CEMP-E
TI 809-26
1 March 2000
using plates over 50 mm (2 in.) in thickness. AWS D1.1 provisions apply for ASTM Group 4 and 5
shapes and for built-up sections with a web plate over 38 mm (1-1/2 in.) in thickness. Both codes apply
these provisions only when the materials are used with welded tensile splices, but have also been
applied to connections such as beam-to-column connections where the flanges are direct-welded for
moment resistance. The special material requirements include a minimum CVN toughness taken from a
specific, nonstandard location in the material. The special provisions listed do not apply when the joint
carries only compression, such as column splices, or when bolted slices are used. Weld access holes
must be preheated to 65oC (150oF) prior to thermal cutting, ground to bright metal, and inspected using
either Penetrant Testing (PT) or Magnetic Particle Testing (MT). Optionally, weld access holes may be
made by drilling and saw-cutting, but PT or MT of the cut surface is still required. For joint welding,
minimum preheat and interpass temperature of 175oC (350oF) must be used, higher than that required by
AWS D1.1 Table 3.2. Weld tabs and backing bars must be removed after completion of the joint. AWS
D1.1 code provisions contain most, but not all, of these provisions. The AISC ASD Specification does not
contain the latest joint details, and therefore AISC LRFD Specification provisions should be used. See
AISC section A3.1c for materials requirements, J2.8 for preheat requirements, J1.6 for access hole
requirements, and J1.5 for weld tab and backing bar removal requirements. See AISC LRFD Figure C-
J1.2 for dimensional and fabrication requirements for weld access holes.
i. Backing Bars. Backing bars are used to close and support the root pass of groove welds when made
from one side of the joint. Joint assembly tolerances are greater when backing bars are used, compared
to joints without backing. Assembly tolerances without backing are typically within 3 mm (1/8 in.), difficult
to achieve with structural steel sections in either the shop or field, but possible for some types of joints
for shop fabrication. With backing, the assembly tolerances are typically enlarged to allow variations of 8
mm (5/16 in.). Welding is more easily performed with backing to support the root pass, eliminating
concerns for melt-through and repair. In some joints, particularly in fatigue and seismic applications, it
may be recommended or necessary to remove the backing bar after use. This adds cost to the operation,
particularly when rewelding and / or finishing of the removed area is necessary.
(1) Steel backing is used almost universally in steel construction. Those applications that require
subsequent backing removal are sometimes done with nonfusible backing materials such as copper,
ceramic or flux. The use of backing materials other than steel is generally considered nonprequalified,
requiring the testing of the WPS with these materials. Extreme caution should be used with copper
backing, as the arc may strike the copper and melt copper into the weld, greatly increasing the risk of
weld cracking.
(2) Welding personnel qualified to weld using backing are also qualified to weld without backing,
provided the weld is backgouged and backwelded. If the joint is not backgouged and backwelded, then
the welder must be qualified to weld without backing. If a welder is qualified without backing, then the
welder may also weld with backing.
(3) The minimum backing thicknesses provided in AWS D1.1 Section 5.10.3 are generally suitable
to reduce the risk of melting thru the backing bar, but very high heat input procedures, particularly with
Submerged Arc Welding (SAW), may require thicker backing.
(4) AWS D1.1 Section 5.10, includes provisions for backing materials, thickness, splicing, and
removal.
j. Weld Tabs. Weld tabs are also referred to as "extension bars", "run-off tabs", and similar terms in
the industry. The purpose of a weld tab is to allow the weld to be started or stopped beyond the edge of
the material being joined. Weld tabs are typically used in butt joint member splices, groove welded
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