TESTING FOR THE ASSESSMENT OF EARTHQUAKE RESISTANCE OF HERITAGE MASONRY BUILDINGS: nondestructive versus destructive, laboratory versus in-situ testing

Some considerations, regarding testing methods, aimed at providing information needed to assess earthquake resistance of heritage masonry buildings, are presented. Various testing methods are available, including non-destructive, semi-destructive, and destructive testing, both in-situ and in the laboratory. Because of specific properties of masonry, non-destructive tests on the basis of propagation of sonic and seismic waves, as well as radar scanning cannot directly provide values of mechanical properties of masonry. They are good for discovering irregularities, such as voids in the masonry, filling the openings in masonry walls and changes in masonry structure. Semi-destructive tests, like shove and flat jack tests provide information regarding the existing stress state in the structural elements as well as shear and compressive strength of masonry. Scratch and impact hammer tests provide information regarding the strength of mortar and units. However, careful calibration of test results, which requires destructive testing in each particular case, is needed to obtain reliable values. Additional specific testing of structural components and assemblages, as well as complete structures, is needed to assess the values of parameters which determine the seismic behavior, such as displacement and energy dissipation capacity, as well as strength and stiffness degradation and deterioration when subjected to cyclic lateral loads. To obtain relevant information, testing methods which simulate actual seismic conditions, should be used. Since it is not easy to reliably reproduce existing masonry in the laboratory, in-situ tests are preferred to laboratory testing of laboratory prepared specimens. Ultimately, real earthquakes represent best testing fields. Although “testing by earthquakes” is expensive by all aspects, from human to material loss, information obtained by learning lessons from earthquakes is precious and most valuable, if thoroughly studied and understood. On the basis of such information, observed phenomena can be simulated by testing, and methods and procedures can be developed to prevent consequences of future seismic events, if timely applied.