UDK 725.94.001.5:699.84(496.1) Građevinar 4/2013 Primljen / Received: 7.2.2012. Ispravljen / Corrected: 13.1.2013. Dynamic analysis of Dolmabahce Prihvaćen / Accepted: 21.3.2013. Dostupno online / Available online: 10.5.2013. masonary clock tower Authors: Professional paper Asena Soyluk, Zeynep Yeşim İlerisoy Dynamic analysis of Dolmabahce masonary clock tower Recent earthquakes around the world have shown that most masonry clock towers are susceptible to structural damage and collapse. An appropriate tower model was erected in order to investigate structural behaviour of a historic masonry watch tower at the Asena Soyluk, Ph.D. Dolmabahce Palace in Istanbul. The initial analysis of self-weight was followed by dynamic Gazi University in Ankara, Turkey analysis, which took into account the influence of deeper soil layers next to tower foundations, Department of Architecture and seismic motions registered for soft and stiff soil conditions during the 1999 earthquake [email protected] in Kocaeli, Turkey. Key words: masonry tower, soft soil, stiff soil, dynamic analysis, earthquake response Stručni rad Asena Soyluk, Zeynep Yeşim İlerisoy Dinamička analiza Dolmabahce zidanog tornja sa satom Zeynep Yeşim Ilerisoy, M.Sc. Nedavni potresi u svijetu pokazali su kako je većina zidanih tornjeva sa satom podložna Gazi University in Ankara, Turkey konstrukcijskim oštećenjima i urušavanju. Kako bi se istražilo ponašanje konstrukcije Department of Architecture povijesnog zidanog tornja sa satom Dolmabahce u Istanbulu, izrađen je model tornja. [email protected] Početno je analizirano djelovanje vlastite težine nakon čega je provedena dinamička analiza koja je uzela u obzir utjecaj dubljih slojeva tla uz temelje tornja te potresna gibanja zabilježena kod mekanih i čvrstih uvjeta tla prilikom potresa u Kocaeli u Turskoj 1999. godine. Ključne riječi: zidani toranj, dinamička analiza, utjecaj potresa, interakcija tla i građevine, potres Fachbericht Asena Soyluk, Zeynep Yeşim İlerisoy Dynamisches Verhalten des Dolmabahce Uhrturms aus Mauerwerk Aktuelle Erdbeben in der Welt haben mehrheitlich gezeigt, dass Uhrtürme aus Mauerwerk möglichen Bauschäden und Einbrüchen ausgesetzt sind. Um das Verhalten der Konstruktion des historischen Uhrturms aus Mauerwerk im Dolmabahce-Palast in Istanbul zu erforschen, ist ein Model des Turmes erstellt worden. Zunächst ist die Einwirkung des Eigengewichts analysiert worden und anschließend ist eine dynamische Analyse durchgeführt worden, in der Einflüsse der tieferen Bodenschichten um die Fundamente des Turmes berücksichtigt worden sind. Dafür sind seismische Aufzeichnungen des Erdbebens in Koceali in der Türkei im Jahre 1999 für weiche und steife Bodentypen eingesetzt worden. Schlüsselwörter: Mauerwerksturm, weicher Boden, steifer Boden, dynamische Analyse, Erdbebenantwort GRAĐEVINAR 65 (2013) 4, 345-352 345 Građevinar 4/2013 Asena Soyluk, Zeynep Yeşim İlerisoy 1. Introduction and the type of underlying soil. Past earthquakes have shown that buildings of similar type, but with different local soil characteristics, Clock towers, which are important meeting points in people’s daily are damaged differently, even under the same magnitude of life, are monumental buildings connecting past to present with earthquake. In fact, the propagation of seismic waves differs historic values. Towers, giving clues of traditional architecture and according to properties of soil through which they pass. Recent being a common heritage of human history, have become symbols of earthquakes in Ceyhan (27.06.1998, M=6.2), Gölcük (17.08.1999, cities. In order to pass on these symbols to future generations, it is of M=7.8), and Bingöl (01.05.2003, M=6.4) in Turkey have revealed crucial significance to preserve them from collapse and damage. The that the maximum damage was observed on meadows having conservation of historical masonry towers has gained in significance soft soil properties, even in cases when they are located far away in the world after the sudden collapse of the Civic Tower in Pavia, from the main fault [11]. This situation shows that there is a strong Italy [1, 2, 3]. Some investigations about such towers, involving both relationship between earthquakes effects and local soil properties. analytical and experimental analyses, are the "Torrazzo" in Cremona [4], Lutes [12] shows that uncertainty about soil stiffness might the Civic Tower in Vicenza [5], the St. Stefano Bell-tower in Venice [6], cause considerable uncertainty about the frequency content of and the eighth-century masonry tower called "Torre Sineo" in Alba [7]. structural response, and may sometimes modify expected values However, these studies do not take into account the change of dynamic of the frequency content. It is crucial to understand the dynamic behaviour of the towers depending on the soil-structure interaction behaviour of masonry towers to improve sustainability, and to (SSI) for different ground motion recordings of the same earthquake. preserve or strengthen these historical monumental structures. Ever since the time of Ottoman Empire, a lot of clock towers in In this study, the structural behaviour of the tower under its self- Turkey have been constructed according to the masonry technique weight is investigated initially with the finite element method. Then, involving natural stones. These magnificent structures, built in to determine the effect of earthquake ground motions, recorded various styles such as baroque or oriental, differ in body shapes and in different soil conditions, on the seismic response of masonry can thus be cylindrical, quadrilateral, polygonal, intertwined prisms, towers, the attention is focused on evaluating seismic response of or structures narrowing by height [8]. It is however known that the the masonry clock tower taking sub-soil conditions into account. strength of historical masonry structures is very low in case of an For this purpose, ground motions recorded at stations with different earthquake action. Turkey, which has a lot of historical structures, soil conditions and located at the same distance from the tower are is located in one of the most active earthquake zones in the world, used. The results obtained for different soil types are compared with and high magnitude earthquakes commonly occur in this region. each other according to the elastic base assumption. According to earthquake zoning map which is based on information The source document for site classifications is defined in the on geologic structure, plate tectonics, historical seismicity, and Specification for Structures to be Built in Disaster Areas, 2007, earthquake occurrence, Turkey comprises five different seismic [9]. The information regarding the basics for site classifications is zones [9]. There are 62 clock towers in the 1st level seismic zone in provided in its commentary. The commentary describes how soil Turkey [10]. However, most of these masonry towers suffer serious deposits amplify the level of ground shaking relative to the level damage, or even collapse, during these seismic activities. Some of bedrock shaking. The amount of ground motion amplification recent examples of collapsed towers are Kocaeli Clock Tower and depends on wave-propagation characteristics of the soil, which Istanbul Bakırköy Psychiatric Hospital Clock Tower [8]. can be estimated from shear wave velocity measurements. In The dynamic behaviour of masonry towers depends on the intensity the Turkish Seismic Code, site classes are defined in terms of the of ground shaking, the frequency content of the earthquake wave, shear wave velocity (Table 1). In this study, stiff and soft soil types corresponding to Z1 and Z4 site classes, respectively, are used. Table 1. Turkish Seismic Code: soil and site classification [8] Soil Shear wave Soil group and Generic description Site class Group velocity [m/sec] top layer thickness 1. Rock (Unweathered Or Stiff) >1000 Group (A), h ≤ 15 m (A) 2. Very Dense Sand, Gravel >700 Z1 Group (B), h ≤ 15 m 3. Hard Clay, Silt Clay >700 1. Soft Rock (Weathered) 700-1000 Group (B), h > 15 m (B) 2. Dense Sand, Gravel 400-700 Z2 Group (C), h < 15 m 3. Very Stiff Clay, Silty Clay 300-700 1. Highly Weathered Soft Rock 400-700 Group (C), h = 15-50 m (C) 2. Medium Dense Sand And Gravel 200-400 Z3 Group (D), h ≤ 10 m 3. Stiff Clay, Silty Clay 200-300 1. Soft Deep Alluvial Layers <200 Group (C), h >50 m (D) 2. Loose Sand <200 Z4 Group (D), h >10 m 3. Soft Clay, Silty Clay <200 346 GRAĐEVINAR 65 (2013) 4, 345-352 Dynamic analysis of Dolmabahce masonary clock tower Građevinar 4/2013 Table 2. Mechanical characteristics of materials Material Model Elements E [GPa] γ [kN/m³] Poisson's ratio n Limestone Solid 8.5 21.9 0.20 Marble Solid 10.0 27 0.26 2. Finite element model of the case study In the light of the above mentioned principles, the Dolmabahce Clock Tower is considered in this paper as case study. This tower Actual behaviour of masonry structures is generally highly is situated outside of the Dolmabahce Palace in Istanbul, and complicated. Thus, many simplifications are necessary these stands in front of its Treasury Gate on a square along the European structures are modelled [13]. For correct definition of the waterfront of Bosphorus, next to Dolmabahce Mosque. The tower behaviour of the structural system, and deformations and was constructed by Sarkis Balyan, a renowned Turkish architect of internal forces in the members due to various loads and Armenian descent, and designed in the Ottoman Neo-Baroque style environmental effects, the basic principles of the finite element between 1890 and 1895 [16]. modelling can be classified as follows [14]: - The simplest model most often gives optimum results. Complex 2. 1. Structural properties of Tower and models that go beyond the aim and scope of the analysis are superstructure modeling unnecessary. - All structural effects that are required for the analysis should The four-sided, four-story tower with a square plan is embedded be taken into consideration when determining dimensions of in the 12 x 12 m marble platform. The floor dimensions of the elements contained in the model.