Kaynaklı çelik yapıların DIN 18800 ve ANSI AWS D1.1'e göre tasarımı
Design of welded connections
- Tez No: 66498
- Danışmanlar: PROF. DR. SELAHADDİN ANIK
- Tez Türü: Yüksek Lisans
- Konular: Makine Mühendisliği, Mechanical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1997
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Makine Mühendisliği Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 148
Özet
ÖZET Kaynak tekniği konstrüksiyonda hiçbir imalat yönteminin sağlamadığı kadar serbestlik sağlar. Dökme parçalara göre kaynaklı konstrüksiyonlarda malzeme uygun şekillendirilebildiğinden daha hafif fakat daha rijit imal edilebilme olanağına sahiptir. Bu nedenlerle verilen tüm koşullara ve isteklere uygunluk bakımından kaynak özellikle elverişlidir. Parçaya ait teknik resimlerin tam olması gerekmektedir. Yanlış anlama ve hatalardan kaçınmak için kaynak mühendisinin imalatın gidişi hakkındaki bütün düşünceleri ve onayı alınmalıdır. Borulu ve borusuz bağlantılarda standartlarda verilen geçiş eğimlerine uyulmalıdır. Uyulmadığı taktirde kuvvet akışında aksama olacağından çentik etkisi oluşacak ve konstrüksiyonun emniyet gerilmesi azalacaktır. Yaşlanma ve gevrek kırılma tehlikesi nedeniyle soğuk şekil değiştirmiş bölgelerin kaynağından kaçınılmalı ve bu bölgelere uygun bir mesafe bırakılarak kaynak yapılmalıdır. Soğuk şekil değiştirmiş yerlerdeki kaynaklar için kalınlığın eğilme yarıçapına oranı en az 1, en çok 10 olmalıdır. Soğuk şekil değiştirmiş bölgeden kaynak en az 5t uzaklığından sonra başlayabilir. Üst üste çift taraflı iç köşe kaynakla birleştirilen plakalarda, iki kaynak arası minimum uzunluk ince parça kalınlığının 5 katı olmalıdır. Dizayn sırasında malzemede segregasyon bölgeleri varmış gibi konstrüksiyon yapılmalıdır. Böylece malzeme seçiminde malzemenin döküm tarzının göz önünde tutulmasına gerek kalmaz. Aşın korozyon şartlarının olduğu yerlerde kesintisiz ve tam nüfüziyetli bir kaynak olabilmesi için kaynak yeri tel firça veya uygun yöntemlerle temizlenmelidir. Tapa kaynağında merkezden merkeze minimum açıklık deliğin çapının 4 katı olmalıdır. Yatak şeklindeki bağlantılarda kullanılan perçin ve cıvata kaynak kombinasyonundaki ortak yük gibi göz önüne alınmamalıdır. Kaynak eğer kullanılırsa bağlantıdaki tüm yükü taşımayı sağlamalıdır. Bununla birlikte bağlantılarda kaynakla birleştirilmiş bir parça diğer parçalara perçin veya cıvatayla bağlanabilir. Her kaynak konstrüksiyonunda distorsyon gürülebilir. Eğer kaynak yerinin mekanik olarak işlenmesi öngörülüyorsa işleme paylan için standart değerleri kullanmak gerekir. Distorsiyonu önlemek için temel olarak konstrüksiyon küçük gruplara aynlmalı, bunlar tek tek işlenmeli ve kaynak sırasına harfiyen uyulmalıdır. XIX
Özet (Çeviri)
DESIGN OF WELDED CONNECTIONS SUMMARY General specifications usually include a provision for the use of stresses in excess of the prescribed working stress for conditions of a transient or temporary nature and for loading combinations that are highly improbable. A good example is a temporary bridge used to carry traffic during some construction phase of the“ permanent ”structure; such a bridge maybe design to be adequately safe with higher unit stresses because of the expected short term use. Similarly, stresses during erection or during the occurrence of natural phenomenon, such as an earthquake or high winds may exceed the basic working stress. An example of an improbable load combination would be full live load at the same time as maximum wind load. Although the varies combinations of loads and the associated increase in allowable stresses are substantially more complex than example cited, the principal reasons for the increase remain the same. The engineer preparing contract design cannot specify the depth of groove ( S ) without knowing the welding process and the position of welding. The subject is explicit in stipulating that only the weld size ( E ) is to be specified on design drawings for partial joint penetration groove welds. This allows The contractor to produce the weld size by assigning a depth of preparation to grooves shown on shop drawings as related to he contractor“ s choice of welding process and position of welding. The root penetration will generally depend on the angle subtended at the root of groove in combination with root opening, the weld position, and the welding process. For joints using bevel - and V groove welds, these factors determine the relationship between the depth of preparation and weld size for prequalify partial joint penetration groove welds. An attempt to tie two fillet welds deposited on opposite sides of a common plane of contact between two parts would result in a point of weakness whose deleterious effects could vary over a wide range. XXThe subject provides that the capacity of different types of welds used in combination shall be determined by adding the separate capacities of separated welds. It must be recognized that this method adding individual capacities of welds does not apply to fillet welds reinforcing groove welds. Tests have shown that balancing welds about the neutral axis of single - or double- angle or similar- type members does not increase the load- carrying capacity of the connection. Therefore, unbalanced welds are permitted. It should be noted that boxing ( end returns ) is not necessary, as tearing is not problem. For good welded design, each flange of any given cross section is a single plate. These flange plates are usually varied in thickness or width, or both, as more or less area is required. The required smooth transition can be made by chamfering the thickness or width, or both, of the larger flange to correspond to that of the lower flange. There is a practical limit to the angle of chamfer, but these standards requires that the slope should not be greater than 1 in 2-1/2 ( an angle of about22°). Transitions may also be made by sloping the surface of the weld. The tubular structure section applies this requirement to a lap tubular joint with a fillet weld only on the outside. Aside from the practical difficulty of welding inside a small tube, the eccentricity is self balancing when the tube as a whole is considered. Joints and welds prohibited by this article do not perform well under cyclic loading. The prohibitions do not apply to welds in those secondary members which are not subject to cyclic stresses. A partial joint penetration groove weld has an unwelded portion at the root of the weld. This condition may also exist in joints welded from one side without backing, and, therefore, the code considers them partial joint penetration groove welds except as modified. The unwelded portions are no more harmful than the those in fillet welded joints. These unwelded portions constitute a stress raiser having significance when fatigue loads are applies transversely to the joint. This condition is reflected in applicable fatigue criteria. However, when the load is applied longitudinally, there is no appreciable reduction in fatigue strength. Irrespective of the rules governing the service application of these particular grooves, the eccentricity of shrinkage force in relation to the center of gravity material will result in angular distortion on cooling after welding. This same eccentricity will also tend to cause rotation in transfer of axial load transversely across the joint. Therefore, means must be applied to restrain or preclude such rotation, both during fabrication and service. The drawings shall set out in full and in a clear manner all structural members essential to the evaluation of the technical documents to the construction work and the supsquent approval of the structure by the engineer. XXINote. To be clear, drawings of members shall include the following : a-) Information on materials ( e.g. the steel grade and property class of bolts ) ; b-) Dimensioned drawings of structures and cross sections ; c-) Drawing of joints ( e.g. showing the relative positions of centroidal axes of linear members ), locations of fasteners and joined members and permitted clearances ; d-) Aspects relating to workmanship (e.g. preloading of bolts, weld preparation); e-) Any factors to be taken into consideration during erection work ; f-) Details of corrosion protection. Filler plates may be used in the spacing parts of different thickness and connections that, due to existing geometric alignment, must accommodate offsets to permit simple framing. Filler plates less than l/4in.(6.4 mm) thick shall not be used to transfer stress, but shall be kept flush with the welded edges of the stress carrying part. The size of welds along such edges shall be increased over the required sizes by an amount equal to the thickness of the filler plate. Any filler plate 1/4 in (6.4mm) or more in thickness shall extend beyond the edges of the plate or connection material. It shall be welded to the part on which it is fitted, and joints shall be of sufficient strength to transmit the splice plate or connection material stress applied at the surface of the filler plate as an eccentric load. The welds joining the splice plates or connection material to the filler plate shall be sufficient to transmit the splice plate or connection material stress and shall be long enough to avoid over stressing the filler plate along the toe of the weld. If longitudinal fillet welds are used alone in and connections of flat bar tension members, the length of each fillet weld shall be no less than perpendicular distance between them. The transfers spacing of longitudinal fillet welds used in end connection shall not exceed 8 in.( 200 mm ) unless end transfers welds or intermediate plug or slot welds are used. Intermitted fillet welds maybe used to carry calculated stress if fillet welds are used to reinforce grove welds in corner and T- Joints, the filled weld sizes shall not be less than 25% of the thickness of the thinner part joint, but need not be greater than 3/8 in. (9.5 mm). If two or more plates or rolled shapes are used to build up a member, sufficient welding ( of the fillet plug, or slot type ) shall be provided to make the parts act in unison but not less than that which may be required to transfer calculated stress between the parts joint. XXllConnection or splices of tension or compression members made by groove welds shall have complete joint penetration welds. Connections or splices made with fillet or plug welds, shall be designed for an average of the calculated stress and the strength of the member ; or if there is repeated application of load, the maximum stress or stress range in such connection or splice shall not exceed the fatigue stress permitted by the applicable general specification. Weld soundness, for complete joint penetration groove welds subject to tension and reversal of stress, shall be established by radiographic or ultrasonic testing. If longitudinal fillet welds are used alone in lap joints of end connection, the length of each fillet weld shall be no less than the perpendicular distance between the welds. The transfers spacing of the welds shall not exceed 16 times the thickness of the connected thinner part unless suitable provision is made ( as by intermediate plug or slot welds ) to prevent buckling or separation of the parts. The longitudinal fillet weld may be either at the edges of the member or in slots. When fillet welds in holes or slots are used, clear distance from the edge of the hole or slot to the adjacent edge of the part containing it, measured perpendicular to the direction of stress, shall be no less than 5 times the thickness of the part nor less than 2 times width of the hole or slot. The strength of the part shall be determinate from the critical net section of the base metal. Cover plates shall preferably limited to one on any flange. The maximum thickness of cover plates on a flange ( total thickness of all cover plates if more than one is used ) shall not be grater than 1-1/2 times the thickness of the flange to which the cover plate attached. The thickness and width of a cover plate may be varied by butt joint welding parts of different thickness or width with transitions conforming to the requirements. Such plates shall be assembled and welds ground smooth before being attached to the flange. The width of a cover plate, with recognition of dimensional tolerances allowed by ASTMA6, shall allow suitable space for a fillet weld along each edge of the joint between the flange and the plate cover. For axially stress angle members, the center of gravity of the connecting welds shall lie between the line of the center of gravity of the angles cross section and center line of the connected leg if the center of gravity of the connecting weld lies outside of this zone, the total stresses, including those due to the eccentricity from the center of gravity of the angle, shall not exceed those permitted by this standards. The fatigue behavior of as welded joints can be improved by reducing the notch effect at the toe of the weld, or by reducing the tensile residual stresses, neither which is included in the measured hot spot strain range which designers use. xxmVarious methods for improving the fatigue behavior of welded joints, are as follows : improving the as welded profile (including the use of special electrodes designed to give a smooth transition at the weld toe), full profile grinding, weld toe grinding, weld toe remelting ( GTAW dressing or plasma arc dressing ), hammer peening, and shot peening. Partial joint penetration groove welds subject to tension normal to their longitudinal axis shall not be used where design criteria indicate cyclic loading could produce fatigue failure. Groove welds, made from one side only, are prohibited, if the welds are made : without any backing or with backing, other than steel. Intermitted groove welds, bevel - groove and J-grooves in butt joints for other than the horizontal position, plug and slot welds on primary tension members, fillet weld size where less than 3/1 6in., are prohibited. Rivets and bolts used in bearing type connections shall not be considered as sharing the load in combination with welds. Welds, if used, shall be provided to carry entire load in the connection. However, connections that are welded to one member and riveted or bolted to the other member are permitted. High strength bolts properly installed as a slip critical type connection prior to welding may be considered as sharing the stress with the welds. Fillets welds connecting a cover plate to the flange in the region between terminal developments shall be continuous welds of sufficient size to transmit the incremental longitudinal shear between the cover plate and the flange. Fillet welds in each terminal development shall be of sufficient size to develop the cover plate's portion of the stress in the beam or girder at the inner end of the terminal development length and in no case shall the welds be smaller than the minimum size permitted. Where a T-, Y-, or K- connection is made by simply welding the branch member(s) individually to the main member, local stresses at the potential failure surface through the main member wall may limit the usable strength of the welded joint. The shear stress at which such failure occurs depends not only upon the strength of the main member steel, but also on the geometry of the connection. Such connections shall be proportioned on the basis of either punching shear or ultimate load calculations as given below. The punching shear is an allowable stress design criterion and includes the safety factor. Ultimate load format may be used in load and resistance factor design, with the resistance factor O to be included by the designer. Strength and stability of a main member in a tubular connection, with any reinforcement, shall be investigated using available technology in accordance with the applicable design standards. General collapse is particularly severe in cross connections and connections subjected to crushing loads. Such connections may be reinforced by increasing the main member thickness, or by use of diaphragms, rings, or collars. XXIVDue to differences in the relative flexibilities of the main member loaded normal to its surface, and the branch member carrying membrane stresses parallel to its surface, transfer load across the weld highly nonuniform, and local yielding can be expected before the connection reaches its design load. To prevent ”unzipping" or progressive failure of the weld and ensure ductile behavior of the joint, the minimum welds provided in simple T-, Y-, or K- connections shall be capable of developing, at their ultimate breaking strength, the lesser of the brace member yield strength or local strength of the main member. XXV
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