Advantages of welding - Steel Structures.

Welding offers many advantages over other joining methods:

• Freedom of design, and the opportunity to develop innovative structures
• Easy introduction of stiffening elements
• Less weight than in bolted joints because fewer plates are required
• Welded joints allow increased usable space in a structure
• Protection against the effects of fire and corrosion are easier and more effective.

1 Aesthetics and freedom of design
Probably the main benefit of welded construction is the freedom  of design, compared with bolted joints.

Some important types of structure, such as orthotropic bridge decks, Vierendeel trusses, tubular frames, tapered beams, and even most T-joints, could not be made as easily by any other method. Welded joints allow  more freedom in the use of rolled shapes, high strength steels, and corrosion- resistant steels.

Provided that the joints are made using appropriate materials and practices, designers should feel free to develop structures that are aesthetic as  well as functional.

Hollow sections, both rectangular and circular, can sensibly be joined only by welding, even if the final connection is by bolting.

2 Stiffness
Welded construction allows a designer to introduce stiffness and strength where required, in the most discreet and/or the most structurally efficient manner. The transfer of load and the stiffness can, with welding, be introduced in a gradual continuous manner, instead of in step changes through bolted pieces.

3 Weight, volume and size
Bolting requires the use of lap joints, which add weight to a structure. For example, the use of site welds, instead of bolted joints, to join plate girders to crossheads saved about 50 tonnes of connection plates, bolts, and nuts in the construction of the new Thelwall Viaduct.

In addition to savings in weight, the use of welded joints provides more usable volume in a typical building. Bolted joints reduce usable volume significantly because current legislation and fire engineering can demand that the fireproofing coatings that must be applied give a minimum thickness over every protruding nut and bolt head.

4 Durability and corrosion resistance
Total life cycle costing, including the costs of maintenance, is becoming increasingly important in all structures. For one aspect of this, the durability, the corrosion of structural steelwork can be retarded by three means – controlling the surrounding environment, effective coating systems, and the use of steels (and weld metals) with improved inherent corrosion resistance.Coating systems, however effective they are on plate surfaces, can only with great difficulty prevent corrosion in all the crevices of bolted joints, but the clean lines of welded structures allow the full effectiveness of modern coatings to be demonstrated.The use of corrosion resistant (weathering) steels (from BS EN 10155: 19931) imparts long life, and although they can be used in bolted connections, they perform poorly in crevices and thus they work far better in welded solutions.

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