JOINT IN STEEL STRUCTURES

The two most common methods used for connecting steel members in structural steel frames are bolting and welding. Experience has shown that welded connections are usually less expensive when done in the shop under controlled conditions, and bolted connections are usually better suited to field conditions. In most structural steel buildings, welds and bolts are used in combinations to produce the most practical and economical connections possible.

Bolts

Bolts  are  used  more  than  any  other  type  of connectors. They are easy to use and, in contrast to all other  types  of  connectors,  require  little  special equipment.  The  development  of  higher  strength  steel sand  improved  manufacturing  processes  have  resulted  in the  production  of  bolts  that  will  produce  strong structural steel connections. Specifications for most bolted structural joints call for the use of high-strength steel bolts tightened to a hightension. The bolts are used in holes slightly larger than the nominal bolt size. Joints that are required to resist shear  between  connected  parts  are  designated  as  either friction-type or bearing-type connectors. Bolted  parts  should  fit  solidly  together  when  they are assembled and should NOT be separated by gaskets or any other type of compressible material. Holes should be a nominal diameter, not more that 1/16 inch in excess of the nominal bolt diameter. When the bolted parts are assembled, all joint surfaces should be free of scale, burrs, dirt, and other foreign material. Contact surfaces with friction-type joints must be free of oil, paint, or other  coatings.

Welds

Welding  is  a  highly  specialized  skill,  and  welding of load-bearing parts of a structure should be performed only by properly qualified personnel. As an EA, you will not   be   expected   to   perform   welding   operations. However, you should have a general knowledge of the principal  welding  processes  and  the  different  types  of welds  and  their  applications,  and  you  should  know  how welding  symbols  are  used  to  identify  welded connections shown in working drawings. The  two  principal  welding  processes  used  instructural work are  electric arc welding and  oxy-MAPP gas welding. In the electric arc welding process, welding heat, sufficient to fuse the metal together, is developed by an electric arc formed between a suitable electrode(welding rod) and the base metal (the metal of the parts being  welded).  In  the  oxy-MAPP  gas  welding  process, heat is obtained by burning a mixture of MAPP gas and oxygen as it is discharged from a torch designed for this purpose. While electric arc welding is normally used for metals  that  are  1/8  inch  or  larger  in  thickness, oxy-MAPP gas welding is usually restricted to thinner metals.

Types of weld

Welded Joints