OVERVIEW OF THE VESUVIUS CASE STUDY ACTIVITY

Transcription

1 M. Indirli, ENEA, Bologna, Italy VESUVIUS SPECIAL SESSION OVERVIEW OF THE VESUVIUS CASE STUDY ACTIVITY

2 The VESUVIUS case study in the framework of the EU COST Action C26 activity In the Delft meeting (November 17-18, 2006), the goal of WG4 has been devoted to any natural hazard except earthquake Resistance to Infrequent Loading Conditions as flood, landslide, extreme wind and snow, avalanche, tsunami and storm surge, coastal erosion, volcanic eruption, etc. The focus has been pointed on: - identification, characterization and modeling of natural disasters (and their interrelations/scenarios); - construction response and possible relevant consequences of combined extreme loadings in the built environment. Since the beginning, the work seemed too huge without a robust Ariadne's thread to follow.

3 The VESUVIUS case study in the framework of the EU COST Action C26 activity Therefore, three directions have been identified for the research: a) the investigation on each single catastrophic infrequent event; b) the set up of a multi-hazard approach, together with the development of a common methodology for risk assessment; c) the identification of a pilot study enough general to join several disciplines in a transversal approach. The Vesuvius extreme dangerousness induced the WG4 to introduce the Vesuvius case study within its research activities, with particular regard to the effects on the constructions produced by a possible eruption. Delft meeting, November 17-18, 2006; Prague Workshop, March 30-31, 2006; Naples, June 8-9, In Naples, the discussion was related to the organization of WG4, deciding to modify its scope and name, which changed in: Risk Assessment for Catastrophic Scenarios in Urban Areas

4 The 1944 Vesuvius eruption COST Action C26 The VESUVIUS case study in the framework of the EU COST Action C26 activity After a general discussion (Timisoara, October 26-27, 2007), a specific enlarged WG4 meeting was organized (Trieste, January 17-18, 2008), where the Vesuvius case study has been focused. Not addressed to the issue of evacuation, the study has been restricted to the modelling of loads acting on structures and the corresponding construction response. The work on Vesuvius continued in the following Action meetings, with the main result to find some paradigmatic sets of structures, to be investigated in the surrounding area of the Neapolitan volcano. (Vilnius, April 11-12, 2008; Naples, 19 May 2008; Madeira, June 5-6, 2008; Malta Workshop, October 23-25, 2008; Naples, January 23, 2009; Southampton, March 27-28, 2009; Rome, June 22-24, 2009; Skiathos, September 4-5, 2009; Aveiro, November 27-28, 2009; Nicosia, March 19-20, 2010).

5 QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. COST Action C26 The VESUVIUS case study in the framework of the EU COST Action C26 activity The work involved several experts of different disciplines and created an enlarged platform for a free and productive discussion. VESUVIUS 2000 Project objectives Flavio Dobran GVES, Napoli, Italy Urban Habitat Constructions Under Catastrophic Events Trieste, 17 January 2008 Earthquake scenarios for the determination of the seismic load on the structures surrounding Vesuvius. Giuliano F. Panza COST C26 ACTION URBAN HABITAT CONSTRUCTIONS UNDER CATASTROPHIC EVENTS JANUARY 2007 TRIESTE, ITALY UNIVERSITY OF NAPLES FEDERICO II Department of Structural Engineering Università degli Studi di Napoli Federico II Napoli 19 Febbraio 2008 Giornata Inaugurale del Centro Studi PLINIVS Centro di Competenza del Dipartimento di Protezione Civile Nazionale QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture. VESUVIUS CASE Presentazione delle Attività del Centro Studi P.LIN.I.V.S. (Per L INgegneria Idrogeologica Vulcanica e Sismica) Trieste, January 2008 PROF. Dr. ENG. Federico M. MAZZOLANI Beatrice FAGGIANO Daniela DE GREGORIO Giulio Zuccaro

6 State-of-the-art on Vesuvius Timisoara, October 26-27, 2007 Trieste, January 17-18, 2008 Vilnius, April 11-12, 2008 Projects and papers

7 State-of-the-art on Vesuvius Principal eruptions of Vesuvius

8 List of recent eruptions of Vesuvius COST Action C26 State-of-the-art on Vesuvius

9 Volcanic actions of Vesuvius Typologies of the principal volcanic actions by Vesuvius on the constructions

10 earthquake COST Action C26 Volcanic actions of Vesuvius

11 pyroclastic flows COST Action C26 Volcanic actions of Vesuvius

12 tephra COST Action C26 Volcanic actions of Vesuvius

13 lava COST Action C26 Volcanic actions of Vesuvius

14 lahar COST Action C26 Volcanic actions of Vesuvius

15 tsunami COST Action C26 Volcanic actions of Vesuvius

16 Identification of the target area The red zone, the most dangerous area around Vesuvius Coordinates N E Altitude 43m s.l.m. Surface 30,66km 2 Inhabitants (2007) Density 2.899,34 inhab./km 2 Istat code Land register code L259 The investigated area: the Municipality of Torre del Greco

17 Identification of the target buildings

18 The survey team - experts of University of Naples Federico II - experts COST ACTION C26 - Experts of PLINIVS Centre, Naples visual examination, the compilation of ad hoc forms The support of PLINIVS Centre has been fundamenntal, for knowledge and experience

19 The investigation methodology 1) volcanic vulnerability

20 The investigation methodology 2) MEDEA: seismic damage mechanisms 3) Additional information specific for cultural heritage for the Vesuvian Villas

21 The investigation methodology The PLINIVS Study Centre developed: computerized tool to build up the seismic impact in the volcanic areas around Vesuvius and Campi Flegrei tools intended to evaluate a reasonable estimate of the cumulative damage impact scenario as a consequence of a Vesuvius eruption of assigned intensity The model is integrated in a Geographic Information System (GIS) and refers to Vulnerability Functions and on cumulative damage on the buildings The tool is intended to control the progressive impact up to the final impact scenario

22 The investigation methodology The quick methodology for the volcanic vulnerability assessment and the survey form have been developed within the EXPLORIS European project ( ) developed by the PLINIVS Centre. At the moment, EXPLORIS considers only three volcanic phenomena: earthquakes (EQ) ash falls (AF) pyroclastic flows (PF) The eruptive event is studied from the first precursory seismic event up to the final pyroclastic flow, by evaluating the damage accumulated on the buildings and the distribution of damage on the territory at each step of the process. The evaluation of the volcanic impact on the constructions is very complex and depends on the possible eruptive scenario, which has been assumed. The combination of the three volcanic phenomena can increase the damage on buildings, in comparison with the effects of each phenomenon acting separately.

23 The investigation methodology THE VOLCANIC VUNERABILITY ASSESSMENT The methodology is based on the assignment of specific vulnerability classes with respect to each exceptional action, in function of the structural elements typology. EQ: 4 classes As, Bs, Cs, Ds with vulnerability decreasing according to the combinations of horizontal and vertical structures. AF: 5 classes Ar, Br, C1r, C2r, Dr with vulnerability decreasing in function of roof typologies. PF: 3 classes Ap, Bp, Cp for masonry buildings 3 classes Dp, Ep, Fp for the RC buildings with vulnerability decreasing in each group in function of vertical and horizontal structures.

24 Examples of building classification in the historic centre of Torre del Greco

25 The volcanic vulnerability assessment: examples of results The impact of ash-fall is strongly dependent on the wind direction during the eruption; the model considers 16 possible sectors of prevalent wind.

26 Mitigation actions earthquake Considering the high seismic vulnerability levels and the construction density in the Vesuvius area, cost-effective mitigation measures should be provided. It is possible to choose cheap and reliable technical solutions (such as iron chains in masonry buildings, the insertion of infill panels or resistant elements in soft floors of reinforced concrete buildings), but also to adopt, in case of seismic reinforcement, specific solutions able to respond effectively also to other volcanic phenomena, such as pyroclastic flows or ash fall. One solution is the construction of pitched roofs by overlapping light structures in CFS (Cold Formed Steel). This allows to chain vertical structures by increasing the resistance to seismic actions (box behaviour) and simultaneously prevent the deposit of ashes and the structural risks related to overloading of the roof, also in consideration of a possible earthquake following the ash fall phase. Should be avoided the employ of widely used reinforcement systems not satisfying the conditions of volcanic risk, such as FRP (Fiber Reinforced Polymers) Global mitigation strategies related to seismic risk in case of a volcanic event may include planning for widespread interventions, defining the areas that require priority actions.

27 Mitigation actions Pyroclastic flows Pyroclastic flows can produce high damages to the built environment in areas near to the vent. Although they would have a limited action range, the effects can be critical because of the combination of mechanical impact and thermal stress on the vertical surfaces of buildings. The main damages come from the impact on openings. Mitigation strategies mainly concern the reinforcement of infill panels in r.c. buildings and measures for the protection of openings.

28 Mitigation actions Ash fall Ash fall is one of the eruptive phenomena with greater risk for existing buildings and infrastructure, as the expected impact involves (with different levels of intensity) a very large area, which definition is strictly linked to the direction and intensity of the wind, as well as to the type of eruption. Mitigation strategies, beside the need to develop an operational plan for the removal of ash on roofs and transport networks, mainly concern the repairing and reinforcement of roofing systems in order to increase the load carrying capacity. Pitched roofs with wooden or steel structure, reducing the deposits of ashes, would be at risk only in proximal areas where the surface of the cover present disconnections or missing parts. In this case, given the adequate inherent fire resistance of commonly used coating materials is enough to replace the missing elements in order to prevent the passage of hot ashes under the roof covering. In case of flat roofs it is possible to identify two main types of intervention: the reinforcement of the roof slab in order to increase the resistance according to the expected overload, or the realization of a sloped roof over the existing one.

29 Mitigation actions Lahar The lahars are a relevant risk factor for buildings and structures in volcanic areas. The response of structures and buildings technical elements to the action of lateral forces produced by lahars depends mainly on construction type and materials employed, as well as specific characteristics such as size in plan and elevation, number, size and position of openings, spatial distribution and presence of protective elements around the building able to divert the flow, etc. Structures, infill panels and ground floor openings are the technical elements most at risk in case of lahars. The reinforcement of these elements yet does not guarantee the survival of the building in case of direct impact with mudslide and debris, especially in the case of compact urban areas, where a "tunnel effect" can increase speed and height of the flow after the passage inside particularly narrow roads. For this reason the most effective mitigation strategies are related to environmental engineering interventions, to be made in risk prone areas and designed to contain or divert lahars. Measures such as retention basins, alternative artificial canals, high-strength reinforced concrete containing structures, may be appropriate solutions to mitigate risk.

30 Conclusions The mitigation of volcanic risk on buildings and infrastructure can significantly reduce the expected damage after an eruptive event. Even the impacts of high destructive type of eruptions, such as Sub-Plinian, can be strongly reduced by the application of one or more mitigation measures, responding to the different phenomena involved. It is therefore necessary to start from a comprehensive knowledge of the construction types available in risk-prone areas, providing specific interventions that take into account the cumulative effects given by the expected time history of the event. Hence, an effective design approach aims to put in relation technological features of existing buildings, parameters and data from probable scenarios, opportunities given by mixing together conventional technologies and advanced materials.

31 Conclusions Furthermore, considering the economical, political and social weight of the strategies for the mitigation of volcanic risk in densely populated areas, a valid evaluation method of the effectiveness of the proposed solutions can give scientific support to strategic choices and emergency plans. Therefore, tools for assessment and comparison between different solutions and mitigation scenarios are needed, trying to put together the different factors involved, such as economical and social sustainability, cultural and historical value, implication on emergency plans and on post-eruption rehabilitation and reconstruction interventions.

32 THANK YOU FOR THE ATTENTION COST Action C26 Conclusions In the case of the Vesuvius red zone, long-term strategies capable to reduce the urban density are also strongly necessary. It shall be very important to transfer strategic buildings, to stop the increasing of illegal constructions, to convince the people to live in places far from the volcano. Finally, a safety belt around the Vesuvius belt should be re-created, in order to reduce the consequences of an eruption.