ALBERT

Description: About 10% of the almost 20,000 buildings damaged by the 2002 Molise, Italy, seismic sequence were reinforced concrete (RC). The most frequent type of damage affected the infill masonry walls, but in some cases cracks in concrete columns were observed. Heavy damage to both infills and structural elements was restricted to a few cases in the meizoseismal area. Almost all the affected municipalities were only classified as seismic in May 2003, following this earthquake. Consequently, construction generally used vertical-load-bearing moment-resisting frames with no explicit design for seismic lateral forces. In particular, the reinforced concrete buildings typically consist of cast-in-place unidirectional RC slabs lightened with hollow clay tiles, supported by RC beams and columns. Usually no shear walls are present, except in some cases for the elevator shaft. This paper covers: a) an overview and statistical analysis of damage to RC buildings, and b) a detailed analysis of two damaged buildings.

Description: The San Salvatore Hospital in Coppito was closed shortly after the 6 April 2009 L'Aquila earthquake, even though the buildings on its campus experienced only limited and localized structural damage. The decision to close part or all of an essential facility such as a hospital can be easily made in the heat of the moment after a disaster, but reopening even portions of such a facility is far more complex and raises a large number of operational issues. A documented pre-established program for post-event safety inspections, as well as training in its implementation for both on-site and backup personnel, is vital to the continued operation of any essential facility. While continued operation after an event may be the targeted goal, it may not actually be fully achieved, in particular for older facilities, and some disruption is to be expected. Management of realistic expectations is a vital part of the program for post-event safety inspections.

Description: The 2002 Molise, Italy, earthquake struck a relatively limited geographical area where the communities are mainly agrarian. While most buildings in the region are masonry, there are significant differences in the type of masonry construction, as material characteristics and construction practices had changed over the centuries. This paper focuses on the masonry buildings that predominate in domestic construction. The most significant features that contributed to the damage pattern appear to be (1) construction criteria, techniques, and details that were inadequate for seismically active areas, particularly in buildings constructed or substantially modified over the past 100 years, and (2) site effects resulting from differences in amplification and frequency of the vibrations that locally increased the destructiveness of the earthquake. The observed damage did not correlate to the vulnerability that would be assigned to the structures under the European Macroseismic Scale.

Description: On October 2002, a seismic swarm occurred on Mt. Etna. One of the strongest events caused severe damage, up to a European Macroseismic Scale intensity of VIII that contrasts with its local magnitude of 4.4. The occurrence of significant damage at such a small magnitude is repeatedly observed in the area and is traditionally attributed to shallow source. Recorded strong-motion accelerograms and broadband seismograms demonstrate that there is one more cause for the severe damage, that is, an anomalously strong low-frequency (0.1 or =3 stories) reinforced concrete buildings and elements like church facades. The frequency cutoff below 1.25 Hz in the Wood-Anderson response attenuates the peak-to-peak amplitudes used to assess local magnitudes. Therefore, M (sub L) values are not representative of the real strength of volcanic earthquakes. Because a prompt magnitude (and damage potential) assessment is crucial for civil protection actions, a procedure is proposed which, in near-real time, can be successful in identifying potentially damaging earthquakes of Mt. Etna through the computation of pseudovelocity response spectra. The procedure provides a magnitude value that is derived on a statistical basis from the Housner (1952) spectral intensity computed in the low-frequency band. This parameter is a suitable near-real-time indicator of large earthquake-induced building shaking and could also be applied for a preliminary estimate of the epicentral macroseismic intensity.

Description: On October 2002, a seismic swarm occurred on Mt. Etna. One of the strongest events caused severe damage, up to a European Macroseismic Scale intensity of VIII that contrasts with its local magnitude of 4.4. The occurrence of significant damage at such a small magnitude is repeatedly observed in the area and is traditionally attributed to shallow source. Recorded strong-motion accelerograms and broadband seismograms demonstrate that there is one more cause for the severe damage, that is, an anomalously strong low-frequency (0:1 〈 f 〈 1 Hz) radiation deviating from the conventional Brune (1970) spectral scaling. Therefore, these earthquakes cause large ground displacements and long (≈20 sec) durations of shaking. The integration of digital accelerograms yields a maximum peak ground displacement as large as 1.8 cm at a distance of 18 km. Based on the sharp local attenuation of ground motion in the study area, we infer that peak ground displacements near the epicenters did exceed 10 cm. The occurrence of large displacements caused selective damage to medium-rise (≥3 stories) reinforced concrete buildings and elements like church façades. The frequency cutoff below 1.25 Hz in the Wood–Anderson response attenuates the peak-to-peak amplitudes used to assess local magnitudes. Therefore, ML values are not representative of the real strength of volcanic earthquakes. Because a prompt magnitude (and damage potential) assessment is crucial for civil protection actions, a procedure is proposed which, in near-real time, can be successful in identifying potentially damaging earthquakes of Mt. Etna through the computation of pseudovelocity response spectra. The procedure provides a magnitude value that is derived on a statistical basis from the Housner (1952) spectral intensity computed in the low-frequency band. This parameter is a suitable near-real-time indicator of large earthquake-induced building shaking and could also be applied for a preliminary estimate of the epicentral macroseismic intensity.

Description: Published

Description: 2724–2738

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

Description: JCR Journal

Description: reserved

Description: The use of in-field acquired data to characterize the seismic response of building and bridges immediately after an earthquake, is discussed in this paper; in particular, we discuss how dynamical tests could help the assessment phase and could indicate if the structure is in condition to continue its regular use. In this perspective, two different case-studies will be discussed: the first is concerned with the interpretation of a particular behavior exhibited by a group of four buildings characterized, despite of the similarities among them, by strongly different seismic response (two of them collapsed and the other two survived with a medium damage level) and the second one is concerned with a campaign of dynamical tests finalized to a possible damage detection on a r.c. bridge. Concerning the first case study it is worth noticing how, during the 6 April earthquake in L’Aquila, two couples of similar (nearly twin) buildings belonging to the same urban intervention, exhibited a dramatically different response. In the two couples, the first couple constituted by two four-story buildings and the second couple by two three-stories buildings, one element collapsed suffering the well-known soft story mechanism, while the other one survived with a damage pattern not so strong, as expected considering the similarity with the collapsed one. The in situ measurements conducted in the framework of microzoning activities provided the opportunity of gathering useful information about the dynamical properties of the soil, thus evaluating possible site amplification effects. A key role was played in this case by a local amplification of the seismic intensity, due to the geology of the site. On the same time, dynamical tests on the survived buildings enlightened their dynamic characteristics and permitted the updating of the FE models used in the structural analysis. Linear and nonlinear models of the buildings have been developed, aiming to explain the different behavior. Even the use of simple linear models taking into account the contribution in stiffness of the infilled masonry walls permitted a coherent interpretation of observed phenomena. By using more accurate nonlinear finite elements models, it was possible to reconstruct the evolution of the seismic response and to obtain a more clear unfolding of the collapse mechanism. The key role of the infilled walls has been enlightened putting into evidence how a good construction of such non-structural elements could dramatically influence the global structural behaviour. Some laboratory tests on specimens of infill walls, extracted from the collapsed building, guided the selection of the mechanical parameters of the equivalent truss elements used in the models. With the second case-study we discuss a different, interesting and effective use of dynamical measures on damaged structures, when the same measures have been conducted in a not-damaged (or reference) condition. In this case, the dynamical tests could enlighten the stiffness reduction and can help to localize the occurred damage. With this purpose some test conducted in L’Aquila (Italy) after the 6 April 2009 earthquake on the r.c. Belvedere Bridge, will be discussed.

Description: Published

Description: 643-666

Description: 4T. Sismologia, geofisica e geologia per l'ingegneria sismica

Description: JCR Journal