1 Symposium with International Participation on Strengthening and Preserving Historical Buildings and Cultural Heritage II, October 2009, Diyarbakır, Turkey SEISMIC PERFORMANCE EVALUATION OF EMİR BAYINDIR CUPOLA IN AHLAT Dilek Okuyucu 1, Barış ERDİL 2 Middle East Technical University, Ankara, Turkey ABSTRACT Cupola, in some cases termed as tomb, (kümbet in Turkish) is the special name for the monumental mausoleum of a distinguished person in Turkish architecture. Ahlat town near Lake Van is hosting a number of exotic cupolas dating back to even 12 th century. The area is somehow, denoted as first level of seismic zone in official Turkish Seismic Zoning Map. Emir Bayındır Cupola in Ahlat is one of the spectacular examples of cupola type grave style. This monument is reported not to have any structural evaluation and curing at least in the last four decades; while it has some observable serious structural deterioration, cracks that can threaten the monument during seismic excitations. Seismic performance of Emir Bayındır Cupola was evaluated analytically within this perspective. Geometrical dimensions of the structure were measured and in-situ, visual structural evaluations were performed first then the analysis was performed. The main objective of the study is to take attention for special Turkish cupola architecture and its open air museum, Ahlat. So that, a number of spectacular cupolas as well as Seljukian grave stones, even dating back to early 12 th century, in this land need structural evaluation, protection, restoration and structural rehabilitation by means of cultural heritage respect and transferring them to future. This manuscript provides information about Ahlat, its cupolas and grave stones; then seismic performance evaluation and results of the analytical study for Emir Bayındır Cupola. Keywords: Cultural Heritage, Anatolia, Akkoyunlu Period, Cupola, Earthquake, Masonry Seismic Evaluation, Macro Modeling, Seismic Strengthening. 1 PhD Candidate, METU, Ankara, Turkey & Res. Asst., Atatürk University, Erzurum, Turkey 2 PhD Candidate, METU, Ankara, Turkey & Res. Asst., Yüzüncü Yıl University, Van, Turkey
2 Uluslararası Katılımlı Tarihi Eserlerin Güçlendirilmesi ve Geleceğe Güvenle Devredilmesi Sempozyumu II, Ekim 2009, Diyarbakır, Türkiye AHLAT EMİR BAYINDIR KÜMBETİ DEPREM DAVRANIŞ ANALİZİ Dilek OKUYUCU 1, Barış ERDİL 2 Orta Doğu Teknik Üniversitesi, Ankara, Türkiye ÖZ Kümbetler, Türk mimarisinde bir takım hizmet ve özellikleriyle toplumda öne çıkan insanlar için yapılmış olan anıtsal mezarlardır. Van Gölü kenarında yer alan Ahlat, yapımı 12. yüzyıla kadar tarihlenebilen çok sayıda özgün kümbete ev sahipliği yapmaktadır. Bununlar birlikte, bölge Türkiye Deprem Bölgeleri Haritası nda 1. derece deprem bölgesi olarak ifade edilmektedir. Yerinde yapılan incelemelerle, Ahlat taki bu önemli kültür mirasımızı korumak ve gelecek nesillere devredilebilmek gayesiyle, bölgedeki çok sayıda kümbetin ve yine 12. yüzyıl başlarına kadar tarihlenebilen, anıtsal nitelikli Selçuklu mezar taşlarının yapısal olarak incelenmesi ve gerekli görülenlerin restorasyon, koruma ve yapısal güçlendirme çalışmalarının yapılması gerekliliği kanısına varılmıştır. İlçedeki Emir Bayındır Kümbeti, bu özel mezar yapısı türünün, mimari farklılılar açısından en dikkat çeken örneklerinden birisidir. Yapıda gözle görülebilen ve olası yer hareketlerinde yapıyı tehdit edebileceği düşünülebilecek hasarlar ve çatlaklar mevcut olmasına rağmen, son kırk yıl içerisinde herhangi bir inceleme ya da onarım yapılmadığı ifade edilmiştir. Bu noktadan hareketle, Emir Bayındır Kümbeti nin dinamik yükler altındaki davranışı analitik olarak incelenmiştir. Öncelikli olarak, yapının geometrik boyutları ölçülmüş, genel durumu gözle yapılan inceleme ile detaylandırılmış ve sonrasında deprem davranışı bilgisayar modeli üzerinde analitik olarak incelenmiştir. Çalışmanın asıl amacı, çok özel bir Türk mimarisi ürünü olan kümbet geleneğine ve bu bağlamda, açık hava kümbet müzesi niteliğindeki Ahlat bölgesine dikkat çekmektir. Metinde öncelikli olarak Ahlat bölgesi kümbet ve mezar taşları hakkında bilgi verilecek, Emir Bayındır Kümbeti için yapılmış olan yapısal analiz çalışmasının detay ve sonuçları sunulacaktır. Anahtar Kelimeler: Kültür Mirası, Anadolu, Akkoyunlu Dönemi, Kümbet, Deprem, Yığma, Sismik Değerlendirme, Makro Modelleme, Sismik Güçlendirme 1 Doktor Adayı, ODTÜ, Ankara, Türkiye & Araştırma Görevlisi, Atatürk Üniversitesi, Erzurum, Türkiye. 2 Doktor Adayı, ODTÜ, Ankara, Türkiye & Araştırma Görevlisi, Yüzüncü Yıl Üniversitesi, Van Türkiye.
3 INTRODUCTION Numerous civilizations survived on Anatolian land since the centuries, remaining their fingerprints in forms of visual architectural products on the land area and cultural remains in public life in forms of traditional applications. This multicolored, open air museum is, unfortunately, located on one of the most active seismic zones of the earth. Seismic excitations damage vulnerable existing buildings, somehow causing life losses on the Anatolian Peninsula. This reality creates a need to protect our historical structures in the name of cultural heritage respect. Historical buildings are basically made of brick and/or stone masonry. In structural engineering perspective, masonry structures are very well known to be quite vulnerable to seismic excitations. In order to carry our architectural-historical heritage to the next generations by means of structural protection; seismic performance evaluation is first needed and then, considering the evaluation results history-friendly seismic rehabilitation, protection and proper restorations of ornaments, etc. are required to be applied for the specified structure. Emir Bayındır Cupola in Ahlat Bitlis / Turkey was evaluated by the special interest of the authors within this context. This structure, being one of the unique examples of Turkish Islamic monumental cupola (tomb) tradition, is reported to be constructed in 1481 during Akkoyunlu period, in Ahlat. The cupola is a remarkable example of two layers of cupola roofing system; an inner dome representing endlessness of the sky in Islamic view and a covering cone representing Turkish tent tradition from Middle Asia. This approximately six centuries old structure is unsymmetrical in plan and is stated to have a number of observable structural problems, like wide cracks and stone deteriorations. Moreover, any structural treatment is reported within the last four decades. Anyway, cupolas land of Ahlat is located near Lake Van and this area is denoted as first level of seismicity zone in Turkish Seismic Zoning Map. This region has experienced strong ground motions in the history and numerous low magnitude excitations are still occurring as a kind of seismic fatigue loading. In order to investigate the seismic performance in engineering point of view and to see the structural deficiencies of Emir Bayındır Cupola, the structure was modeled and analyzed in 3D. First, the architectural dimensions were obtained, data related to current status of the monument was collected and then structural model of the building was generated in SAP2000 Nonlinear Finite Element Analysis software. Macro modeling approach was taken into consideration in structural modeling. Response spectrum method was applied for dynamic analysis. The seismic vulnerability of the cupola by means of high tensile stress concentrations reaching beyond the capacity was observed by the analysis. The main objective of the study is to take attentions to cultural heritage in Ahlat region. The area hosts a number of Seljukian stone work products which can be assumed as formal documents expressing the existence times of Seljukians on Anatolian peninsula. This paper provides information about Ahlat cupolas and Seljukian grave stones, the historical and structural value of the Emir Bayındır Cupola. Structural model and analysis details for seismic performance evaluation of the cupola will be explained, results will be discussed in the whole manuscript.
4 AHLAT CUPOLAS and GRAVE STONES Ahlat, a city used by Alp Arslan, who opened the doors of Anatolia for the Turks, as a base before his famous victory in Malazgirt, can be considered an outdoor museum with its unique cupolas and grave stones. Ahlat is exhibiting its historic heritage of mosques, cupolas, graves, bridges, baths and aqueducts. The city has numerous structures that have witnessed the passage of time, such as a Seljuk graveyard, a castle, Hasan Padişah's cupola, Emir Bayındır's cupola, Sheik Necmettin's cupola, Erzen Hatun's cupola, the İskender Pasha Mosque and Bayındır Bridge, etc.. Figure 1. Seljukian Grave Stones and Hasan Padişah Cupola While it is named after Urartian King Lat, Ahlat contains numerous works of art and architecture from the Seljuk and Ottoman empires. Legend has it that King Lat, ruling the territory near Lake Van, was badly wounded during an attack against the city by the Med. The king's daughter cried for her father, mourning and shouting: "Ah! Lat. Oh, dear Lat! until the Med conquered the city. When the Urartian king died, this city he loved very much was named after him. The legend also claims that the Urartian people, the oldest inhabitants of the city, called it "Halads" while Armenians referred to it as Shaleat," Syriacs "Kelath," Arabs "Hil'at" and the Persians and Turks called it "Ahlat." The city's inhabitants were introduced to Islam during the time of Omar, the second caliph. Eyad bin Ghanem, who conquered Jazira, also conquered Ahlat, making it part of the Islamic state. The cupolas located at the entrance of the city, particularly that of Abdurrahman Gazi, are among the prominent works of architecture that stand out as symbols of the city's Muslim identity. Abdurrahman Gazi's cupola and the historic mosque near it are located on a green patch of land covered with roses on a hilltop with a vantage point over Lake Van, hinting at the richness of civilization in the district.
5 Cupolas and Grave Stones in Ahlat Ahlat cupolas resemble Middle Asia Turkish tents by the shape. Thus, cupolas can be assumed as the convertion of the tent art of Turkish life into architectural products. Therefore, it is obvious that Turks have introduced cupola architecture into Islamic art. This art was in an other shape called Kurgan in Turkish life, before they met with Islam. Cupola (tomb) architecture starts in 11 th century, within Seljukian period. It is possible to see this kind of monumental graves on the Turkish migration route from Horasan to Anatolia. Cupolas are generally constructed for the publicly known and important people like : Rich people who could finance the cupola construction by themselves Some important, successful military commanders Some religiously important people Some important people of public management and their family members It is reported that Ahlat hosts 19 cupolas in total. 4 of these cupolas were destroyed, remaining only the graves. Hacı Nene Cupola, Yeşil Cupola and Usta Şagirt Cupolas are the examples of this damaged ones. Ahlat cupolas belong to Seljukian, İlhanlı, Karakoyunlu and Akkoyunlu periods. Figure 2. Erzen Hatun Cupola (left) Emir Ali Cupola (middle) Hasan Padişah Cupola (right) Cupolas in Ahlat, characteristically, have a square base. Some of them were constructed with four walls following the base and ending up in the same fashion, some of them were transformed into octagonal form and closed thus in pyramidial shape. Total of 12 cupolas with cylindircal web exist in Ahlat. Cylindirically webbed cupolas jumped from square base to dodecagon form, then were transformed into cylindirical form ending up with a tent type ceiling. Cylindirical cupolas were constructed with two storeys. Grave was placed in basement, the upper story was arranged for praying. Other than the cylindirical webbed cupolas, some cupolas which were coverted from square shape to octagon in elevation. This type cupolas are one storey structures. It is also reported that, there are 6 cupolas which could not be finished in Ahlat.
6 One cupola generally covers 3-4 graves. Ornaments on the cupolas are generally special amblems for a specified family, nation, religious person, etc. Some of the ornaments are termed as stone jewelleries. Çark-ı Felek ornament is the most commonly observed one representing the spin of the globe. Ahlat also hosts special Seljukian grave stones other than the cupolas. Seljukian Graveyard is located in between İkikubbe neighborhood and Harabaşehir, being the largest graveyard of Ahlat. Meydanlık Graveyard hosts approximately 1000 gravestones in different shapes and ornamentings which are dated from early 12 th century to 16 th century. Besides, 7 graves in tumulus type, named as Akıt by public, exist in Ahlat. This graveyard covering the most important grave stones are accepted like a kind of formal document that implies the Turkish existence time in Anatolia.. Figure 3. Examples of Seljukian Grave Stones in Ahlat Ahlat type of stone works like cupolas and grave stones are reported to be constructed using Ahlat stone (ignimbrite). This stone is very soft when it is out of the natural source, then it gains strength the by time it is faced to athmosphere. Therefore, the special ornaments and difficult structural shapes of cupolas are thougth to be constructed sudden after the stone was obtained from its source. Histrocial value and richment of Ahlat can be further underlined by more cultural heritage examples. Large-scale projects should be implemented in order to first protect and then promote Ahlat and the rich civilization of this town to the world. Authors focused on Emir Bayındır Cupola in Ahlat with a special interest, after area visit. This two storey cupola is a spectacular example in shape with its openings. Besides, this massive stone masonry structure is thougth to be vulnerable to seismic excitations due to its slender structural details and structural deficiencies like cracks, etc. The cupola will be introduced in detail and then seismic behavior analysis of the cupola will be presented below.
7 EMİR BAYINDIR CUPOLA An inscriptive band below the cornice of the cupola announces that the building was built for Bayindir ibn Rüstem, who died in It was commissioned by his wife Sah Selime Hatun and completed in The architect is unknown, but Baba Can Bey is mentioned as the builder on an inscriptive plaque found on the small mosque of Emir Bayindir to the north of the cupola. Cupola belongs to Akkoyunlu Government period. It was restored in 1967 by General Directorate of Religious Endowments. Figure 4. Views of Emir Bayındır Cupola The cupola was built as a part of a complex including a small mosque and zawiya (zaviye), which is now completely lost now. The spherical cupola (tomb) is raised about 2.50 m above the ground on a crypt and covered with a dome topped with a shallow conical crown on the exterior. The narrow door of the crypt, which is placed off center on the east façade, has sunken below the ground level and is reached by seven steps. It is about 6.50 m 2 on the interior and lit by narrow slits on the east, west and south walls. A barrel vault aligned east-west supports the chamber above. Figure 5. Geometry of Emir Bayındır Cupola
8 The cylindrical body of the cupola sits on the square crypt whose corners are chamfered on the exterior to create a dodecagon base for the cupola chamber. The entryway faces the qibla wall of the mosque and is accessed with a double staircase. The door is framed by three decorative bands and crowned by an unusual muqarnas vault with floral carvings. Elongated niches on each side of the door are framed with a band of diamond motifs carved into the stone. The southern hall of the cylinder facing the lake is opened with ten short columns defining nine windows. The columns are about 1.00 m high and have heavy muqarnas capitals are connected with small arches. The parapet below is carved with ornate niches aligned vertically with the columns. The niche facing the qibla is left shallow to accommodate a mihrab niche inside the cupola. The inscriptive band, bordered by decorative bands is placed below the muqarnas cornice. The cupola is made of red (Ahlat) stone. The cupola is reported not to have been treated within the last forty years. Stone deteriorations and cracks were observed on the cupola body, by visual inspections of authors. Some stone spillages on the three of the columns in the size of approximately 20x20x4 cm exist. A number of serious cracks on arches in between the column muqarnases can be easily observed. Besides, tension cracks developing from cupola web up to ceiling side seem to be quiet important. SEISMIC BEHAVIOR OF EMİR BAYINDIR CUPOLA Emir Bayındır Cupola is a spectacular example of Turkish cupola tradition. It is reported that, the architecture Baba Can Bey had constructed this type of cupola only twice; one in Azerbaijan and the other in Ahlat. Emir Bayındır Cupola is a slender structure with its columns and openings in the web. It is made of stone masonry. Some serious cracks and deteriorations exist in the cupola body; probably will be threatening the structure during even a moderate seismic excitation in the future. Authors desired to investigate the seismic behavior of Emir Bayındır Cupola within this perspective, especially for the determination of critical sections to crack under dynamic forces such as earthquakes. It is more convenient to perform elastic calculations initially for the analyses before protection and restoration of historic structures. Therefore, using SAP2000 software, the cupola was analyzed under gravity forces due to the self-weight of the structure and under dynamic loads by linear response spectrum method. Material Properties One of the most challenging cases of the analysis of historical masonry structures is no doubt estimation of material properties due to a number of uncertainties. Cupola is a stone masonry, made of Ahlat stone (ignimbrite). Some analysis related to ignimbrite reports inappropriateness of structural utilization due to its weak mechanical properties and poor durability abilities. Ignimbrite is basically suggested for decorative works. It has a porous structure and not suggested for the applications in the regions of strong freezing thawing climate cycles. However, cupolas in Ahlat are made of ignimbrite and carry at least the heavy ceilings consisting of dome and cone. Regional name of ignimbrite, Ahlat Stone, is commonly used as cover material in various areas like buildings, mosques, graveyard stones and vaults. The structures constructed with
9 Ahlat stone and in Selçuklu Era, are still preserving their properties. Ahlat stone has various colors like brown, dark brown (chestnut), ash. Ahlat stones are some what soft whey they are extracted from soil, but they harden by the effect of atmosphere. Soft Ahlat stone can be given into desired shape by hand or by machine. 3-4 storey masonry structure constructed with Ahlat stone are present in Ahlat district. It has been thought that, Ahlat stone when prevented from absorbing water can show some degree of heat isolation. Some properties of the Ahlat stone as stated in the literature are given in the table below. Moreover, it should be underlined that varying material property values of ignimbrite are stated in some of the commercial web sites of Ahlat stone suppliers such as compressive strength (in between Mpa), unit weight (in between kn/m 3 ). Elastic modulus ignimbrite is reported to be Mpa in various sources. Table 1. Properties of Ahlat Stone (Ignimbrite)  Property Value TS 1910 TS 2513 Limits Compressive Strength (Mpa) Flexural Strength (Mpa) Water Absorption by Volume(%) Unit Weight (kn/m 3 ) Specific Gravity (kn/m 3 ) Porosity (%) Fullness Ratio (%) Abrasion (cm 3 / 50cm 2 ) Analytical Model and Analysis Emir Bayındır Cupola was modeled in macro modeling approach and analyzed in sap2000, Advanced Structural Analysis Program. Solid elements (total of 2924 solids) were used for cupola body. Dome and cone were modeled as shell elements because of some numerical solution necessities of the software. Mathematical model of the cupola was fined and finalized for exact analysis step by step as explained below. The cupola was first modeled considering the basement walls surrounded by ground. However, first analysis results showed that the results are not seriously affected when the fixity is started from the ground level. Therefore, the model was first simplified, ignoring the thick basement walls surrounded by the ground, as shown in Figure 6, and used for further analysis in order to shorten the analysis time. In the second step of model fining, Model-2 was first analyzed ignoring all existing structural deficiencies. Then considering the first analysis results of Model-2 and current situation of the cupola, different material properties as stated in Table 2 was assigned to simulate the cracked and damaged locations. All analysis was finally reperformed on the final version of Model-2. Table 2. Assigned Modulus of Elasticity Values for Model-2 final Structural Member Situation Modulus of Elasticity (Mpa) Cupola web and Dome relatively fine 4500 Cone and Damaged Columns having local deteriorations 4000 Cracked Arch Locations having observable cracks 2500
10 a b c d Figure 6. Model -1 (a-b) and Model 2 (c-d) for Emir Bayındır Cupola Dead load analysis, modal analysis and linear response spectrum analysis were performed for the cupola on Model-2 final version. Linear-elastic analysis was performed so as to specify critical parts that could exist due to various load effects and to determine overall stability of the structure. Since the structure is stone masonry, stresses and especially tensile stress concentrations obtained by the analysis was considered and evaluated basically. Results of Modal Analysis Analysis Results Modal analysis was performed in order to define the period of the structure that will be used in response spectrum analysis. Moreover, considering the period values together with the stresses under dead loads; Model-2 was fined. Model 2, was modified and decided to be used in further analysis as Model-2 final. The results of the modal analysis are stated in the Table 3 below. Table 3. Modal Analysis Results Mod Number Period (sec) Period (sec) Mod Number Model-2 Model-2 final Model-2 Model-2 final Results of Dead Load Analysis Cupola was analyzed under dead loads (weights of dome and cone). Tensile stress concentrations around the door opening, over the arches in between the column muqarnases and in bracelet zone under ceiling were clearly observed; which mostly coincides with existing wounded situation of the cupola. Since, the tensile stresses around these locations basically vary around 0.60 Mpa being less than the capacity (The flexural capacity of ignimbrite is reported to be 1.60 Mpa (kaynak).the split cylinder strength usually ranges from 50 to 75% of the modulus of rapture. (kaynak) So, the tensile strength of the ignimbrite
11 could vary Mpa.), it is thought that these cracks could have occurred due to material loss of stones decreasing the capacity by durability effects in time or some kind of seismic actions providing more sudden tensile stresses. Further, tensile stresses around 2.50 Mpa of some few members were also obtained under the structure weigth itself. Compressive stresses under dead loads reaching even the capacity (referred to Table xx) were observed in very few elements under the basement of first storey (praying area).compressive stresses was obtained to reach up to 34% of compression strength (referred to Table xx) of the stone material in some of the column webs and especially transition zones from muqarnas to column body. Results of Response Spectrum Analysis Figure xx. Contours under Dead Load Cupola was analyzed under dynamic forces by response spectrum method in both global directions.(tec) Maximum tensile stresses were obtained around the column bases and arches in between the muqarnases, reaching up to 1.50 Mpa, which is beyond the capacity (kaynak). This analysis result can be somehow support the idea that; cracks especially over the arches could have occured due to some past seismic excitations. Figure xx. Stress Contours by Linear Response Spectrum Analysis Considering the dynamic analysis results and seismicity of the region, one can end up with underlining the high vulnerabilty of the cupola for dynamic forces. This implies the necessity of seismic protection of the cupola by a proper technique such as structural tendon systems.( ) CONCLUDING REMARKS
12 Emir Bayındır Cupola in Ahlat was analytically investigated on engineering perspective; after visual inspections in-situ. However, the basic objective of the study was to take attentions to Ahlat and its rich cultural heritage on ordinary world citizens perspective. Seljukian style Ahlat cupolas and grave stones are some kind of formal historical documents of first Turkish attendance to Anatolia dating back to 11 th century. Visual inspections of authors in Ahlat desire to underline the necessity of interdisciplinary partnership for cultural heritage protection in the area. So that; historical masonry of the area was basically made of ignimbrite which is reported to be unsuitable for structural purposes as well as poor durability properties. By in situ evaluations of historical stone works in Ahlat, Emir Bayındır Cupola seemed to be the most vulnerable one among the others with its special architecture and existing situation. So, this structure was chosen to be analyzed by the special interest of authors. Before structural treatment and restorations, structural analysis of the historical masonry is necessary. Some basic remarks of the study can be stated as below. Linear-elastic analysis could be performed initially so as to specify critical parts that could exist due to various load effects and to determine overall stability of the structure. REFERENCES
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