Ahşap yapı elemanlarının tahribatsız hasar tespit yöntemleriyle incelenmesi
Inspection of wooden structural elements by non-destructive test methods
Yazar: MİNEL AHU KARA
Danışman: DOÇ. DR. MUSTAFA ERKAN KARAGÜLER
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Mimarlık Ana Bilim Dalı / Çevre Kontrolü ve Yapı Teknoloji Bilim Dalı
Derece: Yüksek Lisans, 2017
Konu: Mimarlık = Architecture

Özet:
Ahşap, lifli ve anizotrop bir dokudan oluşan organik bir yapı malzemesidir. Ahşabın doğal, ekolojik ve tabiattan elde edilen bir malzeme olması, ahşabı eski zamanlardan beri insanlığın kullandığı bir yapı malzemesi haline getirmiştir. Ahşap, yapıda kullanıldığında sağlamış olduğu hafiflik ve bununla birlikte yüksek taşıma gücü, yapım aşamasında kolay işlenmesi ve elemanların çivi ile birleştirilme esasına dayanarak inşa edilebilmesi, doğal ve sıcak bir görünüm vermesi ve yapıda ömrünü tamamladığında geri dönüşümünün mümkün olabilmesi gibi avantajlarından dolayı ahşap çokça kullanılmaktadır.
Ahşabın tüm bu avantajlı özelliklerinin yanında, zamanla ahşap malzemede bazı problemler de gözlenmektedir. Bu problemlerden biri ahşabı zamanla yavaş yavaş tahribata uğratan ve ona fiziksel, kimyasal ya da biyolojik yollarla zarar veren bozulmalardır. Ahşapta görülen bu bozulmalar, ahşabın iç yapısını zamanla bozarak önce fiziksel daha sonra mekanik özelliklerini zayıflatmaktadır. Ahşapta görülen bozulmalar özgün malzemede, malzeme kayıplarına en aza indirebilecek şekilde bozulmanın erken safhalarında çeşitli hasar tespit yöntemleriyle belirlenebilmektedir. Böylece yapıda kullanılan özgün ahşap malzemenin, bozulmanın erken safhalarında belirlenmesiyle orijinal ahşap malzeme yapıya tekrar geri kazandırılarak sürdürülebilirliği sağlanmaktadır. Ahşapta hasar tespitinde uygulanan yöntemler, özgün malzemeyi bozulmanın erken safhalarında tespit edip yapıya kazandırdığı gibi aynı zamanda uygulama esnasında özgün malzemeye en az hasarı verecek şekilde uygulanabilmesine olanak tanımaktadır. Yapılan tez çalışmasında, ahşap yapı malzemesinde uygulanan tahribatsız ya da yarı tahribatlı yöntemlerin, tahribatlı hasar tespit yöntemlerine göre sağlamış olduğu avantajları belirlemek ve özellikle tarihi yapılarda kullanılan ahşap malzemede en az hasar yaratarak malzemede hasar tespiti yapmak amaçlanmıştır. Bu amaç doğrultusunda, yürütülen tez çalışması 6 bölümden oluşacak şekilde ele alınmıştır. 
Çalışmanın ilk bölümünde, çalışmanın amacı, önemi, kapsam ve yönteminden bahsedilmiştir. Daha sonra amaçlanan çalışma kapsamında, konuyla ilgili literatür çalışması yapılmış ve konuyla ilgili yapılan çalışmalar incelenmiştir. Bu adımdan sonra çalışmanın deneysel sürecine başlanmıştır. Deneysel süreç ilk olarak saha uygulamasıyla başlamış ardından laboratuvar ortamında devam edilmiştir. Deneysel çalışmada tomruk halinde alınan masif ahşap elemanlar (çam, meşe ve ladin) ile restorasyonu devam etmekte olan tarihi bir yapıdan elde edilen ahşap elemanlar kullanılmıştır. Çalışmada kullanılan numuneler laboratuvar çalışması için, kesilerek uygun boyutlara getirildikten sonra numunelerin malzemede yaratacak olduğu hasar derecesine göre sırasıyla; ultrases, sertlik, geri tepme çekici, basınç ve eğilme deney yöntemleri uygulanmıştır. Deneysel sürecin tamamlanmasıyla, deneylerden elde edilen sonuçlar değerlendirilmiş ve  yorumlanmıştır. Dördüncü bölümde, deneylerden elde edilen sonuçların korelasyon bağıntıları elde edilerek, deney sonuçlarının değerlendirilmesi ve irdelenmesi yapılmıştır. Çalışmanın beşinci bölümünde tüm çalışmaya dair sonuç ve önerilerde bulunulmuştur. Bu doğrultuda yapılan çalışmalar sonucunda ahşapta uygulanan tahribatsız hasar tespit deney yöntemleri ile tahribatlı hasar tespit deney yöntemleri arasında güçlü korelasyon ilişkileri saptanmış ve ahşapta tahribatlı hasar tespit yöntemleri uygulamadan, tahribatsız hasar tespit yöntemleri ile de hasar tespit çalışmalarının yapılabileceği sonucuna varılmıştır. Bunun yanı sıra deneysel çalışmalardan sertlik ve geri tepme çekici deney yöntemleri, ahşabın lif doğrultusuna bağlı kalmadan, liflere paralel ve liflere dik doğrultularda birbirine yakın sonuçlar elde edilmiştir. Bu durumda, söz konusu deney yöntemlerinin ahşabın anizotrop yapısına bağlı kalmadığı düşünülmektedir. 
Tüm deneysel çalışmaların sonucunda ise bir sonraki yapılacak olan çalışmaların farklı ağaç türleri ve farklı hasar tespit yöntemleri ile uygulanarak çalışmaların yürütülmesi, aynı zamanda yapılacak olan çalışmaların da saha uygulamalarıyla da desteklenmesi önerilmektedir. Tezin son bölümünde ise tüm çalışmaya dair genel bir değerlendirme yapılarak tahribatsız hasar tespit yöntemlerinin saha uygulaması açısından kolay, pratik ve güvenilir bir yöntem olduğu sonucuna varılarak çalışma sonlandırılmıştır.

Abstract:
Wood is an organic, fibrous and anisotropic building material. Since wood is a natural, ecological and natural material, wood has been a building material used by mankind since ancient times. Wood is widely used because of its lightness which is achieved when it is used in construction and its high carrying capacity, its easy processing in construction stage and the fact that its elements can be built on the basis of joining with nails, giving a natural and warm appearance and being able to recycle when the life is completed. 
In addition to all these advantageous properties of wood, some problems are observed in timber material over time. One of these problems is that the wood gradually deteriorates over time and causes damage to it by physical, chemical or biological degradations. These degradations seen in the wood break down the inner structure of the wood with time, weakening the physical and later mechanical properties. The degradations seen in wood can be determined by various damage detection methods in the early stages of degradation in the original material, so as to reduce the most damage to material losses. Thanks to the original wood material by determining it in the early stages of the deterioration, thus sustainability is ensured. The methods applied to damage detection in wood allow the original material to be detected in the early stages of degradation and at the same time to be applied with minimal damage to the original material during application. 
In the thesis study, it is aimed to determine the advantages of non-destructive or semi-destructive methods applied to timber building materials according to destructive damage detection methods. Also, it is aimed to determine the damage to the material by creating the least damage on the wooden material used mainly in the historical buildings. For this purpose, the thesis work which is carried out has been dealt with in 6 sections. 
In the first part of the work, the purpose, the importance, the scope and the method of working are mentioned. Later on, a related literature study has been done within the scope of the aimed study and the studies related to the subject have been examined. Result of the examinations, microscopic and macroscopic structure of wood were examined. In this context, pith, annual rings, sapwood, and heartwood were mentioned. Then, in the context of the physical properties of wood; the relation of wood to water, density, thermal expansion, thermal conductivity and acoustic properties were discussed. The effect of the inner structure of the wood on the wood strength was investigated and the effect of the knots, slits and fiber arrangement on the wooden strength of the wooden interior was investigated. Another factor affecting the strength of wood is the water content in the wood structure. The strength of the wood decreases as the water content in the wooden structure increases to the level of fiber saturation. There is no change in the strength of the wood after this point. Another property of wood is the hardness property, which is technological feature. The hardness of wood material changes according to the density of the wood, the structure of the wood and the moisture content in the wood. After studying the structure, physical, mechanical and technological properties of wood material, the damage to the wood material was investigated. In this context, physical, chemical and biological damages were examined, and also mechanical damage caused by wood structure was examined. Damage caused by biological damage, especially from these types of damage, causes great physical and mechanical damage. The main damage of these types of fungi, insects, bacteria and sea creatures. When they first start to form in wood, they form inside the wood and are not visible from the outside. However, when a large amount of damage occurs in wooden materials, the damage can be perceived from outside by the naked eye.
After considering the damage to wooden materials, methods of detecting damage in wooden materials have been investigated. Damage detection methods in wooden materials; non-destructive, semi-destructive and destructive damage detection methods. With these methods, it is possible to detect the damage in wooden materials without any damage to the wooden material by means of non-destructive damage detection methods. Non-destructive damage detection methods; acoustic, optical, thermographic, electromagnetic, nuclear magnetic, chemical and biological methods are classified under the heading. Non-destructive damage detection methods are newly implemented methods, but at the same time most methods are practical but expensive methods in terms of application. Semi-destructive damage detection methods are methods that enable damage detection by creating small scale damage on wooden materials. These methods have been analyzed under the headings of electrical and mechanical methods. Another method of destructive damage detection is methods that cause damage to wooden materials and lead to loss of wood materials. These methods, which are the first methods used to detect damage in wooden materials, mostly consist of mechanical tests. Within the context of methods, compression, bending, tension, shear and torsion tests are applied. 
After the literature investigations, the thesis started to experimental process. In order to carry out the experimental studies in a systematic way, an experiment program was developed first. The experiment program was designed to cover both field and laboratory applications. The experimental process first started with field application and then continued in the laboratory environment. 
Experimental studies in the field application was started with semi-destructive test method is performed on an ongoing restoration of a historic building. The historical building is a historical lodge in Aksaray. The building is a two-storey wooden building and the construction technique is the wooden carcass construction technique on the basement floor. The flooring system is made of wood and the exterior is wood coatings. The roof system is a wooden roof system, covered with a wooden roof overlaid with alaturka tiles. In practice, the positions of the wooden elements on the structure are determined first. Wooden elements from 1 to 9 are marked on the structure and coded according to the number on the structure. Then, the rebound hammer test method was applied to the wooden elements on the structure. In practice, the same timber element is distinguished from damaged and undamaged regions, and the rebound hammer test method was applied. After this process the wooden elements on the structure were removed and brought to the laboratory environment.
In the laboratory environment, both the massive wooden elements taken from the logs and the wooden elements taken from the historical structures were subjected to the experiment. For the experimental work to be done, the wooden elements were cut into suitable sample sizes. Again, before this process, the nails and metal parts on the inside of the timber elements taken from the historical structure and not visible from the outside were checked with Profometer 4 device. Thus, timber elements taken from the historical structure have been made ready for cutting. ith the cutting plan made on all wooden elements, the wooden elements are cut to the appropriate sample sizes according to the devices to be used. The specimens are 4x4x16 cm in diameter, perpendicular to the fibers and parallel to the fibers in the cutting plan. Some massive wooden elements taken from the logs and wooden elements taken from the historical structure due to lack of sufficient size, 4x4x16 cm. sizes were not possible. Different types of samples were obtained for such damaged wooden elements. Experimental studies have been carried out on the massive wooden elements taken from the logs and damaged timber elements in the laboratory environment, starting from the non-destructive damage detection method, to the destructive damage method, respectively. In this context, firstly ultrasonic test method which is the non-destructive damage detection method followed by semi-destructive hardness and recoil attracting and finally destructive test methods such as pressure and bending test methods.
Firstly, 6 samples from each solid wood log and 6 samples from each wooden item obtained from the historic building were selected for ultrasonic testing. In practice, the probes of the device are placed on the sample in a reciprocal manner and measurements are made on the samples, both parallel and perpendicular to the fibers. Thus, according to the passage speed and duration of the voice, a comment was made on the damage of the material and the internal structure of the material. In practice, Proceq Tico and Proceq Pundit Lab model ultrasound devices were used. Because of the different sizes of damaged wood specimens used in the experimental work, it is not possible to work with one type of frekans in ultrasonic measurements. For this reason, the appropriate frequency range has been determined according to the distance between the two probes placed on the sample in accordance with BS 1881-203 standard. 
After the ultrasonic test, hardness test method was applied on the wood samples. In practice, two different types of Shore A and Shore D hardness durometers were used for the hardness device to comply with ASTM D 2240. Shore A from durometers is suitable for measurement in the range of 20 to 90 A durometer, The Shore D durometer is suitable for measurements over 90 ° read with a Shore A. In the measurements, hardness measurements were made on a single surface of solid pine, oak and spruce samples parallel to the fibers and perpendicular to the fibers. In the samples taken from the historical structure, the hardness of all the surfaces of the samples was measured because of the different degree of damage and the difference in the condition existing on one surface. 
The rebound hammer test method is a semi-destructive method, in which a force is applied to the surface of the wooden elements to obtain data on the surface impact resistance of the wooden element. The application was carried out with two different types of rebound hammer devices, Proceq Silver Schmidt Hammer and Proceq Original Schmidt Hammer. In practice, measurements were taken to be parallel to the fibers and perpendicular to the fibers.
After that two samples were taken from the specimens which were subjected to ultrasound, hardness and rebound hammer test methods and whose lengths were parallel to each other in the longitudinal direction, and compression test method was applied. The samples were cut into cubes of 40x40x40 mm, which are suitable dimensions for the machine so that the pressure test can be carried out. In practice, the perpendicular compression test was applied to the 2 coded samples of the samples taken from the massive and historical structures while the 1 coded samples were subjected to pressure tests parallel to the fibers. Following this process, the cubes were subjected to a pressure force perpendicular to the fibers and perpendicular to the fibers in the Form + Test Seidner D 7940 pressure machine. 
As the last test method the bending test method was applied on the samples. In the samples 3 and 4 coded specimens were subjected to vertical bending, while 5 and 6 coded specimens were subjected to parallel bending test method. The samples were placed parallel to the fibers and perpendicular to the fibers, centered on the machine table. In the bending test, the value at break of the specimens was recorded.
With the completion of the experimental process, the results obtained from the experiments were evaluated and interpreted. Then the fourth part of the study was passed. In the fourth chapter, the correlations of the results obtained from the experiments are obtained and the results of the experiments are evaluated and examined. Thus, attempts have been made to capture correlations between destructive, semi-destructive and non-destructive test methods.
In the fifth part of the work, the conclusions and suggestions for the whole work were made. As a result of the studies carried out in this direction, strong correlations between destructive testing methods and non-destructive testing methods applied in wood were determined. In addition to this, the hardness and rebound hammer test methods from experimental works have obtained similar results in parallel to the fibers and perpendicular to the fibers, without being bound to the fiber direction of the wood. In this case, it is considered that the test methods do not depend on the anisotropic structure of the wood. 
As a result of all the experimental works, it is suggested that the following works should be carried out by applying different tree types and different damage detection methods and also the field works should be carried out at the same time. In the last part of the thesis, a general evaluation of the whole work was carried out and it was concluded that the non-destructive damage detection methods are an easy, practical and reliable method in terms of field application.