Limitations on Use of Fasteners and Welds

Structural steel fabricators prefer that job specifications state that shop connections shall be made with bolts or welds rather than restricting the type of connection that can be used.
This allows the fabricator to make the best use of available equipment and to offer a more competitive price. For bridges, however, standard specifications restrict fastener choice. High-strength bolts may be used in either slip-critical or bearing-type connections (Art. 5.3), subject to various limitations. Bearing-type connections have higher allowable loads and should be used where permitted. Also, bearing-type connections may be either fully tensioned or snug-tight, subject to various limitations. Snug-tight bolts are much more economical to install and should be used where permitted.
Bolted slip-critical connections must be used for bridges where stress reversal may occur or slippage is undesirable. In bridges, connections subject to computed tension or combined shear and computed tension must be slip-critical. Bridge construction requires that bearingtype connections with high-strength bolts be limited to members in compression and secondary members.
Carbon-steel bolts should not be used in connections subject to fatigue.

In building construction, snug-tight bearing-type connections can be used for most cases, including connections subject to stress reversal due to wind or low seismic loading. The American Institute of Steel Construction (AISC) requires that fully tensioned high-strength bolts or welds be used for connections indicated in Sec. 6.14.2.
The AISC imposes special requirements on use of welded splices and similar connections in heavy sections. This includes ASTM A6 group 4 and 5 shapes and splices in built-up members with plates over 2 in thick subject to tensile stresses due to tension or flexure.
Charpy V-notch tests are required, as well as special fabrication and inspection procedures.
Where feasible, bolted connections are preferred to welded connections for such sections (see Art. 1.17).
In highway bridges, fasteners or welds may be used in field connections wherever they would be permitted in shop connections. In railroad bridges, the American Railway Engineering Association (AREA) recommended practice requires that field connections be made with high-strength bolts. Welding may be used only for minor connections that are not stressed by live loads and for joining deck plates or other components that are not part of the load-carrying structure.



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