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Bolts and Welds

Bolts and Welds Introduction

The construction of structural steelwork unavoidably involves connections. The methods used in forming connections comprise riveting, bolting and welding. Rivets were once a popular form of connector in structures but are now rarely used. Bolted connections are preferable for site construction, whereas welded connections are the most economic way of joining steel components in the fabrication workshop.

PrEN1993-1-2(2003) only provides limited information on the fire performance of bolts and welds in Annex D comprising mechanical properties with temperature relative to adjoining beams.

Bolted Connections
There are two basic types of bolts comprising ordinary bolts and high strength friction grip bolts. Ordinary bolts depend on their strength on contact between the bolt shank and the sides of the holes in the plates to be fixed. They are available in two basic grades: Grade 4.6 normal strength bolts (commonly known as black bolts) and Grade 8.8 high strength bolts. Friction grip bolts are tensioned so that they clamp the plates together. The friction developing between adjacent faces generates a very rigid connection. Friction grip bolts are made of high strength steel.

Welded Connections
Most structural welding is now done by the electric-arc method, where an electrode (or welding rod) is fused to the parent metal by means of heat generated by high current electricity. The two basic types of weld are fillet welds and butt welds. Under normal conditions butt welds, particularly with full penetration, can be simply treated as strong as the parent metal. This assumption is still valid for high temperatures. Fillet welds specified in terms of throat size and leg length have lower design stresses than the parent metals, and they are more vulnerable to high temperatures than butt welds.

Material Behavior
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