The 20 – 29 May 2012 earthquake events occurred along Emilia Romagna segment of Po Plain valley (Pianura Padana), a NW – SE oriented basin along the Southern tectonic boundary of Adria plate, with Northern Apennines. Major earthquake sequence events’ focal mechanisms, evince the activation of low angle thrust structures, separating the earthquake activity on at least 2 distinct fault planes, with similar slip characteristics. Both planes seem to be on the same seismogenic source, on the Western part of 1570 events’ source, interpreting the delimitation of the seismic activity of the May – June 2012 earthquake sequence. Widely observed secondary effects were categorized with respect to spatial distribution, density and trend, to: i) individual liquefaction cases, ii)Strictly oriented liquefactions and lateral spreading due to exposure of unconformities to surfacial liquefaction-prone geological formations and iii)extended liquefactions of confined liquefiable formations (at a depth of≈10m) and lateral spreading along river strike. This depth resulted in less surfacial deformation and differential subsidence, as well as very limited structural damage. Only fences, pavements and other light weight structures have been heavily damaged, deformed and dislodged. The incurred structural damage is extremely heavy for the churches and the cultural heritage, as well as for the industrial infrastucture of the region, besides the death toll and injuries. The available strong motion records are not adequate in order to explain in a rational and reliable way the above mentioned heavy damage. Based on years’ experience in post earthquake investigations and on results of numerous full scale tests of structures on shaking tables, the authors concluded that the main reasons of the damage is the extremely high vertical ground shaking (of the order of 1.0 g) in combination with the moderate horizontal motions. Due to this very high value of the vertical ground shaking, impact phenomena are observed as well as total or partial loss of friction (due to the loss of gravitational forces).The incurred damage are grouped in general categories possessing similar characteristics. The majority of the observed damage of churches is mainly due to collapse of their roofing systems. This occurred due to resonance-like vertical vibration of the timber trusses of the roofs. This was proved by analysing representative dimensions of timber trusses with the overburden mass and, it was found that their fundamental periods are between 0.06 and 0.10 sec. On the other hand, a predominant period of the vertical component is, according to the recorded first event of 20th May 2012, 0.06 to 0.07 sec. Thus, intensive up and down motions are induced in the whole trusses and in their horizontal lower beams resulting in dislocations from their supports on the walls. On the other hand, it is well known that the arrival time between P (vertical) and S (horizontal) waves in epicentral regions is quite small. This resulted in a convolution between vertical and horizontal ground motions. The top of the walls, where are the supports of the trusses, were significantly displaced as free standing vertical cantilevers due to the loss of connection with the truss. In this way the trusses totally lost their supports and collapsed. In examining the debris one may guess what structure between the two (truss or wall) collapsed first. A proof of the dominance of the vertical component might be based, among others, on the response of bell towers that in the majority of the cases were not significantly damaged and on the fact that the mode of collapse is inside the ground plan of the building. Quite similar observations are also valid for the damaged industrial facilities. The natural vertical periods of the roofs are also, between 0.06 and 0.10 sec. The constructed supports are from functional point of view quite similar to those used for the support of the timber trusses in the churches (just simply supported cantilevers). Nevertheless, by using the conventional bolts in the supports, it is not certain whether or not the situation would be ameliorated. In order to prevent the effects of the high frequency impact type of the vertical ground motion a kind of absorbing elastomeric devices could be used in the supports of beams and trusses besides the conventional anchoring systems. Also, a kind of base isolation devices, that should not depend on friction at the base of the structures might be used. Finally, the partial collapse of the ceramic factory is attributed to the rhythmic phenomena of destruction. After the present communication was completed, it has just been released the important and technically very interesting vertical strong motion record of the second event, presenting a peak ground acceleration of the order of 0.9 g, a fact that comes in full agreement with the findings and arguments exposed in the present paper.
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ASSESSMENT OF THE MOST DAMAGED HISTORIC CENTRES OF THE REGION EMILIA ROMAGNA DUE TO THE EARTHQUAKE OF THE 20th AND 29th OF MAY 2012
The Emilia Romagna earthquake of the 20th of May 2012 has damaged some of the historic centres closer to the epicentre of this event. Aftershocks and a second earthquake on the 29th of May 2012 registered in the same region have caused around 30 dead people, 350 of injured people and several damage types to historic assets. In this paper the typical features of the residential constructions in the areas damaged by these earthquakes are introduced and the seismic vulnerability of the Comune of Cento is carried out by using the FaMIVE approach. The same area has also been surveyed by the Italian Civil Protection to assess the safety of the buildings with the aid of AeDES form. The damage scenario observed on site, the safety judgements conducted by AeDES and the forecasted vulnerability obtained by FaMIVE will be illustrated for some building clusters selected in the Comune of Centro.
SEISMIC DAMAGE ASSESSMENT OF SCHOOL BUILDINGS AFTER 2012 EMILIA ROMAGNA EARTHQUAKE
In the paper the usability checks performed on precast RC gyms and masonry school buildings, located in the Municipalities of San Pietro in Casale (BO), Bomporto (MO) and Bondeno (FE) after the seismic events occurred on 2012 May 20th and 29th, are reported and discussed.
First, the main features of surveyed buildings have been identified. Later on, on the basis of the detected damages, their seismic deficiencies have been recognized. Finally, the indication of some appropriate simple interventions for retrofitting studied buildings has been given.
THE SEISMIC BEHAVIOUR OF ANCIENT MASONRY BUILDINGS AFTER THE EARTHQUAKE IN EMILIA (ITALY) ON MAY 20TH AND 29TH, 2012
The seismic sequence that occurred in Emilia Region on May 2012 caused serious damage to specific building types (e.g. industrial sheds designed without any aseismic prescriptions) and cultural heritage buildings. The distinctive features of the seismic motion, recorded also very close to the epicentre, are a significant spectral displacement demand at long periods and a very high vertical component. These are very critical for structures characterized by long periods, as churches or bell tower, or for standing out elements, as pinnacles or battlements. The paper presents a preliminary damage assessment of traditional masonry constructions (both ordinary and monumental), made by solid brick masonry with lime mortar. Observed damage has been interpreted through simplified mechanical models, by using the displacement-based approach. It is worth noting that the behaviour of ordinary residential buildings was quite good, thanks to the good connection between masonry walls and the localization of cracks in the spandrels, which guaranteed high displacement capacity.
DAMAGES AND COLLAPSES IN INDUSTRIAL PRECAST BUILDINGS AFTER THE EMILIA EARTHQUAKE
The present paper describes the collapses in precast industrial buildings caused by the 2012 Emilia earthquake. This kind of buildings, not designed with seismic criteria, has been found very vulnerable for several reasons, such as the absence of connecting systems between the various precast monolithic elements, the inadequacy of connection systems of external precast walls to the bearing elements (columns and beams), the interaction between non-structural walls and structural elements, and the inadequacy of the foundations.
THE EMILIA-ROMAGNA EARTHQUAKE: DAMAGES TO PRECAST/PRESTRESSED REINFORCED CONCRETE FACTORIES
Immediately after the seismic event (started on May 20th, 2012) which struck the Padana Flat area between the municipalities of Ferrara, Modena, Reggio Emilia, Bologna (Emilia-Romagna Region), Mantova (Lombardia Region) and Rovigo (Veneto Region), an ENEA team of experts (Maurizio Indirli, Bruno Carpani, Elena Candigliota, Alessandra Gugliandolo, Francesco Immordino, Giuseppe Marghella, Anna Marzo, Giuseppe Nigliaccio, Alessandro Poggianti, Maria-Anna Segreto) supported the Italian Civil Defense, in order to perform prompt investigations regarding the safety evaluation of different typologies of structures (bridges, industrial factories, residential houses, etc.) made by various kinds of materials (masonry, reinforced concrete, precast/prestressed reinforced concrete, mixed). General information is given in several preliminary reports [among them, Decanini et al., 2012). In particular, this article is devoted to the behaviour analysis of precast/prestressed reinforced concrete (p/p. r.c.) construction, widely used in the affected area since the second half of the last century, trying to deepen some crucial aspects of the matter.
THE OCTOBER 23 (MW = 7.2) AND NOVEMBER 9 (MW = 5.7), 2011 VAN, TURKEY EARTHQUAKES. A GEOSCIENTIFIC AND ENGINEERING REPORT
On 23 October 2011 (13.41 LT) a disastrous earthquake with a magnitude of MW = 7.2 occurred in Van Province of eastern Turkey. That is the region where the Arabian Plate drifting towards north-northeast collides with the Eurasian Plate, while the other smaller plates in the region are moving apart as if pushed by the stronger Arabian. As a result, the seismic history of the region is quite rich usually resulting in severe losses. The death toll due to the main shock reached 604 people and injured 4,152, with at least 188 pulled out of the rubble of collapsed buildings. The most heavily damaged Ercis city was at a distance of 35-40 km to the north of the causative fault. The city of Van suffered much less damage, being to the south of the fault at a distance of 25-30 km. The damage was concentrated mainly in the old city centers of both cities. On the 9th of November 2011 (21.23 LT) a strike slip earthquake of MW = 5.7 occurred very close to the city center of Van, associated with a different fault. Due to this shock, an additional number of 40 people were killed and 260 injured, while the Bayram Hotel, in Van city, where the authors stayed from 25 to 29 October 2011, collapsed. The hotel building was visually inspected by the first author following a widely accepted methodology and it was considered to be earthquake safe. The available cross-checked information concerning the mechanism of the hotel’s collapse is, at first glance, contradicted by the strong motion records presented in the paper. Unfortunately, during the main shock in both Van and Ercis cities, there were no strong motion recordings. In order to infer some basic characteristics of the ground motion due to the main shock, strong motion records from an aftershock, occurring in the same focal volume with that of the main shock, were used. Observations of the response of structures immediately after the main shock were carried out by the authors during their reconnaissance trip and led towards the same goal. The heaviest damage was observed to engineered reinforced concrete buildings. There are some cases of modern and even recently built, multistoried buildings with rather good reinforcement detailing that suffered extended damage or even collapse. On the contrary, nearby non-engineered, low-rise simple or traditional masonry houses, weathered the earthquake in the epicentral region almost without any damage. Most of the reinforced concrete structures are quite flexible, without shear walls, and used a flat-slab constructional system of rather small thickness compared to their spans. In spite of those characteristics justifying high flexibility, no noticeable horizontal motion or pounding was observed between adjacent buildings. For this reason it was thought helpful to present a critical evaluation of the published Turkish seismic building codes since 1940. A crucial subject directly related to the incurred damage and discussed by the authors is the widespread practice of building construction in the region that it is not according to the Turkish earthquake code requirements. It is shown that due to the main shock the numerous and heavy losses in Ercis city were due to the dominance of a severe vertical seismic component, while those in Van city due to resonance phenomena caused by the relatively weak horizontal ground motion. The losses due to the event of 9th November in Van city are attributed to the catalytic function of the vertical seismic component. The resulting collapse is usually quite abrupt and does not allow occupants time to egress safely.
The complete Issue 1, 2012 could be downloaded from the home page.
RELIABILITY OF CODE-PROPOSED MODELS FOR ASSESSMENT OF MASONRY ELASTIC MODULI
SUMMARY – In this paper the results of an experimental investigation aimed to the assessment of Young moduli, rigidity moduli and other mechanical properties for different types of masonry are shown.The mechanical characteristics predicted by models proposed by some technical codes were compared against experimental data.This study was motivated by the suggestion of the Masonry Standards Joint Committee’s (MSJC) code that, while proposing the use of such models, acknowledges the lack of testing in support of their validation. The experimental investigation has included compressive tests on components (blocks and mortar), diagonal compressive tests and ordinary compressive tests (orthogonally to beds joints) on portions of masonry. The details of the experimental campaign and the prediction capacity of the above models, for the types of masonry investigated, are presented.
The complete Issue 1, 2012 could be downloaded from the home page.