.12):1 =NNu, adhRk, pMc (6.12)4Nu,adh = load at loss of adhesion as defined aboveNRk,p = characteristic resistance for pullout failure given in the ETA for concrete strengthclass and state of concrete (cracked, non-cracked) corresponding to the evaluatedsuitability test.4 = 1,3Mc = partial safety factor given in the ETAThe minimum value of 1 of all suitability tests is decisive. If the value of 1 is less than 1,0 then thecharacteristic resistance NRk,p shall be reduced according to 6.1.2.2.1(b).The evaluation of the load at loss of adhesion is not required when failure occurs between mortar and embeddedpart along the entire embedment depth (see definition of uncontrolled slip). In this case the factor 1 shall betaken as 1,0.ETAG 001-5- 22 -