Designated Seismic Systems – Where and How it’s used ?
The term “Designated Seismic Systems” – where and how it is used in our codes and standards – has caused a certain amount of confusion. The purpose of this article is to dispel that confusion – to the extent possible.
In the 2012 IBC, the term “Designated Seismic Systems” is used in the following sections only:
Section 1704.3.2 Seismic requirements in the statement of special inspections.
Section 1705.11 Special inspections for seismic resistance. This section includes 1705.11.4 Designated seismic systems, which reads as follows:
“The special inspector shall examine designated seismic systems requiring seismic qualification in accordance with Section 1705.12.3 and verify that the label, anchorage or mounting conforms to the certificate of compliance.”
Section 1705.12 Testing and qualification for seismic resistance , including Section 1705.12.3 Seismic certification of nonstructural components, which refers to ASCE 7-10 Section 13.2.
In ASCE 7-10, the term “Designated Seismic Systems” is used in Section 13.2.2 Special Certification Requirements for Designated Seismic Systems. It is also used in Section 13.6.6 Utility and Service Lines. But that section, as the title suggests, is not about designated seismic systems themselves. It states: “The possible interruption of utility service shall be considered in relation to designated seismic systems ….” The term is further used in Appendix 11A QUALITY ASSURANCE PROVISIONS. However that ASCE 7 appendix has never been adopted by the IBC.
The following table lists the definitions of “Designated Seismic Systems” in every edition of the IBC since its inception in 2000, in the ASCE 7 Standards that provide the bases of the seismic design provisions of those codes, and in the NEHRP Provisions that in turn form the bases of the seismic design provisions of those standards. It can be seen that ASCE 7, in its 2002 and 2005 editions (and in the prior 1998 edition, which was the first one to have its seismic design provisions based on those of the  NEHRP Provisions), modified the NEHRP definition to include the seismic force-resisting system of the structure itself. This modification was never accepted by the IBC, which has always adopted the NEHRP definition. In its 2010 edition, ASCE 7 has harmonized its definition with that of the IBC by not including the seismic force-resisting system.
2012 IBC Section 102.4.1 states: “Where conflicts occur between provisions of this code and referenced codes and standards, the provisions of this code shall apply.” Thus, even before reconciliation in ASCE 7-10, the different definition of “Designated Seismic Systems” in ASCE 7 did not have any practical impact in most of the United States where the IBC is adopted.
It should be obvious from the above that the term “Designated Seismic Systems” is used in our codes and standards to trigger inspection, testing, and certification requirements for architectural, mechanical, and electrical components with Ip = 1.5, which are required to be designed by ASCE 7 Chapter 13 – typically in buildings assigned to Seismic Design Category C, D, E, or F.