||Mechanical Assessment of Fire Damage of the Ancient Greek Temple of Marble Stone
Historical masonry heritages buildings existing in earthquake-prone countries have been affected many times by earthquakes in their long histories. The Parthenon, Athens in Greece is one of the most famous buildings, and it well known that the Parthenon was damaged seriously by earthquakes and especially human disasters. Therefore, restoration works have been performed carefully since 1975. In addition, marble stone constructions, for example marble column, also suffered serious damage by two historical fires. However, a lot of researches, studies or monitoring results on earthquakes have been reported so far, there have been insufficient knowledge and lack of information on the mechanical characteristics of marble stones affected by high temperature caused by fires. Hence the Acropolis Restoration Office has not made the restoration plan that takes into account fire damages. Such fire damage might reduce seismic safety of those marble constructions, as seismic activity in Greece is high in Mediterranean Sea area. As well as, it might cause serious issues to be solved for restoration of heritage marble structures. The scope of the present study is to describe the mechanical material properties of marble stones affected by high temperature and to estimate the state of suffering or the scale of the suffering with the thermal stress simulation to the marble multi-dram column. Therefore, in the present study, we conducted four heating tests, three compressive tests, and thermal analysis for the measurement of physical properties to marble specimens, and then we performed the heating simulation by ANSYS code. In addition, the international collaborative research had been established with the National Technical University of Athens (NTUA) and TSMA since 2008, the present study is a part of those studies .In the experimental study, the cracks occurred on the marble specimens caused by the thermal shock during cooling time. Moreover, the heated specimen expanded with the passage of time by moisture absorbing, and then cracks significantly were developed. Accordingly, moisture absorption affected deterioration process of marble. In addition, the compressive strength of marble specimen began to decrease at the temperature of 300 ℃ and the specimen heated at over 750 ℃ collapsed naturally during cooling time. In the result of thermal gravimeter and differential thermal analysis, there were CaCO3 and CaO in the specimen heated at 800 ℃. On the other hand, CaCO3 completely disappeared in the specimen heated at 1,000 ℃. Moreover, it was found that the thermal conductivity and thermal expansion rate of marble have irreversibility caused by high temperature. Furthermore, we verified whether this non-destructive method could be suitable for the field survey to the actual buildings with the non-destructive test using by the resonant frequency tester. Marble stone has crystal direction, we also checked effects of each crystal direction to the modulus of elasticity and the modulus of rigidity. The marble specimen having vertical crystal direction and the compressive strength were correlated on each other, however the specimen having horizontal one didn’t have the relation to the compressive strength. From the result, non-destructive method may be suitable to the actual buildings for estimation of the compressive strength as long as the crystal direction is noted. In order to grasp hourly variation of a marble multi-dram with time history simulation of temperature of whole a multi-dram column, we performed the non-stationary heat conduction analysis and thermal stress analysis by finite element method on the computer utilizing the results presented in the previous experimental studies as the reference modeling data. In the result of thermal stress analysis by ANSYS code to a marble dram model, the compressive stress was caused along the circumferential direction of the marble dram. In addition, the tensile stress was also caused in the radial direction at the depth of about 30cm from the surface. Moreover, from the result image of the heat distributions obtained by the heating simulation, it is found that there were the significant difference in temperature between surface and internal marble dram. Hence, there were also a difference of thermal expansion coefficients between surface and internal one while marble dram was cooled after heating. Thus, it is seen from the above result that micro cracks occurred within around this area.
三重大学大学院 工学研究科 博士前期課程 建築学専攻