The Aspect of Seismic Protection in the Conservation of Cultural Heritage P. Velkov Makedonida Association for Heritage Education, Promotion and Valorization, Skopje, Republic of Macedonia ABSTRACT: The seismic protection has still not found its place in the complex process of conservation of cultural heritage. "Rereading" of this standard chart of the conservation plan is needed in order to integrate seismic protection in the conservation process. More research is needed to improve the seismic safety measures. These measures should be introduced in guidelines and codes provisions. Training in seismic protection is needed, of all the specialists involved in the conservation process: planners, engineers, architects, landscape historians and archaeologists. KEYWORDS: Cultural heritage, seismic protection, conservation

1. PREPARATION OF A CONSERVATION PLAN

Planners, architects, engineers and archaeologists all have different approaches to project planning in the process of conservation relevant to their disciplines. However, conservation usually involves a variety of disciplines, and it is necessary to adopt a more general approach, by definition an interdisciplinary one. This polyvalent character of the approach can be most easily demonstrated when one considers the choice of the consultants for the preparation and execution of the conservation plan. The plan should include the participation of: - architects with proven abilities in conservation - architectural historians - civil engineers with proven abilities in conservation - historical archaeologists - landscape historians - specialists in conservation method

It is important to note that each of these profiles refers to disciplines with a distinct methodology. An architectural historian can hardly be replaced by employing an architect and a historian. Further more, though it is very hard to employee an expert who would have training and/or experience in all the above-mentioned disciplines, it is most useful to work with specialists who have a broad experience in more than one discipline. Whereas architects and archaeologists are often trained in different aspects of the conservation method and have a solid background in history, they seem to be rarely familiar with any of the engineering aspects of the conservation process. This counts vice versa, at least as much, also for the civil engineers that rarely have any training in traditional building techniques or history of construction. Integrating of the so called engineering aspects, like the problem of seismic protection, is therefore one of the most sensible parts in the elaboration and in the execution of the conservation planning.

The general approach of a conservation plan can be presented in a well-known chart putting forward the most important stages of the process (1).

STAGE I

UNDERSTANDING THE PLACE

Gathering evidence (documentary and physical)

Co-ordinating and analysing evidence |

Assessing and stating significance

STAGE II |

CONSERVATION POLICY AND ITS IMPLEMENTATION |

Gathering information for the development of conservation policy

Requirements for Client's requirements retention of significance or feasible uses

| | |

Developing a conservation policy |

Stating conservation policy and evolving strategies and options for its implementation

Chart 1 Basic elements and sequencs in a conservation plan, (J.S. Kerr, 1996)

The sequence of the work in the process of the planing is very important. The work naturally falls in two stages: - the first refers to the gathering and the assessment of evidence and the assessment of significance

of the site; - The second one concerns with developing of the conservation policy and setting out strategies for

its implementation. The split into two stages is important for the integrity of the process. The process has to be at the

same time integral. It should allow that certain aspects of the conservation process, if necessary, were treated consequently at each stage.

2. INTRODUCING THE SEISMIC RISK

Actually, the basic chart for the conservation plan can be also used for introducing the conservation seismic protection.

In order to provide an adequate seismic protection it is very useful to introduce the seismic aspect starting from the very first stage of the conservation chart The Understanding of the place . It is convenient to in quote the following aspects from the chart:

- Stage I, Understanding of the Place: Gathering Evidence

The evidence can be documentary and physical. Neither can be neglected as each collaborates and compliments the other. In seismic terms this means gathering evidence for the seismic history of the site.

In regions with major seismic hazard documentary evidence about disastrous seismic events can often easily be found and interpreted. However, even in places with lower seismic hazard, there is often valuable evidence to be found in the archives: let us just quote the examples of the earthquakes

at Genoa in the XVI century, or the disastrous earthquake that stroke the city of Basel at the end of the XV century. This kind of information can be most useful when understanding the seismic risk of the site. Often declared unreliable due to lack of adequate interpretation, these documents can actually supply the key to the optimal conservation solution providing at the same time satisfactory seismic protection. They only have to be read and interpreted by professionals trained in seismic protection.

Physical evidence is as important. It tells the story of what actually happened, the way the fabric and the composition of the heritage site as a whole have been transformed during its lifetime. However, whereas the physical evidence contrary to the documentary can not lie, it can often be misinterpreted. The wooden horizontal layers introduced in traditional masonry are often interpreted as special measures providing seismic protection after an earthquake (Maisonneuve, '98), however very often they were used first of all to simplify the erection of massive rubble stone walls providing homogenous and horizontal wall sections.

Detailed inspection of the site is crucial for understanding the physical evidence. Intending interpreters, traditionally artistes and/or engineers should try to equip themselves with background knowledge about the historical period (s), and the typical building materials and techniques used during these periods. Only then the lessons learned from the past seismic events and the original seismic design, if any, can be reliable. - Stage I, Understanding of the Place: Co-ordination and Analysis of Evidence The conventional break-up of evidence into documentary, oral and physical makes discussion and teaching convenient. Maintaining these distinctions in the presentation of a conservation plan, however, is to destroy or weaken the essential interdependence of the types of evidence itself. Such fragmentation and repetition is a hangover from ages when disciplinary demarcations were jealously guarded.

This counts also for the specific aspects in the conservation plan like the seismic one. In the presentation of the analysis it is however rather convenient to present the seismic aspect in a separate chapter. All the evidence and its sources should be stated in the analysis. This gives confidence and gives the client a chance to check up the analysis if needed. - Stage II, Conservation Policy and its Implementation: Gathering Information for the Development

of Conservation Policy As far the seismic aspect is concerned it is of highest importance to get detailed information about the requirements and the constraints arising from the statement of significance of the site. The statement itself should offer a priority list of the requirements and the constraints regarding the site significance. It is also very important to get detailed information about the clients requirements and resources. This information will provide the basis about the actual decision which protection measures will be taken. In most of the cases the seismic protection itself will considerably increase the cost of the intervention. Therefore, compromises in the choice of the intervention will be often necessary. - Stage II, Conservation Policy and its Implementation - Conservation Requirements for Retention

of Significance versus Safety Provisions So called requirements from the engineers, like the requirements regarding seismic safety, have very often been regarded as totally antagonistic regarding the conservation requirements for retention of the cultural significance of the site. This however can very often be avoided proposing adequate measures followed by detailed analysis which will proof their efficiency regarding seismic safety but also regarding the conservation requirements themselves. This sounds rather obvious but has unfortunately still not become a regular practice in the conservation process.

- Stage II, Conservation Policy and its Implementation: Clients Requirements, Limits of Protection Measures

It is necessary to inform the client about the levels of seismic safety that different seismic measures can provide. The choice of an adequate solution will be often dictated by the clients requirements, providing that a statutory level of seismic safety is satisfied.

It is worth noticing than in some cases, however, a compromise between the two aspects, the conservation and the seismic, will be difficult to find. In that case is very important to make sure, that the conservation intervention itself does not at least increase the seismic risk of the site. The client should be informed about all the risk regarding the implementation of the conservation plan. - Stage II, Conservation Policy and its Implementation: Developing a Conservation Policy The success of this process depends largely of the quality of the preliminary work. If this has been done adequately all the elements including the seismic safety requirements will fit well in this rather difficult puzzle. Whereas the proposal for the seismic protections measures should come from the specialists for seismic protection, it is the permanent communication and discussion with all the consultants involved in the Plan that will make the chosen solution be the optimal one. - Stage II, Conservation Policy and its Implementation: Stating Conservation Policy The optimal seismic protection solution will be further elaborated and presented while stating the conservation policy as a specific aspect in the conservation process. Generally, it should be presented before the guide that treats the conservation of the fabric, but after the basis of the approach and the measures providing the retention of the cultural character of the site.

3. REDUCING THE SEISMIC RISK IN THE CONSERVATION POLICY AND ITS IMPLEMENTATION

In spite of the fact that in the last two decades public awareness to seismic risk has considerably risen all around the world, the seismic protection has not been really integrated satisfactory enough in the conservation of cultural heritage. Lots of things still remain to be done to improve this conservation process and reduce the seismic risk while preparing and executing conservation plans. Let us consider the possible directions for future work:

3.1.Research

Apart from research related to evaluation of seismic hazard, at the actual state of the art we can distinguish three types of research related to sesimic risk of heritage sites:

- Research that focuses on evaluation of behaviour and damage patterns on specific types of

heritage sites (places) after a strong earthquake This type of research is very important. It gives a clear idea of what actually happens when an earthquake occurs. When it happens, it is very important to make a detailed survey and analysis of all the heritage sites struck by the earthquake. This can be a costly and time consuming process, but it is very important because it helps us identify the priorities and also the remedies in heritage conservation against seismic risk in the future. A perfect example is the survey study done in Italy on seismic behaviour of ancient churches after the disastrous earthquake that struck the region of Friuli in North-eastern Italy in May 1976 (Doglioni et.al. '94). All the churches damaged by the earthquake (more than a hundred) were included in the study. Behaviour patterns of damaged and collapsed buildings were identified. Guidelines for the reducing the seismic risk of ancient churches were also stated. Fortunately, strong earthquakes like this one are rare in the world. Therefore we have to rely on other types of research as well.

- Research that focuses on experimental verification of methods and technology of conservation This is the type of research that we cant do without. Thanks to the experimental research, we can transform traditional conservation techniques used for centuries into modern and scientifically proven methods. Unfortunately, due to its high costs, this kind of research is rare. Therefore it is very important to make good use out of it. Most useful are the experiments that would focus not only on the efficiency of the method providing seismic safety, but also to the behaviour of the heritage site as a whole. A very illustrative example is the work done in the Institute of Earthquake Engineering and Engineering Seismology in Skopje, on reducing of seismic risk of Byzantine Churches in Macedonia (Sendova '98). The efficiency of the conservation method reducing the seismic risk of Byzantine churches was proven by tri-dimensional experiments on models of a XIV century church from region of Skopje. In this kind of research one has to be very careful when extrapolating the results to other cases heritage sites. - Research that focuses on prediction of seismic behaviour of cultural places (sites, buildings, parts of cities and cities) using statistic methods These so-called vulnerability studies have been very popular in the last decades. There have been quite a few that were dedicated to behaviour of heritage sites, particularly to the behaviour of old urban nucleus (Thibault&Velkov '94). The behaviour of the heritage site in this case historical buildings is predicted using methods of analogy and statistic based on learnt experiences from past earthquakes. Since, in most of the cases, these kind of experiences come from earthquakes that have struck other heritage sites and not the one which is the subject of the research, it is very important to couple the research with some kind of experimental work that would provide relevant physical data for the heritage site under consideration. In the case of historical buildings, for example, this experimental work should focus on identification of the mechanical characteristics of the walls and the their elements, like the bricks, the stones, the mortar, etc.

3.2. Charters and statutory requirements

The latest edition of the ICOMOS charter (ICOMOS '01) does not unfortunately give any guidelines concerning seismic risk. Some elements relative to safety of architectural heritage conservation are presented in the draft document of ICOMOS about structural restoration of architecture (Reccomendation '01). Oddly enough, these two documents although published by the same house do not use the same terminology. For example in the draft document for structural restoration (Reccomendation '01), the term restoration is used as a general expression meaning conservation where as according to the definition given in the Burra Charter presented in the International Charter for Conservation and Restoration (ICOMOS '01), restoration means returning the existing fabric of a place to a known earlier state by removing accretions or by resembling existing components without the introduction of a new material . This unfortunate practice of inadequate use of the terminology leads to confusion and makes the documents like the draft for architectural conservation (Reccomendation '01) difficult to understand and follow in practice.

In order to find some provisions that deal with seismic risk we have to look in the international codes. The European code EC8 deals with seismic risk in the annex F (ENV 1998-1-4, '96). The document is important because it gives a definition of the monument safety level regarding seismic risk, distinguishing, seismic safety of a heritage site (monument) from the seismic safety of other sites: A monument safety level corresponds to a situation in which the maximum probable earthquake (during an assigned time of reference, considerably longer than for ordinary buildings) is expected to produce repairable damage only and no fatal artistic damage.

However, the document becomes rather ambiguous when it tends to explain and even regularise the delicate issues regarding the conflict between the safety of the site and its architectural/artistic integrity: Where there is a conflict between structural safety and architectural/artistic integrity, some kind of cost benefit analysis should be explicitly carried out, where the benefit is an increase of safety and the cost is a loss of architectural integrity. In such cases two teams of respective Specialists should debate the question and rich a joint decision. From the perspective of the above explained

methodology ( Chapter 1), it seems that the loss of architectural ingertity or using our terminology - loss of the cultural significance of the place , in most of the cases, could hardly be expressed in terms of cost. Furthermore, putting together two teams to debate seems not a very favourable solution for a successful conservation plan. The two teamsshould work as one throughout the implementation of the conservation plan, from its beginning until its finalization. The priority of the team should be the conservation of the cultural significance of the site. All the other aspects in the conservation plan, including the seismic safety, should be subordinated to it.

It seems obvious that more recommendations based both on research and lessons learnt from conservation practice are needed. They should be stated as guidelines but also as basic statutory requirements within codes and provisions on national and international level.

3.3. Training

Training of specialists is probably the most important tool that would provide better protection of cultural heritage against earthquakes. First of all, the engineers and architects involved in the Conservation Plan should be trained in earthquake engineering. The Institute for Earthquake Engineering and Engineering Seismology from Skopje, Macedonia has played a pioneer role in this aspect. Thanks to the help of the Dutch and the German Government, for more than 20 years it has organised a three month summer course on earthquake engineering, paying special attention to the protection of cultural heritage.

This however is not enough. For a successful conservation plan, it is very important that all of the specialists involved in the process of conservation have a notion of seismic protection, not only the architects and the engineers. This can help resolve the conflicts between the requirements for the retention of the cultural significance of the place (the heritage site) and the requirements regarding seismic safety. Here again, we shall quote one example from Macedonia: the Ohrid Summer University (Balkan cultural Identities '03). Starting from this year, the Summer University gathering art historians, architects, historians and archaeologists from the Balkans, included a one-week seminar dedicated to conservation of cultural heritage. One of the aspects of the seminar was the protection of cultural heritage against seismic risk.

REFERENECES

James Semple Kerre The Conservation Plan , The National Trust of Australia, Sydney, 1996; Patrick de Maisonneuve Le temps, les hommes, larchitecture, , Club du Rocher, Paris, 1998; International Charter for Conservation of Monuments and Sites, ICOMOS, Paris, 2001; Recommendations for the Analysis , Conservation and Structural Restoration of Architectural Heritage,

ICOMOS, Paris, 2001; Particural Consideration for Historical Buildings and Monuments , Eurocode 8 : Anexe F of the ENV 1998-

1-4: 1996, Brussels, 1998; F. Doglioni, A. Moretti, V. Petrini Les chiese et il terremoto , Edizioni Lint Trieste, Trieste, 1994; Veronika Shendova Seismic Strenghtening and Conservation of Byzantine Churches ( IX XIV century ) , in

Macedonian, Ph.D. Thesis, IZIIS, Skopje, 1998; Ch. Thibault et P. Velkov Evaluation of the Seismic Stability for the Old Urban Nuclei of Nice , ERCAD

Conference, Technical University Berlin, pp. 1047-1054, Berlin, 1994; Ohrid Summer University : Balkan Cultural Identities , Euro-Balkan Institute, Unveristy of Saint Cyril and

Methodius, Skopje, 2003

The Aspect of Seismic Protection in the Conservation of Cultural HeritageP. Velkov