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D1.8 Seismic Supplement Welding Manual
www.lincolnelectric.com
9
The seismic load resisting system (SLRS) has been renamed as seismic force resisting system (SFRS) to be
consistent with terminology as revised in AISC seismic provisions and is “the assembly of structural elements
in the building that resists seismic loads.” These are the specific components in a building, such as columns,
beams, girders and braces, and the connections that join those components designed to resist seismic loads.
The SFRS does not typically include all the various structural elements in a building. See D1.8, clause 3.1.
Demand Critical welds are defined as “welds designated by the Engineer in Contract Documents, and
required to meet specific requirements of this code.” The most rigorous requirements of D1.8 are imposed
upon welds designated as “Demand Critical” (DC). See D1.8, clause 3.2.
The protected zone (PZ) is “that portion of a member of the SFRS… in which inelastic straining is anticipated
to occur….” Special limitations apply to attachments and fabrication practices associated with this zone.
See D1.8, clause 3.3.
It is important to note that D1.8 requires the Engineer to specify in contract documents the locations of
members that are part of the SFRS, which welds are Demand Critical, and the portion of members that
comprise the protected zone. Illustrative examples are contained in the commentary, although such
examples are not prescriptive or definitive. Contract documents should contain the specific requirements
applicable to a particular project. See D1.8, clause 1.2.1.
Three Kinds of Welds
When a structure is designed in accordance with the AISC Seismic Provisions, the welds on the building will
fit into three categories. The applicable code depends on the characteristics of the weld, as illustrated in the
following table:
Welds that are not on the SFRS as designated by the Engineer in contract documents are governed by
D1.1, and no special requirement for seismic considerations apply. Welds on the SFRS, but not designated
Demand Critical by the Engineer in contract documents, are governed by D1.8, but the additional provisions
for Demand Critical welds do not apply. Demand Critical welds (which, by definition, must be part of the
SFRS), are subject to all the applicable requirements of D1.8, as well as those additional provisions that
apply to Demand Critical welds. See D1.8, Commentary C-1.1.
TABLE 1: CODE COVERAGE FOR VARIOUS WELDS
Not Part of SFRS Part of SFRS
Not Demand Critical Demand Critical
Code Coverage AWS D1.1 AWS D1.8 AWS D1.8 DC