Seismic behaviour of ordinary masonry buildings during the 2016 central Italy earthquakes

Abstract

Between August 2016 and January 2017 nine shallow earthquakes ranging from 5.0 and 6.5 of moment magnitude affected Central Italy, involving several municipalities wherein unreinforced masonry buildings are more than three quarters of all constructions. Damage state has been very severe, with sixteen settlements belonging to the municipalities of Amatrice, Arquata del Tronto, Accumoli. Castelsantangelo sul Nera and Norcia experiencing a cumulative European macroseismic scale intensity larger than IX. Ground motion demand in terms of peak ground velocity was approximately two or three times what expected for a 475 years return period while the pseudoacceleration response spectra showed values between once and twice gravity acceleration for the period range typical of two and three storeys unreinforced masonry buildings. Moreover, since October 2016, such large seismic demand acted on structures damaged from previous shocks testifying the effects of damage accumulation, too. The significant shaking alone cannot explain the extremely severe damage of some settlements, with large portions of whole blocks completely collapsed, highlighting the need for investigating the specific vulnerability factors and construction features of unreinforced masonry buildings in the affected area. In fact, although some deficiencies already highlighted in previous Italian earthquakes (e.g. inadequate structural connections) have been surveyed also during this sequence, a marked vulnerability of masonry and its mortar has been noticed, in particular in the area between Amatrice and Arquata del Tronto. On the contrary, the historical constructions in Norcia performed much better, as a result of the 1860 seismic code and of the retrofitting interventions implemented after the different earthquakes occurred in the last two centuries. Finally, a number of demolished and rebuilt constructions performed very well, and this was also the case also of modern hollow clay blockwork buildings that protected not only human life, but also cost of construction and continuity of use.

Shaking table tests on a masonry building monitored using smart bricks: Damage detection and localization

“…The shaking table tests were performed by using a 4 × 4 m 2 shake table with six degrees of freedom, frequency range from 0 to 50 Hz, maximum acceleration of 3.0 g, maximum velocity of 0.5 m/s, and maximum displacement of 0.25 m. URM building specimen's foundation was anchored to the shaking table by using posttensioned steel rods. Figure shows the selected seismic input with its three components of acceleration, measured through the accelerometers positioned on the structure's foundation, that corresponded to the waveform of the Norcia Mw6.5 earthquake, which occurred on 30 October 2016 at 06:40 UTC (epicenter coordinate latitude 42.84° and longitude 13.11°) and recorded by the NRC seismic station of the Italian Strong Motion Network (RAN) in Norcia . Shaking table tests were performed considering the seismic sequence reported in Table , increasing the intensity of the ground motion at each stage to achieve a progressive damage on the sample.…”

“…Figure 5 shows the selected seismic input with its three components of acceleration, measured through the accelerometers positioned on the structure's foundation, that corresponded to the waveform of the Norcia Mw6.5 earthquake, which occurred on 30 October 2016 at 06:40 UTC (epicenter coordinate latitude 42.84 • and longitude 13.11 • ) and recorded by the NRC seismic station of the Italian Strong Motion Network (RAN) in Norcia. 34,35 Shaking table tests were performed considering the seismic sequence reported in Table 2, increasing the intensity of the ground motion at each stage to achieve a progressive damage on the sample. A dynamic identification test was carried out at the beginning of stage 1 and after each main earthquake, by applying a Gaussian white-noise acceleration input having a standard deviation of 0.05 g. After each shaking stage, a visual inspection of the URM building specimen was performed in order to evaluate the evolution of the structural damage.…”

Triplet Test on Rubble Stone Masonry: Numerical Assessment of the Shear Mechanical Parameters

“…Water was added to the mortar mixture until a plastic consistency was reached. The addition of natural clay to the mortar mixture produced a hydraulic lime similar to the ancient lime [39]. Here, it is relevant to say that the test equipment consisted of a pair of rigid steel plates (measuring 30 mm in thickness) mounted around the masonry wall panels to simulate a shear box (see Item 1 in Figure 1c).…”

Seismic Vulnerability of Buildings in Historic Centers: From the “Urban” to the “Aggregate” Scale

“…The seismic activity that hit the central area of Italy in 2016 stresses, once again, the fragility of those territories characterized by the presence of small medieval historic centers made of poor masonry structures (Fiorentino et al, 2018;Sorrentino et al, 2018). For this reason, their seismic vulnerability assessment is a very timely topic that needs to be faced urgently.…”