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Lateral Force-Resisting Structural Elements and Systems Project

Summary:

This project supports the refinement by 2015 of key seismic provisions in U.S. model building codes and standards that are used for modeling and designing lateral force-resisting elements. There are three parallel tasks:

  1. Develop accurate behavioral models for deep, slender wide-flange steel beam-columns subjected to large ground motion-induced displacements. This is the initial implementation of the long-term research plan provided by the NIST-funded ATC-90 project[2]. Experimental research is being performed in a separate task order with the NEHRP Consultants Joint Venture. This task will utilize the results of that experimental research in analytical studies that enable refinement of model building code provisions and nonlinear analysis procedures.
  2. Develop accurate behavioral models and corresponding new design provisions for reinforced concrete walls that address wall slenderness and ground motion-induced uplift forces. This research focuses on findings in buildings that were damaged in the 2010 Maule, Chile, earthquake and will utilize the results of experimental tests that will be performed in a separate project at the U.S. Army Engineer Research and Development Center.
  3. Produce a compendium of previously unpublished data on the practical use of cold-formed steel (CFS) systems in low-rise construction in areas of moderate to high seismic activity. Information on the seismic performance of these CFS systems is needed by the design community and for codes and standards development. The combined experimental and analytical research was conducted by the U.S. Army Engineer Research and Development Center (ERDC) on various CFS shear panel configurations from 1998 through 2004 to support the development of CFS Seismic Design Guidance. A report documenting the results of this research was never published because of research program changes.

 


[2] Research Plan for the Study of Seismic Behavior and Design of Deep, Slender Wide-Flange Steel Beam-Column Members, NIST GCR 11-917-13.

 

Description:

Objective: This project supports refining key seismic provisions in U.S. model building codes and standards that are used for modeling and designing lateral force-resisting elements including:

  1. Develop by 2015 accurate behavioral models for deep, slender wide-flange steel beam-columns that are subjected to large ground motion-induced displacements and high axial and flexural loads;
  2. Develop by 2015 accurate behavioral models and corresponding new design provisions for reinforced concrete walls that address wall slenderness and ground motion-induced uplift forces; and
  3. Produce by 2013 a compendium of previously unpublished data on the practical use of cold-formed steel (CFS) systems in low-rise construction in areas of moderate to high seismic activity.

What is the new technical idea?

  1. Accurate steel beam-column models: In modern earthquake-resistant steel frame design, lateral force resistance is often concentrated in a few frames or bays in frames. Columns in these areas are subject both to significant axial force (particularly in lower stories) and to bending. Increasingly, these wide-flange beam-column sections are being selected to be deeper and more slender to increase  in-plane stiffness. This increased stiffness reduces earthquake motion-induced drift, but member cross-section characteristics can lead to member instabilities as demands increase. The American Institute of Steel Construction (AISC) has identified improving the characterization of this behavior as a critical research need[3]. In characterizing the response of such deep, slender wide-flange steel beam-columns to large lateral deformations, the behavior of plastic hinge(s) that develop in these sections is particularly critical. Available test data on slender beam-columns loaded in this manner are limited. Expanding the data set supports enhancing the accuracy of building codes and design standards, developing improved design and assessment provisions, and assisting designers in identifying behavior as required for nonlinear Performance Based Seismic Engineering (PBSE) (ASCE 41[4]) analysis. Experimental testing of such elements will be performed by the NEHRP Consultants Joint Venture (NCJV) for NIST in 2013 and 2014 under task order. This project will use the results of the laboratory tests to calibrate nonlinear models of these elements that will form the basis for improved behavioral models to improve codes and standards and to support design practitioners.
  2. Accurate reinforced concrete (R/C) wall models: The 2010 Chile earthquake highlighted possible shortcomings in some design configurations of R/C structural walls - many walls that were designed in general accordance with customary U.S. practice, except for confinement detailing, exhibited poor performance under strong shaking, including out-of-plane buckling that may have been due in part to wall slenderness. This behavior is the primary focus of ongoing post-earthquake analysis in NEHRP Consultant Joint Venture (NCJV) work on two separate NIST task orders[5],[6] related to wall design and Chile earthquake implications. The consensus of the experts on the NCJV tasks is that the observed poor Chilean wall behavior, though not yet well understood, has negative implications for current US design practices. It has been postulated that large uplift-induced tension excursions contributed to the observed behavior. Regardless of whether the slenderness of the walls alone or in combination with other factors resulted in the wall failures, it is clear that slenderness is of concern.

    Current US model building codes do not have limits on wall slenderness. With increasing architectural demands to limit construction costs and open up building usable space in the absence of these limits, the inadequate performance of walls as observed in Chile could be realized in future U.S. earthquakes. Improved R/C wall performance was ranked as an urgent technical need identified in the May 2012 NIST NEHRP Research Roadmap Workshop hosted by Building Seismic Safety Council (BSSC). This project addresses the behavior of slender walls, with an ultimate impact on U.S. building code requirements (IBC[7], ACI[8]). The project will assimilate the results of NIST-funded laboratory testing of R/C wall sections at the U.S. Army Engineer Research and Development Center (ERDC) Construction Engineering Research Laboratory (CERL) with a thorough program of nonlinear analytical modeling that will produce new wall modeling techniques for use by practitioners and suggest wall detailing improvements that can be incorporated in model building codes and standards.

  3. Cold-formed steel (CFS) shear panel design: CFS shear wall systems were initially conceived without significant consideration for engineering them to meet specific lateral force, displacement, or ductility requirements. As the use of these systems has extended further into applications in areas of moderate to high seismic activity, the need for proper engineering of the earthquake-resistance of low-rise buildings has become more acute. In the Research Needs section of the 2003 Edition of the NEHRP Recommended Provisions[9], the BSSC Provisions Update Committee (PUC) expected to “consider new AISI standards for cold-formed steel design …” The Research Needs section of the 2009 Edition of the NEHRP Recommended Provisions[10], noted that “research is needed to determine detailing requirements to achieve intended seismic performance of light-frame shear walls,” for both wood and CFS systems. In the May 2012 NIST NEHRP Research Roadmap workshop, participants identified requirements for light-framed shear walls, including CFS systems, as a high priority area of research need.

    Some of this needed information is available from previously unpublished work. From 1998 through 2004, ERDC/CERL conducted extensive experimental and analytical research that supported the development of draft CFS Seismic Design Guidance for the US Army Corps of Engineers.  This research examined numerous detailing factors that impact lateral load force capacity, drift capacity, and ductility. A report documenting the results of this research was never published. The previously unpublished ERDC/CERL data concerning the practical use of CFS systems in low-rise construction in areas of moderate to high seismic activity will be published as a report for use by practioners, researchers  and codes and standards developers.

What is the research plan?

  1. Accurate steel beam-column models: This research undertakes a program of coordinated experimental and analytical study that is outlined by NIST GCR 11-917-13[11].  An FY 2012 task order will be awarded to the NCJV for a comprehensive experimental research program will characterize the behavior of at approximately 20 deep, slender beam-column members that are considered stability-sensitive at large deformations.

    NCJV in turn will sub-contract with one or more testing laboratories specializing in large scale structural testing under simulated seismic loading of this kind (e.g., member sites of the NSF-funded Network for Earthquake Engineering Simulation - NEES) to perform the experimental testing. A test loading protocol will be developed for the beam-column elements such that plastic hinges form, enabling analysis of the inelastic behavior of these specimens under different combinations of axial loads and bending moments, to obtain interaction information in the inelastic regime, which is currently unavailable.

    This project will synthesize the experimental results with complementary analytical modeling that will lead to developing design relationships, including axial load-bending moment interaction equations, for model building code provisions. The numerical modeling will employ advanced nonlinear finite element analysis, to provide statistically significant data and validate design and modeling recommendations. Using the modeling guidelines developed in this project, changes in boundary conditions from the idealized ones of the experiments will be analytically evaluated, as will the larger question of inelastic stability of simple frames. Appropriate recommendations for future work will also be identified. A detailed research plan, including the names of all project participants, will be developed following the NCJV initiation of the experimental testing program. This project description will be revised following testing contract award to reflect the additional detail that will be provided by the research plan.

  2. Accurate reinforced concrete (R/C) wall models: The research goals will be achieved through a combined numerical simulation and experimental research program. The experimental program, which has been funded via an FY 2012 Interagency Agreement with ERDC, will design, construct, instrument, and test approximately 25 R/C shear wall panels that will be designed to fail in flexure, but with varying construction details. The testing program will be conducted at the ERDC /CERL in Champaign, IL. The major variables of the testing program will be: wall slenderness (wall height-to-thickness ratio), absolute wall thickness, gravity stress as a function of unconfined concrete compressive strength (f’c), wall confinement and detailing, and loading protocol. A loading protocol will be developed to investigate the effect of significant early loading in tension (from uplift forces) during an earthquake, and its impact on wall performance and buckling behavior. The portion of the research supported by this project includes nonlinear analysis, project oversight, and coordination with ongoing NCJV task orders that involve analyzing the responses of buildings in the 2010 Chilean earthquake. An extramural project oversight committee composed of key R/C researchers and practitioners will be formed in 2013 to assist with the experimental program formulation and to provide technical feedback. Upon completion of the research program, building code recommendations for the ACI 318 Building Code and IBC provisions will be developed with an ultimate impact on U.S. building code requirements (IBC[12], ACI[13]) and design practices.

  3. Cold-formed steel (CFS) shear panel design: This project will utilize the results of previously unpublished ERDC experimental testing and nonlinear analyses of CFS shear panels with a variety of different details that impact seismic behavior to produce a series of design tools and recommendations for consideration in new model building codes and standards.  References used in the original conduct of this research and the unpublished report will be revised to current versions of those documents.  Recommended design equations and guidance narratives (e.g., local buckling and P-delta calculations) will be updated to address the updated references. Example design calculations presented in the unpublished report will be updated to be consistent with the revised design relationships based on the current references. ERDC will prepare a final report. To the extent that the existing ERDC test data are stored in forms that are compatible with the NEEScomm Project Warehouse and the Data Repository at Purdue University, ERDC will transfer the CFS data to that repository.

  4.  


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

    [4] Seismic Rehabilitation of Existing Buildings, ASCE/SEI 41-06, American Society of Civil Engineers, 2006.

    [5] NEHRP Consultants Joint Venture Projects ATC-92 (Task Order 19) Comparison of US and Chilean Building Code Requirements and Seismic Design Practice 1985-2010.

    [6] NEHRP Consultants Joint Venture Projects ATC-94 (Task Order 21) Analysis of Seismic Performance of Reinforced Concrete Buildings in the 2010 Chile Earthquake, Including Effects of Non-Seismic-Force-Resisting Building Structural Elements.

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

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

    [9] Research Needs Identified During Preparation of the 2003 Edition of the NEHRP Recommended Provisions for Seismic Regulations for New Buildings and Other Structures, FEMA 450, Building Seismic Safety Council/Federal Emergency Management Agency, 2004.

    [10] Research Needs Identified During Preparation of the 2009 Edition of the NEHRP Recommended Provisions for Seismic Regulations for New Buildings and Other Structures, FEMA 470, Building Seismic Safety Council/Federal Emergency Management Agency, 2009.

    [11] See foot note [1].

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

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

     

Major Accomplishments:

Recent Results:

There is limited progress to date on the three tasks in this project, since most of the work envisioned for the project is starting in late 2012.

Outputs:

  • In the development of accurate steel beam-column models, the NCJV completed NIST GCR 11-917-13[2]. This research plan forms the basis for the experimental and analytical research that is covered by the above-mentioned new technical idea and research plan. To initiate the experimental research, NIST completed an NCJV task order SoW in FY 2012. The experimental research is planned for completion in 24 months, late FY 2014 (Harris/McCabe).
  • In the development of reinforced concrete wall models, a thorough literature review and preliminary design calculations for basic sizing of wall speciments were completed. A detailed Interagency Agreement (IAA) that outlines all parameters of the planned experimental testing was developed and coordinated for selecting the testing laboratory as ERDC/CERL in Champaign, IL.
  • From 1998 through 2004, ERDC-CERL conducted extensive experimental and analytical research that supported the development of draft CFS Seismic Design Guidance. Experiments included 20 monotonic and cyclic tests of shear panels in a load frame, capped by a series of shake table tests of a two-story model CFS structure with reinforced concrete diaphragms. A first edition of design guidance based on initial aspects of the research was published by the U.S. Army Corps of Engineers in 2002[14]. Following the completion of a draft report in 2004, one peer-reviewed journal article was published[15], but the work was not carried further because of laboratory mission change. Thus, the public availability of this work has been limited.

Standards and Codes:

In most instances, new measures that impact seismic provisions of U.S. national model building codes and standards will first be considered in the appropriate update cycle for the NEHRP Recommended Seismic Provisions for Buildings and Other Structures, which is produced by the BSSC PUC for the Federal Emergency Management Agency (FEMA). The “Provisions” are updated on approximately 5-6 year cycles by BSSC, with current update activity aimed at a 2014 production date.  Given the schedule for this project, it is therefore likely that the final results of this research will be considered after the 2014 Provisions update cycle, although preliminary results may be available earlier.

  1. Accurate steel beam-column models: The project outcome will be a comprehensive guidelines  document for structural engineering practitioners that contains improved interaction relationships for use in member selection, as well as information regarding how to model deep, slender wide-flange steel beam-columns for nonlinear analysis required for PBSE evaluations. The document will be compatible with existing and developing model building code provisions, principally AISC 360[16] Chapter H and AISC 341[17] Chapter D and E. This project will also contribute to ASCE 41[18] in providing modeling guidance for accurate depiction of plastic hinges, assessment of current provisions in model building codes and design standards, and new provisions for adoption.
  2. Accurate reinforced concrete (R/C) wall models: The results of the task will be formulated to provide guidance in building code format on slenderness and tension controlled actions of R/C walls, for inclusion in future versions of IBC, ASCE 7 and ACI 318.  In particular, Chapter 21 Section 21.9 concerning special structural walls contains a number of areas where information developed through this project can be used to update requirements these include Sections 21.9.2.3 concerning reinforcement detailing, 21.9.5 concerning design and 21.9.6  concerning boundary elements. The updated model building code requirements, plus the data from the testing and analytical work, will add to the knowledge base to provide tools for designers involved in PBSE work, including strengthening of existing structures using ASCE 41.
  3. Cold-formed steel (CFS) shear panel design: The expected project outcome is a guidance document that will be used by structural engineering practitioners in the design of low-rise CFS systems in seismically active areas and by researchers who will be able to refer to this early work as they continue to perform CFS research. The document formatting will be compatible with existing and developing model building code provisions for CFS systems. Specifically, the outcome will be formulated to be compatible with Section 14.1.3, Cold-Formed Steel, of ASCE 7; Sections 14.1.1-14.1.5 of ANSI/AISI S100[19]; Sections 14.1.1-14.1.3 of ANSI/AISI S110[20]; and Sections 14.1.1-14.1.4 of ANSI/AISI S213[21].

 


[14] Technical Instructions – Design of Cold-Formed Steel Load Bearing Steel Systems and Masonry Veneer / Steel Stud Walls, TI 809-07, Headquarters, U.S. Army Corps of Engineers, 2002.

[15] T-W Kim, J. Wilcoski, and D.A. Foutch, Analysis of Measured and Calculated Response of a Cold-Formed Steel Shear Panel Structure, Journal of Earthquake Engineering, 2007.

[16] Specification for Structural Steel Buildings, ANSI/AISC 360, American Institute of Steel Construction, Chicago, IL, 2010.

[17] See foot note [3].

[18] See foot note [4].

[19] North American Specification for the Design of Cold-Formed Steel Structural Members, ANSI/AISI S100, American Iron and Steel Institute, Washington, DC, 2007.

[20] Standard for Seismic Design of Cold-Formed Steel Structural Systems – Special Bolted Moment Frames, ANSI/AISI S110, American Iron and Steel Institute, Washington, DC, 2007.

[21] North American Standard for Cold-Formed Steel Framing – Lateral Design, ANSI/AISI S213, American Iron and Steel Institute, Washington, DC, 2007.

 

Start Date:

October 1, 2012

Lead Organizational Unit:

el

Staff:

Principal Investigator: Dr. John (Jay) L. Harris, III

Co-Investigator(s): Dr. Matthew Speicher, Dr. Steven L. McCabe[1], Travis Welt

 


[1] Current plans include seeking a new reinforced concrete expert to be on staff, following the departure of the current staff expert in June 2012. The new expert will work on this project.

 

Contact

General Information:
Dr. John (Jay) L. Harris, III, Project Manager
301-975-6538 Telephone

100 Bureau Drive, M/S 8604
Gaithersburg, MD 20899-8604