Çok düşük dayanımlı beton silindirlerin geri kazandırılmış pet lifli polimer ile güçlendirilmesi
Very low strength concrete cylinders strengthening with recycled pet fiber polymer
Yazar: NESLİHAN ASLAN
Danışman: DOÇ. DR. MEDİNE İSPİR ARSLAN
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Yapı Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2023
Konu: İnşaat Mühendisliği = Civil Engineering
Dizin: Lifli kompozitler = Fiber composites ; Yapısal güçlendirme = Structural empowerment ; Çevresel sürdürülebilirlik = Sustainable environment

Özet:
Dünya genelinde en çok can alan doğal afetlerin başında deprem yer almaktadır. Bu durum da depreme karşı alınan tedbirleri zorunlu hale getirmektedir. Deprem anında açığa çıkan kuvvetleri karşılamaksızın gevrek davranış sergileyen yapılar, can ve mal kaybına sebebiyet vermektedir. Tasarıma uygun inşa edilmeyen, yeterli beton basınç dayanımına sahip olmayan beton ile inşa edilen ve yeterli donatılanmaya sahip olmayan yapılar deprem anında hasara uğramaktadır. Meydana gelecek hasarı ya da yıkımı minimum seviyeye indirebilmek amacıyla yapıların daha sünek hale getirilmesi amaçlanmaktadır. Bu amaçla yapıların güçlendirilmesi son yirmi yılda dünya genelinde oldukça tercih edilen bir uygulama haline gelmiştir. 
Yapıların güçlendirilmesinde kullanılan geleneksel lifli polimerler, yapıların dayanımını artırsa da sünek davranış konusunda istenildiği kadar etkin değildir. Yükleme anında açığa çıkan gevrek davranışın önüne geçebilmek amacıyla PET lifli polimer malzemeler ile sargılamalar üzerinde çalışılmaktadır. Sağladığı sünek davranışın dışında geri kazandırılarak üretiliyor olmasıyla hem çevre dostu hem de ekonomik olan PET lifli polimerler geleneksel lifli polimerlere tercih edilebilir.
Bu çalışma ile düşük dayanıma sahip beton yapılarda PET LP ile güçlendirmenin yapı üzerindeki etkilerini araştırabilmek amacıyla düşük dayanımlı beton silindirle çalışılmıştır. Farklı lif yoğunluğuna sahip liflerin kullanıldığı sargılamalarda farklı sargı tabaka sayısına sahip olacak şekilde sargılanmıştır. Sargılamanın ardından güçlendirmenin numunenin davranışı üzerindeki etkisini inceleyebilmek amacıyla numuneler monoton ve tekrarlı artan yüklere maruz bırakılmıştır. 
Gerçekleştirilen deneysel çalışmaların sonucunda PET LP ile güçlendirmenin yapıların    dayanımda, şekildeğiştirme kapasitelerinde ve sünekliliklerinde iyileştirici etkiye sahip olduğu görülmüştür.   Elde edilen sonuçlar doğrultusunda hem uygulama kolaylığı sağlaması ve diğer güçlendirme malzemelerine kıyasla ekonomik olması hem de sürdürülebilir bir malzeme olması sebebiyle yapıların güçlendirilmesinde kullanılmak üzere tercih edilebilir bir malzeme olduğu sonucuna varılmıştır.

Abstract:
Earthquake is one of the most common natural disasters in the world. This situation makes it necessary to take measures against earthquakes. Countries in the earthquake zone in which our country is located are in search of new methods in order to control the effect of the earthquake. Structures that exhibit brittle behavior without meeting the forces emerging during an earthquake cause loss of life and property. Structures that are not built according to the design, built according to the old regulation, built with concrete that does not have sufficient concrete compressive strength, and do not have adequate reinforcement are damaged in the event of an earthquake. It is aimed to make the structures more ductile in order to minimize the damage or destruction that will occur. For this purpose, strengthening of structures has become a highly preferred practice throughout the world in the last two decades.
Today, the wrapping method, which is used to strengthen the structures in order to increase the strength and ductility values of the carrier elements of the structures, has become a very preferred application. The reason for this is that this application prevents the time and cost of demolishing and rebuilding existing structures. It is easy to apply in existing structures and does not cause production to stop during application. With the wrapping method, the resistance of the structures to environmental conditions such as corrosion and humidity increases. Conventional fibrous polymers are widely used, which enable existing structures to be strengthened by providing ease of application. Conventional fibrous polymers used in the reinforcement of structures increase the strength of the structures, but are not as effective as desired in terms of ductile behavior. In order to prevent the brittle behavior that occurs during loading, PET fibrous polymer materials and wraps are being studied. Apart from the ductile behavior it provides, PET fibrous polymers, which are both environmentally friendly and economical, can be preferred to traditional fibrous polymers because they are produced by recycling.
In recent years, there are studies using traditional fibrous polymers. As a result of these studies, it was determined that the deformation and ductility capacities of concrete samples increased significantly. However, sudden failures cannot be avoided in studies using conventional LPs. For this reason, the use of Polyethylene Terephthalate (PET) fibrous polymers with a much higher deformation capacity has been considered today. Unlike fibers such as carbon, glass, aramid, PET FRPs significantly increases the ductility of the structure and absorb the earthquake energy in a substantial amount. However, it is a material with a low modulus of elasticity. PET is a transparent polymer with good mechanical properties under varying loads and good chemical resistance. Studies in the literature are insufficient to represent buildings with low strength concrete pressure in the existing building stock. Reinforcement studies were carried out on samples with low concrete compressive strength, albeit in limited. Among these studies, the number of studies wrapped with PET LP is very limited. Therefore, in this thesis, it is aimed to determine the effect of wrapping on the behavior of the cylinder after the cylinders with low concrete compressive strength are reinforced with PET FRP.
In this study, low strength concrete cylinder was used to investigate the effects of PET FRP strengthening on low strength concrete structures. It is aimed both to contribute to the literature and to represent the structures made of low-strength concrete, which constitute a significant part of the building stock in our country, by working on low-strength concretes, which are thought to be missing in the literature. In windings in which fibers with low and high fiber density are used, the samples were wrapped in single and double layers in order to determine the effect of different winding layers on the strengthening. In order to examine the effect of strengthening on the behavior of the specimen after winding, the specimens were subjected to monotonous and repetitive increasing loads. Fiber density, number of wrap layers and loading pattern are the parameters of the experimental study.
In recent years, the concept of sustainability has been rapidly increasing its importance. As in many sectors, measures are taken in the construction sector to ensure both the elimination of waste and the reduction of material consumption. In addition to the performance advantages of PET FRPs such as high deformation capacity, it is a very important material for sustainability as it is obtained by recycling wastes. The fact that the fiber-reinforced polymer material to be used in reinforcement is obtained without recycling is quite environmentally friendly, both in terms of eliminating the existing waste and reducing the amount of raw material to be spent for the production of a new material.
In this experimental study, concrete cylinders with a diameter of 150 mm and a height of 300 mm were reinforced with PET FRP in the transverse direction, and their behavior was investigated by subjecting them to monotonic and cycling increase loads. While straingage was used to measure the deformations that may occur in the samples in the transverse and longitudinal directions at the time of loading, axial strains were measured using 50 mm capacity LVDTs (linear variable displacement transducers)
As a result of the experimental studies carried out, it has been seen that the reinforcement with PET FRP has an improving effect on the strength, deformation capacity and ductility of the structures. Considering the fiber density of the polymer material used in the wrapping, which is one of the main comparison parameters, it has been observed that PHD fabrics with high fiber density have a higher contribution to both strength and axial elongation capacity compared to those with low fiber density.In line with the results obtained, it has been concluded that it is a preferable material to be used in the strengthening of structures because it provides ease of application, is economical compared to other strengthening materials and is a sustainable material. In addition, the data obtained as a result of the experimental studies were put into the existing analytical models and the results were tried to be estimated. Considering the fiber density of the polymer material used in the wrapping, which is one of the main comparison parameters, it has been observed that PHD fabrics with high fiber density have a higher contribution to both strength and axial elongation capacity compared to those with low fiber density.
Axial stress and strain results were estimated by replacing the data obtained as a result of experimental studies in existing analytical models. The maximum strength and the corresponding strain values of the cylindrical specimens strengthened by wrapping in the transverse direction with PET FRP were substituted in the empirical relations known from the existing studies and the results were compared. As expected, studies involving PET LP-wrapped samples of the models used made the closest estimates to the experimental results. While the Fahmy model is successful in estimating the strength capacity value from the prediction values calculated using different models, the Dai model is successful in estimating the strain capacity. The models used were insufficient in estimating true values.