2.4.1 Introduction

Everywhere in the world, most of the highly populated cities (but also a large amount of little towns and villages) are prone to natural hazards, defined as processes, occurring in the bio-sphere, that may constitute a damaging event. The main hazardous catastrophes are earth-quakes, volcano eruptions, landslides, tsunamis, coastal erosions, floods, hurricanes, drought, etc. With regard to urban areas, both wild and man-induced fires can be also considered. Con-sequently, the disaster risk DR (probability of harmful consequences, expected loss of lives, people injured, property, livelihoods, economic activity disrupted, environment damaged, etc., see Figure 2.4.1) results from the combination between hazard H, vulnerability V (human con-dition or process resulting from physical, social, economic and environmental factors, deter-mining probability and scale of damage from the impact of a given hazard) and physical expo-sure E (elements at risk, an inventory of those people or artifacts exposed to hazards), divided by the RM factor (Risk Management).

The Risk Assessment (RA) is an estimate of the social and economic impact that hazards can have on people, buildings, services, facilities and infrastructures. It is worth noting that, in ab-solute terms (UNPD 2002, Munich Re Group, 2004) the economic cost of disasters has been increasing over decades (Figure 2.4.2).

In addition, the city aggregates enshrine notable cores (like urban and social tissues, histori-cal and architectonical constructions, precious monuments, museums and archaeological evi-dences) of invaluable value; such kind of patrimony, which must be handed down intact to pos-terity as far as possible, is often protected by international and inland cultural heritage boards. Nevertheless, a huge amount of such treasures is lost for ever, due to past natural catastrophes; just some highlighting examples can be reminded: the 79 A.D. Vesuvius eruption, Italy (when Pompeii, Ercolano and Stabiae were completely covered by pyroclastic flows); the disruption of San Francisco (California, USA) and Valparaiso (Chile) during the 1906 earthquakes; the 1963 Vajont landslide, Italy (which swept away some small towns); the Firenze’s flood (1966); the Lisbon great fire (1988); the Indian Ocean tsunami (2004); the hurricane Katrina (2005). Thus, the accomplishment of an effective pre- and post-disaster risk management is a crucial tool, in order to minimize disaster impacts and implement potent policies and coping capacities of the society or individuals, managing the multifaceted nature of risk, realizing integrated hazard models and adopting appropriate governance for development and reconstruction planning. To these purposes, different strategy levels have to be foreseen; during the emergency phase, it is necessary to understand, well and quickly, the dynamic development of each environmental process, provide a detailed damage assessment and address prompt civil defense interventions; furthermore, prevention policies are also mandatory: hazard mapping, vulnerability studies, building inventory, mitigation programmes and citizenship preparedness.

2.4 Consequences of other natural disasters on constructions, except volcanic eruptions

Carlos Coelho Civil Engineering Department, University of Aveiro, Portugal

Ruben Paul Borg Faculty for the Built Environment, University of Malta, Malta. Vlatko Sesov University of Skopye, Macedonia Maurizio Indirli ENEA, Bologna, Italy

Figure 2.4.1. Risk definition.

Figure 2.4.2. World natural catastrophes (up) and economic losses (down) from 1950 to 2005 (source Munich Re).

In the last decade, Geomatics (emerging technology playing a vital role in natural disasters

mitigation) has been developing; it is a conglomerate of measuring, mapping, geodesy, satellite positioning (GPS), photogrammetry, computer systems and computer graphics, remote sensing RS (Shinozuka, 2005), geographic information systems GIS (Valpreda, 2003) and environmen-tal visualization. The earth observation satellites provide comprehensive, synoptic and multi-temporal coverage and monitoring of large areas for a wide range of scales, from entire conti-nents to details of a few meters in real time and at frequent intervals. This approach, started primarily with earthquake applications, broadened rapidly to tsunami, hurricanes, storms, wild-fires, landslides and other matters (Indirli, 2007).

2.4.2 A brief summary on risk assessment

Nowadays, a proper risk assessment must foresee a multidisciplinary approach, implementing interactive digitized databases, collecting a huge amount of input data and organizing a user-friendly instrument with strong import-export capabilities. The integrated use of several tools (hazard models, building classification and inventory database resources, RS and GIS mapping, etc.), the identification of analyses procedures and algorithms, the elaboration of reliable out-puts have to be foreseen. The basic steps for a correct risk assessment (Table 2.4.1) are dis-cussed in the following paragraphs (FEMA 386-2, 2001). Moreover, the database should be

flexible, freely available for use by any country and organization through Internet access, open-source, capable to be multi-hazard and international in scope, encouraging the worldwide com-munity to participate to its development and validation (Indirli, 2007).

Table 2.4.1. Definition of the main risk assessment procedures.

process outputs

step 1 identify hazards

• definition of the study region • study region • creation of a region base map • base map • hazard of interest identification • hazard of interest list step 2 profile hazards

• hazards database construction • updated and completed hazard profiles • performing a data gap analysis • map of hazard areas • profile and priority of hazards • hazards prioritized list step 3 inventory assets

• inventory database construction • inventory data tables and maps • performing a data gap analysis • inventory data

• data sources list

step 4 estimate losses and risk assessment tools

• construction of estimate losses scenarios and risk assessment tools

• loss and exposure for the study region

• evaluation of the results • risk assessment outputs • tables

• maps

step 5 consider mitigation options

• mitigation options identification • mitigation options list • mitigation options verification

2.4.2.1 Hazard identification The first step regards the identification of natural hazards that might affect the community or the territory (Table 2.4.2). Accidental actions such as fires, internal explosions and seismic events are, more or less, covered by the Eurocode program. Avalanches, erosion, extreme snow, extreme winds, floods, landslides, rockfalls, tsunamis, volcanic eruptions, etc., represent infre-quent natural actions that are not covered by the Eurocode program. It has to be noted that most of these phenomena are characterized by large fluid masses moving with a different degree of velocity according to their density and viscosity.

If volcanic eruptions or tsunamis do not depends on climatic phenomena, the other disasters find natural origins and, due to climate changes, they seem to become not so infrequent as be-fore. The main problem is that, by definition, exceptional and infrequent events are associated to very low probability of occurrence. Therefore, databases concerning these events are rather limited. One of the goals of the COST Action C26 (COST, 2006) being to define a suitable methodology to predict the structural behaviour of constructions under extreme conditions, one of the first step lies in the identification and in the classification of the relevant infrequent events and, when possible, to describe the associated scenarios. It is important to avoid omis-sions, considering the full range of potential hazards (including new and unexpected ones), as-sessing whether they may affect the area considered. Several investigation lines are due: histor-ical information, newspapers and Internet websites, modern event experience, technical information and experts’ opinion, review of existing plans and reports. The results can be sum-marized in models and maps. After the preliminary research described above, it is indispensable to focus on the most prevalent hazards in the community or territory, through an accurate con-sultation of specific hazard websites (if any). Hazard grouping is a crucial point: a list may give the impression that hazards are independent of one another; on the contrary, they are often re-lated (primary and secondary hazards). The identification of global hazard factors for a given

area (or a building), is another crucial step to carry out, due to the difficult definition of combi-nation methods and algorithms (Indirli, 2007).

Table 2.4.2. List of possible natural hazards.

natural hazard type • earthquake

• tsunami

• landslide and mudslide

• subsidence

• hurricane

• tornado

• flood

• coastal storm and erosion

• volcanic eruption

• drought

• wildfire

• winter storm (ice and snow)

• avalanche

• …

Table 2.4.3. Natural hazard profile.

hazard event • specific occurrence

frequency • how often

probability • likelihood (statistical measure)

duration • how long an event lasts

magnitude • severity (technical measure)

intensity • effect of an event at a particular place

hazard areas • geographic areas within study region

2.4.2.2 Hazard profile In order to profile hazards and their potential consequences, of particular interest are the fre-quency of occurrence, magnitude and intensity, location and/or spatial extent, duration, sea-sonal pattern, speed of onset, and availability of warning (Table 2.4.3, Indirli, 2007). Some haz-ards (such as floods, coastal storms, wildfires, tsunamis, and landslides) occur in predictable areas and can be easily mapped. Other hazards (such as tornadoes, which can occur anywhere) may be profiled simply by recording the maximum potential wind speed. This type of infor-mation will be used to evaluate the potential impact to individual structures or elements in the selected area. Several kinds of consequences can be investigated: effects on people, critical fa-cilities and community functions, property, and sites of potential secondary hazards. The use of both historical information and modeling is recommended. Aiming to determine which hazards merit special attention, great attention must be paid to compare and prioritize risks, create and apply scenarios, investigate data sources.

The definition of complete, accurate and detailed base maps of different scales (from global to local) is fundamental (also creating GIS platforms and elaborating satellite imagery), where objects (like buildings, roads, rivers, coastlines, etc.) must be well distinguishable. Hazard lev-els areas (Low, Moderate, High, Extreme) have to be clearly identified.

Focusing on seismic hazard maps, nowadays several studies can provide more accurate tools for the urban environment protection, like neo-deterministic models and earthquake scenarios

(to be preferred especially when dealing with objects that should be 100% safe, as strategic fa-cilities and cultural heritage). In fact, Seismic hazard assessment, necessary to design earth-quake-resistant structures, can be performed in various ways, following a probabilistic or a neo-deterministic approach. Case studies indicate the limitations of the PSHA (Probabilistic Seis-mic Hazard Analysis) currently used methodologies, deeply rooted in engineering practice, providing indications that can be useful but not sufficiently reliable (Decanini et al., 2001, Klügel et al., 2006), as shown in recent examples (earthquakes of: Michoacan 1985, Kobe 1995, Bhuj 2001, Boumerdes 2003, Bam 2003, E-Sichuan 2008, L’Aquila 2009 events). In fact, the PSHA could not be sufficiently reliable to completely characterize the seismic hazard, be-cause of the difficulty to define the seismogenetic zones and evaluate correctly the occurrence of the earthquakes (frequency-magnitude relations), and the propagation of their effects (atten-uation laws). A more adequate description of the seismic input can be done following a neo-deterministic approach (Neo-Deterministic Seismic Hazard Assessment NDSHA), which allows for a realistic description of the seismic ground motion due to an earthquake of given distance and magnitude (Panza et al., 2001). The approach, that is feasible to apply at urban scales, is based on modelling techniques that have been developed from the knowledge of the seismic source generation and propagation processes. It is very useful because it permits the definition of a set of earthquake scenarios and the computation of the associated synthetic signals, without having to wait for a strong event to occur. A complete description of the neo-deterministic methodology, from the definition of the hazard to the seismic input calculation for the design of a building, is given in Zuccolo et al. (2008). This methodology provides algorithms for the space-time medium terms forecasting and the realistic simulation of ground shaking, including seismic input synthetic time series, calibrated against observations, whenever possible; thus, the use of methods that showed many shortcomings (based on acceleration peak values and proba-bilistic earthquake return periods) can be overcame. An important example is the UNESCO-IUGS-IGCP project 414 (Panza et al. 2002) for the seismic microzonation of several towns (e.g. Delhi, Beijing, Rome, Naples, Santiago de Cuba, Bucharest, Sofia). Furthermore, this approach has been extended to Chile (Indirli et al. 2006; MAR VASTO, 2007). A similar approach is ad-visable to evaluate the occurrence of tsunamis, together with the development of reliable ana-lytical models of sea waves propagation and accurate recording systems (Panza et al., 2000).

With regard to flood, concepts as flood elevation and flood hazard areas must be very well defined; in the USA, BFE (Base Flood Elevation), is the elevation of the water surface resulting from a flood that has a 1% chance of occurring in any given year; SFHA (Special Flood Hazard Area) is the shaded area that identifies an area that has a 1% chance of being flooded in any given year.

Usually, tornadoes strike random and in a wide portion of territory; they are classified by the Fujita Measurement Scale (from category F0 for light tornadoes to F5 for incredible tornadoes); to profile the hazard, it is necessary to choose the design wind speed with accuracy, (that is provided in USA by ASCE, the American Society of Civil Engineers).

Coastal storms, due to typhoons or hurricanes, can cause tidal elevation increase (called storm surge), inland flooding and water force, wind speed, and erosion. Storm surge water lev-els depend on wind speed and are measured by the five categories (from minimal to cata-strophic) of the Saffir-Simpson Scale.

The best predictor of future landslides is past landslides, because they tend to occur in the same places. This hazard is very complex and require geologic expertise. Landslide inventories identify areas that appear to have failed in the past; landslide susceptibility maps depict areas that have the potential for landslides; landslides hazard maps show the real extent of the threat: where landslides have occurred in the past, where they are likely to occur now, and where they can occur in the future.

2.4.2.3 Hazard independent effects

2.4.2.3.1 The effect of Snow Exceptional snow loads For altitudes smaller than 1500 m, exceptional snow loads are specified in EN1991-1-3:2003, and the code is based on the assumption of a return period equal to 50 years. Exceptional snow loads are considered as accidental loads (EN, 1991a-b).

Avalanches Avalanches are one of the infrequent actions not taken into account in the Eurocodes. It is pos-sible to identify two main types of avalanches (Givry and Perfettini, 2004) depending on the state of the snow: dry snow or powder avalanche and wet snow avalanche. The difference be-tween these two kinds of phenomena defines their mode of failure, their way of displacement down the slope and their relative power. Nevertheless, it is to be noted that there is a transition between these two extreme modes that are qualified as dry, damp, moist, wet and saturated. Compared to a dry snow avalanche, a wet snow one is slower and the runout distance is shorter. However, the impact on obstacles (trees or constructions for instance) is very important due to the high density of wet snow. Being slower, wet snow avalanches appear to be less dangerous for humans than dry avalanches, but regarding construction it is the opposite. Nevertheless, if the robustness of the construction can be strongly affected by wet snow avalanches, the open-ings are affected by dry snow avalanches due to its related high pressure, similar to a blasting effect. A dry snow avalanche is not really affected by the site topography as the wet snow ava-lanche reduces with the slope. The avalanche path corresponds to a terrain feature where an av-alanche occurs. It is composed of a starting zone, a track and a deposition or runout zone.

2.4.2.3.2 The effect of Wind Extreme winds Cyclones, hurricanes, tornados or typhoons are extreme winds whose dynamic action leads generally to severe damages on constructions. The name of the extreme winds depends on their geographical location and on their maximum speed. To be initiated, tropical cyclones need cer-tain thermodynamic conditions to be respected above a large mass of warm water. Therefore, they form above seas or oceans. They are named hurricanes in the Atlantic Ocean and typhoons in the Pacific Ocean. Tornados are initiated above the earth during a severe storm when special thermodynamic conditions are found between huge cloudy masses and winds. Cyclones Three types of cyclonic perturbations are commonly defined: tropical depressions, tropical storms and tropical cyclones (Chaboud, 2003). A tropical cyclone is constituted by an eye at its centre, which is a relatively warm and calm zone, surrounded by an area about 16–80 km wide in which the strongest thunderstorms and winds circulate around it. Up to now, the extreme wind speed due to a tropical cyclone is estimated to be equal to 305 km/h. To be initiated and sustained, tropical cyclones need large unstable volumes of warm water (more than 26°C over 60 m in depth) so, their strength decreases over land because of the lack of water. This is why the coastal regions are much more affected by cyclones than inland regions, the wind speed de-creasing as much as the depression progress on earth. Tornados Much smaller than a tropical cyclone regarding its influence diameter, a tornado is a violently rotating column of air starting from the lower part of a cumulonimbus cloud and in contact with the earth. Presenting different shapes, the form of a tornado is typically a visible condensation funnel, whose narrow part moves on the earth. On the path of the displacement, the damages on constructions are generally localised but very important due to the high speed of the rotation. In most cases, a cloud of debris collected on the way, moves around the funnel at its lower part and it contributes to increase the damages. If the radial action of the vortex is important, it is generally combined with a vertical suction opposite to the gravity which amplifies the damages. A powerful tornado may extract light constructions from their foundations. Most of the torna-does create a very localised strong wind whose speed may reach 175 km/h. Their lower part is generally about 100 m and they travel only on a small distance (about 10 km) before they dissi-pate. Nevertheless, much more powerful tornadoes have been observed: with a wind speed close to 500 km/h, with a base diameter close to 1.5 km and whose way on the ground may be longer than 100 kilometres.

2.4.2.3.3 The effect of Water River floods River floods are one of the main hazards encountered by people living in the whole European Union. Since these floods can take numerous forms, such as flash floods, estuarine floods, mud floods…, almost all kinds of landscapes can be impacted. In the past decades, an increase in

terms of frequency and of importance of such catastrophic events has been noticed, and can be related to numerous causes: modification of land occupation (increase of impervious areas, changes in agricultural practices), erratic river banks management (artificialized hydrosystems) and the effects of climate changes on storm events frequency. Coastal floods Highly energetic wave regimes, some negative effects from coastal interventions, littoral occu-pation, exterior interventions in harbors, the weakening of river sediment supply and the gener-alized sea level rise and other effects of climate changes (frequency of storm events, rotation of waves provenience) can be pointed out as the main causes of the increasing number of con-structions exposed to waves. Overtopping and flooding are being more frequent events on the coastal zones, jeopardizing buildings and infrastructures. Erosion All European coastal states are to some extent affected by coastal erosion. About 20 000 km of coasts, corresponding to 20%, faced serious impacts in 2004. Most of the impact zones (15 100 km) are actively retreating; some of them in spite of the coastal protection works done (2 900 km). In addition, another 4 700 km have become artificially stabilized (European Com-mission, 2004). The dynamical variability of sandy beaches, where the alongshore sediment transport is controlled by waves, currents, wind, water level, sediments sources and sinks and sediments properties, can represent erosion situations with exposure of constructions. The main causes for coastal erosion are the generalized sea level rise, caused by climate change, some negative effects from coastal interventions, littoral occupation, exterior interventions in har-bours, which cause serious perturbations in the littoral drift system and river sediment supply reduction (Coelho et al., 2006). The river sediment supply has been weakening due to sand min-ing, for construction and navigation, and dam construction with consequent sand retention and hydrological regime regularization (Santos et al., 2002). One of the usually preferred solutions to solve erosion problems is beach artificial nourishment. This can represents a very expensive solution, when the sedimentary deficit is very high, and there is not any sand deposit availabil-ity to such high values. However, it is essential to try to mitigate coastal erosion processes in specific locations. At the moment, the so-called hard coastal defences are indispensable to pro-tect some of the existing settlements, but should be foreseen an adequate plan of monitoring of the existent coastal defence structures, keeping the maintenance costs of the structures at low level. Regarding the political point of view, it is crucial to regulate urban seafront extension. In some cases, the policy options of managed realignment – identify a new line of defence and re-settle the populations in the hinterland – have to be considered. The solution for coastal erosion problems must pass through a compromise between the passive acceptance of erosion, some beach nourishment and coastal intervention for urban front protection. Tsunamis Tsunami are series of waves created by the fast displacement of huge volumes of water (an ocean for instance) strongly and rapidly affected by a natural phenomenon at a huge scale. Generally, they can be initiated by earthquakes, submarine volcanic eruptions or landslides (seabed slides) for example, but not by strong winds whose impulsion is not short and strong enough. The effects of a tsunami can be classified as insignificant to catastrophic regarding coastal population and constructions. The waves move as growing circles from the initial loca-tion to all the surrounding coats at high speeds (700 km/h is a mean value in the Pacific Ocean) with a large wavelength (hundreds of kilometres) and they can travel great transoceanic dis-tances with small overall energy loss. Far from coasts, most classical tsunamis have wave heights smaller than one meter but in their motion, they mobilise the whole water column from the surface to the sea bed. That explains why, when it approach the coast where the sea bottom become less deeper, the wave front becomes higher and can reach 20 m or more, and the resid-ual energy creates a violent displacement. Most of the damages are due to the enormous mass of water accompanying the initial wave front. On the one hand, they are originated by the wave impact on obstacles and, on the other hand, by the flood resulting from the sea level rising. The energy of the phenomenon is sufficient to project any kinds of objects found on its path (ships for instance but also any kind of debris) and sometimes far from the coast. Their combination is powerful enough to shear weak brittle houses at their base or to submerge and to create bending actions on rather high constructions depending of the wave height. The influence area depends

also on the relief but it can be measured several kilometres far from the coast itself whose posi-tion can be strongly affected. Other details can be found in Rossetto et al. (2010a).

2.4.2.3.4 The effect of Volcanoes Volcanic eruptions This topic is largely discussed in another part of the Final Report (Section 2.5).

2.4.2.3.5 The effect of landslides and rockfall Landslide describes a wide variety of processes that result in the downward and outward movement of slope-forming materials including rock, soil, artificial fill, or a combination of these. The materials may move by falling, toppling, sliding, spreading, or flowing. The various types of landslides can be differentiated by the kinds of material involved and the mode of movement. Other classification systems incorporate additional variables, such as the rate of movement and the water, air, or ice content of the landslide material. Although landslides are primarily associated with mountainous regions, they can also occur in areas of generally low re-lief. In low-relief areas, landslides occur as cut-andfill failures (roadway and building excava-tions), river bluff failures, lateral spreading landslides, collapse of mine-waste piles (especially coal), and a wide variety of slope failures associated with quarries and open-pit mines. The conventional stability analysis of slopes where sliding is possible along some definable surface is usually preformed by calculating the factor of safety, i.e. by comparing the shearing re-sistance available along the failure surface. With the shearing stresses imposed on the failure surface. Most analytical methods are based on limit equilibrium, with typical failure forms such as infinite slope or finite slope with planar or curved failure surface considered. However, the recently introduced performance-based approach, emphasis is placed not on whether the slope is stable or unstable, but on the magnitude of deformation after failure. Several techniques are currently available to asses the post-failure velocity and travel distance of the moving mass. The basic model assumes that during the shaking a slope will suffer displacement only when the ground acceleration exceeds a threshold value, the critical acceleration, which can be de-rived from the static factor of safety of the slope in question. The sliding mass will continue to move until the shaking drops below the critical acceleration. If the cumulative displacement caused by shaking, known as Newmark displacement is sufficient to cause a reduction in the shear strength of the soil or rock mass then a re-calculation of the slope stability is carried out using residual shear strength parameters to establish whether failure occurs. Thus the analysis is bi-linear, allowing for a change in the strength parameters of the slope forming materials based on the deformation of the slope.

2.4.2.4 Combination of hazards scenarios. In this section, just some action combinations of exceptional events are presented, evaluating realistic scenarios.

2.4.2.4.1 Snow and avalanches Considering the combination of exceptional events, wet snow or dry snow avalanches are never combined together due to their different origin. An avalanche is never combined with an earth-quake even if this last may be the creating factor because they do not occur in the same time in-terval. Winds and avalanches are never combined because the wind action being smaller, it can be expected to be included in the avalanche load case. Snows and avalanches are obviously combined because heavy snow is generally the creating factor.

2.4.2.4.2 Extreme winds and rains In most cases, extreme winds are associated to torrential rains creating floods which amplify the damages effects. The extreme winds due to tropical cyclones are often combined with tor-rential rains, high waves, and storm surges: strong wind creates a high pressure able to damage civil engineering structures themselves and, on the other hand, it transforms debris into flying objects able to damage covering and cladding; heavy rains can create river and stream floods but also landslides; storm surges, by increasing the sea level, can produce extensive coastal flooding up to about 50 km inland depending on the relief.

2.4.2.4.3 River and coastal floods Combination of heavy rainfall with severe marine conditions (storms and/or high tides) can highly increase the damaging potential of flood events. Usually, storm events, with important winds and rainfalls, low atmospheric pressure, high tides and significant wave heights represent natural conditions for floods combination in coastal and estuarine areas. In fact, fluvial and coastal floods are frequently related and present common characteristics. Coastal shores and river banks management is very important to reduce flood damaging costs and control the con-sequences of flood events. Land use is very important on soil erosion and thus, on river sedi-ment transport. On the other hand, fluvial floods are usually associated with important sediment transport rates. These sediments represent the natural nourishment of the coastal areas, prevent-ing coastal erosion. In estuarine regions, the extreme rainfall events can present more negative impacts when associated to high tide periods, mainly during spring tides. Storms and low at-mospheric pressure can amplify the consequences. In spite of all this, the subject of combined flood effects of river and sea actions is still poorly referred in the literature.

2.4.2.4.4 Landslides and other actions Although there are multiple types of causes of landslides, there are three that cause most of the damaging landslides around the world, described as follows and combining more than one ac-tion. Landslides and water Slope saturation by water is a primary cause of landslides. This effect can occur in the form of intense rainfall, snowmelt, changes in ground-water levels, and waterlevel changes along coast-lines, earth dams, and the banks of lakes, reservoirs, canals, and rivers. Landsliding and flood-ing are closely allied because both are related to precipitation, runoff, and the saturation of ground by water. In addition, debris flows and mudflows usually occur in small, steep stream channels and often are mistaken for floods; in fact, these two events often occur simultaneously in the same area. Landslides can cause flooding by forming landslide dams that block valleys and stream channels, allowing large amounts of water to back up. This causes backwater flood-ing and, if the dam fails, subsequent downstream flooding. Also, solid landslide debris can “bulk” or add volume and density to otherwise normal streamflow or cause channel blockages and diversions creating flood conditions or localized erosion. Landslides can also cause over-topping of reservoirs and/or reduced capacity of reservoirs to store water. Landslides and seismic activity This topic is also discussed in another parts of the Final Report. Many mountainous areas that are vulnerable to landslides have also experienced at least moder-ate rates of earthquake occurrence in recorded times. The occurrence of earthquakes in steep landslide-prone areas greatly increases the likelihood that landslides will occur, due to ground shaking alone or shaking- caused dilation of soil materials, which allows rapid infiltration of water. Widespread rockfalls also are caused by loosening of rocks as a result of ground shaking. Saturated soil condition due to rainy days and very steep inclination of the natural and manmade slopes makes soil very vulnerable to earthquake shaking. Landslides and volcanic activity This topic is also discussed in another part of the Final Report. Landslides due to volcanic ac-tivity are some of the most devastating types. Volcanic lava may melt snow at a rapid rate, causing a deluge of rock, soil, ash, and water that accelerates rapidly on the steep slopes of vol-canoes, devastating anything in its path. These volcanic debris flows (also known as lahars) reach great distances, once they leave the flanks of the volcano, and can damage structures in flat areas surrounding the volcanoes.

2.4.2.5 Inventory assets

Inventory assets organize a huge amount of data, better if stored on a GIS platform (Table 2.4.4), about patterns that can be affected by hazardous events. An example of potentially vul-nerable assets is shown by Figures 2.4.3-2.4.4, taken from HAZUS-MH (HAZUS, 1992), brief-ly described in the paragraph 4. HAZUS can summarize the number and value of structures in the area considered by the types of structure or the occupancy class. Critical buildings and fa-cilities must be classified separately (Indirli, 2007).

Table 2.4.4. Inventory assets.

demographics • population, employment, housing

building stock • residential, commercial, industrial

essential facilities • emergency operations centers, hospitals, schools, shelters, police and fire stations

transportation

systems

• airways, highways, railways, waterways

lifeline utility systems • potable water, waste water, oil, gas, electric power, communication systems

high potential loss facilities • dams and levees, nuclear facilities, military installations

hazardous material facilities • facilities housing industrial/hazardous mate-rials

cultural heritage • historical centers, archaeological remains, monuments, museums

Table 2.4.5. Building data requirements by hazard.

building characteristics floo

d

eart

hq

uak

e

tsun

ami

torn

ado

coas

tal

sto

rm

lan

dsl

ide

wild

fire

type/type of foundation X X X X

code design level/construction date X X X X X X

roof material X X X

roof construction X X X

vegetation X

topography X X X X

distance from the hazard zone X X X X X

lowest floor elevation X X

base floor elevation X X

In order to gather building-specific information, the following data must be provided: build-

ing size; replacement value to its pre-damaged conditions; content value; function use or value; displacement cost due to hazard; occupancy or capacity. Other data, summarized by Table 2.4.5, are hazard-specific.

It is worth noting that the system can be implemented depending on the features of the coun-tries considered; for Europe, specific categories can be defined for cultural heritage assets and historical centers, which are widespread, critical and precious.

Vulnerability factors can be calculated with particular regard to masonry buildings, by in-cluding specific algorithms already developed by the scientific community (Bernardini et al. 1990, D’Ayala et al. 2003, Valluzzi et al. 2004). A remarkable study on vulnerability evaluation and building inventory is the Sana’a GIS implementation (Figure 2.4.5) after a detailed in-field survey, provided by the Ferrara University to the Yemeni authorities, in the framework of the Conservation and Rehabilitation Plan for the Old City and other historic neighbouring settle-ments. A digitized database has been carried out classifying all the buildings in various catego-ries, depending on their architectonic relevance, according to the ICOMOS Washington Charter (ICOMOS 1987).

Finally, a GIS-based application can join hazard and vulnerability data, merging together in-puts coming from updated cadastral maps, RS satellites images and in-field DGPS surveys (di-agnostics investigations and damage assessment included).

Thus, geo-referred risk maps (Figure 2.4.6), in which single building structural features are linked to the surrounding environmental and social context, must identify house by house, giv-ing a sharp classification of the danger level (Midorikawa 2005).

Figure 2.4.3. Organization of building data in HAZUS-MH.

Figure 2.4.4. Building classification system in HAZUS-MH.

Figure 2.4.5. Sana’a GIS database. Figure 2.4.6. 3D Digital mapping joining hazard and vulnerability for earthquakes (source Midorikawa).

2.4.2.6 Estimate losses

In this analysis, the information must be provided together with the data of the previous steps; a true “risk assessment” takes into account all the possible hazards than just a single event. Table 2.4.6 shows a brief summary of estimate losses. Building damage (structural, content, use and function) is a reliable indicator of risk. The level of building damage can be used to rank risks from various natural hazards and estimate risk in absolute terms. Human losses can be calculat-ed in a credible way by using HAZUS procedures obtained for earthquakes.

Table 2.4.6. Estimate losses.

building types • concrete, pre-cast concrete, reinforced and unreinforced masonry, steel, wood, etc.

building occupancies • residential, commercial, industrial, education, agriculture, religion, government, etc.

essential facilities • Emergency Operations Centers, hospitals, schools, police and fire stations, shelters, etc.

transportation/lifelines • highways, railways, light rail, bus station, ports, ferries, airports, bridges, tunnels, etc.

utilities • waste water, potable water, oil, gas, electric power, communication facilities, etc.

The loss estimate analysis can be concluded calculating the loss to each asset, the damage for each hazard event, and finally creating a composite map showing the most affected areas. It is important to note that the risks to existing structures (i.e. great part of European historical cen-ters), built before the introduction of updated standards, must be accurately evaluated in the risk assessment procedures. Risk assessment must take into account all the data coming from post-earthquake in-situ damage investigations. In addition, RS image processing can also provide a damage prompt evaluation for large areas, comparing the situation “before” and “after” the event (Figure 2.4.7, Indirli, 2007).

2.4.2.7 Mitigation options

Tables 2.4.7 and 2.4.8 show the principal mitigation options (general overview and hazard-targeted respectively). The adoption of updated building and safety codes is mandatory.

Figure 2.4.7. Satellite images of Bam (Iran) before (left) and after (right) the 2003 earthquake (source QuickBird).

Figure 2.4.8. Rescue for children at the school site at San Giuliano di Puglia after the 31st October, 2002 earthquake.

Figure 2.4.9. Well-elevated and embedded pile foundation (left) and nearly failed house due to insuf-ficient pile embedment (right) after the hurricane Katrina (USA).

Table 2.4.7. Mitigation options, general overview.

regulatory measures • legislation which organizes and distributes responsi-bilities to protect a community from hazards

• regulations that reduce financial and social impact of hazards through measures (insurances

• new/updated design and construction codes • new/modified land use and zoning regulations • incentives that provide inducements for implementing

mitigation measures repair and rehabilitation of existing structures • removal or relocation of structures in high hazard are-

as • repair and strengthening of essential and high-

potential-loss facilities protective and control structures • deflect destructive forces from vulnerable structures

and people • erect protective barriers (safe rooms, shelters, protec-

tive vegetation belts, etc.)

Table 2.4.8. Mitigation options, hazard-targeted.

earthquake regulatory measures flood regulatory measures

• building codes • master planning regulations

• guide development outside flood-prone areas • new development to address flood hazards • codes to address rehabilitation of older buildings

repair and rehabilitation

of existing structures

repair and rehabilitation

of existing structures

• raise earthquake resistance • retrofitting/hardening • strengthen and repair of structural and non-

structural elements

• rehabilitation of older buildings • acquisition/demolition • relocating intact buildings out of floodplain • retrofit of infrastructures

protective and control structures protective and control structures

• securing around buildings and critical in-frastructures

• stabilizing soils and securing hazardous sites before new construction

• decreasing run-off • increasing discharge capacity • containing, diverting or storing flood water

With regard to earthquake, the adoption of revised set of rules by several Government Au-

thorities is a step already achieved in many earthquake-prone countries, especially after the Northridge (1994) and Kobe (1995) seismic events, but also following the primary school col-lapse of San Giuliano di Puglia (Figure 2.4.8), Molise Region 2002, Italy (Presidenza del Con-siglio dei Ministri, 2003; Line Guida, 2006; Indirli et al. 2004a-b).

Another significant case is given by the hurricane Katrina (FEMA 2006a); the main recom-mendations (both for flood and wind) include the adoption of updated building codes (IBC 2006, IRC 2006, NFPA 5000 2006), incorporating flood load (ASCE 7-05, 2006) and flood-resistant construction standards (ASCE 24-05, 2006), with particular regard to foundations (Figure 2.4.9); design wind speeds are provided by ASCE 7 (ASCE 7, 2006); the use of FEMA 550 (FEMA 2006b) is also mandatory. Thus, the comparison of codes and standards regarding the mitigation of natural hazards, inside and outside the European Community, should be a fun-damental step of the future work.

Other details are given in Section 4.4.

2.4.3 Vulnerability Assessment

Due to the different characteristics of the events, in this section are presented just some exam-ples. However, general procedure can be referred. Usually, the vulnerability assessment de-pends of several parameters related with local conditions. The map representation of the vul-nerability will allow the identification of the constructions best location to reduce danger, by ranking priorities. Different scales of risk analysis may be considered; the study scale will de-

terminate the studied consequences, the associated responsibilities and the action possibilities. The risk is the combination of hazard occurrence and issue damages. The action is the hazard itself and issues can be persons, structures, infrastructures, communications, environment and economy. The next sections represent examples of analysis with snow, water and landslide ac-tions, allowing a better comprehension of the described procedures.

2.4.3.1 Snow In the Alps, the hazard is classified into 3 categories: the red zone where it is strictly forbidden to build any kind of new construction because of the high probability of danger; the blue zone where it is possible to build some constructions but where some special specifications are re-quired; the white zone which is expected to be without danger. An approximation of the refer-ence dynamic pressure Pd may be evaluated using the Bernoulli relationship: Pd = 1/2 ρ V2 if ρ is the average snow unit weight (kg/m3) and V the displacement speed of the avalanche (m/s).

So, a dry snow avalanche with a unit weight equal to 10 kg/m3 and a speed of displacement equal to 77.5 m/s (≈280 km/h) gives the same pressure (≈30 kPa) than a wet snow avalanche whose unit weight is equal to 400 kg/m3 and speed to 12.25 m/s (≈44 km/h).

The avalanche loading on constructions may present very high values. For the blue zone, 30 kPa (corresponding to the previous examples) is a reference value used in many European countries in the case of a wet snow avalanche; this value comes from Switzerland which is con-sidered as the reference country in Europe regarding this phenomenon. It is to be noted that trees, stones or ice blocks can amplify the effect of a wet snow avalanche by the addition of an impact load. Its value depends on the reference dynamic pressure. For instance, in Switzerland, a value of 100 kN is used with Pd = 30 kPa as 33 kN is used with Pd = 10 kPa; this load is ex-pected to be applied of a surface equal to 500 cm2 at any level of the avalanche.

Avalanches risk mitigation efficiency depends on the accurate knowledge of the studied sys-tem. The avalanche risk analysis may be described in several main phases: definition of the study scale and limits; determination of the constitutive elements and their function; identifica-tion of the risk scenarios; quantification of those scenarios in terms of occurrence and conse-quences; proposing of mitigation actions. The definition of risk analysis scale is very important as it conditions the risk analysis result and the efficiency of the study process. Indeed, a risk analysis at the mountain scale will generate an important loss of time if it is expected to know the damage risk of a resort building regarding a potential avalanche hazard that may progress in a particular slope; in this case, the risk analysis should be made at the slope scale. To simplify, it is possible to relate the object and the scales of this kind of studies: at the mountain scale: global environmental impacts; at the massif scale: local environmental impacts; at the slope scale: economical and sociological impacts on persons, structures, infrastructures, communica-tions, etc.; at the snowy coat: behavioural knowledge of the avalanche departure, flow and de-posit. Considering a risk analysis at the civil engineering point of view, the scales of main in-terests are the slope scale and the snowy coat scale. Risk scenarios are basically the chains of events starting from an avalanche departure that lead to catastrophic damages on issues: per-sons, structures, infrastructures, communications networks, etc. When risk scenarios are identi-fied, quantified (departure occurrence and consequences effects) and classified by order of im-portance, it becomes possible to reduce the risk probability (prevention action) or the risk gravity (protection action) in order to put a snowy slope into secure conditions.

Two categories of construction disposals are available to protect buildings against avalanche risk: overall disposals and specific disposals for each construction. The build principles that correspond to overall disposals are: building grouping, orientation and shape of buildings, non-increasing of the risk for the neighbourhood, prevision of an avalanche outlet. The building principles that correspond to specific disposals for each construction are: foresee an access and an entrance on the non-exposed facades, design facades without hold-in corner when there are facing the avalanche-prone slopes, no storage of polluting or dangerous product in poorly re-sistant constructions, foresee an appropriate distribution of the places: the more vulnerable places have to be localized upstream in the avalanche direction. The protection works are clas-sified into two main categories, depending on their location in the departure zone (active pro-tection) or in the flow or deposit zones (passive protection). In both cases, these actions can be provided permanently (without human intervention) or temporarily (with decision taken). The

main works of permanent active protection are: reforestation on seat, wind barrier, snow barri-er, buzzard roof, wind transfer, tire racks, wicker racks, and fillets.

The main works of permanent active protection are: galleries, stems, deflectors, stopping dike, stakes, and road detector of avalanche. The major part of temporary protections consists in the application of several rules to the population in order to prevent a direct exposure to the avalanche risk: traffic restrictions and regulation. This may be done in order to proceed to an evacuation, or on the contrary to maintain people in a safe location until the end of the critical period.

2.4.3.2 Water Flood vulnerability analysis and risk assessment are important for hazard effects mitigation. Erosion and floods are a common problem in Europe which is observable on a medium-term scale. Several causes of varying degree are contributing to it. On the one hand are the dynamic nature of coastal and river zones and climate change, and on the other are the anthropogenic in-fluences. It is increasingly clear that people and assets in some littoral and fluvial urban fronts are endangered and that serious damage and high costs should be expected. To effect sustaina-ble actions, plans should be conceived based on a medium to long-term evolution assessment.

Due to inherent uncertainty the assessment of future conditions can only be done on the basis of scenario evaluations, for which numerical models comprising the present state of knowledge may be used as a tool. To help in ranking action priorities, vulnerability and risk must also be assessed. The risk can be accomplished by crossing vulnerability and degree of exposure in-formation in risk maps depicting spatial analysis (as a recommendation from the European Un-ion, Directive 2007/60/CE, see Directive, 2007). Parameters, such as wave energy, tides, ba-thymetry and topography, shoreline morphology, sediment budget and meteorological conditions are important for a vulnerability analysis. However, zones which are very vulnerable to floods may not necessarily be considered as at risk. An approach similar to the vulnerability analysis needed to be established for evaluating the degree of exposure. Storm surges in combi-nation with river floods can be highly damaging to infrastructure or property, and cause sub-stantial human and economic losses. In terms of exposure levels the parameters considered im-portant are population density, economic activities potentially affected by floods, and ecological, cultural and historical values exposed to devastation by sea actions or floods. Spa-tial classification facilitates mapping the degree of exposure. Risk maps consist of a classifica-tion obtained from crossing vulnerability with degree of exposure. Analysis based on the spatial classification and weighting of the parameters is important for the evaluation of the vulnerabil-ity and the risk of floods (see also Coelho et al., 2009).

2.4.3.3 Landslide Vulnerability to landslide hazards is a function of location, type of human activity, use, and frequency of landslide events. The effects of landslides on people and structures can be less-ened by total avoidance of landslide hazard areas or by restricting, prohibiting, or imposing conditions on hazard-zone activity. Local governments can reduce landslide effects through land-use policies and regulations. Individuals can reduce their exposure to hazards by educating themselves on the past hazard history of a site and by making inquiries to planning and engi-neering departments of local governments. They can also obtain the professional services of an engineering geologist, a geotechnical engineer, or a civil engineer, who can properly evaluate the hazard potential of a site, built or unbuilt. The hazard from landslides can be reduced by avoiding construction on steep slopes and existing landslides, or by stabilizing the slopes. Sta-bility increases when ground water is prevented from rising in the landslide mass by: � covering the landslide with an impermeable membrane; � directing surface water away from the landslide; � draining ground water away from the landslide; � minimizing surface irrigation.

Slope stability is also increased when a retaining structure and/or the weight of a soil/rock berm are placed at the toe of the landslide or when mass is removed from the top of the slope.

2.4.4. Damage assessment methodologies

Following a natural disaster, engineers undertake structural assessments for many different pur-poses; for example, for the assessment of structural safety, quantification of the severity of the event effects or for insurance loss calculation. These purposes are common irrespective of the hazard that may have caused the structural damage. A critical review and comparison of exist-ing methods for the post-event damage assessment of structures under different natural hazards is presented. These hazards have different levels of development in terms of structural assess-ment methods and universal acceptance of these methods. Structural damage assessments are an integral and essential part of the recovery process from a natural disaster, and occur inde-pendently of the nature of the hazard causing the disaster. Immediately after the event engineers must assess all buildings within the affected area to assess damage, safety, and usability, to identify buildings requiring emergency strengthening (e.g. to avoid collapse during aftershocks or further volcanic ash fall), to provide reliable data to the authorities, and to plan further relief and rehabilitation measures. A systematic collection of damage data reduces the time required to complete the work, ensures that no valuable information is lost, and leads to a realistic as-sessment of building capacity. This first stage of structural assessment is often carried out through rapid screening. In the next phase, structures deemed unsafe are assessed in more detail to determine the extent of required repair or need for demolition. In addition to their use for re-covery, structural damage assessments often provide data for future research studies on the re-vision of existing urban plans. The methodology to be adopted for the structural assessment must therefore strike a balance between the need for a rapid and efficient procedure, and the need for detailed data collection for future studies. A comparison of different damage assess-ment methodologies is presented in Rossetto et. Al. (2010b). Again, some examples of hazards damage assessment are presented here.

2.4.4.1 Cyclones A simple classification of potential damages due to cyclones is described in Table 2.4.9, de-pending on the wind speed.

Table 2.4.9. Possible damages to constructions as function of the sustained wind speed

Wind speed (km/h) Damages < 150 Negligible damages to constructions. Some coastal flooding.

150-180 Minor damages to roofs and openings. Significant flooding damages.

180-210 Some structural damages to small constructions (mainly curtain wall failures). More important flooding damages near the coast: small structures destroyed and larger structures damaged by floating debris.

210-250 Significant structural damages. More important curtain wall failures with some complete roof structure failures on small constructions. Important erosion of coastal areas.

> 250 Complete roof failures on most constructions and industrial buildings. Some complete building failures. Flooding causes major damage to lower floors of all concerned structures.

2.4.4.2 Landslides Three kinds of landslide impacts and damages in constructed areas can be outlined: submer-sions, logjams and dams or bridges failure have caused collapses and destruction of buildings; landslides and massive erosion highly damaged the communication networks (roads, electrici-ty…); sediments carried out by the flow have invaded the building, while water imbibed the masonry, causing a long term weakening of the structures.

2.4.4.3 Earthquakes This topic is widely discussed in another Sections of the Final Report. Several methods for post-earthquake inspection and rapid assessment of buildings have been developed in a number of countries. Among these, procedures used in Japan (JBDPA, 1990), USA (ATC 20, 1989; ATC 20-1, 1989; ATC20-2, 1995), New Zealand (NZSEE, 2009), the Balkans (UNDP/UNIDO, 1985) and Italy (Protezione Civile 2010a-c; MEDEA, 2005; GNDT_INGV, 2010a,b) deserve

particular attention (Kappos, 2003). An example of the Japan methodology is presented in Ta-ble 2.4.10.

Table 2.4.10. Criteria for assigning degree of damage (DD) in Japan

DD Damage state of structural member

I visible but narrow cracks on surface of concrete (crack width w<0.2mm)

II visible cracks on surface of concrete (0.2mm <w<1.0mm)

III local spalling of cover concrete, major cracks (1mm<w<2mm)

IV full spalling and crushing of concrete, exposed reinforcing bars

V buckling of bars, crushing of concrete core, visible vertical deformation of column/wall

Table 2.4.11. Tsunami damage scale descriptions for masonry structures typical of Sri Lanka

proposed by EEFIT (2006)

Damage State Damage description for structure

None (DM0) No visible structural damage to the structure observed

Light (DM1) Damage limited to chipping of plaster on walls, minor cracking visible. Damage to win-dows, doors. Damage is minor and repairable. Immediate occupancy

Moderate (DM2)

Out-of-plane failure or collapse of parts of or whole sections of masonry wall panels without compromising structural integrity. Masonry wall can be repaired or rebuilt to re-store integrity. Most parts of the structure intact with some parts suffering heavy dam-age. Scouring at corners of the structures leaving foundations partly exposed but repair-able by backfilling. Cracks caused by undermined foundations are clearly visible on walls but not critical. Unsuitable for immediate occupancy but suitable after repair

Heavy (DM3)

Out-of-plane failure or collapse of masonry wall panels beyond repair, structural integri-ty compromised. Most parts of the structure suffered collapse. Excessive foundation set-tlement and tilting beyond repair. Collapse of wall sections due to scouring and damage non-repairable. Structure requires demolition since unsuitable for occupancy

Collapse (DM4) Complete structural damage or collapse, foundations and floor slabs visible and ex-posed, collapse of large sections of foundations and structures due to heavy scouring

2.4.4.4 Tsunami In the case of tsunami, very few guidance documents have been developed for use in post-event damage assessments. The Intergovernmental Oceanographic Commission of UNESCO (IOC, 1998) has published a post tsunami field guide developed from existing earthquake and tsunami field guides and more recent tsunami surveys (Farreras, 2000). While concentrating on collect-ing scientific data such as tidal levels, run-up elevations and bathymetric data, it indicates that structural damage should be collected where possible, noting the possible cause of the damage and distinguishing tsunami damage from earthquake damage in a near source event. The guid-ance for building damage assessment is brief and recommends rough (non-specialized) classifi-cation of damage, estimating the nature and category of the damage and its apparent cause.

Several approaches exist for identifying tsunami intensity (e.g. Ambraseys, 1962; Papado-poulos and Imamura, 2001). However, these methods do not provide techniques for identifying structural damage. Most of the literature presenting rapid field investigations largely bases their damage assessments on earthquake assessment methodologies directly. Rigorous, multi-stage building assessments using forms such as those of ATC-20 (ATC 20, 1989) have not been car-ried out, or at least have not been published. Instead, the damage scales in EMS-98 are the most commonly used (e.g. in Miura et al., 2006). A few studies have attempted to modify earthquake damage assessment methods and scales to take into account damage relating to fast-flowing wa-ter, such as foundation failure due to scour or floating debris impact damage. A modified ver-sion of the EMS-98 damage scales for use in tsunami damage assessment in Thailand and Sri Lanka following the Indian Ocean Tsunami was proposed by Rossetto et al. (2007) and EEFIT (2006). In these studies damage attributed to different building types was also adopted to assign intensity values to the surveyed locations, using a modified version of the Tsunami Intensity

scale of Papadopoulos and Imamura (2001). An example of the damage scale descriptions for masonry buildings proposed by EEFIT (2006) is shown in Table 2.4.11.

Taking into account damage to different structural types allows the intensity values to be compared in countries with different building stocks, to obtain a comparative intensity for tsu-nami impact assessment. The results of these surveys do not provide sufficient information however to improve knowledge on the structural response of buildings under tsunami loading and therefore are not useful for the re-evaluation of codes of practice, assessment of existing structures etc.

2.4.4.5 Volcanic eruption This topic is largely discussed in another part of the Final Report (Section 2.5).

2.4.5 An example of field investigation: L’Aquila Earthquake

Even if the topic regarding earthquakes is largely discussed in another parts of the Final Report, the field investigation in the city of L’Aquila (Abruzzo Region, Central Italy) after the April 6th, 2009 seismic event (a general description of the seismic event and its consequences is given in Indirli, 2010) is here briefly discussed, because it involved some of the authors. After the earth-quake, the PLINIVS Centre (Naples), coordinated by Prof. G. Zuccaro, made an extensive dam-age survey of the whole historic centre of L’Aquila, with the contribution of experts of COST Action C26 (COST 2006). The COST researchers, in addition to an overall review of the con-sequences of the earthquake in L’Aquila and its surroundings, performed a detailed damage as-sessment of structures of three areas of the historic city centre. The AeDES (Protezione Civile, 2010a) and the MEDEA (MEDEA, 2005) survey methodologies were utilised, with respect to masonry and reinforced concrete structures (see details in Borg et al., 2010; Kouris et al., 2010).

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