Joint prequalification

Welded joints which conform to all codes and specification provisions for design, materials and workmanship are designated as prequalified joints.

These include specific fillet, groove, plug and slot welded joints of sufficient variety to cover most requirements of structural work. These joints have been thoroughly tested and are recommended for general use in the fabrication of buildings and bridges.

The types of groove weld to be used for various joint arrangements, thickness of materials, welding processes and welding positions are usually specified on the engineer’s design sheets or drawings. Therefore, the draughtsman seldom selects the type of groove weld. However, should it be necessary to verify design information or to select an appropriate groove weld to detail a shop splice, reference should be made either to the fabricator’s standard welds or to the codes and specifications published by various authorities.

5.4.2. Welding positions

The position of a joint when the welding is performed has a definite structural and economic significance. It affects the ease of making the weld, the size of electrode, the current required and the thickness of each weld layer deposited in multi-pass welds.

Fig. 5.6. Examples of flare welds and other welds in operation STRUCTURAL DETAILING IN STEEL

The basic weld positions are

(a) flat: the face of the weld is approximately horizontal and welding is performed from above the joint

(b) horizontal: the axis of the weld is horizontal. For groove welds the face of the weld is approximately vertical; for fillet welds the face is usually at 45° to the horizontal and vertical surfaces

(c) vertical: the axis of the weld is approximately vertical

(d ) overhead: welding is performed from the underside of the joint.

5.4.3. Welding symbols

Shop details and erection plans for welded construction must provide specific instructions for the type, size and length of welds and their locations on the assembled piece. This information is usually given by means of welding symbols. Most structural fabricators have adopted the basic method described in the American Welding Society booklet Standard Welding Symbols, AWS A2.0. The symbols in this system, commonly used in structural work are shown in Fig. 5.4.

Three basic parts are needed to form a welding symbol: an arrow pointing to the joint, a reference line upon which dimensional data is placed and a basic weld symbol device indicating the weld type required. A fourth part of the welding symbol, the tail, is used only when it is necessary to supply additional

Fig. 5.7. Construction of a welding symbol

data such as specification, process or detail references. See Fig. 5.7 for the construction of a welding symbol.

An indication of specification references in the tail is necessary only when two or more electrode classes are required for the welding on a particular drawing. Normally, this information is carried in the general notes or on a job data sheet. The same is true for process references. However, since specification references usually determine the process, process references will be needed only for electrogas, stud or other kinds of welding where the electrode specification does not describe the process or method. When references are not needed to supplement the welding symbol, the tail is omitted.

The symbol for welds should be made large enough to be easily recognised and understood. Some fabricators supply welding symbol templates to their

Fig. 5.8. Basic welding symbols for groove and intermittent welds (based on EC3). The extracts from DD ENV 1993 Part 1.1 are reproduced with the permission of BSI under licence number 2000SK/

0364

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draughtsmen. These may also be purchased from suppliers of drafting equipment.

The construction and application of welding symbols for groove welds are basically similar to those for fillet welds. However, whereas fillet welds are represented by a single basic symbol (the triangle), groove welds involve seven basic symbols. These may be combined with each other or compounded with supplementary weld symbols to cover a wide variety of weld profiles and edge preparations. The shapes of the basic weld symbols for groove and intermittent welds are shown in Fig. 5.8.

Reference lines and any information placed on them are arranged to read like other notes on a drawing: from left to right if the reference line is horizontal and from bottom to top if it is placed vertically on the sheet.

Reference lines are usually placed in horizontal or vertical positions.

Fig. 5.9. Welding symbols — additional data (American practice — courtesy of Lincoln Electric Co.)

The arrow may be located at the right or left end of the reference line and may point upward or downward from it. The arrow is drawn at an angle of about 45° to the reference line, except when some other arrangement is necessary to avoid crowding a portion of the drawing. The arrow head should never be placed on the reference line or on a continuous extension of the reference line. Some angular break should always be employed.

Weld dimensions are placed on the welding symbol with the weld size to the left of the basic weld symbol or device and the weld length to the right.

Weld dimensions are placed on the same side of the reference line as the device. When a device is required on both sides of the reference line and the weld size and length are identical for the arrow and other side of the joint, it is unnecessary to repeat dimensional data above and below the reference line.

Additional data on welding symbols, as used specifically by Lincoln Electric Co., USA, is given in Fig. 5.9.

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6. Design detailing of major steel