TechBrief Series 2012: Seismic Design of Steel Special Braced Frame Systems and Structural Wood Diaphragm Systems

To develop a TechBrief (a topical, tightly written, and well-illustrated discussion of a practical problem faced by engineering design and construction practitioners) on each of two topics:  (1) design and analysis of steel special braced frame systems (concentric and eccentric) and (2) design and analysis of structural wood diaphragm systems for use as earthquake lateral-load resisting systems

Objective: A 2003 report [1] noted that the technical literature is "… becoming too large and technically difficult for most practicing professionals to examine. As the technical literature becomes more complex, designers are reluctant to employ the principles conveyed out of concern that building officials who have jurisdiction may not sanction the ideas." No practitioner-oriented publications focused on the seismic analysis, design, and detailing of concentric and eccentric steel braced frames or on structural wood diaphragms, exist. This project will synthesize practitioner and research information on key areas associated with these two topics.            

What is the new technical idea? This project will synthesize available practitioner and research information on the key areas associated with:

(1) Steel braced frame systems (concentric and eccentric): stiffness and strength characteristics and their impacts on analytical modeling, capacity design provisions, design and detailing of braces, adjacent members (including shear links) and connections thereof, anchorage requirements (per AISC 341 [2] and ACI 318[3] Appendix D), innovative configurations (e.g., zipper frames and two-story eccentric braced frame (i.e., V and inverted-V type), combined flexural and axial load interaction, and implications for Performance-Based Seismic Engineering including nonlinear modeling recommendations. It is anticipated that NIST will award a task order for this TechBrief to the NEHRP Consultants Joint Venture (NCJV) as soon as possible following receipt of 2012 funds.

(2) Structural wood diaphragm systems in building structures: analysis, design, and detailing. Formal engineering texts used in U.S. universities provide little discussion of this topic. Moreover, the U.S. national model building code and its references [4], or the National Design Specification for Wood [5] also do not provide extensive information on the seismic design of diaphragms and their components (e.g., collectors and chords). Further, minimum and maximum diaphragm forces, prescribed in ASCE 7-10 [6] and their intended application to diaphragm components, are often questioned. Practicing professionals are thus left without definitive guidance on the design, analysis, and construction of wood diaphragms. It is anticipated that NIST will award a task order to the NCJV for this TechBrief, following the award of the steel braced frame TechBrief task order.            

What is the research plan? The project will be performed by the NEHRP Consultants Joint Venture and managed by NIST EL. The task order will be structured such that a leading practitioner and a leader researcher in the structural steel field will lead the effort, thus ensuring that both best practices and cutting edge research will be included.

A detailed research plan, including the names of all project participants, will be developed by the contractor during the task order proposal development process. This project description will be revised immediately following task order award to reflect the additional detail that will be provided.

 

The Missing Piece: Improving Seismic Design and Construction Practices, ATC-57, The Applied Technology Council, 2003.

[2] Seismic Provisions for Structural Steel Buildings, ANSI/AISC 341, American Institute of Steel Construction, Chicago, IL, 2010.

[3] Building Code Requirements for Structural Concrete, ACI 318-08, American Concrete Institute, Framingham, MI, 2008.

[4] International Building Code, International Code Council, Washington, D.C. 2009

[5] National Design Specification for Wood Construction, ANSI/AF&PA, American Wood Council, Leesburg, VA 2005

[6] Minimum Design Loads for Buildings and Other Structures, ASCE 7-10, American Society of Civil Engineers, Reston, VA 2010

These TechBriefs will be the eighth and ninth in a series of documents that address various seismic analysis and design issues. A TechBrief on Steel Special Moment Frames and Composite Steel Diaphragm Systems has been previously published. Currently, National Council of Structural Engineer Associations (NCSEA) is providing webinars on Techbrief Nos. 1 through 4.            

Recent Results: None – this is a new project.           

Standards and Codes: The expected project outcome is a clear and succinct document that will be used by structural engineering practitioners. The document will be completely compatible with existing and developing model building code provisions, principally AISC 360[1] and AISC 341, IBC and NDS. [1] Specification for Structural Steel Buildings, ANSI/AISC 360, American Institute of Steel Construction, Chicago, IL, 2010.