PROPOSAL OF REDUCING PERMITTED SEISMIC DAMAGES ON IMMOVABLE CULTURAL PROPERTIES ( BUILDING STRUCTURES )

Pored Pravilnika br.52/85 [10], postojeća zakonska regulativa za odredjivanje projektnih parametara seizmičnosti, koja se kod nas koristi, definisana je „Pravilnikom o tehničkim normativima za izgradnju objekata visokogradnje u seizmičkim područjima“, (Pravilnik br. 21/88 i 52/90), [11], [12]. U praksi se još koriste i preporuke „Evrokoda 8“ (EC8), [8] . U okviru navedenih pravilnika GOV su svrstani u odgovarajuće kategorije za koje je predvidjen dozvoljeni seizmički rizik u okviru njihovog veka eksploatacije. Međutim, oko nas postoji mnoštvo istorijskih građevinskih objekata od velikog kulturno-istorijskog značaja čije bi delimično ili potpuno rušenje bilo nenadoknadiv gubitak za najširu društvenu zajednicu. Prema ZKD br. 71/94 [13] ovi objekti su svrstani u kulturna dobra koja su u zavisnosti od svog značaja razvrstana u tri kategorije: kulturna dobra od izuzetnog značaja, kulturna dobra od velikog značaja i kulturna dobra. Kulturna dobra mogu biti pokretna i nepokretna. U nepokretna kulturna dobra spadaju objekti visokogradnje (NKDVG).


PREDLOG SMANJENJA DOZVOLJENOG SEIZMIČKOG OŠTEĆENJA NA NEPOKRETNIM KULTURNIM DOBRIMA VISOKOGRADNJE PROPOSAL OF REDUCING PERMITTED SEISMIC DAMAGES ON IMMOVABLE CULTURAL PROPERTIES (BUILDING STRUCTURES) 1 INTRODUCTION
In addition to the Code no.52/85 [10] , the existing regulations for determining the design parameters of seismicity used in our country are defined by the "Code on technical standards for construction of building structures in seismic areas"-(Code no.21/88 and 52/90) [11], [12].In practice, recommendations of "Eurocode 8" (EC8), [8] are also used.Within the mentioned codes the BS are ranked within corresponding categories for which the permissible seismic risk in their service life has been determined.
However, there are many historical building structures from near and distant past, having high cultural-historical importance, whose partial or total collapse would represent the irreplaceable loss for the wide social community.According to LCP no.71/94 [13] these buildings are categorized, in terms of their importance, as cultural property, classified in three categories: cultural property of outstanding importance, cultural property of high importance and cultural property.Cultural property can be movable and immovable.Building structures belong to immovable cultural property (ICPBS).
In the recently published paper related to the reduction of seismic risk for ICPBS [5], there was a general emphasis on the instruction about the activities which should be undertaken so as to reduce the seismic risk for ICPBS and the level of permissible damage for them.Thence, ICPBS are categorized in two categories ICPBS I and ICPBS II categories of vulnerability to seismic action, which cover ICPBS of outstanding cultural importance of ICPBS of high cultural importance, respectively.However, another category is added in this paper, and that is ICPBS of outstanding cultural importance listed by UNESCO.In addition, within any of the mentioned categories, the following factors were singled out: a) serviceability of the structure, which comprises life hazard of employees and visitors (BU) in the building; b) architectonic factor (Bach); c) artistic factor without painted surfaces (BA) and d) artistic with painted surfaces (BAP).The serviceability factor indicates running activities in ICPBS, regarding the personnel employed in it and interested visitors.The architectonic factor relates only to ICPBS with all architectonic characteristics and their values.The artistic factor without painted wall surfaces includes single decorative elements which are in part attached to the structure.This comprises integral sculptures etc.Eventually, there is the artistic factor with painted wall surfaces, which comprises painted surfaces of bearing and partition walls.Therefore, this paper comprises a more detailed categorization as well as the factors of ICPBS as a basis for new construction categories, the possibility for analytical determination of seismic load they are able to sustain within the permissible damage limits.
In order to conduct the procedure of remediation and strengthening of ICPBS in seismic areas whose cultural historical value is determined in accordance with LCP no.71/94 [13], the paper proposes categorization of ICPBS into special structural categories.Therefore, it is proposed that the separate categories of ICPBS with the abovementioned factors are the basis of the new "Code for remediation and strengthening of ICPBS in seismic areas", or to be appended to the existing Code no.52/85, [10].

Law on cultural property
Lots of old buildings in our environment, by their form (architectonic design, artistic content, structural design, etc), social-historical importance, have obtained nowadays a special value and significance being a part of national cultural heritage [7].Such buildings were declared cultural properties and categorized in LCP no.71/94 [13].The article 1 of the law Basic provisions regulates the cultural property protection and usage system and determines the conditions for their uslovi za obavljanje delatnosti njihove zaštite, koja podrazumeva i zaštitu od zemljotresa.Sama kulturna dobra prema čl. 2. ovog Zakona predsatvljaju stvari i tvorevine materijalne i duhovne kulture od opšteg interesa i kao takva uživaju posebnu zaštitu, takođe, predviđenu ZKD br.71/94 [13].
Zavisno od svoje funkcije, objekti su svrstani u V kategorija koje su kvantifikovane koeficijentom kategorije, Ko.Objekti visoke gradnje od najvećeg interesa za zajednicu svrstani su u grupu objekata van kategorije (nuklearne elektrane; objekti za transport i protection, including protection from earthquake.Cultural properties according to the article 2 of this Law are the objects and products of material and spiritual culture of general interest, as such enjoying special protections, also determined by LCP no.71/94 [13]. According to the same article, the cultural property, depending on the physical, artistic, cultural and historical properties, are divided into immovable cultural property: cultural monuments (including ICPBS), spatial culturalhistorical entities, archaeology sites and famous locations, and movable cultural property, works of art and history, archive materials, films and old and rare books.Each of these groups depending on their significance is ranked into three categories: I -cultural property of outstanding importance, II -cultural property of high importance and III -cultural property.
The Institute of monument protection of the Republic of Serbia records 222 ICPs of outstanding and 622 ICPs of high cultural importance on the territory of Serbia.Table 1, provides 10 buildings of ICPBS belonging to these categories.
Most of ICPBS date back to the period before 20th century, while few belong to the first half of the 20th century.
ICPBS as artefacts, reflect the social, technological and artistic development level of the society at time of their creation, providing an irreplaceable contribution to the diversity of space where they are located.In addition, they signify the historical continuity to the development of social communities in an area.Thus ICPBS have a special cultural-historical importance in a social community life, serving a social function.Even though LCP no.71/94 [13] provides for protection of such structures, i.e. earthquakes, it has not been conducted with sufficient efficiency to consider the ICPBS as adequately protected.

Existing building regulations for building construction in seismic areas
The technical standards for construction of BS in seismic areas of VII, VIII and IX degree according to MKS-64 scale are laid down in the general provisions of the standing Code no.21/88 , [4], [11].All BS in the Republic of Serbia and former SFRY are located in the seismic areas, according to the SFRY seismology maps [3] made for the earthquake return periods of 50, 100, 200, 500, 1000 and 10 000 years which are an integral part of the Code no.21/88 [11].
According to the standing Code no.21/88, [4], [11] the buildings in the seismic areas are designed so that the highest intensity earthquakes can cause damage of supporting structures, but without building collapse.
When the out-of-category and I category buildings are built, the design and maximum earthquake the building is exposed to are calculated.For determination of the seismic risk in designing the II and III category buildings, Seismology map of SFRY is used [3], for the return earthquake period of 500 years.
Nowadays as well, structures of cultural-historical importance are being built.It is for example, the St. Sava Cathedral in Belgrade, which is still unfinished, but besides other things it has its artistic value (architectonic appearance, mosaics, ornaments, etc.), or some other structure built in the period when some of the existing codes of building in seismic areas was valid.In that event, it is recommended to apply more strict criteria for assessment of seismic load design for the structures of prominent cultural-historical importance, i.e. those which are compliant to the recommendations of protection of historical structures.It is a similar situation with Eurocode 8, which is being increasingly used in our country.Here, in the framework of the basic requirements of earthquake engineering, two conditions should be completed: The first condition comprises that during an earthquake design, HRS must not collapse, neither completely nor partially, and it must retain its structural integrity and adequate bearing capacity.The second condition comprises that BS must withstand the effects of an earthquake whose occurrence probability is higher than the design earthquake action, with no damage or dysfunction whose repair cost is non proportionally high in comparison with the value of the structure itself.In Eurocode 8, the importance of structure and its category is prescribed by national authorities.Eurocode 8 does not consider ICPBS separately.
In case of building damage due to seismic action or some changes on them, (reconstruction or extension), Code no.52/85 [10] is implemented.This code is used for revitalization, strengthening, rehabilitation or expansion of damaged or dilapidated building structures, too.
A considerable number of buildings for housing and other purposes was built prior to enactment of any regulations for construction in seismic areas, which is most often the case with ICPBS.However, with aging, the structures generally lose a portion of seismic resistance they originally had.According to the Code no.52/85 [10] which refers to rehabilitation and revitalization of structures which are damaged as a result of an external action or should be strengthened irrespective of whether they were built in compliance with the existing code on building structures construction, they are strengthened according to the construction category to which they belong, regarding their characteristics and current regulations.

Expected damage of ICPBS in the seismic areas of Serbia
On the basis of the macroseismic scale, it is possible to assess the expected damage on the structures, if the type of structure and intensity of earthquake expected on the given area for a certain return period are known.
Here, on the basis of macroseismic scales MKS-64 and EMS-98, the expected damage on ICPBS for the expected intensities between V and IX degrees is provided.However, for a more detailed tests of seismic resistance of ICPBS and other BS, various static and dynamic linear and nonlinear numerical analyses are used.Lately, pushover analyses have been increasingly used (analysis of increasing horizontal load), which belongs to the static nonlinear analysis.
According to the construction style ICPBS mostly belong to the different forms of masonry buildings, and timber structure buildings.The expected damage of ICPBS due to the earthquake effects can be estimated according to the macro-seismic scales of MSK-64 and EMS-98 [3], [9], [15].Both scales have the same division of 12 degrees which coincide in most part.According to these scale ICPBS mostly belong to the B and C (D) types, while there is a low presence of type A, table 2.
On the basis of the Seismological map of Serbia [3] the territorial presence of the strongest expected intensities for the return periods of 100, 200, 500, 1000 and 10 000 years was done, with the probability of Imax ≥ 0.63, Table 6.

The level of permissible damage of ICPBS and their categorization
Protection of ICPBS should provide their survival in time, but without it they are losing their authenticity and serviceability.The paper considers several factors used to determine adequate protection of ICPBS: human safety in earthquakes; architectonic; artistic without painted surfaces and artistic with painted surfaces.Regarding that usually there are visitors inside cultural properties as well as employees, their lives are also at risk.If only the safety of visitors and employees of a building is considered, "the minimum intervention on the building" relates to making the structure of the building "acceptably safe" which will protect the lives of the visitors and employees, and where the working process during earthquakes of low intensity will not be interrupted.However, in the case when ICPBS have a monumental value, and in addition to their social and historical significance they also have architectonic and artistic significance, with or without painted surfaces, the question of "acceptable safety" and thus of the "minimum intervention on the building" remains unresolved.
In fact, it is necessary to consider every aspect of its cultural value, and in accordance with it provide the assessment of acceptable seismic safety level.The damage scale provided in table 3 and its quantification characteristics in table 4 are used for this purpose.
By analyzing the types of damage, it was concluded that the level of acceptable damage is when it is still possible to restore the structures with the minimum loss of their authenticity.Thus, the 3 rd level of damage is permissible during the action of the strongest earthquake for the chosen return period for the following factors: human lives protection (BU), protection of ICPBS for the aspect of architectonic value (BAch) and potential of their conservation and for artistic elements on ICPBS without painted (BA) surfaces.Regarding that heavy structural damage is expected at 3 rd level of damage, falling of large areas of mortar and collapse of partition Obzirom da se u 3 nivou oštećenja očekuju teška ne strukturna oštećenja, očekuje se i opadanje velikih komada maltera kao i pojava rušenja pregradnih zidova.Otuda se za oslikane površine (BAP) dozvoljava 2 nivo oštećenja [6], [17].
After the permissible levels of damage on cultural heritage structures have been specified in this way, it is necessary to determine the level of seismic resistance of ICPBS as well as the level of seismic hazard it is exposed to on a given location.
In order to reliable determine the level of seismic resistance of ICPBS being considered, it is recommended to implement a non-linear static analysis of gradual increasing lateral load (pushover analysis).This numerical analysis employs the finite element method.
With adequately collected data about the structural characteristics of ICPBS itself and characteristics of material it is made of, it is possible to obtain quantitative amounts of deformations on the structure at the given gradually increasing lateral load (pushover analysis).The obtained horizontal deformation is expressed by the amount of horizontal displacement at the top of ICPBS.The pushover analysis facilitates accurate determination of the preset levels of permissible damage on ICPBS according to the horizontal displacement of the top of ICPBS.Therefore, this analysis is implemented on all the factors of the specified individual categories referring to ICPBS, preserving life of employees and visitors in the building, and to the architectonic and artistic factors with and without the painted surfaces.It completes the pushover curve, i.e. the curve of seismic resistance with new characteristics regarding vulnerability of examined ICPBS.
For the same ICPBS, the elastic response spectrum is also determined and provided in accelerationdisplacement format (ADRS).In the process, the ground acceleration is assumed as a maximum value for the appropriate return period obtained on the bases of PSHA or DSHA for the given location.
It is possible to determine what damage is expected on the given ICPBS by analyzing the obtained pushover curve which represents the ICPBS seismic resistance curve with clearly identifiable areas where various levels of damage of the specified individual factors are expected, and by analyzing the spectral curve which represents seismic load on a location, figure 1.
The pushover analysis also facilitates analytical investigation of the impacts of subsequent interventions on ICPBS in order to obtain an ICPBS with the increased seismic resistance in comparison with its previous condition.
For reasons of the overall importance of ICPBS, and also in order to maintain them during a long time period within the existing seismic hazard, it is necessary to increase the level of their seismic resistance above the regular BS level.In this sense the seismic resistance ICBPS should be calculated to the effect of the strongest earthquake with a return period that is longer than the return period laid down by national code for ordinary BS, which belonged to a given ICBPS without an BS.
The length of return periods for ICBPS depends on the cultural-historical categories they belong to, i.e. to the permissible level of damage of their factors.Further in the text, for the purpose of easy access to the reference, the matrices of BS and ICPBS categories are displayed in the range of return periods of the strongest expected earthquakes which are expressed through the perioda od Osnovnog operativnog do Maksimalnog projektnog zemljotresa, od 60% do 10% i manje verovatnoće neprevazilaženja, respektivno, tabele 7, 8 i 9.
various non-exceedance probabilities for the 50-year service period of structures.The damage types for certain categories of BS and ICPBS are given in the span of return periods from the Basic operative to the Maximum design earthquake, between 60% and 10% and the lower probability of non-exceedance, respectively, tables 7, 8 and 9.
According to the Law no.21/88, [4], [11] (for BS) the Basic operative earthquake is unclearly distinguished, while Maximum design earthquake corresponds to the strongest earthquake occurring once in the return period proscribed by the Law no.21/88 for the given type of the structures.In the paper, the Basic operative and Maximum design earthquakes are clearly distinguished, since they became a part of the practice of many national codes.Basic operative earthquake causes structural damage corresponding to type 1 damage, while the maximum design earthquake is expected to cause type 3 damage on the structures.
Based on the categorization of ICPBS according to the mentioned matrices, the level of required seismic resistance for the given ICPBS is determined, and on that basis the mentioned analyses are performed in order to undertake adequate measures for strengthening and protection of the structure itself.
The values of the range coefficients can be obtained on the basis of the abovementioned matrices where the return periods for building structures and matrix for ICPBS are presented along with the values for individual historical structures which can be used in strengthening.Najčešći oblik smanjenja štetnog seizmičkog dejstva na GOV koje se ujedno može primeniti na NKDVG postiže se ojačavanjem njegovih strukturnih elemenata primenom seizmičkih sidrara i veza, ramova za učvršćivanje, horizontalnih strukturnih elemenata, ramova za otporne momente, itd.Pritom treba voditi računa da sе ne naruši istorijski izgled i vrednost NKDV koje se obezbeđuje [1].

METHODOLOGY OF REDUCTION OF SEISMIC EFFECTS ON ICPBS
The most frequent form of reduction of negative seismic effects on BS which can be applied on ICPBS is strengthening of their structural elements by implementing anchored ties, braced frames, bond beams, momentresisting frames, etc.During the process, the care has been taken to preserve the appearance and value of ICP being protected [1].In addition to the classical methods, seismic isolation of the base for BS is used with a goal to replace traditional rigid connection between the upper section of buildings and their base.This is achieved by constructing the superstructure supporting the building and lower structure which is founded in the ground.The separation zone between these structures represents the most ovih konstrukcija predstavlja najznačajnije područje za implementaciju novih tehničkih i tehnoloških inovacija u important zone for implementation of new technical and technological innovations with the aim of reduction of IGO-B IGO-A IGO-AA cilju smanjenja seizmičkog dejstva na objekat.Na slici 2. dat je primer dve vrste laminiranih jakih ležajeva iz zone razdvajanja koji su primenjeni na Apple Towers Sendai (Japan), slika 3, [2].Prvi od njih slika 1a, napravljen je od naizmeničnih slojeva gume i čeličnih ploča.Pomeranjem levo i desno sistem izoluje zgradu od podrhtavanja koji dolaze iz tla.Sa intenziviranjem podrhtavanje tla, aktivira se klizni seizmički izolator 1b, koji je izgrađen od laminirane gume.Mehanizam klizanja ovog izolatora postiže se uz dodavanje smole koja omogućava fino klizanje preko ležaja što dovodi do apsorbcije jakog podrhtavanja.seismic effects on the structure.Figure 2 provides an example of two kinds of strong laminated rubber mass bearings in the separation zone, implemented on the Apple Towers Sendai (Japan), figure 3 [2].The first of them, figure 1a, is composed of alternating lamina of rubber and steel slabs.Its lateral, left-right motion isolates the building from the ground tremors.With the intensification of the soil tremor, a sliding seismic isolator 1b made of laminated rubber is activated.The sliding mechanism of this isolator is achieved by addition of resin allowing for the fine sliding over the bearings, which absorbs the strong tremors.
Nakon uvođenja obaveze o zaštiti od dejstva zemljotresa na NKDVG, potrebno je prilikom sprovodjenja konkretnih aktivnosti obratit pažnju na sledeće pojedinosti: da se utvrdi obim zahvata koji bi se u praksi sproveo; da broj zahvaćenih NKDVG odgovara realnim moguć-This type of seismic isolation in general reduces the swaying of the building, especially of its upper section, reduces the risk of objects in toppling over, and it can be considered as favourable method of seismic isolation for ICPBS

CONCLUSION
The standing legal standards used in our country and referring to BS in seismic areas fails to cover ICPBS as a separate building category with its requirements of protection from the negative earthquake effects.
No collapse requirement, which is a crucial requirement implemented in the Codes on aseismic building of BS, their remediation and extension on seismic areas, comprises that during the most intensive earthquakesthey sustain structural damage but will not collapse.It is inapplicable to ICPBS.Actually, only significantly small damage referring to the common BS can be tolerated for ICPBS due to their cultural importance.
The necessity of preserving ICPBS and protecting from damage caused by seismic effects created the need to introduce the new categorization of ICPBS into special construction categories, which would facilitate their adequate strengthening, remediation and reconstruction in seismic areas and they are: IG-AA Category of ICPBS of outstanding cultural importance listed by UNESCO IG-A Category of ICPBS of outstanding cultural importance IG-B Category of ICPBS of high cultural importance.
Here the ICPBS which contain painted wall surfaces are separately categorized and presented in table 9.It was done because the maximum damage at which the painted surfaces retain their authenticity do not exceed type 2 damage.At a damage higher than type 2, a larger part of painted surface is destroyed, whereby the painted work of art loses its authenticity and cultural-historical value, even when it undergoes a successful restoration.The following categories of ICPBS with painted wall surfaces are singled out: IGO-AA Category of ICPBS with painted walls surfaces of outstanding cultural importance listed by UNESCO IGO-A Category of ICPBS with painted walls surfaces of outstanding cultural importance IGO-B Category of ICPBS with painted walls surfaces of high cultural importance.
The 3 rd level of damage after the action of the strongest expected earthquake in the chosen return period is permitted in the case of other factors: protection of human lives (BU); protection of ICPBS itself, from the aspect of its architectural value (BAch) and potential of its conservations, as well as artistic elements on ICPBS without painted surfaces (BA).
These categories should be contained within a new Code for strengthening, rehabilitation and reconstruction of IPCBS in seismic areas, or as separate categories added to the existing Code no.52/85 [10] which refers to ICPBS.
After introducing obligation of protecting ICPBS from the earthquake effects, on the occasion of performing the concrete activities, it is necessary to pay attention to the following details: the extent of the intervention which nostima društva, kako finansijskim tako i stručnim; da se propiše procedura za verifikaciju prikupljenih podataka i zahteva koji se odnose NKDV, procedure moraju da budu jasno definisane i obavezujuće; utvrđivanje seizmičkog hazarda na lokaciji na kojoj se nalazi NKDVG.
Napomena: Faktore su uveli autori pošto omogućavaju da se u okviru samog NKDVG izdvoje više i manje značajni činioci koji čine kulturno dobro i kao takvi da budu prepoznati i da dobiju odgovarajuću zaštitu. is performed in practice should be determined; the number of included ICPBS should correspond to the actual financial and professional capacity of the society; the procedure for verification of the collected data and requirements relating to ICPBS should be developed, clearly defined and obligatory; the seismic hazard on the location where the ICPBS is situated should be defined.

PROPOSAL OF REDUCING PERMITTED SEISMIC DAMAGES ON IMMOVABLE CULTURAL PROPERTIES (BUILDING STRUCTURES)
Nedeljko STOJNIC Dusko KUZOVIC All interventions pertaining to remediation, strengthening and reconstruction of building structures (BS) in seismic areas, to which belong the immovable cultural property (ICP) buildings which are ranked as building structures (ICPBS), are constructed according to the (Code no.52/85), [10].This code permits structural damage of buildings without collapse in the event of the strongest earthquakes.However, this condition is unacceptable for ICPBS which have a status of high and outstandingly high importance according to the Law on Cultural property (LCP no.71/94) [13].Because of their special value and importance for cultural heritage ICPBS should not only survive the most intensive earthquakes, but their damage should be considerably reduced in comparison with ordinary BS.Therefore the paper proposes to divide ICPBS into three categories: ICPBS outstandingly high importance listed by UNESCO 2) ICPBS of outstanding cultural importance and 3) ICPBS of high cultural importance.For all categories, the factors for determination of ICPBS value are introduced, and therefore is determined the level of permissible damage they can be exposed to and potential risk of the loss of life in ICPBS which can be a basis for a new "Code for strengthening and remediation of ICPBS in seismic areas", or can be appended to the existing Code no 52/85, [10].
Key words: Aseismic regulations, cultural heritage, permissible seismic damage

Figure 2 .Figure 3 .
Figure 2. The laminated rubber bearing (a) and sliding seismic isolator (b) are key structural elements for construction which provides seismic isolation (Photo: APA Group)

Table 4 .
Damage quantification for MSK-64 and EMS-98 scalesFor territory of the Republic of Serbia, the earthquakes intensity of V, VI, VII, VIII and IX degrees are expected to occur which can cause damage of ICPBS.In table 5, intensities of potential earthquakes with the potential effects on ICPBS are given.

Table 5 .
Seismic intensities with their effects on ICPBS

Table 6 .
Territorial presence of seismic intensities according to the return periods

Table 9 .
Category of ICPBS with painted wall surfaces