The L’Aquila earthquake struck at 03.32 local time on the 6th of April 2009. The early response task force for the emergency was set up and managed by the Civil Protection, with the Executive committee established by 4.15 a.m. The DI.COMA.C. (Direction of Command and Control), the coordinating body set up by the Civil Protection Department, was set up at 9 a.m. in the national training centre of Italy’s financial police force (Guardia di Finanze) in Coppito, near L’Aquila. The National Fire Brigades took a leading role in the emergency response, contributing to search and rescue, evacuation of the historic centre of L’Aquila and were later involved in safety interventions on damaged residential structures and historic churches. The Civil Protection also assisted the population with shelter, hospitalization and first aid. They also carried out field surveys to assess the damage to buildings, cultural heritage and infrastructure, and gathered information for a detailed macroseismic intensity assessment. The activities carried out by the Civil Protection are reported to have cost around €456 million (DPC 2010a).
Damage assessment
The Civil Protection emergency team (DI.COMA.C.) coordinated the post-earthquake building damage assessment. Damage assessments were made at a dwelling, rather than building, level. A total of 76,600 inspections on private dwellings and 2,600 on public units were carried out, with peaks of 1,500 dwelling surveys/day (DPC 2010b). This was made possible thanks to volunteers affiliated with universities, local municipalities, industry, the National Research Centre (CNR), and national and local sections of professional institutions (engineers, architects, etc). The first level survey form for post-earthquake damage and usability assessment, AeDES, was adopted to classify each building according to its damage and useability, following the methodology proposed by Baggio et al. (2007). This form is designed for the survey of ordinary buildings used for habitation and/or services. Therefore, the use of this form for the assessment of buildings with particular structural typologies (industrial warehouses, sport structures, theatres, churches, etc.) is excluded. The form allows for a quick survey and a first identification of the building stock, with the collection of metrical and typological data of the buildings.
Tables 1 and 2 summarize the outcome of the usability and damage assessment, at the date of March 2010, when 5,000 engineers and technicians completed the survey on 73,521 dwellings. Although the AeDES forms are not designed for the assessment of cultural heritage buildings, it is observed in Table 1 that they have been used to assess some such structures, and these are likely to be included within the “masonry” and “mixed type” categories of Table 2.
Table 1 Usability assessment of 73,521 damaged dwellings in March 2010 (www.protezionecivile.it)
Table 2 Outcome of the usability and damage assessment in function of the structural type (www.reluis.it)
It is important to note that the AeDES classification of usability was used by the Government to obtain a first evaluation of the earthquake losses and apportion the economic resources for repair and reconstruction. They were also used to guide the amount of resources building owners are entitled to for repair and reconstruction (see Sect. 4).
Disposal of rubble
In the aftermath of the earthquake, the problem of demolition and rubble management arose. Preliminary calculations showed a total rubble volume ranging from 1.5 to 3 million cubic metres were to be dealt with (DPC 2010b). The Italian environmental code (D. Lgs. 152/2006) follows European regulations and is very clear on the fact that soil and demolition material are considered as rubble and should be appropriately disposed of, but it was unclear how the environmental code should be applied in an emergency situation.
Given the amount of material and the substantial difficulty in assessing qualitatively the composition of rubble, the Government promulgated a brand new regulation on the subject (OPCM 3767, OPCM 3771, OPCM 3782, OPCM 3797, OPCM 3813, OPCM 3817), such that during the reconstruction, rubble can be identified and classified as:
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1.
Rubble of a building damaged or collapsed during the 6th April earthquake, or demolished afterwards for safety reasons.
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2.
Rubble originating from the retrofit and/or reconstruction of private buildings (“B”, “C” or “E” damage category)
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3.
Rubble originating from small retrofitting works on private buildings (“A” damage class)
To date, 746,418 tons of rubble have been brought to disposal, with more of the 50 % of this during the year 2012 (www.commissarioperlaricostruzione.it). A very efficient and relatively cheap control system was set up to track the rubble chain from site to disposal. Rubble is classified as hazardous or not, based on its nature, identified as suitable for reuse where possible and treated to obtain aggregates for reconstruction or else appropriately disposed of in case of contamination or lack of suitability.
Shoring of structures
Following the earthquake there was an immediate need to ensure the safety of buildings. Hence, an extensive program of shoring works was deployed to stabilize buildings in AeDES classes “B”, “C” or “E”, while decision on their repair or demolition were taken. This was particularly important in the historic centre of L’Aquila in order to safeguard cultural heritage from further damage caused by aftershocks. These safety interventions were carried out by the Civil Protection with the support of the Ministry of Cultural heritage, Universities and Fire Brigades teams.
Temporary works after an earthquake are mainly an engineering issue, which needs to be solved at two different scales (Grimaz 2011): at an urban level and at the single building level. At urban level, the historic centre is the heart of the community, housing strategic, commercial, governmental and social functions that need to be restored in the least possible time. Route access to and safe use of the buildings that house such functions need to be guaranteed, by clearing debris and by stabilizing adjacent damaged structures. At the single building level delayed collapse of the building through potential mechanisms activated by aftershocks needs to be avoided.
The most extensive post-earthquake deployment of temporary works in L’Aquila are shoring structures, since overturning of masonry facades (or parts thereof) is the most commonly observed failure mechanism (Modena et al. 2010). Safety interventions for this failure mode are seen to involve traditional wooden or steel truss systems (Fig. 1). The struts and ties form a buttress that prevents the overturning of the entire façade. The trusses are connected transversally and braced to prevent buckling and create a spatial truss. The possible effect of hammering between the facade and the shoring system, which may be triggered by aftershocks, is prevented by anchoring the top of the propping system to the wall, and the base to the foundation of the wall or to an independent system able of resisting the seismic load. A second system, made of vertical steel posts and horizontal ties is used extensively when floor structures have detached from facades and these show a crack pattern consistent with in-plane failure. Variations on this system comprise horizontally laid wooden planks, polyester straps or steel cables which wrap around the building with the aims of confining the masonry of the façade and of anchoring it to orthogonal walls (Fig. 2). The example in Fig. 2a is more appropriate when the connection between adjacent facades needs securing or when a combined mechanism causing out-of-plane failure of the façade and in-plane failure of its orthogonal walls is present. The steel cable system shown in Fig. 2b is suitable for restoring the box behaviour of buildings with corner failures. In cases where the causes of failure are likely to comprise both in-plane and out-of-plane failures, a combination of the two shoring systems is required (Modena et al. 2010).
The types of system used for shoring depend not only on the type of the developed/potential mechanism, but also on the location of the building, its connection to adjacent buildings and their state of damage, the outer space available and the ease of access. An alternative shoring system to the traditional one, shown in Fig. 3, was observed for buildings belonging to building aggregates, which exhibited out-of-plane failure of a façade facing onto a narrow street. This system comprises a series of vertical composite posts connected transversally at every metre or so depending on the geometry of the façade, and is contrasted to a paired system on the other side of the street. Both are independently anchored to the ground. This intervention also prevents overturning of opposite façades facing onto the same street and guarantees access by creating a safe passageway. Finally, propping systems made of wooden struts are often applied to openings and support horizontal structures in order to make them reasonably safe for recovery interventions.
Many of these shoring systems, implemented in 2010, are still in place at the time of writing, as relatively few interventions of repair and restoration have taken place in the historic centre of L’Aquila, although activity was re-started at the end of 2012. Indeed in the document “Raccomandazioni per la realizzazione delle opere provvisionali”, annex B to the DI.CO.MAC prot no 8033 of 05/05/2009 (www.protezionecivile.it), it is explicitly stated that, based on previous reconstruction experiences in Italy, the shoring should be implemented with materials that are not greatly affected by weathering. It proceeds to recommend that steel components be used. One of the issues that remain open in any of the provisions inspected, especially the ones with post-tensioned elements, either plastic or steel, is how effective they currently are after having been in place four years. It was not possible to assess this in the short timeframe of the EEFIT mission, however, it is expected that the effectiveness of these interventions will degrade if they are not regularly inspected and maintained, and eventually re-tensioned.
Shoring of existing structures was almost exclusively used for masonry structures, with very few observations of reinforced concrete buildings. It is considered that the primary reason for this relates to the number, vulnerability and historical significance of the masonry structures viewed. However, a secondary explanation relates to the inherent residual strength of reinforced concrete structures that are stable in the temporary condition but require retrofit to return them to full service. It should also be noted that severely damaged reinforced concrete structures had either collapsed or been demolished at the time of the EEFIT return mission.
An example of where a reinforced concrete structure had been temporarily shored, is shown in Fig. 4, where ground floor bays of the structure were propped with back-to-back steel channel cross bracing. In this instance the building has susceptibility to a ‘soft storey’ collapse that is mitigated by the shoring system selected.
Microzonation studies
The variability of the damage distribution in the Aterno valley has been widely associated with site effects (both soil and topographic amplification) highlighting the need for a rigorous microzonation study. Microzonation studies are essential to first flag areas vulnerable to site effects and then to quantify potential amplification of the ground motion (ideally for various hazard levels), which in turn is important for urban planning, post-earthquake reconstruction and rigorous structural design.
An extensive geotechnical investigation was conducted after the earthquake at sites in the historic city centre and suburban area of L’Aquila in order to obtain input data for site seismic response analyses to support the design of repair and strengthening measures for important public buildings. In particular, Amoroso et al. (2011) present a review of results obtained by seismic dilatometer tests (SDTM) executed in the area of L’Aquila between 2009 and 2011. Some of these tests were carried out in the first months following the earthquake, as part of investigations planned for the geotechnical characterization of sites selected for the construction of new temporary houses (C.A.S.E. Project, see Sect. 5.1). SDMT results have also been used, together with down-hole, surface wave (MASW) and refraction microtremor (ReMi) tests, in the seismic microzonation project of the area of L’Aquila promoted by the Italian Department of Civil Protection (MS-AQ Working Group 2010). In addition, four deep boreholes (from 100 to 300 m below ground surface) have been performed in the historic centre of L’Aquila during the period between June and August 2010 to detail the geological setting of the city subsoil and give specific indications regarding the depth of the bedrock (Amoroso et al. 2010).
The SDMT test procedure consists of the combination of the mechanical flat dilatometer (DMT) with an add-on seismic module for measuring the shear wave velocity \(\hbox {V}_\mathrm{S}\) of soil deposits. It was observed to be an effective, quick and cost-saving alternative to conventional Down-Hole tests in soft to firm soils (e.g. Mayne and Schneider 1999). A disadvantage of the SDMT is the impossibility of penetrating very hard soils. However, a new procedure for obtaining SDMT \(\hbox {V}_\mathrm{S}\) profiles in non-penetrable soils (e.g. in gravel or even in rock) was developed by Totani et al. (2009) using boreholes backfilled with sand. This new technique has been extensively used at several sites in the historic centre of L’Aquila (i.e. Piazza del Teatro, Palazzo Camponeschi, Palazzo Carli, Fontana 99 Cannelle) and in the suburban areas (i.e. Cese di Preturo, Pianola, Roio Piano, Santa Rufina, Ponte Rasarolo on the Aterno River), characterized by the presence of mostly coarse-grained non-penetrable soils. In most of the above sites the maximum test depth has been 16–23 m, while in some cases the backfilling procedure permitted \(\hbox {V}_\mathrm{S}\) measurements to be obtained by SDMT down to very large depths (i.e. Palazzo Camponeschi and Fontana 99 Cannelle).
The site investigations results indicate that the upper portion of the subsoil in the city centre generally consists of up to 100 m of “Megabreccia” formations (composed by fine to coarse calcareous fragments embedded in sandy-silty matrix with highly variable degree of cementation), overlying fine to medium grained lacustrine deposits of more than 200 m depth placed on the calcareous bedrock. The shear wave velocity in the “Megabreccias” generally increases with depth from about 400 to 1,200 m/s, with some dispersion essentially due to the variability in the silty-sandy matrix and its cementation. In the underlying lacustrine silt, investigated by SDMT up to a depth of 133 m at the site of Fontana 99 Cannelle, the measured \(\hbox {V}_\mathrm{S}\) values range between 400 and 600–700 m/s. These results highlight the presence of an inversion of the shear wave velocity with depth in the subsoil of the historic centre of L’Aquila.
SDMT tests have also been performed in backfilled boreholes at various sites located in the western outskirts of the town, in the densely populated districts of Coppito (including the sites of San Salvatore Hospital and the strong motion station AQA-Aterno River, part of the Italian Strong Motion Accelerometric Network RAN), Pile and Pettino. The \(\hbox {V}_\mathrm{S}\) measured at the above sites, mostly in gravel or calcareous breccia, results generally higher than 400 m/s and increases with depth, reaching values of the order of 1,000 m/s at 15 m below ground surface.
The accurate definition of the shear wave velocity profiles described above, in conjunction with advanced laboratory investigations of the soil shear stiffness degradation with cyclic strain and related hysteretic dissipation (through resonant column, torsional shear and cyclic simple shear tests), has allowed a detailed seismic microzonation study of L’Aquila city centre and its suburban area (MS-AQ Working Group 2010). Site specific response spectra have been generated for twelve different macroareas using one- and two-dimensional numerical approaches. The rock input motions for the numerical simulations have been obtained through the definition of uniform hazard spectra derived from a probabilistic evaluation of time-dependent seismic hazard and from the evaluation of the seismogenetic potential of the faults in the area. It should be noted that the uniform hazard spectrum has been shown to be conservative for long return period earthquake shaking and the conditional mean spectrum has been recently proposed as a more appropriate target for ground motion selection (e.g. Baker and Cornell 2006; Cimellaro 2013).
The results of the microzonation study have highlighted a consistent under-prediction of the spectral accelerations at short periods using the response spectra proposed by the Italian seismic regulation (NTC 2008), especially for areas where the inversion of the shear wave velocity with depth was observed in-situ.