Discussion of “Structural Monitoring and Integrity Assessment of Medieval Towers” by Alberto Carpinteri and Giuseppe Lacidogna

Abstract

The authors of the paper presented the results of different experimental measurements conducted on the Torre Sineo and Torre Astesiano towers. Geometrical survey and crack determination, flat-jack tests, thermal camera photography, and long-term acoustic emission AE monitoring were the main activities, in addition to some lab experiments concerning flat-jack and AE tests on simple masonry column test specimens. A number of existing vertical stress and Young’s modulus E measurements on masonry walls were conducted by using the flat-jack technique at the foundation level, ground floor, and third floors, mostly at the inner surface of the masonry walls. The location selection is not consistent and has an arbitrary pattern. The discusser believes that the role of analytical modeling in structural monitoring and integrity assessment studies was disregarded in this study. If the distribution of vertical stress values obtained from flat-jack tests is evaluated from an engineering point of view, a large scatter in the values is observed e.g., Fig. 6 a of the discussed paper, Torre Sineo flat-jack testing points at foundation level, and Table 1 of the paper . The masonry wall is thickest at the foundation level and constitutes almost two-thirds of the tower width in both directions. Locations A, B, and C are spaced very closely to one another and therefore are expected to have similar stress values, whereas the vertical stress z values obtained from the flat-jack tests are 2.455, 0.297, and 1.059 MPa for the three locations, respectively. A reality check for the measurements necessitates a preliminary finite-element modeling FEM reflecting the general geometry of the tower. The wall corners and 1% inclination of the tower are expected to cause some differences between stress readings but are not expected to be more than eight times those given in the experimental measurements. Therefore, a preliminary FE model is constructed by using the available information given in the paper, using about 2800 pieces of eight noded solid elements, for a total of about 13,000 degrees of freedom, as shown in Fig. 1. The geometrical properties are taken approximately from the plan and elevation drawings available in the paper, and unit mass is assumed to be 2100 kg /m3. Self weight DL analysis revealed that the expected level of stresses in the inner surface of the tower at foundation level is smaller than that obtained for the ground floor level because of thicker walls at the foundation level. Analysis results predict that the stresses are about 0.15 MPa and 0.5 MPa around the measurement locations at the foundation and ground levels, respectively. The spatial distribution of the stress indicates no significant and sharp stress changes—as opposed to the flat-jack