Issue 50

I. Dakanali et alii, Frattura ed Integrità Strutturale, 50 (2019) 370-382; DOI: 10.3221/IGF-ESIS.50.31 381 This study focuses on the quantification of the role of parasitic stresses, developed due to the technique used to restrict and load the specimens, having as a case study the ‘marble-cement paste-titanium bar’ complex appearing during the res- toration of marble epistyles of the Parthenon temple. For this purpose, Dionysos marble prisms are tested in a variety of configurations (3 different classes), having a threaded titanium bar centrally placed and connected by means of suitable cement paste. Pulling-out and pushing-in of the bar are considered in juxtaposition. Innovative sensing techniques (AE) permitting detection of failure and damages at the interior of the complex are used, together with standard measuring and recording equipment. The time variation of the load for the 3 classes of tests, together with the corresponding LVDT measurements, constitute the basic dataset of the study, pro- viding an insight to the evolution of failure modes through changes of curves’ inclination before the maximum load. The AE sensors’ measurements versus time indicate when sliding starts and reveal characteristics of the failure modes, via observed changes in the number, energy and duration of recordings. Experimental results seem to be strongly influenced by the load application procedure as well as by the support conditions, indicating the need to reconsider standard testing configurations. Modifications to the initially adopted ones are suggested aiming at finding an experimental set-up that focuses perfectly on the pull-out phenomenon, not only in this case (marble- paste-bar) but in any bar extraction (concrete–reinforcement bar). Preliminary results from two alternative test configurations and procedures are promising since they are compatible with the failure mode being dependent only from the strength and cohesion of the interface between the marble and the cement paste. R EFERENCES [1] Lebidaki, E., (2011). The restoration of the monuments of the Athenian Acropolis, 2 nd ed., Ministry of culture and tourism-acropolis restoration service, Athens. [2] Korres, M., Toganides, N., Zambas, C. and Skoulikidis, Th. (1989). Study for the restoration of the Parthenon, Ministry of Culture, Committee for the Preservation of the Acropolis Monuments (in Greek), Vol.2a, Athens. [3] Acropolis Restoration Service. (2011). Principles and Methods. Available at: http://www.ysma.gr/en/restoration- principles-and-methods, (accessed 10/01/2017). [4] Looney, T.J., Arezoumandi, M., Volz, J.S. and Myers, J.J. (2012). An experimental study on bond strength of reinforcing steel in self consolidating concrete, International Journal of Concrete structures and Materials. 6 (3), pp 187-197. DOI: 10.1007/s40069-012-0017-9 [5] Thompson, M.K., Jirsa, J.O., Breen, J.E. and Klingner, R.E. (2002). Bond and development length of deformed bars. Austin: Texas, Department of Transportation. [6] Achillides, Z. and Pilakoutas, K. (2004). Bond behavior of fiber reinforced polymer bars under direct pullout con- ditions, Journal of Composites for Construction, 8(2), pp. 173-181. DOI: 10.1061/(asce)1090-0268(2004)8:2(173) [7] Alvarez, M. (1998). Einfluss des Verbundverhaltens auf das Verformungsvermögen von Stahlbeton. ETH Zürich, Diss., Basel: Birkhäuser (IBK Bericht 236). DOI: 10.3929/ethz-a-002000033 [8] Kourkoulis, S.K., Papanicolopulos, S.-A., Marinelli, A. and Vayas, I., (2008). Restoration of antique temples: Experi- mental investigations on the pull-out behaviour of anchors in marble, Bautechnik, 85(2), pp 109-119. DOI: 10.1002/ bate.200810010 [9] Dakanali, I., Stavrakas, I., Triantis, D. and Kourkoulis, S.K. (2016). Pull-out of threaded reinforcing bars from marble blocks. Procedia Structural Integrity, 2, pp 2865–2872. DOI: 10.1016/j.prostr.2016.06.358 [10] Kourkoulis, S.K., Marinelli, A. and Dakanali, I. (2016). A combined experimental and numerical study of the pull-out mechanism of threaded titanium bars embedded in marble blocks, ECCOMAS Congress 2016 - VII European Congress on Computational Methods in Applied Sciences and Engineering, M. Papadrakakis, V. Papadopoulos, G. Stefanou, V. Plevris (eds.), Crete Island, Greece. DOI: 10.7712/100016.2174.8066 [11] Grosse, C.U. and Ohtsu, M., (2008). Acoustic Emission testing, Basics for research - Applications in Civil Engineering, Springer-Verlag Berlin Heidelberg. DOI: 10.1007/978-3-540-69972-9 [12] Kaphle, M. (2012). Analysis of Acoustic Emission data for accurate damage assessment for structural health monitoring applications. (Doctoral dissertation), Queensland University of Technology. [13] Miller, RK., McIntyre, P. (1987). NDT handbook-acoustic emission testing, Columbus, OH: American Society for Nondestructive Testing. [14] Mistras group Hellas ABEE, http://mistrasgroup.gr/acoustic_emission_theory_eng.htm (accessed 10/01/2017). [15] Ohtsu, M. (2010). Recommendation of RILEM TC 212-ACD: acoustic emission and related NDE techniques for crack detection and damage ecaluation in concrete. Materials and Structures, 43, pp 1187-1189. DOI: 10.1617/s11527- 010-9639-z