Appendix 1 is new in this edition of the Provisions.
1.1. SCOPE
The detailed requirements for nonlinear response history analysis are contained in the building code’s referenced standard: ASCE/SEI 7 (ASCE, 2022). The specific chapter that contains the requirements in ASCE/SEI 7 is Chapter 16, Nonlinear Response History Analysis. Other documents, such as PEER/TBI (2017) and LATBSDC (2017), also provide recommendations and guidance for implementing nonlinear response history analyses. This appendix is intended to complement these documents.
It is intended that the seismic force-resisting system design meets the requirements specified in the Provisions. The appendix specifies load and resistance factor design (LRFD) be used to be compatible with ASCE/SEI 7 and the guideline documents because their acceptance criteria is formulated using LRFD principles. Exceptions to meeting the requirements specified in the Provisions may be taken if the nonlinear response history analysis results indicate the building’s performance meets the acceptance criteria. For example, a common exception that is taken is to not design columns in a buckling-restrained braced frame for simultaneous yielding of all the connected braces but rather design the columns for the axial forces resulting from the nonlinear response history analysis. Another common exception is to use a system beyond the permissible height range for the system, as specified in ASCE/SEI 7.
AISC Seismic Provisions for Evaluation and Retrofit of Existing Structural Steel Buildings (ANSI/AISC 342) (AISC, 2022c) is a primary source for modeling and acceptance criteria. While intended for existing structures, the ANSI/AISC 342 provisions also provide modeling and acceptance criteria for the members and components found in new structures and is the reason that it is being referred to as the primary source for this appendix. The predecessor for most of the material found in ANSI/ AISC 342 is ASCE/SEI 41 (ASCE, 2017). Since the early 2000s, the modeling and acceptance criteria found in ASCE/SEI 41 has been used in the nonlinear response history analysis (NLRHA) of new structures. Thus, the approach of referencing ANSI/ AISC 342 in this appendix for new structures has precedence. Other documents, such as Guidelines for Nonlinear Structural Analysis for Buildings, Part I—General (GCR 17-917-46v1) (NIST, 2017a), Guidelines for Nonlinear Structural Analysis for Buildings, Part IIa—Steel Moment Frames (GCR 17-917-46v2) (NIST, 2017b), and Recommended Modeling Parameters and Acceptance Criteria for Nonlinear Analysis in Support of Seismic Evaluation, Retrofit, and Design (GCR-17-917-45) (NIST 2017c), also provide detailed modeling information.
The scope of this appendix is currently limited to special systems consisting of structural steel or structural steel acting compositely with reinforced concrete: special moment frames (SMF), special concentrically braced frames (SCBF), eccentric braced frames (EBF), buckling-restrained braced frames (BRBF), special plate shear walls (SPSW), and composite plate shear walls—concrete filled (C-PSW/CF). These systems are chosen in part because (a) they are the ones typically being designed and evaluated using nonlinear response history analysis, and (b) the modeling of these systems, while complex, exhibits behavior that is reasonably well replicated by analysis. Furthermore, robust research testing results are available from which calibration models can be developed, and recent guidelines on nonlinear modeling, mentioned previously, provide the necessary modeling and acceptance criteria.