Any deviation from these design considerations as reflected in detail drawings may introduce additional stresses to the structure and affect its strength and durability. In India construction site fabrication is most common even in large projects due to inexpensive field labour, high cost of transportation, difficulty in the transportation of large members, higher excise duty on products from shop. As it is manually operated it requires considerable skill to produce good quality welds. The ideation stage can be as creative or as standard as the client desires. As soon as the current is switched on, the stud is moved away automatically to establish an arc. For panels in box girder webs, spot heating may be employed to reduce the concavity produced by the welding around the panel perimeter. Since this welding is carried out under controlled condition, the weld quality is normally good. hެUmo�0�+�q�D��;R���N}ӂ�I�x)$(q����g'�A�B6EV������.���q�� |�Լ�"�/�F�4�~"B_$ The primer is applied directly on to the cleaned steel surface. Aside from that, the different parts and sections that you’ve specified will have been test… In another method ‘the steel piece is immersed in a suitable acid and the scale and rust are removed’. %PDF-1.5 %���� The sequence and importance of shop operations will vary depending on the type of fabrication required. It is frequently used to produce camber in rolled beams. Hence, the fabricator should adopt good fabrication practices that reduce the detrimental effect of residual stresses. This is balanced by the compressive stresses induced in the cold regions of the parent plate. However in some applications manual cleaning is used and depending on the quality of the cleaned surface they are categorised into Grade St-2 and Grade St-3. Presetting the flange plate at an angle initially may reduce the angular rotation due to a single fillet. Sometimes both presetting and prebending may be required, e.g. A few decades back, it was a common practice to assemble components in the workshop using bolts or rivets. Fabrication of steel work carried out in shops is precise and of assured quality, whereas field fabrication is comparatively of inferior in quality. Fabricators have dedicated and skilled teams of engineers and architects who can put your vision to paper. There are three methods of fastening namely bolting, riveting and welding. While good quality welds are the priority of welders and weld inspectors, minor defects do normally creep in. Inadequate or erroneous camber, in fact, introduces huge secondary stresses in the members instead of eliminating these as originally desired. No alloying occurs and the coating, which is produced, consists of porous overlapping platelets of metal. The heat must be evenly applied right through the material, if not, unwanted curvature may occur in the plan of the section. SUPPLY AND FABRICATION OF STRUCTURAL STEEL SHEET 7 OF 20 ISSUE Ro TCE FORM 329 R3 5.7.7 Electrodes other than low-hydrogen electrodes shall not be permitted for thickness of 20 mm and above. This is an arc welding process and is extensively used for fixing stud shear connectors to beam in the composite construction. If the defects are within acceptable limits, they are accepted. This process is sometimes referred to as Metal-Inert Gas (MIG) welding. Fabricated steel is an expensive investment. It has, therefore, become all the more important to motivate the fabricators to appreciate the usefulness of Quality Assurance Plans and introduce the system in all their works and at site as well. An alternative method of applying metallic coating to structural steel work is by metal spraying of either zinc or aluminium. In this method the surface is cleaned using an oxy-acetylene torch which works on the principle of differential thermal expansion between steel and mill scale. Adopting suitable methods that can resist contraction can control the distortion. A fabricator's work starts from the point of procurement of raw materials including fasteners and ends with the dispatch of the fabricated items to site for erection. The use of a thicker plate can reduce the fillet weld angular distortion due to increased stiffness. Some of the common defects in welds these are: These entire weld defects are discussed in the chapter on ‘Weld – Static and Fatigue strength – I’. The type of welding electrode used would decide the weld properties. This is basically a semi-automated or fully automated welding procedure. All these activities are explained briefly in the subsequent parts of the section. The metal, in powder or wire form, is fed through a special spray gun containing a heat source, which can be either an oxy-gas flame or an electric arc. In addition to being simple tofabricate, welded connection considerably reduce the size of the joint and the additional fixtures and plates. The finishing coats provide the first-line defence against the environment and also determine the final appearance in terms of gloss, colour etc. This, in turn, may generate twisting moments at the supports. A NEW MIX DESIGN METHOD FOR HIGH PERFORMANCE…, Fastening (bolting, riveting and welding). It is not greatly influenced by the method of application. 1. Acceptance Norms: One pore of dia. Punching holes is a cold-working operation and can, therefore, cause brittle fracture. The skill of personnel at site also tends to be inferior and hence the quality of finished product tends to be relatively inferior. Hence in the case of MMA, stringent quality control and quality assurance procedures are needed. They are usually classified according to the main corrosion-inhibitive pigments used in their formulation, e.g. If a few weld runs are first made on one side, and the plate turned over and then the same number of runs are made on the second side (i.e., sequential welding), a ‘balanced' weld will be produced with little distortion. H��S�n�0��+�(��e>���.�6��䠰v�&��A�KQ���iHz��3;��U��!�O�\x/����(��wB+j5�Z�!HE�y'��!����hʋzy�� Wp�\@y�N�A��S����]�,�f��u9���{�oa����5��wM����x���ٟ�����]��c��װo�������j���X�j���$͙��d/���\}������4訍�-M�\~��إ? Flame cleaning is another method of surface cleaning. Gag press is generally used for straightening beams, channels, angles, and heavy bars. As the pool cools, molten metal at the fusion boundary solidifies, forming a solid bond with the parent metal. This can be reduced by using a double V butt weld. Under cyclic loading fatigue cracks can initiate from such punched holes. In India, the Welding Research Institute, BHEL, Trichy, Tamil Nadu, conducts periodical courses for welders and weld inspection personnel. > 2.4 mm not accepted. As a rule all columns and struts should be checked for straightness on completion of fabrication. chlor-rubber base intermediate coats that form a film by solvent evaporation and no oxidative process, may be applied on to an epoxy primer that forms a film by an oxidative process which involves absorption of oxygen from the atmosphere. In a similar manner a cambered plate may be straightened by applying triangular heating with the bases of the triangles parallel to the plate edges to be shortened. Step 1: Ideation. Most fabrication shops have a range of machines, which can form holes for connections in structural steel work. Shop fabrication of structural steel 1. These stresses can even reach yield stress. Upon cooling, the subsequent shrinkage produces a shortening of the member, thus pulling it back into alignment. 82 0 obj <>stream Some distortion from welding is due to transverse and longitudinal contraction of weldments. Blast cleaning is the accepted way of carrying out surface preparation in a well-run fabrication shop. In order to ensure that the fabrication can be carried out in accordance with the drawings, it is necessary that inspection and checking is carried out in accordance with an agreed Quality Assurance Plan (QAP). Nowadays welding is the most common method of shop fabrication of steel structures. Its use is currently restricted to smaller thickness plates. Welders who are employed in actual fabrication are, infact, graded according to their training and skills acquired. Download Seminar Flyer and Order Form. The distortion caused by a double fillet weld is important in box or plate girder webs where stiffeners are attached to only one side of the web. Nevertheless, for the sake of completeness, these methods are briefly enumerated below. The cutting head moves along the edge of the plate, planing it to a neat and smooth finish. In a similar manner two T sections can be welded, prebent back to back, to prevent final curvature in the web plate. ��E:�2f,*m��'Ej~.d&]�Iz� .7�/n*�A N_�mu@�w'��Q6|���t:�)`҃���_�:}�q 3�����0=y#,E�a�_�MQ��O �-�"�9��cfc�� ����� � ��� 56 0 obj <> endobj endstream endobj 60 0 obj <>stream Efforts shall A typical angular rotation of the plates due to a single V butt weld. Studies show that punching may produce short cracks extending radially from the hole, thereby enhancing the possibility of initiating brittle fracture at the hole when the member is loaded.
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