30 November 1998
SEISMIC DESIGN GUIDANCE FOR SHEAR WALLS (DIAGONAL STRAP SYSTEMS)
1. INTRODUCTION. The design guidance presented here is tied directly to the 1997 NEHRP (FEMA
302 and 303), because this will form the basis of the 2000 International Building Code. U.S. Army Corps
of Engineers, Seismic Design for Buildings, TI 809-04 is the general military standard for seismic design
of buildings, and this is also based on FEMA 302 and 303. TI 809-04 supplements the FEMA 302 and
303 with additional guidance for military buildings that is primarily based on the 1997 NEHRP Guidelines
for the Seismic Rehabilitation of Buildings (FEMA 273 and 274). These and other TI 809-04 guidance
that differ from the FEMA 302 and 303 are summarized in paragraph 2 of this chapter. The basis for
unique seismic guidance presented here is provided in technical report found at the URL address:
http://owww.cecer.army.mil/techreports/wilcfstr.post.pdf , Development of Cold-Formed Steel Seismic Design
Guidance, U.S. Army Construction Engineering Research Laboratory. Design guidance is also based on
the following references:
Cold Formed Steel Design Manual, American Iron and Steel Institute, 1996 Edition.
Manual of Steel Construction Load and Resistance Factor Design (LRFD), American Institute of
Steel Construction (AISC), 2nd Edition, 1994.
Seismic Provisions for Structural Steel Buildings, AISC, 1997.
Minimum Design Loads for Buildings and Other Structures, American Society of Civil Engineers
(ASCE) 7-95, 1995.
State-of-the-Art Report on Anchorage to Concrete, American Concrete Institute (ACI) 355.1R-91,
Unique guidance for cold-formed steel is included in this chapter, while guidance that remains unchanged
from FEMA 302 and other standards is included in Appendix C as indicated in the paragraphs that follow.
Appendix C also contains limited background on the development of the guidance provided in this
chapter. The source of all guidance is referenced in the text. Figure 3-1 gives a flowchart for seismic
design of cold-formed steel shear walls. Appendix D presents an example problem showing the
application of Chapter 3 and Appendix C seismic design guidance. An update to the spreadsheet,
http://owww.cecer.army.mil/techreports/wilcfsxl.post.pdf design program using the example problem is
2. TI 809-04, SEISMIC DESIGN FOR BUILDINGS. TI 809-04 is the military standard for the seismic
design of buildings, and it provides additional guidance primarily based on FEMA 273 and 274.
Additional guidance related to the design of cold-formed steel buildings is summarized as follows:
Classification of Buildings: Definitions of Seismic Use Groups (Table 4-1) and Seismic Design
Categories are expanded (Table 4-2a and 4-2b). The Seismic Use Groups are used in TI 809-04
to define Performance Objectives.
Ground Motion: Ground Motion A is the FEMA 302 defined 2/3 site adjusted maximum
considered earthquake (MCE) levels. TI 809-04 defines another ground motion level, Ground
Motion B, which is defined as of the same MCE levels.
Performance Objectives: TI 809-04 defines three performance levels: 1) Life Safety, 2) Safe
Egress, and 3) Immediate Occupancy defined in Table 4-3. These levels are combined with the
two design motion levels to define performance objectives for each of the four seismic use groups
as described in Table 4-4. These objectives are 1A (Life Safety), 2A, 2B and 3B.
Minimum Analytical Procedures: Chapter 5 defines three analytical procedures and the minimum
procedure that must be used for each performance objective. Linear analysis with response
modification factor, R as described in FEMA 302 is used for performance objective 1A. Linear
analysis may also be used for Performance Objectives 2A, 2B and 3B, but with a modification
factors, m for deformation controlled structural components or elements.