Errera, S. J.

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Missouri University of Science and Technology (Missouri S&T): Scholars' Mine

Missouri University of Science and Technology Scholars' Mine International Specialty Conference on Cold-Formed Steel Structures (1990) - 10th International Specialty Conference on Cold-Formed Steel Structures Oct 23rd, 12:00 AM The 1989 Addendum to the AISI Specification S. J. Errera Follow this and additional works at: https://scholarsmine.mst.edu/isccss  Part of the Structural Engineering Commons Recommended Citation Errera, S. J., "The 1989 Addendum to the AISI Specification" (1990). International Specialty Conference on Cold-Formed Steel Structures. 1. https://scholarsmine.mst.edu/isccss/10iccfss/10iccfss-session8/1 This Article - Conference proceedings is brought to you for free and open access by Scholars' Mine. It has been accepted for inclusion in International Specialty Conference on Cold-Formed Steel Structures by an authorized administrator of Scholars' Mine. This work is protected by U. S. Copyright Law. Unauthorized use including reproduction for redistribution requires the permission of the copyright holder. For more information, please contact scholarsmine@mst.edu. Tenth International Specialty Conference on Cold-fonned Steel Structures St. Louis, Missouri, U.S.A., October 23-24, 1990 THE 1989 ADDENDUM TO THE AlSI SPECIFICATION by Samuel J. Errera* Abstract The evolution of the AISI Specification for the Design of Cold-Formed Steel Structural Members is reviewed. The most significant changes in the 1989 Addendum to the Specification are discussed. Current research projects aimed at further enhancements to the Specification are briefly described. Introduction The year 1990 marks the fifty-second consecutive year that the American Iron and Steel Institute (AISI) has sponsored research on cold-formed steel design to develop and enhance the Specification for the Design of Cold-Formed Steel Structural Members. In recent years some of the research has been co-sponsored by the Metal Building Manufacturers Association (MBMA). The Steel Deck Institute also has co-sponsored research in the past on composite construction utilizing cold-formed steel decking. The Metal Lath/Steel Framing Association is expected to co-sponsor research this year. The main part of this report will discuss the changes in the Specification included in the 1989 Addendum resulting from recent research. But first it will review briefly the evolution of the AISI Specification, and sub-sequently discuss some of the current and proposed AISI research projects. Evolution of the AISI Specification for the Design of Cold-Formed Steel Structural Members The first edition of the "Specification for the Design of Cold-Formed Steel Structural Members" was adopted in 1946 after considerable research, mostly at Cornell University under the direction of Professor George Winter. AISI-sponsored research on cold-formed steel began at Cornell in 1939 (Winter 1952). Subsequent editions of the Specification appeared in 1956, 1960, 1962, 1968, 1980 and most recently in 1986. Each of these editions was made possible by additional research at Cornell, the University of Missouri-Rolla, and many other places in North America and throughout the world. In all these editions the Specification was produced by a com-bination of researchers and designers under the auspices of the American Iron and Steel Institute. Recent editions have been compiled under the direction of the AISI Advisory Croup on the Specification for the Design of Cold-Formed Steel Structural Members. Great care has been taken to insure that producers, consumers and the general interest constituency have balanced representation on the Advisory Group which currently consists of approximately 40 well-known competent engineers. * Technical Consultant, Bethlehem Steel Corporation, Bethlehem, Pennsylvania 669 670 The first edition of the Cold-Formed Steel Design Manual appeared in 1949, followed by subsequent editions in 1956, 1961, 1962, 1970-73 (in parts), 1977, 1983 and 1986 (AISI 1986). The Manual gradually grew to include supplementary information, illustrative examples, charts arid tables of structural properties, and appendices. The 1962 Edition included the first Commentary by Dr. Winter. Over the years the Specification and the Manual grew in comprehensiveness and complexity. Many additional design situations were covered; new steels were included, and the limiting thickness of steels covered by the Specification was increased from about 1/4" to 1". Today the 1986 Edition of the Manual includes seven parts: Part I - Specification Part II Commentary Part III- Supplementary Information Part IV Illustrative Examples Part V - Charts and Tables Part VI - Computer Aids (Flow Charts) Part VII - Test Procedures While the 1986 Edition of the Specification is more comprehensive then ever, strenuous efforts were made to make it no more complicated than necessary. However, many users and potential users consider the Specification "too complicated", and efforts are underway to do something about this. Cold-formed steel design is, of course, inherently more complicated - and, therefore, more challenging - than most steel design using hot-rolled shapes and plates. The first reason for this is the local buckling of flat elements with relatively large width-to-thickness ratio, and the need to consider post-buckling strength. Another reason is the infinite number of shapes that can be produced by cold-forming, which then must be analyzed for their structural behavior. Format Changes in the 1986 Specification In order to make the Specification as easy to use as possible, a Subcommittee on Simplification developed a new format for the 1986 Edition (Pinkham 1986). The previous versions had grown somewhat unevenly through the years, with new and revised text being added as developed. The subcommittee on Simpli-fication produced a totally revised format with the following chapters: A. General Provisions B. Elements C. Members D. Structural Assemblies E. Connections and Joints F. Tests for Special Cases 671 Chapter A, General Provisions, includes the limits of applicability of the Specification, and information on materials, loads, structural analysis and design, and reference documents. Basic information on allowable width-thickness ratios and effective widths of elements is given in Chapter B. The design criteria for individual members are given in Chapter C. Here all the information on flexural members, for example, is now grouped together. The special provisions for structural assemblies are given in Chapter D, and all details for design of connections and joints are contained in Chapter E. The details of tests referred to in other sections of the Specification are given in Chapter F. It is hoped that the logical sequence of the presentation will make it easier for the user to follow and understand the 1986 Specification. The 1986 Specification was the first to use the effective width concept for unstiffened elements as well as stiffened elements (Johnson 1986, Pekoz 1986). 1989 Addendum In order to take advantage of current research, the plan of the Advisory Group is to issue a revised specification every six years, with an addendum at the intervening third year. The 1989 Addendum to the 1986 AISI Specification (AISI 1989-1, 1989-2) includes the following changes based on recent research. Low-Strain-Hardening Ductile Steel Section A3.3.1 of the 1986 Specification states that the provisions of Chapter B through E are limited to steels having a ratio of tensile strength to yield point of not less than 1.08, and a total elongation of not less than 10% in a 2-inch gage length. Exceptions for particular cases are noted in Section A3.3.2. The change proposed for the 1989 Addendum (Macadam 1988) permits the use of steel with a lower Fu/Fy ratio for certain flexural members providing the following criteria are satisfied: (1) local elongation in a 1/2" gage length across the fracture shall be not less than 20% and, (2) uniform elongation outside the fracture shall be not less than 3% as determined by prescribed procedures. F is the tensile strength of the material, and F is the yield point. tlse of such material is restricted to purlins and gIrts designed on an elastic basis, with P/p less than 0.15, where P is the applied axial load and Pa is the allowabl~ axial load. Lateral Buckling Strength In Section C3.1.2 on lateral buckling strength of flexural members the sequence of the presentation has been improved by first presenting the general lateral buckling equations, followed by simplified equations for specific cases. Application of the equations for doubly-, singly-, and point-symmetric sections also has been clarified. 672 Beams Having One Flange Through-Fastened to Deck or Sheathing For beams having the tension flange attached to deck or sheathing and the compression flange unbraced (for example, a roof purlin or wall girt subject to wind suction) the bending capacity is less than that of a fully braced member, but greater than that of an unbraced member. This partial restraint is a function of the rotational stiffness provided by the panel-to-purlin connection. The 1986 provision requires "a rational method of analysis" or "full scale testing" to determine allowable loads. Based on extensive experimental results {LaBoube et aI, 1988} a new provision contains factors that represent the reduction in capacity from a fully braced condition for C and Z sections on simple and continuous spans for fairly wide parameter ranges, thus simplifying the design under these conditions. Combined Axial Load and Bending (Section CS) In Equation ~S-2, the parameters Maxo and Ma 0 are replaced by M x and M ,respect1vely, where M and Mare theYallowable moments a~out tR~ centroidal axes consid~~ing lat~ral buckling strength, which M and M do not consider. This change provides a proper strength ~~~elope consia~¥ing lateral torsional buckling, and also provides consistency with the AISC Specifications. Wall Studs and Wall Stud Assemblies (Section D4) The 1989 Addendum states that the load-carrying capacity of a stud may be computed considering the attached sheathing, or neglecting the sheathing and considering the steel only. When sheathing is utilized for stability of the wall studs, the sheathing must retain adequate strength and stiffness for the expected service life of the wall, and additional bracing shall be provided if required for adequate structural integrity during construction and in the completed structure. Design limitations listed in the Commentary of the 1986 Edition are moved forward to the Specification. For studs with perforations, stub column tests and/or rational analyses are recognized as a suitable basis for design. In addition, the effective length factors K ,K and Kt are removed from Equations D4.1-8, D4.1-10 and D4.1-11. TheXequXtions are based on tests with only sheathing as bracing, and inclusion of the effective length factors could lead to unconservative designs when both sheathing and strap or channel bracing are present. Further revisions of wall stud design criteria are under study. Floor, Roof or Wall Steel Diaphragm Construction (Section DS) The structural performance of a diaphragm construction can be evaluated by either calculation or test. Several analytical procedures exist,as do standard methods for load testing, which are identified in the Commentary {AISI 1989-2}. This new section in the Specification gives factors of safety for welded and mechanical connections under various loading conditions, thus filling a void in the Specification and establishing a recognized approach for the design of steel diaphragms. 673 Tension Loads on Arc Spot Welds (Section E2.2) This important addition to the Specification states that the nominal tension load. P • on each arc spot weld between sheet and supporting member shall not exceeli P = 0.7 t d F n a u where t. d and F are respectively the thickness. average diameter of the spot weld.aand teRsile strength of the material. each as defined in the Specification. The equation is based on experimental results (Albrecht. 1988)'. thus the following limitations apply'for its use: the minimum edge distance must not be less than the weld diameter; F shall not exceed 60 ksi; the AWS electrode stress level designation shall b~ not less than 60 ksi; and the thickness of the sheet shall be not less than 0.028". This provision permits design for a fairly broad range of applications. Additional research is underway at University of Missouri-Rolla to investigate the behavior of higher strength steels and other design conditions. Other, mostly editorial. changes also are included in the 1989 Addendum. Load and Resistance Factor Design Another significant achievement in the evolution of cold-formed steel design is the completion of a draft of the AISI Specification and Commentary on Load and Resistance Factor Design of Cold-Formed Steel (Hsiao. 1989). After several years of research under the direction of Professor W. W. Yu with Professor T. V. Galambos as consultant. the draft has been approved by the AISI Advisory Group. and will be issued for public review and comment. A companion design manual is in preparation. Research Toward Future Specification Changes In the current fiscal year AISI is funding research on several topics discussed briefly below. several of which are subjects of papers at this Conference. Behavior of Panels - This is the third year of an investigation at Cornell University to increase the competitiveness and reliability of steel panels by improving the accuracy of design provisions. Purl ins Brac.ed by Standing-Seam Panels - This project. co-funded by MBMA at Virginia Polytechnic Institute and State University. currently in its second year. is aimed at developing a reliable design procedure for purlins braced by standing-seam roof panels. Design of Strut Purlins - A second project co-funded by MBMA at Virginia Polytechnic Institute and State University. also is in its second year. The objective is to determine the capacity of typical purlin systems to resist axial load in the presence of bending, and develop specifications to insure improved performance under severe storm conditions. 674 Stability of Channel and Zee Flexural Members - This project will investigate whether certain braces can be eliminated for C's and Z's, and resolve possible confusion in interpretation of the current Specification. X-Brace Anchorages - Another project is co-funded by MBMA to determine the pUll-out strength of X-brace rods and cables anchored in column webs to satisfy new seismic design requirements, and develop a suitable design procedure for the anchorage. Sheathing as Bracing - The objective is to prepare a summary of existing information on non-metallic sheathing as bracing for steel studs, and propose any required modifications of Specification Section D4 on wall studs and wall stud assemblies. Preliminary Design Guide - A first edition of a Preliminary Design Guide has been approved for publication; it covers braced flexural members only, and provides simplified design procedures for such members. Additional work is planned to cover lateral buckling and interaction of axial and buckling loads. Web Crippling - This project is exploring the web-crippling behavior when flanges of flexural members are attached to supporting members, to determine if current design procedures are too conservative. If so, it will propose liberalization of web-crippling requirements. Design of Wall Studs - This anticipated project is to be co-sponsored by Metal Lath/Steel Framing Association to test individual studs and full scale wall assemblies to determine bracing requirements, effects of perforations, effects of load eccentricities, and design requirements for tracks. Web Elements with Openings - Another anticipated project to be co-sponsored by Metal Lath/Steel Framing Association, is to develop procedures for evaluating the load capacity of flexural members having web openings of various sizes and shapes, and to develop appropriate design guidelines. The Advisory Group and its subcommittees are currently evaluating proposals for the AISI fiscal year May 1, 1991 to April 30, 1992. on needed research can be addressed to any member of the Advisory Summary and Conclusions research Comments Group. The 1986 Edition of the Specification for the Design of Cold-Formed Steel Structural Members, with the 1989 Addendum, represents the culmination of over 50 years of research, experience in design and construction, and observed performance of cold-formed steel structures. The Specification and Manual are much more comprehensive than earlier editions. Continuing research in North America and elsewhere in the world will be utilized in refining and improving the Specification, and promoting the competitiveness and reliability of cold-formed steel design and construction. 675 References 1. Albrecht, R. E. (1988). "Developments and Future Needs in Welding Cold-Formed Steel," Proceedings of the Ninth International Specialty Conference on Cold-Formed Steel Structures, University of Missouri-Rolla, Rolla, Missouri. 2. American Iron and Steel Institute (1986). Cold-Formed Steel Design Manual, Washington, D.C. 3. American Iron and Steel Institute (1989-1). "Specification for the Design of Cold-Formed Steel Structural Members", August 1986 Edition with December 1989 Addendum, Report CF89-1. 4. American Iron and Steel Institute (1989-2). "Commentary on the Specification for the Design of Cold-Formed Steel Structural Members", August 1986 Edition with December 1989 Addendum, Report CF89-2. 5. Hsiao, L-E., Yu, W-W., and Galambos, T. V. (1989). "Load and Resistance Factor Design of Cold-Formed Steel", Civil Engineering Study 89-5, University of Missouri-Rolla. 6. Johnson, Albert L. (1986). "AISI's 1986 Cold-Formed Steel Design Specification - An Overview", Eighth International Specialty Conference on Cold-Formed Steel Structures, University of Missouri-Rolla, Rolla, Missouri. 7. LaBoube, R. A., et al. (1988). "Behavior of Continuous Span Purlin Systems", Proceedings of the Ninth International Specialty Conference on Cold-Formed Steel Structures, University of Missouri-Rolla, Rolla, Missouri. 8. Macadam, J. N., et al. (1988). Formed Members", Proceedings of Conference on Cold-Formed Steel Rolla, Rolla, Missouri. "Low-Strain-Hardening Ductile Steel Cold-the Ninth International Specialty Structures, University of Missouri-9. Pekoz, Teoman (1986). "Development of a Unified Approach to the Design of Cold-Formed Steel Members", Eighth International Specialty Conference on Cold-Formed Steel Structures, University of Missouri-Rolla, Rolla, Missouri. 10. Pinkham, Clarkson W. (1986). "Reformatting the AISI Cold-Formed Steel Design Specification", Eighth International Specialty Conference on Cold-Formed Steel Structures, University of Missouri-Rolla, Rolla, Missouri. 11. Winter, George (1952). "Light-Gauge (Thin-Walled) Steel Structures for Buildings in the United States of America", International Association for Bridge and Structural Engineering, Preliminary Publication. 

The 1989 Addendum to the AISI Specification

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The 1989 Addendum to the AISI Specification

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