Applicability of Nonlinear MDOF Modeling for Design

Codes, standards, and guidelines commonly used in the evaluation and rehabilitation of existing buildings recognize and allow various performance-based engineering analysis methods, but much of their focus is on nonlinear static procedures (NSPs). The NSPs codified in those documents are based on single-degree-of-freedom (SDOF) models, which are easy to understand but may not capture adequately the complex behavior of structures with multiple-degree-of-freedom (MDOF) effects. The NEHRP Consultants Joint Venture has completed a project (ATC-76-6, with results published in NIST GCR 10-917-9) to improve the practical application of NSPs and nonlinear response history analysis (NRHA) to structures with MDOF effects. The NIST GCR 10-917-9 project report summarizes both recent MDOF modeling research and current structural analysis practice as specified in codes, standards, and guidelines and as implemented by leading practitioners. The work of the project includes synthesis of available research and performance of new problem-focused studies. The primary studies compare results from NSP and NRHA for both detailed structural archetypes and simplified models. Issues addressed in ancillary studies include examination of demand parameter sensitivity to ground motion selection and scaling methods, direct determination of NSP target displacement, and practical implementation of the nonlinear analysis methods. Based on available past research and on the new studies, the project report provides guidance on selection of simple nonlinear analysis methods appropriate for design, on implementation of nonlinear analysis methods, and on incorporating uncertainty in nonlinear dynamic and nonlinear static analysis. Related to the ATC-76-6 project, this paper provides background, a summary of the work performed, and a summary of key findings and recommendations. Related papers provide more detail of the technical work performed.