PSI - Issue 44

Guadagnuolo M et al. / Procedia Structural Integrity 44 (2023) 942–949 Guadagnuolo et al. / Structural Integrity Procedia 00 (2022) 000–000

947

6

To determine an analytical relationship that can correctly describe the phenomenon would again require the introduction of many parameters that can only be deduced experimentally and would be limited to specific surface treatments and failure modes. The bar slippage can occur inside the adhesive, the concrete, between bar and adhesive, and between concrete and adhesive. In the case of properly placed bars, the failure should occur within the concrete with the removal of a layer of material ranging in thickness from a few millimeters to involving greater thicknesses of concrete, since the shear strength of the latter is generally much less than that of the adhesive (CNR DT200 R1, 2013). On the other hand, when cracks develop on the concrete surface, a conical envelope is formed, leading to a complete separation of the surrounding portion of concrete bounded by the conical crack (Mosallam et al. 2022). In all cases, the theoretical strength of the mechanism is far from the experimental one. 5. Discussion and results The gap between N exp and N Rs can be considered a plus to be added to the theoretical force N Rs to predict the experimental strength N exp . Since the resin develops a larger bond strength than the theoretical prediction, it is possible to see the amount to be added as a stress contribution along the lateral surface S b (S b =π·d b ·L eff ) of the bar concrete interface cylinder. The stresses corresponding to the two forces N exp and N Rs are provided by: exp Rs b b N N * S S     (2) The values of the stress  * are plotted against the difference  *-  (rate to be added to the theoretical force N Rs ) in Figure 2 for all the 157 experimental literature data considered (47+18+92=157). Two groups of data can be identified in Figure 2, which appear to have distinct trends: the blue dots identify pull out tests where the concrete support had a strength of less than 28 MPa, while the red dots identify tests in which the substrate had a strength greater than 28 MPa. In both cases, the values are arranged almost according to linear trends, which allows the following easy regressions:

* 1.0746 ( * ) 0.0038 * 1.0674 ( * ) 0.0059            

( (

28 MPa) 28 MPa)

f f

 

c c

(3)

Equations (3), joined to Eqn. (1) and (2) could be used to assess a pull-out force with potentially greater accuracy. Of course, further investigation and feedback are needed for other experimental data.

20

15

Stress  * [MPa] 5 10

f c < 28 MPa f c > 28 MPa

0

0,0

2,5

5,0

7,5

Stress rate  *-  [MPa]

Fig.2 Rate t*-t for 157 experimental data