Emilia Earthquake Research Articles

InSAR Analysis of Post-Liquefaction Consolidation Subsidence after 2012 Emilia Earthquake Sequence (Italy)

InSAR Analysis of Post-Liquefaction Consolidation Subsidence after 2012 Emilia Earthquake Sequence (Italy)

Monitorare per conservare: il caso della Torre Ghirlandina di Modena

The monumental complex consisting of the cathedral, tower and main square of Modena (Northern Italy) has been a UNESCO World Heritage Site since 1997. The visible tilting of the Ghirlandina tower has always generated concerns for its preservation, even more after the recent seismic events. This paper highlights the role of structural monitoring for the conservation of the site, with particular reference to the data acquired during the recent Emilia earthquakes. Unexpectedly, the inclination of this leaning tower decreased after the major seismic event. Some considerations are presented regarding the difficulty of modelling this kind of effects on buildings with complex historical stratifications and the application of the observational method, derived from geotechnical engineering, is proposed. The importance of structural monitoring is once again recalled, in order to preserve world heritage and comply with the principle of minimum intervention.

SISMO-Fast: energy-based method for rapid seismic vulnerability assessment of industrial precast RC buildings

Single-storey precast RC buildings not originally designed to withstand seismic actions showed their vulnerability during the Emilia Earthquake events (2012). The legislation that followed this catastrophic event has highlighted the need to assess and raise their seismic performance, even if interventions are limited to the connections between structural elements. The need to evaluate the conditions of existing buildings and to compare the effectiveness of risk mitigation interventions has highlighted the importance to have rapid assessment tools to check seismic vulnerability. The procedure proposed below begins by considering a simplified energy approach and allows the quantification of the seismic vulnerability of a precast RC building using few significant parameters.The proposal, for this specific type of building, works by comparing the characteristics of a new structure, assumed to be like the one to be assessed and designed for the seismic action of the specific site, to the existing structure to be assessed. The seismic vulnerability is subsequently defined in terms of the percentage of deviation of the real structure from the ideal one. The quantification of the percentage of deviation, based on macro-parameters, is estimated in terms of the capacity to absorb and resist the seismic input, described through energy. The SISMO-Fast method is based on the evidence of damage mechanisms observed during the site survey performed after the 2012 Emilia earthquake and other recent seismic events. The procedure has been used, for rapid seismic vulnerability assessment of some industrial precast RC buildings in different seismic areas, providing always reliable results.

Observational loss database of typological precast RC buildings damaged after the 2012 Emilia Earthquake

The Emilia Earthquake occurred in 2012 in a highly industrialized area, characterized by the presence of about one firm every 9 inhabitants. The industrial heart of the region hosts many important clusters, from the Motor Valley to Food, Wellbeing, Fashion and Health devices. The main activities are conducted in production districts with several different long-span buildings like storages, deposits, warehouses, factories and silos. Among these, those made of precast reinforced-concrete (RC) elements were heavily damaged by the seismic sequence, resulting in a huge amount of economic losses due to damage to structures, products and machineries, business interruption and casualties. In the aftermath of the earthquake, the Region defined the criteria for the request of funds for the reconstruction of the buildings, the restoration of the products, the reparation of the equipment, and the temporary relocation of the activities. Thus, a large number of documents was collected reporting a variety of information concerning the seismic damage, the structural properties of the buildings, and the economic costs.In this work, through a process of progressive selection and refinement of the data, a database of seismic economic losses of damaged precast RC buildings was created. The main principles for the creation of the repository and the categorization of the information are illustrated. Hence, the losses were statistically analysed to derive useful consequence functions based on the investigation of diversified trends of the repair costs at different damage levels. The outcomes presented in this study may be adopted to perform loss assessment evaluations to guide the decision-makers in establishing priorities of structural interventions to reduce the consequences of future earthquakes in industrial areas.

Seismic damage and loss evaluation in precast industrial buildings through low-cost accelerometers

Past seismic events, in particular the Emilia earthquake (2012), showed how the damage caused in highly industrialized areas could cause serious problems with large-scale economic effects. It is interesting to highlight how these effects are both immediate, due to the seismic vulnerability of old precast industrial buildings, and in the long term since the restoration operations are typically long due to the difficulty of assessing the real structural health state, particularly for the difficulty in reaching and inspecting components sensitive to damage, such as the connections. This work has the objective of finding a procedure, through relatively low-cost MEMS accelerometers, which allows to record and process the seismic accelerations experienced by the various structural elements. The paper considers the application of a procedure that allows identifying the state of health of the system through the application of damage indexes found in the literature and a first estimate of costs and recovery times to bring the building back to its pre-earthquake conditions. The procedure has been applied to a selected case study

TH Analyses and Simplified Approach for Precast RC Frames Retrofit with Dissipative Fuse Devices Sismocell

Precast RC structures are a typology of construction widely spread in Italy among industrial buildings, made of single-storey isostatic RC frames built, in past decades, without any connection between beams and columns. The Emilia Earthquake (2012) caused extensive damages in this kind of buildings that have a significant mass located at roof level and lack of connections between horizontal and vertical elements. The recent seismic events highlighted that the lack of connections is the main vulnerability of existing precast RC buildings and at the same time that large displacements are determined between beams and columns. In order to improve the seismic performance of precast RC buildings a cost-effective solution is to dissipate energy at roof level, avoiding at the same time any loss of support between elements. Dissipative fuse devices (Sismocell) placed at beam-column joints are able to dissipate energy and guarantee an effective connection between elements. To evaluate the improvement achieved with the use of Sismocell devices, non-linear time history analyses are usually performed, taking into account the plastic hinges at column base. This work aims to quantify the improvement that can be obtained using Sismocell devices, in terms of reduction of effect of actions in different typologies of structures, remaining in the range of elastic behavior of materials. The TH analyses have been performed on different frame configurations with different seismic input, comparing the behavior of models with hinged connections and connections equipped with dissipative fuse devices. In order to define the optimal force of plastic activation of Sismocell devices, different device sizes have been considered. The results have been analyzed in terms of reductions of shear and moment at base of the columns, with different scaling factor applied to seismic input. Finally, a proposal of a simplified approach based on linear analyses has been compared to TH results.

3D numerical characterization of a dissipative connection system for retrofit of prefabricated existing RC sheds

Prefabricated industrial sheds featured a high seismic vulnerability during the 2012 Emilia earthquake (Italy). The buildings typically exhibited a rigid collapse mechanism that was a consequence of the loss of support between columns, beams and roof elements.The study presents a numerical characterization of a novel dissipative connection system (DCS) designed to improve the seismic performance of industrial sheds. The device, which is placed on the top of the columns, exploits the movement of a rigid body on a sloped surface to provide horizontal stiffness and control the lateral displacement of the beam.A 3D finite element model of the prototype is formulated in Abaqus and used to switch the backbone curve from the scaled model to the full-scale device. A parametric study is conducted to evaluate the influence of the slope of the contact surface and the coefficient of friction on the output force of the system.In the second part of the study, non-linear dynamic analyses are performed on a finite element model of a portal frame implementing, at beam-column joints, either the DCS or a pure friction connection. The results highlight the effectiveness of the DCS in controlling beam-to-column displacements, reducing shear forces on the top of columns, and limiting residual displacements that can accrue during ground motion sequences.

Collapse mechanisms of churches: typical recurrence rates and damage levels from the analysis of field data after the 2012 Emilia earthquake

Within the context of fast procedures for the evaluation of seismic damage, an interesting tool is given by the special form in use for churches. The procedure implemented in this form is based on the set of 28 local collapse mechanisms which have been identified as meaningful to deal with the typical Italian configuration of churches; for each mechanism, a damage level from 0 to 5 has to be specified and a global damage index is therefore computed. An interesting application of the above procedure has been possible for a wide group of churches in the province of Mantua, which suffered damage from the 2012 Emilia earthquake. Specifically, it has been possible to access data and analyze 159 forms. Through a detailed analysis of them, it has been possible to define, for each different collapse mechanism, the recurrence rate and the corresponding distribution of damage levels. In this way, it clearly appears, on the one side, which mechanisms are likely to be activated and, on the other side, in which cases high damage levels can be easily reached. This kind of analysis has resulted into a clear picture of the architectural typologies and construction techniques in use in the region; moreover, suggestions have come in terms of seismic prevention, as clear evidence has been given to the damage mechanisms which are more likely to be activated.

Combining SH- and P-wave seismic reflection survey to support seismic response analysis. A case study from Cavezzo (Italy) after the 2012 Emilia earthquake

In some geological settings, such as thick sedimentary basins, the deeper layers may also significantly contribute to the amplification of the ground motion during an earthquake, particularly at low frequencies. To properly quantify the influence of the deeper geology on the seismic ground motion at the surface, the use of indirect geophysical exploration techniques is particularly suitable, as it can produce realistic representations of the subsoil structure over a large range of depths. This paper focuses on the acquisition and processing of combined shear- (S) and compressional-wave (P) seismic reflection data to obtain an accurate geological/geophysical model with reliable seismic velocities for local-scale seismic site response studies, as needed for hazard assessment and calculation of earthquake scenarios. As an application case, we focus on a microzonation study performed for the Cavezzo municipality in Northern Italy. The investigated site is located in the epicentral area of the 2012 Emilia earthquake in the Po Valley, which is a typical deep sediment-filled basin. Specifically, in this study we were able to: (1) confirm the advantages of reflection seismic prospecting for soft-sediment basin characterization; (2) evaluate the resolution of S- and P-wave signals and their depth of penetration; (3) improve the knowledge on the geological structure of the Cavezzo area by measuring S- and P-wave interval velocities in Plio-Quaternary formations.

Post‐earthquake estimates of different ground motion intensity measures for the 2012 Emilia earthquake

AbstractEstimates of the earthquake ground motion intensity over a geographical area have multiple uses, that is, emergency management, civil protection and seismic fragility assessment. In particular, with reference to fragility assessment, it is of interest to have estimates of the values of different ground‐motion intensity measures in order to correlate them with the observed damage. To this purpose, the present paper uses a procedure recently proposed in the literature to estimate the ground‐motion intensity for the 2012 Emilia mainshocks, considering different ground motion intensity measures and directionality effects. Ground motion prediction equations based on different site effect models, and spatial correlation models are calibrated for the Emilia earthquakes. The paper discusses the accuracy of the shakemaps obtained using the different soil effect models considered and presents the obtained shakemaps as supplementary material. The procedure presented in the paper is aimed at providing ground motion intensity values for seismic fragility assessment and is not intended as a tool to estimate shakemaps for rapid emergency assessment.

Large-scale seismic damage scenario assessment of precast buildings after the May 2012 Emilia earthquake

AbstractIn May 2012, two strong earthquakes hit the northern Italy revealing the significant seismic vulnerability of precast reinforced concrete structures and causing severe damage and many collapses, and high economic losses. After the lesson learnt from these events, more reliable seismic design criteria have been established for the design of new structures and different approaches have been proposed for the seismic assessment of the existing structures. In this context, the paper presents the results of a first application of the PRESSAFE-disp method, recently proposed by the authors, allowing to define the fragility curves of precast RC buildings at various limit states, including collapse. A stock of 91 precast buildings in the industrial area of San Felice sul Panaro (Modena) was selected as a benchmark case study to verify the reliability of the method in assessing seismic damage scenarios. In particular, with reference to the 2012 seismic ground-motion, two large-scale stochastic models are outlined to predict the number of the buildings collapsed in the area. The first one is based on a Monte Carlo simulation which incorporates the evaluation of the uncertainties, while the second one is a direct simplified calculation. Comparative considerations on the outcomes of the two methods for different seismic intensities are discussed, including the directionality effect of the ground-motion. To test the soundness of the simulations, the results of the two methods are compared with the real data collected through in-situ surveys. The procedures proposed here result, on average, in good agreement with the observed damage scenario. It is worth noting that, due to the inherent simplicity of the methods, they could be implemented to perform scenario-based seismic loss assessments to estimate the financial consequences of an earthquake affecting one or more industrial areas, and to drive the decision-making process for the seismic retrofit of existing precast RC buildings.

Latest findings on the behaviour factor q for the seismic design of URM buildings

Recent earthquakes as the 2012 Emilia earthquake sequence showed that recently built unreinforced masonry (URM) buildings behaved much better than expected and sustained, despite the maximum PGA values ranged between 0.20–0.30 g, either minor damage or structural damage that is deemed repairable. Especially low-rise residential and commercial masonry buildings with a code-conforming seismic design and detailing behaved in general very well without substantial damages. The low damage grades of modern masonry buildings that was observed during this earthquake series highlighted again that codified design procedures based on linear analysis can be rather conservative. Although advances in simulation tools make nonlinear calculation methods more readily accessible to designers, linear analyses will still be the standard design method for years to come. The present paper aims to improve the linear seismic design method by providing a proper definition of the q-factor of URM buildings. These q-factors are derived for low-rise URM buildings with rigid diaphragms which represent recent construction practise in low to moderate seismic areas of Italy and Germany. The behaviour factor components for deformation and energy dissipation capacity and for overstrength due to the redistribution of forces are derived by means of pushover analyses. Furthermore, considerations on the behaviour factor component due to other sources of overstrength in masonry buildings are presented. As a result of the investigations, rationally based values of the behaviour factor q to be used in linear analyses in the range of 2.0–3.0 are proposed.

Liquefied sites of the 2012 Emilia earthquake: a comprehensive database of the geological and geotechnical features (Quaternary alluvial Po plain, Italy)

This paper presents a comprehensive geological and geotechnical study of the whole area affected by liquefaction following the 2012 Emilia earthquakes, including all the available information from the field reconnaissance surveys, in situ tests, and laboratory analyses. The compilation was performed at 120 liquefied sites to verify and validate the reliability of liquefaction charts in alluvial sediments, and to assess liquefaction induced by the 2012 seismic sequence in the Emilia plain. The results reveal a wide range of grain sizes (from clean sands to sandy silts) and compositional characteristics (quartz-rich to litharenitic) in the 2012 ejecta, and show a strong relationship between the liquefaction and stratigraphic architecture of the subsurface. The availability of in situ tests at the liquefied sites makes it possible to verify and validate the reliability of the liquefaction charts in alluvial sediments with respect to the real observations. For the analyzed Emilia case studies, the use of non-liquefiable crust provides better estimations of the liquefaction manifestations when coupled with the thickness of the liquefiable layer rather than with the liquefaction potential index. Altogether, this work makes available to the international scientific community a consistent liquefaction database for in-depth earthquake studies.

PRESSAFE-disp: a method for the fast in-plane seismic assessment of existing precast RC buildings after the Emilia earthquake of May 2012

The existing precast reinforced concrete structures not specifically designed against earthquakes have proved to be very sensitive to seismic demands. After the lesson learnt from the Emilia earthquake of May 2012, causing many collapses and severe damage, reliable seismic design criteria have been established for the design of new precast structures and for the strengthening of the existing ones. Despite this, a large percentage of the existing precast buildings in the Italian territories actually has not been object of interventions and remains in an unsafe condition with regard to the seismic actions. In this context, the methods for a rapid seismic assessment can be very helpful both to estimate the current safety level of large building stocks and to plan the necessary strengthening interventions, possibly at the large scale of an industrial area. To this aim, the paper proposes the PRESSAFE-disp (PRecast Existing Structure Seismic Assessment by Fast Evaluation-displacements) method, useful for the fast evaluation of the fragility curves of precast structures. The damage criteria, applicable both to structural elements and non-structural cladding elements on the perimeter, have been selected in order to capture the damage mechanisms observed during the building inspections conducted by the authors in the aftermath of the 2012 Emilia earthquakes. The method allows a comprehensive explanation of the seismic in-plane behaviour of existing precast RC buildings and could be effectively adopted, for example, in earthquake loss estimations and seismic risk assessments of large Italian industrial areas, as well as of wide seismic-prone territories of the Mediterranean area.

An inter-disciplinary/multi-step approach in defining the input motion for the seismic analysis of masonry buildings struck by the May 29, 2012 M6.0 Emilia earthquake in Northern Italy

Numerical simulations of earthquake damage on buildings require the definition of a reliable and appropriate seismic input (e.g., acceleration time histories and/or response spectra) in order to validate the accuracy of structural models in reproducing the observed level of damage – or no damage – associated with a particular earthquake. However, for sites that are not located close to active seismic stations, the definition of the ground motion that would have likely been recorded during an earthquake is not a trivial task.In this paper, we present the results of a case study where the seismic input at the sites of construction of three modern unreinforced masonry buildings caused by the Emilia May 29, 2012 M6.0 earthquake has been recreated following three different methods involving natural, artificial, and deconvolved accelerograms. The differences in the results are compared and contrasted highlighting the intrinsic limitations of the three different approaches while addressing an appropriate use of the seismic input when assessing the seismic performance of the three buildings.

Pullout tests on the connection to an existing foundation of a steel warehouse rebuilt after the 2012 Emilia (Italy) earthquakes

The tests described in this paper were aimed at evaluating the tensile capacity of the anchorages connecting an automated pallet warehouse with an existing RC foundation. The warehouse is a new steel structure erected in the place of a previous warehouse collapsed due to the Emilia earthquake, but whose foundation remained undamaged. The investigated fastening consists of 10 post-installed, bonded threaded rods with diameter (d) and embedment depth (hef) of 20 and 500 mm, respectively. Neither anchor arrangement nor embedment depth (hef > 20d) was covered by current standards for fastening design. To reproduce the in-situ actual conditions of the fastening, an unconfined test configuration was used. The maximum loads achieved were more than 3 times greater than the seismic demand for the fastening. The tests highlighted the crucial role played by the reinforcing steel which was present in the foundation. Concrete-related failure mechanisms, such as the combined pullout and concrete cone failure mechanism typical of bonded anchors, were not activated. The observed crack patterns rather suggest the onset of a flexural failure mechanism of the concrete slab. This feature is confirmed by analytical calculations showing that, at the maximum loads achieved in the tests, the top reinforcement was likely to be yielded. In six preliminary unconfined tension tests on single anchors, steel rod failure was achieved, associated with limited cracking of the concrete surface in proximity of the anchor.

Crescent-Moon Beam-To-Column Connection for Precast Industrial Buildings

The 2012 Emilia earthquakes caused significant damage to existing precast reinforced concrete (RC) industrial buildings not specifically designed to resist seismic actions. The main failure mechanisms were related to the loss of support of beams and roof elements caused by high relative displacements, to the failure of the mechanical connections and consequent fall of cladding panels, to the damage at the base of the columns and to the collapse of RC forks at the top of the columns. In all cases, the behavior of the connections, and specifically of beam-to-column connections, demonstrated to be crucial, given that they may inhibit the exploitation of strength and ductility reserves in precast elements. This paper presents a beam-to-column connection restraint-device for precast industrial buildings. The device can be applied to existing structures to transfer horizontal seismic forces between beams and columns and to increase the energy dissipation of the system. Design criteria were defined with the aim to limit the relative maximum displacement at the beam-to-column interface and to mitigate the out-of-plane overturning of the beam. Numerical analyses were carried out to define a suitable shape of the device and to investigate its effectiveness in terms of both local and global behavior. To validate the computational results, experimental tests have been also carried out. The tests allowed to classify the device as “dissipative” according to UNI EN 15129. Finally, the design procedure has been validated considering a one-story industrial building case study designed in accordance with the Italian building code.

HVSR analysis of a layered saturated half-space using diffuse-field theory

SUMMARYThe recently constructed diffuse field theory from isotropic energy equipartition has been well developed in elasticity for full-wave interpretation of horizontal-to-vertical ratio (HVSR), which links the signal autocorrelation with the imaginary part of Green's function. Here, the theory is extended to the saturated layered medium within the framework of Biot's theory to account for the offshore environment. The imaginary parts of Green's functions are obtained using direct stiffness method accompanied with Fourier–Hankel transform. In particular, the upgoing wave amplitudes are modified to tackle the overflow during wavenumber integral and allow for fast calculations. After validating the method from the perspectives of Green's function calculation, emphasis is laid on evaluating the inaccuracies of HVSR calculation induced by model misuses in the lack of prior geological and geotechnical information. The numerical results considering the effects of layer sequence, impedance ratio, porosity and drainage condition show that the predominant frequency of the one-phase medium is slightly less than the two-phase medium with the maximum shift no more than 0.1 Hz, while their amplitude differences can be prominent as impedance ratio and porosity increase, with the maximum difference up to 29 per cent. The shallowest soft layer has the dominant effects on HVSR amplitudes, whereas the buried low-velocity layer at depth over one-wavelength contributes little to the peak amplitude. Finally, the method is applied to a realistic case at Mirandola, Northorn Italy, which suffered extensive liquefaction-induced damages in 2012 Emilia earthquake. The well identified pattern of the experimental HVSR using the two-phase medium model illustrates the application potential of our method to further assist the subsurface geology retrieval.

Seismic Retrofitting Solutions for Precast RC Industrial Buildings Struck by the 2012 Earthquakes in Northern Italy

In 2012, the North of Italy was hit by a seismic sequence characterized by two main events occurred on May 20 and 29 with MW = 6.1 and 6.0, respectively. Those earthquakes were particularly severe toward precast Reinforced Concrete (RC) structures not designed for seismic resistance. In the past years, the authors implemented a database collecting damage data and typological information on the industrial buildings struck by the Emilia earthquakes. That database was used to develop empirical fragility curves, which highlighted the considerable vulnerability of precast buildings conceived in accordance with pre-seismic code provisions. More recently, the interventions of seismic retrofitting on the same buildings, funded by the Emilia-Romagna region and designed by engineers which were directly hired by the companies, were examined in detail and critically revisited. A selection of these interventions is presented in this paper, which analyzes the effectiveness of the various retrofitting solutions, with a specific attention to the force transfer mechanisms between existing structures and strengthening systems. The interventions are divided between column strengthening (based, for example, on RC or steel jacketing) and interventions aimed at providing the building with a suitable earthquake resistant system (based, for example, on either the use of the existing cladding panels or the implementation of new bracing systems). Graphical representations of the analyzed solutions with the relevant construction details are provided.

Empirical damage and liquefaction fragility curves from 2012 Emilia earthquake data

The study focuses on the effects of liquefaction on structures taken from data on about 1000 private residential masonry buildings located in several municipalities struck by the 2012 Emilia earthquake. Survey data were collected by teams of experts coordinated by the Italian Department of Civil Protection in the immediate post-earthquake emergency phase. They included information on building characteristics and the level and extent of the damage to structural and non-structural components. Furthermore, according to data related to the reconstruction process, information on the liquefaction-induced type and extent of the damage was also collected. Through a comparative analysis of the empirical damage, it was found that liquefaction strongly affected the buildings, confirming its relevance in the damage scenario under specific subsoil conditions. Based on this evidence, the article proposes a correlation between structural damage and liquefaction when it comes to deriving proper preliminary empirical fragility curves. A suitable parameter to define liquefaction effects at ground level is introduced and correlated to damage grades defined according to the European Macroseismic Scale: EMS-98.