Issue 50

I. Dakanali et alii, Frattura ed Integrità Strutturale, 50 (2019) 370-382; DOI: 10.3221/IGF-ESIS.50.31 380 According to the raw data from the first attempt of the double pull-out configuration (Fig.16a), it seems that the ultimate pull-out load is lower than that in other pull-out tests (Fig.16b). A possible explanation could be that the marble does not interfere with the pull-out of the bar and the frame’s load is opposed only by the strength and cohesion of the marble- paste interface. The bar’s deformation assumes also lower values compared to the other two occasions (pull-out 1 st class, pull-out 2 nd class) and this could prove that the assembly parts (marble, bar) are not under stress, with the only active part being the interface between marble and cement paste (Fig.16b). From a different perspective (Fig.16c), in an effort to “neglect” the maximum load's influence and focus on the load changes for the three different tests, the ratio Load/ maxLoad is provided versus the bar’s strain. The curve’s inclination and the bar’s strain for the double pull-out are notice- ably larger than those of the other two (1 st and 2 nd class). Figure 16: (a) Time variation of load (double pull-out test); (b) Load vs bar’s strain for pull-out test (1 st class), pull-out down (2 nd class) and the double pull-out test; (c) Load/maxLoad vs bar’s strain for pull-out test (1 st class), pull-out down (2 nd class) and the double pull-out test. C ONCLUSIONS urrent research in the field of restoration of the Acropolis monuments addresses the quality of adhesion between marble and reinforcing bars used to rejoin fragmented elements. According to the restoration perception, it is of paramount importance that the ancient marble pieces are protected and not further fractured because of an insuf- ficient connection. Experience from restoration projects when the restored structural member is subjected to tension and bending, stresses the importance of investigating the failure mechanism leading to the debonding and finally to the cata- strophic pull-out of the reinforcing bar from the body of the marble volume. Under certain loading conditions, the pull-out phenomenon dominates the failure mode, for which further study is required even though there is some standardization of the experimental procedure. (a) (b) 2 nd class 1 st class double pull-out (c) 1 st class double pull-out 2 nd class C