Ard çekmeli radye temeller ile betonarme radye temellerin karşılaştırılması
Comparison of post tensioning mat foundation with reinforcement mat foundation
Yazar: HATİCE KÖKAN
Danışman: PROF. DR. TURGUT ÖZTÜRK ; PROF. DR. HÜSEYİN YILDIRIM ; DOÇ. DR. ALİ KOÇAK
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Yapı Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2019
Konu: İnşaat Mühendisliği = Civil Engineering

Özet:
Temel, yükü yapıdan zemine güvenli bir şekilde aktaran zeminle doğrudan temas halinde olan, yapının en alt kısmıdır. Şekil değiştirmelere karşı yeterli süneklikte olmak ve yapısal boyutlar, detaylar, uygulanan yükler karşısındaki davranış açısından incelendiğinde temel tasarımının iki temel amacı vardır. 
Yapı yüklerinin fazla olduğu ve zemin dayanımının kötü olduğu durumlarda radye temel tercih edilmektedir. Ülkemizde radye temeller yaygın olarak betonarme olarak yapılmaktadır. Betonarme radye temellerde; temel yüksekliğinin arttığı durumlarda beton dökülme aşamasında çıkan zorluklar ya da kademeli olarak dökülmesi, donatı sıklığı ve buna bağlı olarak yerleşiminde yaşanan zorluklar, betonarme radye temeller için dezavantaj oluşturmaktadır.
Ard çekmenin bilinen faydaları birçok ülkede konut ve hafif ticari ve endüstriyel temellerde, otopark ve otoyollarda, havaalanı pistleri ve yüksek binaların temellerinde uygulanmaktadır.
Ard çekmeli temelin amacı, uygulanan yükleri üst yapıdan zemine güvenle aktarmaktır. Ard çekme kuvveti, yükün bir kısmını taşımaktadır. Kalan yük için, yapının, eksenel etkiden kaynaklanan basınç gerilmelerine bağlı olarak kesme, zımbalama ve burulmaya karşı direnci artmış olacaktır. Ard çekme, dış yükün etkisini azaltarak ve çatlak oluşumunu engelleyerek ya da geciktirerek eğilmeyi azaltmaktadır. Zemin gerilmeleri açısından incelediğimizde ise oturmaları ve eğilmeleri azaltarak uniform bir zemin gerilmesi oluşmasını sağlamaktadır.
Ard çekme sisteminin avantajlarının yanısıra, deneyimli personel gerektirmesi, kriko, kilit mekanizması gibi özel ekipman gerektirmesi, kabloların yüksek gerilmeler uygulandığında güvenlik önlemi alınması gerekmesi bu sistem açısından dezavantaj oluşturmaktadır. Ayrıca gerilme kayıpları, ard çekmenin avantajlı/dezavantajlı olması açısından önemli bir faktördür.
Tez kapsamında 20 katlı bir binanın temeli betonarme radye temel ve ard çekmeli radye temel olarak hem rijit metot hem CSI SAFE yazılımı kullanılarak sonlu elemanlar yöntemi ile çözülmüştür.

Abstract:
The foundations are structural elements that transfer the loads of the structural system to the ground. The main purpose of foundations safely to transfer applied gravity and lateral loads from the superstructure to the soil without undue deformation of either the foundation or the superstucure. During the transfer, loads acting on the structure are transferred from the foundation to the ground and  that settlements and rotations are not occur it is important. Ground stresses occur depending on the type of load, the type of the ground, the stiffness.
In multi-storey buildings, mat foundation is preferred when the soil bearing capacity is very small, building load is too high or the floor basement is below ground water level. The mat foundation minimizes slump differences by jumping weak areas of the foundation like a bridge.
While generally reinforcement mat foundation use in our country, other countries post tensioned foundations system commonly. Despite the widespread use of reinforced concrete mat foundations in our country, the importance of the use of retractable mat foundations is should considered when considering the structural advantages inherent in post tensioning.
Briefly summarizing, post tensioning is a form of prestressing. Prestressing simply means that the steel is stressed before the concrete has to support the service loads. Necessary equipment and material is concrete, prestressing steel, anchorage, duct, grout and bearing plates for post tensioning system. Since the steel is jacking, the prestressing force is reduced. These losses are divided into long and short term. While short-term losses occur during transfer, long-term losses are continuous and continue throughout use. Short-term losses are friction loss, seating of wedges at transfer of prestressing force and elasxtic shortening. Long-term losses include concrete volume change and relaxation of prestressing steel.
The basic principle of post tensioned mat foundation is the same as the inverted slab. The bending moment and tensile forces on the foundations are the opposite of the effects on the slabs. The tendons are designed to help balance the point loads imposed by the columns and distribute the loads uniformly throughout the entire slab. The function of post tensioning in the mat is essentially to pick up the column loads and distribute the more or less uniformly over the entire plan area of the mat.  The tendon layout required for this purpose can be visualized as an upside own flat plate. In ground- supported slabs, the use of post-tensioning tendons puts the concrete into compression before applied loads can deform the slab and before applied tensile stresses cause the slab to crack. Using post tensioned tendons in ground supported slabs can reduces or eliminates restraint to shortening cracks. It can also produce a slab with a higher flexural capacity than a slab of the same thickness that is reinforced with non-prestressed reinforcing. Also post tensioning  method  reduces the foundation thickness. In particular, if we examine the advantage of the thickness of the foundation, there may be difficulties in the casting of very thick concrete. Costly chemicals may be required to prevent to the hydration heat. On the other hand, the amount of concrete used in a post-tensioned concrete slab be up to 30% less than that required in traditional reinforced concrete. 
Within the scope of the thesis, the foundation of a 20-storey building was solved by both rigid method and finite element method using CSI SAFE program. A comparison is done between the two foundations based on serviceability, strength requirements. It has been found to be a very advantageous system in terms of moment, punching and shear force. In addition, when the soil stresses are examined, it is seen that the stresses are uniformly distributed and affect the stress and positively.
The foundation of a 20-storey building is chosen for the solution. Foundation is symmetric both x and y direction. This 4-span system consists of 25 columns in total. There are 3 m cantilever in x and y direction. The console is made to reduce the ground stress value and to create a punching circumference. Concrete class is C45. According to TS 500, cylinder compressive strength is 45 Mpa, axial tension strength is 2, 3 and modulus of elasticity is 36000 Mpa. Steel class is S420. According to TS 708, yielding strength is 420 Mpa. Prestressing strandis made of seven wire. Nominal area is 150 square mm, breaking strength is 1860 Mpa. Tendon made of 12 prestressing strand. Jacking force is 75 %.
A combination of load occurs when different types of loads act simultaneously or together in a structure. For the solution, different types of combinations are occurred. This combinations, for the reinforcement mat foundation, G+Q and 1,4G+1,6Q according to TS500. For the post tensioned mat foundations, G+Q+PT-FINAL and G+Q+PT-TRANSFER combinations are examined for post tensioned.
For reinforcement mat foundation,  control of punching was carried out according to TS 500. The punching formula in  TS 3233 suitable for reinforced concrete slab. Therefore, punching check was performed according to ACI. As a result of the application, while the minimum foundation thickness is 160 cm reinforcement mat foundation, 120 cm on the post tensioned mat foundation. The thickness of the foundation decreased by 25%.
In reinforced concrete foundation design, where the maximum moment is occur need toput Ø24 / 60 reinforcement. The frequency of reinforcement causes difficulties in the application phase.The minimum reinforcement when post-tensioned is applied. 
Particularly in systems where the load is concentrated to a point, post tensioned mat foundations are advantageous. This foundation such as bridge foundation, it is not possible to fit the reinforcement.
Shear force is particularly critical in sub-column regions. In reinforced concrete solution; the shear force value exceeds the design shear force and require additional shear reinforcement. In the other system, the shear force value is greatly reduced and no additional reinforcement is required. 
Result of analysis, the maximum ground stress is 308 kN/m2 for the G+Q combinations and 293 kN / m2 for the G + Q + PT-FINAL combination. Stresses on the ground and settlements are proportional.  For combination of G+Q and G+Q+PT-FINAL, the displacement values are 1.54 cm and 1,46 cm, respectively.
In the x and y direction, the maximum moment value in the support zone is calculated as + 2334 kN.m according to G + Q combination and the value of +1195.3 kN.m is for  G + Q + PT-FINAL combination. In the x and y direction, the maximum moment value in the aperture region was calculated as -882,8  kN.m for G + Q combination and the value of -485 kN.m is for G+Q+ PT-FINAL combination.
Alongside to the advantages of the post-tensioning system, the need for experienced personnel, the need for special equipment such as jacking, locking mechanism, and the need to take security measures when high stresses are applied to the system are disadvantages. In addition, friction losses are an important factor for the advantageous / disadvantageous. The calculated mat foundation was found very high friction losses. It depends on the layout of the cables. Each fold occurs stress loss.These losses were reduced by stretching at both ends. Alternatively, cables may be divided according to applicaton and fiel conditions. Therefore; we should consider friction losses both structurally and economically when designing.