Guide to the Design of Common Irregularities in Buildings – Digital Version

Structural irregularities are not uncommon to encounter in buildings due to the issues that can arise from the coordination of the plan layout, aesthetics, space planning, and other details involved in completing any building configuration.

Data from past earthquakes demonstrated that buildings with irregularities have performed poorly and suffered greater damage when compared with buildings having regular configurations.

In regular structures, the seismic demands imposed on the structure by the ground motion generally tend to be well distributed which leads to the dispersion of energy dissipation and damage. However, for irregular structures, the seismic demands tend to concentrate in the zone of irregularity, resulting in major damage and failure of structural elements in these zones. The actual load paths may differ from those in the design analysis due to these irregularities.

This updated guide based on standards from the 2021 IBC and ASCE/SEI 7-22 explains the impact of building irregularities on structural design with detailed examples of how to analyze and design for different types of buildings in Seismic Design Category B & D.

Badri K. Prasad, S.E., is a President and CEO of OLMM Consulting Engineers, Inc., with offices located in San Francisco and Oakland, California. He is a registered S.E. in California and registered P.E. in Washington State. He has over 30 years of experience in the design of various types of structures, such as healthcare facilities, airports, biotechnology facilities, mid- and high-rise structures, schools, seismic retrofit, among others. He is the past chair of SEAONC seismology’s concrete committee and was instrumental in publishing the committee’s work, “Concrete Slab as Collector Element,” in the 2008 SEAOC Blue Book. He is the author of the concrete example and project manager of NCSEA’s publication Guide to the Design of Diaphragms, Chords and Collectors and is the project manager for this design guide. He is also the author of the concrete design example in the SEAOC Seismic Design Manual. He has published and presented papers at several seminars on buckling restrained braced frames and research papers on base-isolation system.

Douglas Thompson, S.E., SECB, received his Bachelor’s degree from Cal Poly–San Luis Obispo and is president of STB Structural Engineers, Inc. in Lake Forest, He is a past president of the Structural Engineers Association of Southern California. He is a registered P.E., S.E. in six states. He has authored several articles and publications, including the light-frame design examples in the Seismic Design Manuals, the Guide to the Design of Diaphragms, Chords and Collectors, and Four-story/Five-story Wood-frame Structure over Podium Slab. He has been involved with code changes to the UBC and IBC for over 30 years and is a member of the Wood Design Standards Committee and the Wind and Seismic Task Committees with the American Wood Council.

Rafael Sabelli, S.E., is a Senior Principal and Director of Seismic Design at Walter P Moore. Rafael has earned a Special Achievement Award from AISC, as well as the T.R. Higgins Lectureship award. He is active in the development of seismic design standards for steel systems and is a member of the AISC Seismic Provisions Committee, the ASCE 7 Seismic Task Committee, and the NIST Building Seismic Safety Council’s Provisions Update Committee. Rafael is the chair of the AISC Seismic Design Manual committee and was the project manager for the five-volume SEAOC Seismic Design Manual. Rafael is co-author of Ductile Design of Steel Structures.