Code Reference
StructuralASCE 7-22

Section 12.2.1/Seismic Force-Resisting System Selection

ASCE 7-22 Section 12.2.1 and Table 12.2-1 establish permitted seismic systems and their R, Cd, and omega-0 design coefficients.

What this section requires

The seismic force-resisting system (SFRS) must be selected from Table 12.2-1, which lists bearing wall systems, building frame systems, moment frame systems, dual systems, and shear wall-frame interactive systems. Each system has a response modification coefficient (R), deflection amplification factor (Cd), and overstrength factor (omega-0). Higher R values indicate more ductile systems that can be designed for lower seismic forces. Not all systems are permitted in all seismic design categories; some are limited to SDC A-C or have height restrictions.

Why this section exists

The SFRS is the structural system that resists earthquake forces. The R factor allows the designer to reduce the elastic seismic force to account for the system's ductility and energy dissipation capacity. A special moment frame (R=8) can be designed for 1/8 of the elastic force because it can deform significantly without collapsing. An ordinary braced frame (R=3.25) must be designed for nearly 1/3 of the elastic force because it has less ductility. The table ensures that only systems with proven seismic performance are used in high seismic regions.

What plan reviewers look for

Plan reviewers check the structural general notes for the SFRS type and verify it against Table 12.2-1. They confirm the R, Cd, and omega-0 values used in the calculations. They verify that the selected system is permitted for the project's seismic design category and does not exceed any height limitations. They also check that the detailing requirements for the selected system are referenced.

Common violations

System not permitted in the seismic design category
An ordinary moment frame or ordinary braced frame is specified in SDC D, E, or F where only special or intermediate systems are permitted. Higher SDCs require more ductile systems.
R factor mismatch between notes and calculations
The structural general notes state one SFRS type (e.g., special concentrically braced frame, R=6) but the seismic force calculations use a different R value.
Height limitation exceeded
A bearing wall system or braced frame system exceeds the height limit from Table 12.2-1 for the seismic design category. Some systems are limited to 65, 100, or 160 feet in higher SDCs.
Compliance tip
State the SFRS type, R, Cd, and omega-0 on the structural general notes with a reference to Table 12.2-1. Verify the system is permitted for the SDC and does not exceed height limits. Reference the detailing standard (AISC 341 for steel, ACI 318 Chapter 18 for concrete) in the general notes.

Related ASCE 7 requirements

Section 11.4.1 covers seismic design category determination. Section 12.8.1 covers the equivalent lateral force procedure that uses R.Section 12.12.1 covers story drift limits that use Cd. AISC 341 and ACI 318 Chapter 18 provide the detailing requirements for each system type.

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Related sections

2.3.1Load Combinations Using Strength DesignASCE 7-2211.4.1Mapped Acceleration ParametersASCE 7-2212.8.1Seismic Base ShearASCE 7-22