Sandrine Ville

Jesús González-Feliu

INRETS Laetitia Dablanc

The limits of public policy intervention in urban logistics: The case of Vicenza (Italy) and lessons for other European cities

Keywords: urban logistics, local policy, regulations, urban distribution centres, competition

For over fifteen years, the subject of urban logistics has preoccupied many, including public decision-makers. This paper seeks to identify the limits beyond which regulations restricting vehicle access to limited traffic zones may be sanctioned for abuse of power. Here, we present the case of Vicenza (Italy), which has implemented very restrictive regulations. Based on this case study, certain lessons can be drawn for other urban areas in Europe.

Introduction

Freight transport provides an essential link between goods supply and demand. The freight sector is a major source of jobs, but is facing problems related to congestion and environmental concerns, especially in urban areas. With the expansion of urban areas and the growth of their populations, urban goods transport contributes to negative effects like congestion, CO 2 emissions, and local pollution, as well as societal issues such as noise (LET et al. 2006). For example, goods transport is responsible for around 30% of NOx emissions and almost half of particulate matter emissions resulting from urban transport (LET et al. 2006). For these reasons, cities' supply systems must be restructured. This objective of reorganizing goods flows within urban areas in the interest of sustainability is now commonly referred to as "urban logistics" [START_REF] Dablanc | Goods transport in large European cities: Difficult to organize, difficult to modernize[END_REF].

For more than fifteen years, the subject of urban logistics has preoccupied public decision-makers (elected officials and city planners), logistics professionals, freight operators, and researchers. An increasing number of studies are addressing the subject [START_REF] Dablanc | Transport de marchandises en ville. Une gestion publique entre police et services[END_REF][START_REF] Routhier | Mesurer l'impact du transport de marchandises en ville -le modèle Freturb (version 1)[END_REF][START_REF] Taniguchi | City Logistics -Network modelling and Intelligent Transport Systems[END_REF][START_REF] Boudouin | Logistique urbaine : l'optimisation de la circulation des biens et services en ville[END_REF][START_REF] Patier | La logistique dans la ville[END_REF][START_REF] Ambrosini | Objectives, Methods and Results of Surveys Carried out in the Field of Urban Freight Transport: An International Comparison[END_REF][START_REF] Anderson | Urban logistics -how can it meet policy makers' sustainability objectives[END_REF]Munuzuri et al., 2006;[START_REF] Dablanc | Goods transport in large European cities: Difficult to organize, difficult to modernize[END_REF][START_REF] Patier | Du transport de marchandises en ville à la logistique urbaine[END_REF][START_REF] Crainic | City Logistics[END_REF][START_REF] Patier | How to Improve the Capture of Urban Goods Movements[END_REF][START_REF] Quak | Delivering Goods in Urban Areas: How to Deal with Urban Policy Restriction and the Environment[END_REF][START_REF] Dablanc | Freight transport, a key for urban economics. Guidelines for practicionners[END_REF]. It is a central theme of many colloquia, exchanges, initiatives, and experiments. Among the most popular urban logistics concepts is that of an Urban Consolidation Centre (UCC). A UCC is "a logistics facility situated in relatively close proximity to the geographic area that it serves (be that a city centre, an entire town or a specific site such as a shopping centre), to which many logistics companies deliver goods destined for the area, from which consolidated deliveries are carried out within that area, in which a range of other value-added logistics and retail services can be provided." [START_REF] Allen | Good Practice Guide on Urban Freight[END_REF]). To the above definition, we add that public authorities very frequently provide financial support for their operation. Because of their very central locations, UCCs often require significant real estate expenditures, which are generally covered by public funds.

These urban terminals emerged in the 1990s, when there were more than one hundred of them, notably in Germany and the Netherlands. UCCs ran up against difficulties related to municipalities' hesitancy to continue subsidizing experiments. Today, there exist only about 20 genuinely significant consolidation terminals of this kind, notably in Italy (SUGAR, 2010). It is difficult to construct a typology of these terminals because UCCs are very diverse. But whatever its form may be, a UCC's effectiveness seems to depend heavily on the presence of appropriate local regulations, including vehicle access rules for the zone covered by the UCC and benefits accorded to UCC operators. Thus, the question emerges as to how far authorities can carry regulations before they risk legal challenges. This paper will attempt to answer this question through the example of the town of Vicenza in the North of Italy. The Vicenza consolidation centre involved the most daring regulations that we know of, and allows us to identify the effects of such decisions, as well as the legal risks surrounding such measures for European cities today and in the future. After describing UCCs and their principal components, we shall present our case study. First, we shall study the individual regulatory steps toward full UCC implementation. We will look at the motives of the different parties involved, as well as court decisions regarding a complaint lodged by carriers who were unhappy with changes in local regulations intended to favour UCC use. Finally, lessons drawn from the Vicenza case will be generalized to other European cities.

Urban Consolidation Centres: definitions and typology

Until the 1980s, deliveries in urban areas followed the same logic as interurban freight transport. In this schema, each carrier made its own deliveries from one or several grouping/de-grouping terminals located at varying distances from the final recipients. In response to societal and consumer demands, new ways of consolidating flows in dense urban zones have emerged in recent years, aiming for a decrease in the number of vehicles and pollution, as well as an increase in productivity. These new forms of organization are founded on new logistic terminals specifically conceived for urban consolidation. Goods flows are bundled, and their delivery is coordinated. The objective is to serve the city with fewer vehicles that are better loaded and make less frequent deliveries to each recipient. Often, these vehicles run on natural gas or electricity in order to lessen the environmental impact of the new system.

In France, more than twenty UCC projects have appeared in PDUs (Urban Mobility Plans) since the Law on Air and the Rational Use of Energy (LAURE) was passed in 1996. This law required cities to develop PDUs, which include freight transport policy strategies. In Europe, more than one hundred UCCs were implemented, but most of them did not produce the expected results [START_REF] Dablanc | Les centres de distribution urbaine : un tableau comparatif[END_REF]Boudouin, 2006). Experiments were also carried out in Japan, where two UCCs are still functioning today [START_REF] Dablanc | Freight transport, a key for urban economics. Guidelines for practicionners[END_REF]. Only a few of these experiments made the transition into truly operational, financially sound systems. Other types of UCC have appeared (such as construction consolidation centres, specializing in the management of deliveries to construction sites), as well as UCCs in historic cities and heritage sites, e.g. Italian cities, La Rochelle, and Monaco. [START_REF] Dablanc | Goods transport in large European cities: Difficult to organize, difficult to modernize[END_REF]SUGAR, 2010). There are many reasons for the diversity of these European experiments, primarily related to two issues: the economic sustainability of the delivery system paired with the physical terminal, and the reliability of the service it offers.

The first UCCs were private or semi-private initiatives on the part of individual businesses or groups of carriers, and were created in the interest of optimization [START_REF] Dablanc | Les centres de distribution urbaine : un tableau comparatif[END_REF]. Later, environmental concerns prompted public administrations in several countries to design such systems for urban goods distribution in medium-sized towns. It was more difficult for similar projects in larger European cities to make the transition into functioning systems, and they generally did not continue operating over the long term [START_REF] Gonzalez-Feliu | Models and methods for the City Logistics -The Two-Echelon Vehicle Routing Problem[END_REF]. Based on studies of several UCC experiments in Europe [START_REF] Dablanc | Les centres de distribution urbaine : un tableau comparatif[END_REF][START_REF] Dablanc | Transport de marchandises en ville. Une gestion publique entre police et services[END_REF][START_REF] Rosini | City Ports Project Interim Report[END_REF]Boudouin, 2006;Spinedi, 2008;[START_REF] Bestufs | BESTUFS II Bibliografic Overview[END_REF]SUGAR, 2010) we can establish the following typology:

• "Private" or "semi-private" UCCs (carriers' or shippers' projects for internal operations, without a direct influence from public authorities other than some financial assistance). These UCCs have an essentially economic purpose, and contribute to their users' business development strategies. They are generally created by a freight carrier or logistics provider. • "Multi-user" UCCs (projects created by municipal authorities or groups of businesses, with the intent to provide a service open to all potential users). These terminals are generally combined with services promoted and supported by public authorities, and are sometimes referred to as a "public freight service", though this term is still rarely used and has no legal definition in many countries. • "Specialized" UCCs (mainly for construction and airports). They may be temporary (centers associated with a specific construction site or large moving operation) or permanent (in airports, in entertainment parks). However, they do not always serve an urban environment, unlike the two categories described above.

The following lesson can be drawn from fifteen years of experiments in Europe, most of which have been unsuccessful: except in unusual circumstances, the objective of consolidating intra-urban delivery tours is not in itself sufficient to economically justify new infrastructure and changes to carriers' habitual organization. The cost of additional transhipping in the logistic chain is not covered by the financial gains associated with consolidation, especially when done in an urban terminal [START_REF] Gonzalez-Feliu | Mise en place d'une méthodologie pour un bilan environnemental physique du transport de marchandises en ville[END_REF]. A city that would like to implement a scheme for consolidating urban deliveries must therefore take additional financial and regulatory measures to guarantee a comparative advantage for the UCC. It is particularly important to accompany the UCC with regulations favouring its use.

First and foremost, an urban logistics solution must be economically viable (Henriot et al. 2008). The simple presence of a logistic terminal such as a UCC is in no case sufficient to assure a scheme's profitability. In the preparation and planning of a socially, economically, and environmentally sustainable logistic system, several different elements must be considered [START_REF] Morana | Sustainable supply chain management in city logistics solutions: lessons learned from the case of Cityporto Padua (Italy)[END_REF]. Based on suggestions from the European Commission (1998), [START_REF] Dablanc | Transport de marchandises en ville. Une gestion publique entre police et services[END_REF][START_REF] Patier | La logistique dans la ville[END_REF], as well as the conclusions of the second congress of the Italian Association for Urban Logistics [START_REF] Spinedi | Atti del II convegno nazionale city logistics, Roma, maggio 2006[END_REF] and recommendations from the European BESTUFS network (BESTUFS, 2009), we have identified the following components:

• Infrastructure. For the terminals themselves, particular care must be taken in the search for available urban real estate close to the service zone. However, they are not the only relevant type of infrastructure. Lanes or parking areas reserved for freight transport may favour the use of a delivery system in dense areas. • Logistic organization of transport. This item includes the principal design, planning, and optimisation steps for the system's logistic chain. They allow the definition of the logistic system's main organisational strategies. • Technologies. In general, two types of technologies are used. Information and communication technologies (ICTs) promote the exchange of information, vehicle or merchandise tracking, and other transport support operations. Vehicle technologies, specifically those related to the engine, allow reductions in pollutant emissions and help improve air quality. • Communications. This item refers to processes and means for communicating with potential users of the system, as well as other stakeholders directly or indirectly involved in the urban logistics system. • Funding. For most urban logistics systems, private funds alone are not sufficient to cover the costs of establishing a UCC and its vehicle fleet (often composed of "clean" vehicles). Public subsidies and low-cost reuse of existing facilities are the most common forms of assistance when launching an urban logistics project.

Operational costs can sometimes be covered by revenue, notably in cases where the system manager is also the facilities' owner. • Regulations. Public authorities can put legislation or other regulations into place to promote use of the system they offer. These regulations can be restrictive (requiring or strongly inducing vehicles to use the UCC) or founded instead on advantages accorded to users.

The case of Vicenza

As we mentioned above, the creation of a UCC generally implies creating more or less restrictive traffic regulations. For example, the creation of a UCC in La Rochelle, France involved numerous municipal ordinances reducing freight vehicle access to the city centre. Thus, in La Rochelle, lorries over 3.5 tonnes gross vehicle weight are now prohibited from delivering to the historic centre between 6 AM and 7:30 AM. These restrictions have not been controversial. The case of La Rochelle, like that of Vicenza, does however raise legal questions. Both municipalities have decided to make urban goods delivery a public service, which was then delegated to their respective UCCs. As organizing authority for public transport, the La Rochelle metropolitan authority accorded management of three urban transport services (including goods delivery by electric vehicles in the centre) to Veolia after a bidding process. Only UCC vehicles are allowed to use the city's bus lanes, which provides a considerable competitive advantage. Though the delegation of public freight services posed no problems in La Rochelle (as traffic restrictions are fairly limited and have exceptions) 1 , it has been the subject of much debate in Vicenza, where a series of city ordinances has gradually reduced delivery vehicle traffic within the municipal territory until finally all vehicles except the UCC's were forbidden. This policy provoked outcry among transport operators, who created an association and challenged its validity in court. It is for this reason that we have decided to examine the Vicenza case and present our findings here in detail. To do so, we will first recall some facts (3.1), then present the judges' decision (TAR Veneto, the Regional Administrative Tribunal of Veneto) (3.2), and finally look at the Italian State Council's ruling and opinion (3.3).

The facts

The historic centre of the town of Vicenza was given UNESCO world heritage status in 1996. In order to protect its cultural heritage2 Vicenza adopted municipal ordinance 3474 on 20 June 1996, which creates pedestrian and limited traffic zones (LTZ)3 . When the desired results were not achieved, the municipality launched an ambitious program4 intended to rationalize the distribution of goods in the city. To do so, the municipality implemented an urban logistics pilot program 5 , which created a consolidation terminal and assured pick-up and delivery for packages within the LTZ using clean electric vehicles. Vicenza City Centre Logistics (Veloce) 6 was created to carry out the plan and provide goods delivery services to all participants in the zone. This organization was to manage freight flows arriving at and leaving from the logistic terminal, using advanced warehouse management technologies. Additionally, Veloce carried out urban pick-ups and deliveries using clean electric vehicles. The city chose to gradually implement the system so participants would have time to familiarize themselves and adapt to it. A series of municipal ordinances were applied in 2005 and 2006, progressively limiting traffic access to the LTZ. They are as follows:

-Ordinance 22453 of 28 April 2005 created an exception to the ban on delivery vehicles for "air carriers" 7 , who were allowed to use any kind of vehicle in the LTZ during certain time windows, up until 30 June 2005. -Ordinance 35219 of 30 June 2005 then granted "air carriers" access to the LTZ at certain times, but only if they used a low-environmental-impact vehicle. This ordinance remained in effect until 30 September 2005. -Ordinance 36780 of 29 June 2006 created special delivery permits granting freight carriers access to the LTZ within certain time windows with low-impact vehicles. There was a maximum of five permits per carrier. This ordinance remained in effect until 31 August 2006. -Ordinance 47471 of 30 August 2006 renewed the requirement for carriers to use low-impact vehicles to access the LTZ, as well as the need for a special delivery permit. There was a limit of five permits per carrier, and access was permitted only between 7 and 9 AM. This ordinance remained in effect until 31 December 2006.

-Ordinance 72012 of 29 December 2006 restricted LTZ access to only electric vehicles operated by Veloce. No "air carrier" exception was provided.

These severe restrictions on the free exercise of commerce and industry in the historic centre of Vicenza led to discontent among specialized international express carriers such as DHL Express Ltd, TNT Global Express SpA, Federal Express Europe Inc., and United Parcel Service UPS Italia SRL, who then created an association called AICAI (Associazione Italiana Corrieri Aerei Internazionali)8 and challenged the validity of these municipal ordinances in court. According to one of their representatives who we were able to contact, "The case of Vicenza did not endanger our companies in itself. But it was symptomatic of a future challenge from Italian cities as a whole to the presence of our vehicles."

The court of first instance: the ruling of the Veneto Administrative Tribunal on 23 January 2008

The AICAI association requested before the Veneto regional administrative court (TAR Veneto first section) that certain Vicenza municipal ordinances be annulled. At a public hearing on 22 November 2007, the association presented several arguments in support of its request9 :

-Violation of article 6D of decree 261/99 transposing EC directive 97/67/EC concerning liberalisation of the postal sector. As the Veloce company was publically funded, its handling of packages was contrary to the liberalisation of the postal sector. -Violation of European regulation D 2002/2320/EC concerning civil aviation security. In order to provide express postal services, a carrier must be considered a "regulated agent". To obtain this status, the carrier must require its personnel to take classes on the safety and security of freight, maintenance, warehousing, and onboard equipment. While all members of the AICAI association were qualified, Veloce was not. Consequently, it was conducting business illegally. -Abuse of rights and violation of articles 82 and 86 of the EC Treaty. The logistic terminal gives all goods distribution to a single operator. It thus eliminates all competition between carriers. Carriers are required to use the terminal and transfer goods to Veloce if they wish to deliver to the LTZ10 . Though member states and public entities in general are permitted to limit competition (notably by reserving a monopoly over a specific activity) this must be the only way to achieve a public objective. According to AICAI, this is not the case in Vicenza, as the solution chosen by the municipality is inadequate and disproportionate to the desired environmental goal. In addition, the use of small vehicles would increase the number of lorries in circulation and the public health impact would be marginal, as the terminal serves only one small zone.

For its part, the city of Vicenza asserted that the measures taken were entirely justified, given the objective of reducing pollution and protecting health in the city centre. Veloce's transport service was compatible with safety enforcement. Finally, this system was a local public service, and thus did not violate article 13 of legislative decree 223/2006 concerning the right to competition.

The tribunal rendered its decision on 28 January 2008. It confirmed that the regulations in question had created an obligation for carriers to concede their goods to Veloce in order to carry out the final leg of the contracts they established with their clients. Thus, these regulations required carrier substitution, in violation of Italian civil law. In addition, Veloce was forbidden to offer express package services, particularly for packages which had been previously shipped by air, as the company had neither the necessary authorization to do so (article 6, decree 261 of 1999) nor regulated agent status. Nonetheless, the tribunal did not consider the measures taken by the city to be contrary to the liberalization of the postal sector, as their impact was limited to one zone of the municipality rather than the entire national territory.

The tribunal thus ruled in favour of the AICAI association's request, and annulled the measures in question. The city of Vicenza and Veloce then submitted an appeal to the Italian State Council.

The position of the Italian State Council in the Vicenza case: the decision of 3 February 2009

The appellants' arguments

The city of Vicenza and the Veloce company (hereafter referred to as the appellants) offered several arguments in support of their appeal:

-On the alleged violation of national and European legislation concerning the liberalisation of the postal sector by municipal ordinances, and the obligatory substitution of Veloce for private carriers when carrying out the final leg of transport contracts. The appellant maintained that Veloce's intervention is very limited, concerning only the central LTZ area. Consequently, the municipal ordinances in question cannot be interpreted as a general limitation or an attack on the liberalization of postal services. They also stated that Veloce possesses the required legal authorization to conduct express letter and parcel transport because it was created specifically for this purpose. Finally, they underscore that it is in no way an objective of Veloce to replace private carriers. On the contrary, the organization's only goal is to contribute to a reduction in pollution within the central zone while protecting both cultural heritage and citizens' health. -On the violation of legislation concerning air freight security, and the lack of "regulated agent" status. The appellants again recall that the city of Vicenza's objective is not to replace or compete with express air carriers, but rather to protect public health, the environment, and historic heritage sites. The measures taken by the municipality could be adapted to meet airfreight security requirements. -On lack of reason and abuse of power. The appellants reaffirm that the legal basis for the appeal is an article of traffic code law 285 (30 April 1992) which allows municipalities to "limit access to all or certain categories of vehicles in order to prevent pollution and protect historic and artistic heritage (...) by the creation of pedestrian and limited traffic zones". This power is principally exercised by municipalities. Thus, the municipality was simply duly exercising its regulatory powers.

The State Council's opinion

Before announcing its opinion, the Italian State Council briefly recalled the precedent on measures limiting automobile access to centre cities. It mentioned several decisions 11 and recalled that decisions regarding vehicle access to urban centres can be made at the discretion of the competent authorities. Their legality can only be questioned on the basis of legitimacy and justification. The partial restriction of traffic is always justified when it is necessary for the protection of cultural or environmental heritage. 12 The State Council then overturned the lower court's decision on several points:

-The alleged violation of free competition, and anticompetitive practices on the part of Veloce. The State Council declares that this argument is unfounded. Indeed, the municipality of Vicenza did not discriminate among the various international carriers. The idea that the Italian postal service benefitted from an exception, to the detriment of the international air carriers was rejected, for the Italian Post was serving a general public service role. The State council also rejected the argument that the example of Vicenza could create a risk in other municipalities.

-The alleged violation of legislative decree 261 of 1999 and of articles 82 and 86 of the EC treaty by municipal ordinances. According to the State Council, the decision to restrict traffic in the historic centre cannot be annulled based on accusations that it limits free competition. The Council recalls that the principle of free competition concerns all economic sectors, not only the freight transport domain. Additionally, such restrictions are coherent with municipal public health and environmental objectives, and do not seem at all disproportionate.

-The prohibition of public financial contributions to any business, and the consequent illegality of the Vicenza municipality's financial support for the Veloce company. The State Council recalls that this prohibition is not applicable to businesses providing local public services. 13 The Council then underscores that Veloce offers a local express freight public service, and that this service benefits only the municipality of Vicenza. Consequently, public funding is entirely legal.

-Finally, concerning the lack of justification for the measures taken by the city of Vicenza. The coherence of the measures taken with environmental and cultural protection objectives depends on concrete facts, on which the State Council may not pronounce an opinion. 14 Having read this opinion, we can deduce the State Council's ruling: it accepted the appeal by Veloce and the municipality of Vicenza, and overturned the decision of the Veneto Regional Administrative Tribunal. As the state council is the highest Italian administrative judicial body, the decision of 3 February 2009 is considered res judicata and is consequently definitive. Nonetheless, as all national-level means of appeal have 11 Plurimis ex, sect. V, 4 Mars 2008; n. 824, sect. V, 11 December, 2007; 6383, sect. V, 29 May 2006; no. 3259, pour. Plen. 6 February, 1993, n. 3. 12 The state council also specifies that placing restrictions on particular categories of vehicles rather than all vehicles does not constitute unjustified discrimination. Additionally, articles 16 and 41 of the Constitution (supported by the AICAI association) are not violated when measures are applied to a limited urban zone rather than the entire national territory. 13 See Cons. St., Sec. V, 25 August 2008, n. 4080. 14 It declared nonetheless that it is not certain use of small electric vehicles to make deliveries in Vicenza's historic centre will increase the total number of vehicles to 18.

failed, the AICAI association may now bring an appeal before the European Community's court of justice. We may then speculate on the ECJ's position when faced with the Vicenza case.

Firstly, it is not certain that the European Court will agree with the idea that urban goods distribution can be a public service. Of course, the transport sector is the only one for which the EC treaty mentions a need for "public services". 15 However, the notion of "public service" is generally associated with passenger transport rather than freight. Member states do have the option of creating public service obligations, defined as obligations that "...carriers would not assume if they were solely considering their commercial interest." Now, in the case of urban freight delivery there is no "deficiency" in the service provided by private carriers. Consequently, public initiative does not fill a void but rather directly competes with private firms. Thus, it is not certain that the ECJ would agree that such services are of economic interest. 16 Secondly, while the State Council rejected the argument that there was risk of a "snowball effect" on other Italian towns, the threat does seem plausible. Though traffic restrictions in the LTZ of Vicenza will have only minimal economic effects on express freight businesses (as Vicenza is a rather small town), the risk is more serious when we consider metropolitan areas like Milan or Rome, or even larger cities elsewhere in Europe. We must then ask ourselves what lessons other European towns can draw from the Vicenza case. Is this an "Italian exception" to be understood in the unusual context of Italian urban consolidation centres, or on the contrary will it become a point of reference for other European cities?

Lessons for European metropolitan areas

The "Vicenza precedent" that we have just presented concerns a seemingly minor subject in transport law: restrictions on freight transport vehicles' access to city centres. However, we find that this case yields significant lessons for transport, environment, and urban planning practitioners in European cities. The Italian State Council reaffirmed and restated the right of a municipality to considerably restrict the free movement of goods transport vehicles in historic centres. This was done within the specific framework of Italian law, but also based on environmental arguments which are explicitly or implicitly present in numerous regulatory projects targeting freight traffic in large European cities. By rejecting the abuse of power accusations brought against the city by an association of large international express carriers, the State Council has in a sense confirmed that cities may act strongly to protect the environment.

The Vicenza case should be understood in the particular context of Italian urban consolidation centres. Around ten urban consolidation terminals now exist in Italy. They are in different stages of implementation, but all share the purpose of protecting historic centres with rich architectural heritage. We should also note that own-account transport 15 Article 73 of title V, devoted to transport, states that "Aids shall be compatible with this Treaty if they ... represent reimbursement for the discharge of certain obligations inherent in the concept of a public service". 16 European law speaks of "economic interest" rather than public service. Services of general economic interest are public undertakings that member states must hold to specific public service requirements (article 86 -ex-article 90-of the EC Treaty). This is the case for network services like transport, energy, and communications. For further information on this subject, and specifically the question of public aid, see the ECJ's Altmark judgement of 24 July 2003 and the "Monti texts" adopted by the Commission on 13 July 2005.

plays an important role in supplying urban business sites in Italy: 80% of delivery vehicles in cities are own-account, but only 20% of tonne-km are handled on an ownaccount basis. 17 Likewise, even when third-party shipping is used, it is dominated by the padroncini, small individual entrepreneurs. These two groups, the own-account shippers (i.e. shop holders or artisans handling their own supply and delivery) and the small third-party carriers, have a characteristic in common: under-optimisation. They generally do a small number of poorly organized tours, and on average their vehicles are far from full. Urban goods distribution is under-optimized everywhere in Europe [START_REF] Dablanc | Goods transport in large European cities: Difficult to organize, difficult to modernize[END_REF] but this phenomenon reaches an extreme in Italian cities. We can understand that under these conditions, Italian local officials attempt to "force" freight transport optimization in city centres. Thus Vicenza is one of several Italian municipalities that make use of particularly innovative regulations. The example of Parma is also interesting. City ordinance 249 of 29 September 2008 creates an "accreditation" that carriers must obtain if they wish to deliver to the historic centre. If they are not accredited, they must use the services of Ecologistics, a UCC. The criteria for receiving accreditation are the following:

-Use of vehicles meeting the Euro 3 norm (i.e. vehicles manufactured during or after year 2001).

-Vehicles must be loaded to 70% of capacity (in volume or weight).

-Vehicles must possess a geo-positioning system that allows tracking. " 20 This is also the position of La Rochelle, which transferred management of its Elcidis consolidated freight delivery system to Veolia in 2006. In this way, Elcidis benefits from operational subsidies. UCCs that planned on medium-or long-term financial independence were unable to survive; this was the case for many UCCs in Germany, the Netherlands, and Switzerland at the end of the 1990s, and more recently Genoa in Italy.

On the other hand, other cities elsewhere in Europe do not consider the rationalization of freight delivery to be a municipal responsibility, but rather the result of market 17 These figures were cited during a debate between experts and local officials at the Padua City Logistics Expo in 2007. 18 Statements made at the City Logistics Expo mentioned above. 19 The Emilia-Romagna region spent 11 million euros for this tye of projects (SUGAR, 2010). 20 Statements made at the City Logistics Expo mentioned above.

mechanisms within each economic sector present in the city. There, local public action directly targeting freight transport involves more traditional, though updated measures such as delivery vehicle access restrictions based on tonnage or pollution criteria, or traffic and parking plans and the creation of delivery zones on the roadway or within businesses themselves. The introduction of information and communications technologies can reinforce these traditional measures (e.g. cameras able to read license plates and verify lorry access, or devices near roadside delivery areas enforcing maximum delivery times). Any shared delivery terminal in these cities is a result of private initiative, supported if necessary by a few public measures that are nonetheless lightweight and not of a financial nature.

The Italian legal decisions concerning Vicenza are relevant to both schools of thought.

For cities interested in proactive rationalization of urban freight, the Vicenza case reveals the position of large express carriers present in Europe. On one hand, they wish to "green" their urban operations in order to improve their image. In Paris, TNT thus subcontracts all of its central neighbourhood deliveries to Green Logistics, a start-up that offers an urban delivery service using only electrically assisted tricycles. On the other hand, these carriers remain cautious and take legal action when they believe that local authorities are overstepping their legislative bounds or contradicting European competition law. One of the participants in the case against Vicenza confirmed for us that the AICAI's failure before the State Council had not weakened the plaintiff's determination, and that additional legal action would be taken. Other cities in Italy and Europe can thus expect legal challenges if they create UCCs that place heavy access restrictions on delivery vehicles not owned by the UCC. We also see that the administrative judge was accepting of localized policies restricting vehicle access and promoting municipal goods consolidation terminals.

For cities that have not created a centralized delivery system, the Italian State Council's decision may raise concerns about the possible legal obstacles to public action on freight transport and delivery operations. The Italian State Council decision is clearly part of a more general shift in European case law over the last several decades: measures that restrict lorry traffic and logistic operations for environmental reasons have become acceptable [START_REF] Dablanc | Goods transport in large European cities: Difficult to organize, difficult to modernize[END_REF]. European cities find themselves in a situation where action targeting freight transport traffic will be increasingly challenged by freight carriers, but accepted by judges.

Conclusion

In this article, we have commented on an Italian Court decision and evaluated its significance for European cities. This decision by the highest Italian administrative court, the State Council, authorized the city of Vicenza to continue its implementation of a consolidated delivery terminal, which included strong access restrictions on other carriers' vehicles within the city centre. This case is specific to Italian cities and the Italian legal system, but is also significant for other European cities. It demonstrates that large national and international express delivery groups (such as UPS, TNT, and DHL) are increasingly wary of centre-city access restrictions. This increases the risk of legal complications. However, this case may also reassure municipalities that court authorities are generally positive toward municipal measures targeting freight transport vehicles. This acceptance depends mostly on environmental arguments. While urban goods transport is essential for cities' economic well being, it is also recognized as a significant source of pollutants and greenhouse gasses.

The Vicenza case also highlights a unique option chosen by certain European cities: the urban consolidation centre (UCC). A UCC is a localized terminal very close to a city centre, which receives and distributes goods flows for businesses in the central zone in a shared, consolidated manner. Because of their very central location and other reasons beyond the scope of this paper [START_REF] Dablanc | Les centres de distribution urbaine : un tableau comparatif[END_REF]Boudouin, 2006;[START_REF] Allen | Good Practice Guide on Urban Freight[END_REF][START_REF] Dablanc | Freight transport, a key for urban economics. Guidelines for practicionners[END_REF], UCCs are costly affairs and often require public subsidies. The city of Vicenza and around ten other Italian cities have chosen to act directly on the organization of goods flows with UCCs, and have taken financial responsibility for this choice. However, we would not suggest that other cities follow the example of Vicenza or La Rochelle.

Paradoxically, the decision analyzed above supports this point of view. It shows that environmental and public health concerns are sufficient to justify traditional but strengthened municipal measures, such as access restrictions on those vehicles that produce the most pollution. It is perhaps not useful for most European cities to imagine taking more proactive measures like the creation of urban consolidation centres. The primary conclusion of our article is thus the following: cities can benefit from the "positive" side of the Vicenza ruling (the judge's affirmation that municipalities have a large degree of freedom in organizing their traffic and access restriction) while avoiding the additional legal complications and risks associated with coordinated municipal consolidation terminals' projects. These schemes are costly and may create dissatisfaction among freight carriers and logistics firms, leading to legal conflicts. UCCs do have excellent local environmental performance, but affect a very minimal proportion of total goods flows in an urban area 21 . Thus, they help improve environmental conditions, but their contribution is marginal at the metropolitan scale.

While the UCC concept is interesting, UCCs alone are not sufficient to resolve congestion and other freight-related problems. It is therefore important to study alternatives to the single-operator urban consolidation model of Vicenza or La Rochelle, such as collaborative solutions [START_REF] Morana | Sustainable supply chain management in city logistics solutions: lessons learned from the case of Cityporto Padua (Italy)[END_REF], the free use of terminals with incentives for consolidation (Spinedi, 2008), dedicated delivery areas (SUGAR, 2010), low emission zones (SUGAR, 2010) and above all a mixture of public policy, quality standards, technological solutions, and organizational systems which promote urban goods flow rationalization while respecting the legislation on free competition and incorporating changes agreed upon by stakeholders.

  Despite these facts, we do not consider the Vicenza case to be of interest only in Italyit has European significance. First, it is part of a structural change opposing two schools of thought, two different visions of city logistics. Some European cities, including Italian ones but also others like La Rochelle in France or Monte Carlo in Monaco, consider a publically subsidized UCC (preferably paired with restrictive municipal regulations) to be the only way to assure successful rationalisation of urban goods distribution. According to 2007 data on Italy, 40 million Euros were spent on urban consolidation experiments, of which 33 million resulted in truly functional systems. The remaining 7 million financed studies for new projects.18 Public funds come primarily from the regions, 19 the Environment Ministry, the European Union (through INTERREG projects), and municipalities. These funds are used to lease a terminal, buy electric or gas-powered vehicles, or assure the day-to-day operation of UCCs. Client fees are not sufficient to cover expenditures for the complete project (including initial investments) or even operations. The mayor of Parma has stated that "In this case, the market simply does not work spontaneously. Public authorities must accept that financial assistance is necessary and provide it, and that's what we do.

In La Rochelle, few transport firms have their own logistic terminal. They are therefore relatively content to take advantage of Elcidis (the UCC).

Stated motives also included public health concerns.

The ordinance creates time slots during which delivery vehicles will be permitted to park on the street, but only for loading and unloading operations.

Decision

on 28 December 1999.5 The project was adopted in accordance with the general orientations established by the Transport Ministry in the "General Plan for Transport and Logistics", and included in the "National Transport Plan" and the city plan.6 This company was created by resolution 21, on 20 March 2003. 7 "Air carriers" are those who provide express services using air modes for package transport, such as DHL or FedEx.

Italian Association of International Air Express Carriers.

The arguments were presented per municipal ordnance, and their content is thus repetitive. In order to conserve space, we have decided to present them together in summary.

Shippers are also required to go through Veloce if they wish to ship merchandise out of the LTZ.


A Réveillère

P Gehl

D Seyedi

H Modaressi

Development of seismic fragility curves for damaged reinforced concrete structuresPaper Title Line 1 mainshock-damaged reinforced-concrete structures

Keywords: time-dependent vulnerability, damage accumulation, aftershock fragility, dynamic analyses

This communication presents an original procedure to derive fragility curves for previously damaged structural systems. These damage state-dependent functions constitute an important component in the framework of timedependent risk assessment. For instance, they are used to estimate the updated vulnerability of structures exposed to potential aftershocks, based on the knowledge of their damage state after the main seismic event. While the state-of-the-art method for deriving such functions relies on incremental dynamic analysis, the present work proposes an alternative approach based on (i) the application of sequences of ground-motion records to the undamaged structure in order to have a representative panel of structures in each damage state, and (ii) an innovative statistical treatment of the permanent residual drift of damaged structures to derive the fragility functions: the maximum transient additional drift ( is correlated to the intensity measure of the ground motion, and the influence of the initial permanent drift is then eliminated by estimating its distribution for a given initial damage state. The developed procedure is applied to a single story reinforced-concrete frame with a concentrated plasticity model and fragility curves are proposed for various initial damage states.

INTRODUCTION

Most of the seismic risk assessment tools only consider an initially undamaged structure hit by one mainshock event. However, structures may be initially damaged from past earthquakes, and a seismic sequence is commonly made of a mainshock followed by series of aftershocks. In this post-mainshock context, during which the structure is not repaired, the rate of earthquake occurrence is significantly increased (due to the presence of aftershocks) and the physical vulnerability of possibly mainshockdamaged buildings may also increase. In this context, the updated knowledge of the vulnerability of the damaged buildings is of critical importance to accurately assess the associated risk and guide building-occupancy policies after a main seismic event.

A methodology to derive fragility curves for structures which are initially in a given damage state is developed. Contrary to the widely used incremental dynamic analysis, successive dynamic analyses with a set of unscaled natural ground-motion records are performed. Several samples of structures in each damage state, which may differ by their local damage configuration, are generated. The current condition of the structure at a time t 0 is represented by its residual (or permanent) drift ratio at the end of the pre-t 0 events and the additional transient drift (i.e. the maximum transient drift minus the initial permanent one ) obtained from the next dynamic simulation is used to assess whether the structure will reach a higher damage state or not. The main part of the developed procedure is to find a probabilistic relation between the seismic intensity and this additional drift. Distribution of the permanent drift has to be estimated within each damage state for this purpose. Section 2 is devoted to the methodological developments and the description of the time-dependent risk assessment framework, which relies on the existence of state-dependent fragility curves. Finally, in section 3 the methodology is applied to a reinforced-concrete frame in order to derive statedependent fragility curves.

METHODOLOGICAL DEVELOPMENTS FOR STATE-DEPENDENT FRAGILTIY CURVES

Time-dependent risk assessment framework

Previous studies [START_REF] Luco | Dynamic versus static computation of the residual capacity of a mainshock damaged building to withstand an aftershock[END_REF][START_REF] Yeo | Stochastic characterization and decision bases under time-dependent aftershock risk in performance-based earthquake engineering[END_REF][START_REF] Ryu | Developing fragilities for mainshock-damaged structures through incremental dynamic analysis[END_REF][START_REF] Luco | A methodology for post-mainshock probabilistic assessment of building collapse risk[END_REF] have developed a methodology for time-dependent risk assessment. It relies on coupling the performance of the building at the risk-assessment time t 0 and the probabilistic hazard assessment during a considered time-span. The temporal position of the risk analysis is presented on Figure 2.1. The performance of the building at t 0 is by itself a combination of its current Damage State (DS) and of its capacity to withstand further seismic actions. The state of the building at t 0 is characterized by the probability of being in one of the n damage states (defined by an appropriate damage scale): .

For each of these possible initial damages states , the capacity of the building needs to be estimated through state-dependent fragility curves, which give the probability for a structure in state to reach or exceed a given damage state with respect to an Intensity Measure (IM) of a given level a:

Once these components are defined, the initial state of the structural system is described and its fragility to future earthquakes can be quantified as follows [START_REF] Luco | A methodology for post-mainshock probabilistic assessment of building collapse risk[END_REF] (2.1)

In common practice, the building is considered to be initially intact (

) and Equation 2.1 becomes trivial:

. The more general formulation of Eq. 2.1 considering initially damaged structures enables to consider the time dependency and may be used in two main contexts:

-In the short term context, during post-mainshock emergency operations. Typically, in the literature, methodologies have been proposed to assess the safety of mainshock-damaged structures by coupling the aftershock hazard with the updated fragility. From this aftershock risk assessment, a building-occupancy policy is deduced [START_REF] Yeo | Stochastic characterization and decision bases under time-dependent aftershock risk in performance-based earthquake engineering[END_REF]. Similarly, by applying the same methodology to a bridge, Franchin et al. (2009) propose a traffic allowance policy. -In the long term context, the time-span corresponds to the life-cycle of the building, which is exposed to damage accumulation as well (e.g. [START_REF] Yeo | Stochastic characterization and decision bases under time-dependent aftershock risk in performance-based earthquake engineering[END_REF]. After a mainshock, the assessment of the building state at time t 0 can be achieved through various techniques:

-Inspection-based or expert knowledge: it relies on post-seismic observations and the judgement of civil engineers on the actual damages of the inspected structures. -Shakemaps (uncertain hazard): shortly after the occurrence of the seismic event, parameters such as magnitude and localisation are used to estimate shakemaps of the affected areas. Then, if a vulnerability study has been previously carried out, fragility curves can be used to estimate the damage probabilities of the buildings in the area. -Instrumentation: seismic stations can record the seismic ground-motion around the affected area, thus giving a more accurate estimation of the hazard level. Also, for specific and critical structures, it is possible to perform building instrumentation in order to directly measure the lengineering demand on the structure.

As a result, there is a strong need to develop state-dependent fragility curves, which are a necessary step to perform risk assessment in the aftershock time-span. This issue is the subject of the next subsections.

Simulation strategy

Several past studies (Bazzuro et al., 2004;[START_REF] Ryu | Developing fragilities for mainshock-damaged structures through incremental dynamic analysis[END_REF] propose to develop state-dependent curves using incremental dynamic analysis, i.e. a progressive scaling of the ground motion's amplitude without modifying their spectral shape [START_REF] Vamvatsikos | Incremental dynamic analysis[END_REF] in order to have a sufficient number of buildings in each damage state. In this sub-section we present a methodology for developing DS-dependent fragility functions using a set of unscaled natural records. Ground-motions from this set are applied to the structure until each DS is populated with enough outcomes, which may have different local damage configurations. Damaged structures are then used to compute the response to the next ground shaking.

The Engineering Demand Parameter (EDP) used in this framework is the maximum transient inter-storey drift ratio (ISDR), which can be linked to straightforward damage state thresholds (e.g. [START_REF] Rossetto | Derivation of vulnerability functions for European-type RC structures based on observational data[END_REF]. Moreover, the estimation of ISDR through dynamic simulations gives access to the residual permanent drift. We note this quantity since it is the value of the ISDR evaluated at the time t 0 . In the time-dependent framework, the permanent drift is of paramount importance as it represents the updated initial conditions of the structure at t 0 . The starting point of the study is a single structure in intact state, which we subject to a set of N timehistories. This first wave of analyses yields N new structures which are distributed along the different DS classes, depending on the recorded value of . For each initial damage state, 20 combinations of structures / ground-motion records are selected based on a Latin Hypercube Sampling procedure in order to test the range of possible combinations without introducing bias. This sampling methodology is applied to the structures of a DS class ranked based on their initial permanent drift , and to the ground-motions ranked according to the intensity measure (IM) of interest (e.g. Sa or PGA). This step is repeated 25 times in order to populate each damage state with enough structures and to obtain a satisfying statistical significance (see Figure 2.2).

If some DS classes do not contain enough structures, it has been decided to reuse the damaged structures and recombine them until a sufficient number of outcomes in each DS class are reached. Thus, some of the results are obtained with structures that have been submitted to several timehistories. This remains a valid procedure in the sense that the chosen framework focuses on statedependent curves and what occurred to the structure before t 0 have little influence on the future structural response. In the other word, what is important is the actual condition of the structural system at time t 0 , which we choose here to be represented with the initial permanent drift .

This approach enables to get a full representation of the possible outcomes in the different damage states. Therefore it has the advantage of accounting for the variability of the damaged structures when building DS-dependent fragility curves: different combinations of local damage mechanisms are translated into the residual permanent drifts, whose distribution is used to estimate the variability in initial conditions.

Modified regression technique for the estimation of damage distribution

Based on the recorded ISDR values, the objective is now to build the state-dependent fragility curves, defined as follows:

(2.2)

where is the cumulative distributive function of the standard normal distribution, and and are respectively the median and standard-deviation of the fragility curve from DS=i to DS k. The regression technique [START_REF] Fema | Recommended seismic design creteria for new steel moment frame resisting buildings[END_REF][START_REF] Ellingwood | Quantifying and communicating uncertainty in seismic risk assessment[END_REF]) is a widely used approach to derive fragility parameters (µ and ) for undamaged buildings. It relies on correlating the ISDR to the ground-motion IM: since the damage states can be identified by ISDR thresholds. A direct probabilistic relation between DS and IM is then deduced by a simple substitution of variables. In our specific case, we have to consider a structure with a permanent drift due to its loading history prior to t 0 . We assume that the distribution of the maximum transient additional drift, , depends on the ground motion intensity a via the following relation:

(2.3)
The parameters b and c are obtained through the linear regression and is considered as a random variable with normal distribution of zero mean and standard deviation . Introducing drift thresholds, i.e. considering that the building reaches DS k when , , the probability of reaching or exceeding damage state k for a building which has a permanent initial drift is derived from equation (2.3) as follows:

(2.4) For an initially damaged building (DS t0 =i), the permanent drift cannot exceed the threshold of the higher damage state, , so we can assume that is in the range [0;

[. If we note f the probability density function of the permanent drift, the DS-dependent probability can then be expressed as follows:

(2.5) The next step is to estimate f, the distribution of the permanent drift. The population of buildings that are initially in state DS t0 =i corresponds to the buildings whose absolute ISDR is included between and . Within this overall population we have to distinguish two sub-populations depending on the leaning side where that maximal ISDR has been reached (negative or positive values of permanent drifts). For each sub-population we assume a normal distribution of , whose parameters are evaluated by fitting the permanent drifts from the simulation results. For simplifying the notations in this paper, we assume equal weights, equal standard deviation and opposite mean of these two sub-populations, which corresponds to symmetrical structure. A general formulation for non-symmetrical configurations would work identically. The probability density function of therefore reads as a combination of two normal distributions: with (2.6) Using the above equation, the distribution of can be deduced: with (2.7)

Finally, these distributions are used to compute the integral in Equation 2.5 and a lognormal cumulative distribution function is fitted to the curve in order to identify the DS-dependent fragility parameters and in Equation 2.2.

APPLICATION TO A SINGLE FRAME

Description of the structural model

To illustrate the developed methodology, we apply a set of ground-motion records to a single-story single-bay reinforced-concrete frame (3m high and 4m wide). The beams and columns behaviour is considered linear elastic and the damage mechanism is concentrated at the extremities, with the formation of plastic hinges [START_REF] Zareian | A practical method for proper modeling of structural damping in inelastic plane structural systems[END_REF]. The plastic hinges model developed by [START_REF] Ibarra | Global collapse of frame structures under seismic excitations[END_REF] is used and its main parameters are presented in Table 3.1. The main parameters (e.g. yield and capping moment) used for this study correspond to beams and columns elements from a previous work [START_REF] Seyedi | Development of seismic fragility surfaces for reinforced concrete buildings by means of nonlinear time-history analysis[END_REF] on a reinforced-concrete building.

Values for undetermined parameters are adapted from the calibration presented by [START_REF] Haselton | Assessing Seismic Collapse Safety of Modern Reinforced Concrete Moment Frame Buildings[END_REF].

The elastic portion of the elements is assigned a Young modulus of 3.10 7 kPa, while the columns and beams have a respective section of 0.135m² and 0.197m².

We choose the Sa(T1) as the IM of interest for this structure, T1=0.195s being the period of the fundamental mode. The drift thresholds to identify the damage states are those proposed by [START_REF] Rossetto | Derivation of vulnerability functions for European-type RC structures based on observational data[END_REF] for the EMS-98 damage scale (D1 -Slight, D2 -Moderate, D3 -Heavy, D4 -Very heavy). The damage state D5 (Collapse) is not considered in this study, due to the difficulty to obtain reliable simulation results for collapse conditions.

Dynamic analyses

As explained in the previous section, the structure is submitted to successive ground-motions: in this case, we select a set of 175 time-histories from the European Ground-Motion Database [START_REF] Ambraseys | Dissemination of European Strong-Motion Data, vol. 2 using Strong-Motion Datascape Navigator. CD-ROM collection[END_REF]) that are indifferently used as mainshocks or aftershocks. The dynamic simulations are carried out using the OpenSees software. As an example, Figure 3.1 shows the behaviour of the frame submitted to a succession of time-histories (before and after t 0 ). The results of the repeated dynamics analyses are used to perform the regression between the intensity measure and the additional drift, and also to identify the distribution of the permanent drift within each damage state for computing . Figure 3.2 illustrates the methodology for the structures with an initial damage state DS t0 =2. The top histogram shows the actual distribution of the initial permanent drifts. The right histogram represents the set of ground-motions considered for the simulation. The central panel shows the combination of these parameters that have been chosen for performing the simulations, and the colours on the points indicate the results: yellow if the structure has remained in DS t0 =2, resp. red and black if it has increased to resp. DS=3 or 4.

On the top histogram of Figure 3.2, we can clearly see the bimodal normal distribution of the permanent drift (a mixture of two Gaussian distributions): using the Expectation Maximization algorithm, the two sub-populations can be distinguished (i.e. buildings that have reached the DS threshold on the positive or negative direction) and the parameters of are finally estimated. The fact that all buildings, whatever their initial conditions, experience a similar dynamic response is due to the choice of the model for the plastic hinges: no cyclic degradation has been taken into account, therefore the model continues to display the same stiffness and the only evolution is the deformations in the hinges, which are progressively moving towards the next drift threshold. Consequently, in this specific case, the only influent parameter is the value of the permanent drift, indicating how close the building is to the next drift threshold. Following this logic, it can finally be argued that only mainshock simulations are needed and the damaged structures can be artificially modelled by adding a permanent drift or decreasing the drift threshold.

Derivation of state-dependent fragility curves

The results of the application of the modified regression technique (see sub-section 2.3) to the nonlinear dynamic analyses are presented in Table 3.2. The results consist in the and parameters defined in Equation 2.2 for describing the transition probabilities from DS t0 =i to DS=k. The median parameters in Table 3.2 show, as expected, the capacity reduction of the frame, as previously damaged structures tend to have higher probabilities (i.e. lower median values of IM) of reaching further damage states due to an aftershock. It can also be noted that the standard deviation is higher for initially damaged structures: this is explained by the distribution of initial permanent drift, which is the source of additional uncertainties, as opposed to the initial undamaged structure, which state is well defined. Using the estimated fragility parameters, the DS-dependent fragility curves are plotted and displayed in Figure 3.4. Increasing initial damage resulting from past shocks (from solid black to light grey) is responsible for the translation of the fragility curves from the right to the left.

CONCLUSION

In this study, we have proposed an original approach to derive fragility curves for previously damaged structural systems. These fragility functions give the transition probability for one damage state to another and they may therefore be referred as state-dependent fragility curves. The procedure presented here relies on the application of successive sets of unscaled ground-motion records. The key concept is the permanent drift ratio that is used to represent the starting conditions of initially damaged structures. This approach has been applied to a single reinforced-concrete frame and the resulting fragility curves show as expected the higher vulnerability of structures that have been previously damaged. Another important lesson from the application is that the chosen model for the plastic hinges does not induce any important change in the dynamic behaviour of the structure after successive timehistories: a very similar relation (i.e. slope of the regression) between the IM and EDP is found whether the structure is initially intact or damaged. This observation confirms that in this particular case (single-degree-of-freedom structure without cyclic degradation) the only important parameter is how "far" a structure with an initial permanent drift is from the higher drift threshold. Therefore future work could include the application of the procedure to more elaborate cases such as multi-degree-offreedom structures with cyclic degradation. Finally, instead of the drift ratio, the use of EDPs that account for cyclic damages, like the [START_REF] Park | Mechanistic Seismic Damage Model for Reinforced Concrete[END_REF] index, could also be relevant in the specific case of state-dependent fragility curves.

Figure 2 . 1 .

 21 Figure 2.1. Schematic representation of the time-dependent risk assessment methodology at time t 0 . It is based on the performance of the structure at that time t 0 and on the upcoming seismic risk during the time-span t.

Figure 2 . 2 .

 22 Figure 2.2. General simulation scheme for the dynamic analyses

Figure 3 . 1 .

 31 Figure 3.1. Example of successive time-history analysis; Prior to t 0 , the structure has reached a damage state DS t0 =2 and has a permanent drift . After t 0 , the ground-motion of IM=a (red part, bottom panel) brings the structure to DS=3. The correlation is estimated between and a.

Figure 3 . 2 .

 32 Figure 3.2. Damage states obtained (coloured dots, yellow, red and black corresponding resp. to DS=2, 3 and 4) depending on the IM Sa(T1) of the aftershock and on the initial permanent drift of the structures. The top histogram shows the repartition of permanent drifts for the initial damage state DS t0 = 2The simulation results are finally used to perform a linear regression between and the quantity . As an example, this regression is plotted in Figure3.3. Blue points represent the relation for all previously damaged structures (with and the red ones are the regression for only initially intact structures (with . For both cases the slope of the linear fit is almost the same.

Figure 3 . 3 .

 33 Figure 3.3. Comparison of the regression results for the undamaged buildings (in red) and the initially damaged ones (in blue)

Figure 3 . 4 .

 34 Figure 3.4. State-dependent fragility curves using the parameters inTable 3.2

Table 3

 3

	.1. Main parameters used in the plastic hinge model from Ibarra & Krawinkler (2005)
	Parameter	Column spring	Beam spring
	Elastic stiffness (kN.m)	70 000	150 000
	Yield moment (kN.m)	52.5	210
	Plastic Rotation capacity (rad)	0.015	0.02
	Post-capping rotation capacity (rad)	0.161	0.133
	Ultimate rotation capacity (rad)	0.4	0.4
	Strain hardening ratio	0.0018	0.005
	Residual strength ratio	0.2	0.2
	Degradation parameter	1 000 (no degradation)

Table 3 .

 3

	2. Parameters describing the transition probabilities from DS t0 =i to DS=k
	initial DS (i)	DS t0 =0 (intact)	DS t0 =1		DS t0 =2		DS t0 =3
	future DS (k)
	1	3.51	0.58	-	-	-	-	-	-
	2	6.65	0.58	5.18	0.70	-	-	-	-
	3	12.58	0.58	11.30	0.66	8.94	0.74	-	-
	4	32.75	0.58	31.64	0.66	29.76	0.66	22.05	0.71

AKCNOWLEDGEMENT

The research leading to these results has been carried out in the frame of the MATRIX Project, funded by the European Commission's Seventh Framework Program [FP7/2007-2013] under grant agreement n° 265138.