Yapılarda Hareket Problemleri Ve Derz Uygulamaları

Abstract

Bu çalışmanın amacı; yapı derzlerinin doğmasına neden olan yapısal hareketlerin irdelenilerek, farklı hareketler sonucunda oluşturulan derz çözümlerinin yanısıra, birleştirici özelliğe sahip konstrükif derz çözümlerinin sınıflandırılması ve kullanılan derz malzemeleri ile derz uygulamalarının incelenmesini içermektedir. Bu nedenle YAPI HAREKETLERİ başlıklı bölümde, yapılarda ve yapı malzemelerindeki boy ve biçim değişikliklerine sebep olan, yapısal hareketler sekiz ana başlık altında incelenmiştir. Bunlar: 1) Isısal Hareketler 2) Nem Hareketi 3) Don Hareketi 4) Rötre Hareketi 5) Sünme Hareketi 6) Oturma Hareketi 7) Deprem Hareketi 8) Vibrasyon ve Çarpma Hareketi Yapılarda, bu hareketler sonucunda oluşan etkiler, yapı ve yapı elemanları tarafından absorbe edilir, absorbe edilemiyen ve özellikle rijit yapılarda bu hareketler kendilerini önemli ve tehlikeli çatlak ve hasarlar olarak gösterirler. Özellikle rijit sistemler içerisinde yer alan yapı ve yapı elemanları tarafından hasarsız olarak tolere edilemiyeceği kabul edilen hareketlerin serbest bir şekilde oluşmasına imkan sağlarken, birleştirici özelliğe sahip bu özel bölgeler; 1) Hareket Derzleri (Genleşme, Oturma Derzleri) 2) İş Derzleri 3) Konstrüktif Derzler DERZLER başlıklı bölüm altında incelenmiştir. Sonuç olarak; yapı ve yapı elemanlarının etkiliyebilecek yapı hareketlerinin yanısıra, birleşmeler sırasında meydana gelebilecek konstrüktif ve dekoratif problemlerin çözümlenebilmesi için derzlerin oluşturulması, tasarlama aşamasından uygulamaya kadar devamlı göz önünde bulundurulması gereken yapıların, kritik bileşenleri olarak görülmüştür.

Today's structure materials and systems that vary during time are the result of technological developments. First structures were constructed with block system by using soft mortar, made with soil or lime, or without mortar. This type of structures constructed with pieced and soft materials, are capable of absorbing length and shape changes caused by thermal and natural effects, and loading, etc. However, frame structure systems, defined as rigid systems, can not absorb movements caused by various effects and as a result, serious cracks and damages form. To prevent from damages that occur in structures and minimize their effects, structures should be separated into sections that will provide sections independent movement. In the structure system idea, "JOINT" is the definition of points in the structure where continuity or system characterizing property loss and interruption were seen. Preparing joints is one of the important problems that architects concern about. With today's technological possibilities, right and effective thinking and projecting are enough for constructing perfect structures. However, to do effective preparation, structure movement types affecting structures negatively and these effects' reasons should be known. Structure movements can be classified under eight main titles:. Thermal movements. Moisture movements. Frost movements. Contraction movements. Stretch movements. Settlement movements. Earthquake movements. Vibration and hit movements STRUCTURE MOVEMENTS Thermal Movement: Materials expand by thermal effects. Expansion is defined in dictionaries as the increase in volume without any changes in structure. xni By thermal energy effect, atoms vibrate around equilibrium position. During vibration, because of the increase in their bond length, atoms behave like large- diameter atoms. As a result of the increase between atoms, thermal expansion occurs. In a situation where thermal effects and conditions are constant, members with different thermal expansion properties have different expansion ratios. In structures, using different materials with different expansion properties cause some problems. For instance, reinforced concrete and steel, both have large expansion coefficients and large usage areas. Movements can be more than couple of centimeters if they are used together. Length difference that is formed by expansion because of heat difference can be calculated by the formula: Al = LxAtxa where, A 1 = Length difference formed by expansion (m) L = Length of structure member (m) At = Thermal difference (°C) a = Expansion coefficient (m/m "CIO"6) The sun effect on structures is defined as natural thermal expansion. Besides natural thermal expansion, in structures like factories and furnaces working under high temperature conditions, another type of thermal expansion and length changes can be seen. This is defined as artificial thermal expansion. Artificial thermal expansion does not only form by heat increase. In industrial structures and cold stores, which are functioning under too low thermal conditions, expansions formed by thermal differences between inside and outside, can be prevented by using proper thermal insulation. Moisture Movement: Water and moisture affect structure materials. Because of moisture effect, shape and volume changes can be seen in materials. Excluding glass and some metal types, all materials are affected by moisture, and this causes small or large volume differences. Although after drying process materials turn to their original volume, these movements can be harmful for the structure. Water and moisture sources affecting structures negatively are:. Underground and ground water. Precipitation water. Water remained in structure body during construction phase. Humidity around the structure. Water leakage from wrong applications in the structure Moisture effect is the reason for structural deformation on structural materials. XIV Frost Movements: Cold weather causes length changes on structures and structure members. Frost movements cause volume decrease in structures and volume increase and expansion in structure members. Under frost effect, water inside the exterior materials of the structure freezes under temperature 0°C and its volume increases 10%. Maximum ice pressure is used as 1300 t/m2, which is the ice's refraction resistance. Cracks are formed as a result of the ice formed inside the materials. Frost also affects structure grounds negatively. Especially under very low air conditions, thermal insulation must be done in structures like cold air facilities and ice stores to keep the low heat inside the spaces under the ground level; because, ground frost will be very dangerous for the structure and it might collapse the whole structure. Contraction Movement: Cement, which has a bonding property, is a structural material produced by heating mixture of limestone and clay under high temperatures. After mixing cement and water, hydration starts and some important changes are seen in the cement-paste volume, which can be defined as decrease in volume. After this changing step, physical phase, called "contraction", occurs. Contraction reaction is defined as the result of pressure changes caused by evaporation of water, which was absorbed between solid phase layers in cement paste, depending on air temperature and moisture. If cement paste is kept in an open air, it shrinks; if it is placed in water, it expands. Contraction in concrete is primarily dependent on temperature, moisture, and time factors. Member's size and shape are the secondary factors, where cement type, aggregate type, mixing ratios, and water amounts are the thirdly factors affecting on contraction process. Because it is rigid, aggregate inside the concrete has some resistance to contraction. However, contraction is very important for most of concrete structures. Stretch Movement: Generally stretch is defined as permanent shape changes of materials under constant tensile stress after a time period. In concrete, aggregate inside the mixture is normally more rigid than the cement; for this reason, cement paste causes the stretch. Stretch movement stops after a while, but because of movements caused by deformation, some damages occur. Especially, it causes deflection of columns, joists, and slabs. Settlement Movement: As a result of differences of ground types, effects of underground waters, or different loading from different types of side by side structure sections, structures do settlement movement. To stop the movements, sections' ground settlement should be proportional to each other. In opposite condition, structure moves disorderly. As a result, structure movements might be seen which will cause settlement, rotations, cracks, and collapses. Settlement movement affects the structure on the y-coordinate and has the property of bonding the whole structure from foundation to roof. It is not a horizontal movement like expansion movement. xv Earthquake Movement: Earthquake movements are different from the other movement types; they are shorter but more effective on structures. Earthquake can be defined as a short time earth surface vibration caused by sudden breaks on tectonic plate layers. Earthquake effects can be seen in structures as:. Partial or whole settlement. Loss of function caused by deformation, even though structure stands Vibration and Hit Movements: Vibrations formed on structures are frequently repeatable and large amplitude vibrations and they affect dimensioning and preparing the supporting system. Coast structures, industrial structures where machines with high vibration are used, and high-rise structures that are under strong wind effect, can be some examples for this type of structures. JOINTS Joints are used for protecting structures from movements that are impossible to stop before demolishing the structure. In other words, joints can be defined as areas where structure envelope breaks into sections. Three types of joints with different functional and structural properties in structures are:. Movement joints (settlement joints, expansion joints). Construction j oints. Constructive joints Joints also can be classified according to the materials used:. Solid joints. Veneer joints. Flexible joints Solid Joints: Solid joints are seen on veneers formed with supporting wall and joints between thin veneer materials on walls. Veneer Joints: These types of joints are formed by using hard rubber, plastic tapes, special metal and different kinds of profiles. They are adjustable to joint movements. Flexible Joints: Materials that perform impermeability all the time by adjusting structure movements. This type of materials can perform too much deformation and contraction. XVI Movement Joints: Movement joints can be defined as joints that provide possibility for structure and foundation movements for all types of structures. Settlement Joints: Structures settle because of various ground types, underground water, and foundation shapes. Structures are separated from planned and available parts into sections by joints to prevent unwanted results of movements. These joints are called settlement joints. Because settlement joints start from the ground and are vertical movements, they should be continued from foundation to roof. Expansion Joints: Expansion joints are used to prevent shape deformation caused by thermal differences in structures and contractions. Different from settlement joints, expansion joints might not be continued under ground and on foundations. However, because of structural necessity, joints should be continued till to foundations. Because expansion joints continue from ground to roof, joint spaces formed on floors, walls, ceilings, and roofs are closed with special joint-fill profiles and materials. While special insulation details are used on foundations, profiles can be used on other movement joints. Construction Joints: Construction joints are defined as joints formed to provide continuity of the work that should be stopped in various steps of continuous project phases. Construction joints are used in structures where large amount of concrete is needed, in high-rise structures, and in structures where climbing form is used. Generally, construction joints are used in places where inner forces are less. Joint surfaces should be perpendicular to tensile stresses, and joint surface should not be rough. Constructive Joints: Constructive joints are formed as a result of structural member production technology or assembled with other structural members. Joints between tile and tile, brick and brick; in assembled structures, column and joist, wall and wall are some examples of constructive joints. Constructive joints can be used exterior of the building, as well as in the interior. Different properties and strength are expected in joint-fill materials used in both joint types. Exterior materials should be UV and be strong to exterior forces. Materials used interior the building should be strong to mechanical and chemical influences. As a conclusion, none of structures are totally the same, and problems and their solutions are different. Solutions can be suggested in a principle basis for every problem. However, producing solutions without counting special conditions in a situation, is not true. During design phase of projects, data and conditions for every structure are carefully examined and planned from the beginning according to that situations. In structural point of view, same importance is also important; especially critical point details like joints should be sketched and carefully designed. In order not to have problems after construction, maximum attention should be paid during material selection and especially during application processes. In the design process, every individual functioning in the process with different hierarchical rank in the organization structure have important responsibilities and roles.