PSI - Issue 10

D. Mastrogiannis et al. / Procedia Structural Integrity 10 (2018) 319–325 D. Mastrogiannis et al. / Structural Integrity Procedia 00 (2018) 000 – 000

321

3

copy of a fractured and restored epistyle of the Parthenon Temple, a massive structure consisting of three materials (marble, titanium bars restoring structural integrity and cementitious paste interposed between marble and titanium). More specifically the specimens used in the experimental protocol were accurate copies of a typical epistyle of the Parthenon temple, fractured into two asymmetric fragments. The fracture surface was inclined with respect to the longitudinal axis of the restored epistyle by an angle equal to 70 o (Fig.1a). The epistyle was restored by three pairs of threaded titanium bars, according to the pioneering technique developed by the scientific team working for the on going restoration project of the Parthenon Temple (Zambas (1992)). According to this technique, fragmented epistyles are joined together by drilling holes on the body of each frag ment (Fig.1b). The wholes of one of the two fragments are filled with a suitable liquid cementitious material and the treaded titanium bars are driven in the filled holes. After a curing period of about thirty days the holes of the second fragment are, also, filled with liquid cementitious material, the faces of the two fragments are covered with the same liquid paste and the two fragments are driven against each other and the complex is then left to cure for another thirty days. The overall dimensions of the specimens tested in the specific protocol were 145x45x18 cm 3 , with a ratio of the specimens size with respect to that of the authentic epistyles equal to 1:3.

(a)

(b)

Fig. 1. (a) One of the two fragments of the epistyle; (b) The restoring procedure.

The specimens were prepared by experienced technicians of the Parthenon worksite. The material used was Dio nysos marble, given that its properties are very close to the respective ones of Pentelic marble (the authentic building stone of the Parthenon Temple) from mechanical, geological and physico-chemical points of view (Kourkoulis et al. (1999)). Dionysos marble is an orthotropic material, characterized by three distinct anisotropy axes, however, along two of them the mechanical properties are quite close to each other and therefore the material is usually simulated as transversely isotropic one (Exadaktylos et al. (2001a, 2001b)). Obviously, in case of bending, optimum load-bearing capacity is achieved when the material layers are normal to the loading line. After curing (for 28 days) the specimens were submitted to ten-point bending with the aid of an extremely stiff servo-hydraulic loading frame (c apacity 6 MN) and a specially designed system of “I” -shaped beams (Fig.2a). The specific loading scheme is in accordance with the suggestions of older studies by Kourkoulis et al. (2010), concerning the optimum laboratory simulation of the actual loading conditions of the epistyles (after they are placed back in their original position), which is in fact loading by the “dead weight” of the superimposed struc tural elements. The tests were implemented under displacement-control mode, at a rate ensuring quasi-static loading conditions. A detailed description of the overall experimental set-up can be found in a recent paper by Kourkoulis and Dakanali (2017). The response of the epistyle was monitored with the aid of a proper arrangement of sensors, gaining data both from the external surface and the interior of the epistyle (Kourkoulis et al. (2017); Kourkoulis and Dakanali (2017)). Especially for the two sensing techniques considered in this study (PSC and AE), four electric contacts were used to record the PSC and eight acoustic sensors were attached around the fault’s area for the spatiotemporal determination of the location of sources of AE and the determination of their characteristics.