Issue 50

I. Dakanali et alii, Frattura ed Integrità Strutturale, 50 (2019) 370-382; DOI: 10.3221/IGF-ESIS.50.31 379 O NGOING WORK – INNOVATIVE EXPERIMENTAL CONFIGURATIONS lthough the last examined configurations provided encouraging results and it seems that the AE technique managed to detect the onset of the bar's sliding, the parasitic signals were not minimized to the least. For this reason, the specimens are modified again in order to find the proper configuration that focuses perfectly on the pull-out phenomenon, not only in this case (marble-paste-bar) but in any bar extraction (concrete – reinforcement bar). The first new alternative approach includes two pieces of marble. A hole of the same depth and diameter is precisely drilled in both marble blocks. The two pieces are connected with a titanium bar and cement paste, following exactly the same procedure for the restoration of fragmented marble blocks as in the Acropolis’ monuments (Figs.14(a,b)). During the ex- perimental procedure, the lower marble piece is restricted with the rigid metallic plate and the upper piece is forced to move upwards so that the bar slides through the hole (Fig.14c). The second alternative test configuration includes a piece of marble with two holes in the upper and lower edge of the specimen. A bar is inserted to each end (Figs.15(a,b)). The bottom bar is restricted by the lower jaw of the testing frame while the upper one holds the top bar. The upper jaw moves upwards forcing the bars to be pulled-out while the lower jaw remains still (Fig.15). The anchoring lengths at both ends are identical. The bar that was pulled-out was the lower one, while the upper one remained intact in position (Fig.15d). Given the early stages of this investigation, it is to be further studied which of the two bars would be pulled-out at a number of repetitions of the test and under which circumstances. Figure 14: (a) 1 st suggested alternative configuration: the pieces of the specimen, marble blocks and titanium bar (schematically); (b) marble assembly; (c) test configuration (positioning and test procedure). Figure 15: (a) 2 nd suggested alternative test configuration (schematically); (b) test procedure; (c) the onset of the lower bar’s extraction; (d) detail of the failure mode after testing. (c) extensometer upper frame’s jaw lower frame’s jaw marble upper bar lower bar (a) (b) (d) A