Cylindrical tanks are usually used in petro-chemical industry to store water or chemical materials. When their diameters, heights are taken into account, excess stresses will be transferred to the soil that they would be built on. Therefore even if the soil is considered to have sufficient bearing capacity, under the loading conditions over a large area, there can be problems due to bearing capacity, settlements and deformations. When designing a tank, foundation engineering is an important factor to consider. In the design of these wide diameter and flexible based structures, built on the problematic soils, a need for soil improvement as it would be done for a wide area could be costly. Therefore in the geotechnical analysis for these structures, the limit and tolerable values for settlement criteria needs to be considered in terms of structural integrity performances. When wide cylindrical tank structures are built on the weak soils, the settlement performance needs to be considered along with the damages that can occur on the upper structure. Settlements can cause problems in the nearby structures and the pipe connections can be effected. Cylindrical tanks are usually built on compacted granular fill materials or ring foundations with filled granular materials in the middle. In the weak soil conditions, the appropriate soil improvement method is chosen and applied or pile foundation system is used. In this paper, a cylindrical tank constructed on a site where there could be geotechnical problems, is considered. The tank considered is 65m in diameter and has a height of 19m. The settlements that could be critical are compared with the allowable ones stated in literature. Types of settlements that a wide cylindrical tank undergo are; uniform, planar and non-planar rotation, dishing, rotation at the crust and the base of the tank, and settlement at the base of the tank. The settlement calculations done were based on Janbu's tangent modulus method developed in 1967. Uniform settlements occur where beneath the tank at every point similar settlements exist. Planar rotation occurs when there is a differential settlement between two points on the tank. Dishing occurs where differential settlements are observed between two points on the tank and the middle of the tank base settle more than expected. Under the base of the tank, if there is soil with different geotechnical properties, local settlements can occur. Due to different soil strata thickness and deformation modules at the crust of the tank non-planar deformations can happen. In the case considered here, settlement calculations are done for various points on the tank and the total settlement values changed between 32cm to 79.3cm. Therefore as the minimum values for the settlement of the structure is calculated, it is seen that uniform settlement will occur. The settlements that would occur due to dishing or rotation will make up the differential settlements. According to the settlement analysis done, dishing value of 9.6cm is calculated in the centre of the tank. The differential settlements will occur at the crust of the tank which was not within the limits suggested in literature. Settlements due to liquefaction of soil were calculated as well. With different thickness of the liquefiable layers settlement values varied in different parts of the tank. As the structure is flexible, in the case of floating roofed tank systems, due to earthquake loadings, there would be big displacements and deformations that could cause collapse of the structure or damage in the structural system. Therefore the cylindrical tanks that would be constructed in the earthquake zones, dampers can be placed in their foundations. Under the tanks that are big in diameter, differential settlements will occur. Soil improvement can be done to prevent these deformations. Stress distribution in the soil of these heavy structures attenuates at depth. Therefore site investigation needs to be done in detail and at depth. Bearing capacity can be sufficient and settlements can be within limits under static conditions. However when saturated soils are considered, under earthquake loadings, liquefaction analysis needs to be done. Excess settlements can occur due to liquefaction. Steel cylindrical tanks are usually filled with liquid. Depending on the level of fullness, the vibrating frequency of the tank changes and needs to be calculated and dampers can be used. Dynamic analysis needs to be done with considering the local soil conditions. Keywords: bearing capacity, cylindrical tanks, settlement.Geniş çaplı ve esnek taban özelliklerine sahip silindirik tank yapıların tasarımında, problemli zeminlerde iyileştirme gerekliliği ortaya çıkması durumunda, alanın genişliğine bağlı olarak ıslah maliyeti yüksek olmaktadır. Bu tip yapıların geoteknik açıdan analizinde, gerek taşıma gücü gerekse oturma kriterlerinde sınır değerler, yapısal bütünlük performansı yönünden ele alınması gerekmektedir. Tank oturmaları zeminin göçmeye karşı güvenliğine göre daha önemli ve esas tasarım koşuludur. Oturmalar aynı zamanda komşu yapıları ve boru bağlantılarını olumsuz yönde etkileyebilmektedir. Tank yapısı altında gerçekleşen oturmalara bağlı olarak üstyapı formunda deformasyonlar meydana gelmektedir. Deformasyon derecesine bağlı olarak yüzer çatılı sistemlerde, çatı sisteminin sıkışmasına ve sistemin çalışmamasına neden olabilmektedir. Zeminin sıvılaşmasına ve sıvılaşan tabaka kalınlığına bağlı olarak deformasyonlar meydana gelecektir. Yapının esnek olması nedeniyle, deprem yüklerine bağlı olarak, büyük deplasman ve deformasyonlar oluşacak yapıda yıkılma veya hasar oluşmasa dahi yapısal sistemde arızalar meydana gelebilecektir. Bu çalışma kapsamında, tank yapıları için özellikle kritik olabilen oturmalar ele alınmıştır. Literatürde silindirik tank yapıları için verilen, oturma limit değerleri ve bu değerler dikkate alınarak, siltli kil kum tabakalı bir zeminde yer alan silindirik tank yapısı için analiz yapılmıştır. Yapılan hesaplar sonucu oturmalar silindirik tankın bazı noktalarında izin verilebilecek değeri aşmaktadır. Ayrıca tank ekseni boyunca meydana gelen düzlemsel oturma, merkez noktada hesaplanan oturma ile karşılaştırılıdığında çanaklanmaya bağlı olarak oturma meydana gelmiştir. Meydana gelicek oturmaları önlemek için zemin iyileştirilmesi önerilebilinir. Anahtar Kelimeler: Silindirik tank, oturma, taşıma gücü
