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To achieve these objectives, AWC contributes to the development of sound public policies, codes, and regulations which allow for the appropriate and responsible manufacture and use of wood products. We support the utilization of wood products by developing and disseminating consensus standards, comprehensive technical guidelines, and tools for wood design and construction, as well as providing education regarding their application. 2018 EDITION ® NATIONAL DESIGN SPECIFICATION® NDSfor Wood Construction AMERICAN WOOD COUNCIL APPROVED NOVEMBER 16, 2017 ii NATIONAL DESIGN SPECIFICATION FOR WOOD CONSTRUCTION National Design Specification (NDS) for Wood Construction 2018 Edition First Web Version: November 2017 ISBN 978-1-940383-42-2 Copyright © 2017 by American Wood Council All rights reserved. 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AMERICAN WOOD COUNCIL NATIONAL DESIGN SPECIFICATION FOR WOOD CONSTRUCTION iii FOREWORD The National Design Specification® for Wood tion 2.1.2, relating to the designer’s responsibility to Construction (NDS®) was first issued by the Na- make adjustments for particular end uses of structures. tional Lumber Manufacturers Association (now the Since the first edition of the NDS in 1944, the American Wood Council) (AWC) in 1944, under the Association’s Technical Advisory Committee has title National Design Specification for Stress-Grade continued to study and evaluate new data and devel- Lumber and Its Fastenings. By 1971, the scope of opments in wood design. Subsequent editions of the the Specification had broadened to include additional Specification have included appropriate revisions to wood products. In 1977, the title was changed to provide for use of such new information. This edi- reflect the new nature of the Specification, and the tion incorporates numerous changes considered by content was rearranged to simplify its use. The 1991 AWC’s ANSI-accredited Wood Design Standards edition was reorganized in an easier to use “equation Committee. The contributions of members of this format”, and many sections were rewritten to provide Committee to improvement of the Specification as a greater clarity. national design standard for wood construction are In 1992, the American Forest & Paper Association especially recognized. (AF&PA) – formerly the National Forest Products Acknowledgement is also made to the Forest Association – was accredited as a canvass sponsor by Products Laboratory, U.S. Department of Agriculture, the American National Standards Institute (ANSI). for data and publications generously made avail- The Specification subsequently gained approval as an able, and to the engineers, scientists, and other users American National Standard designated ANSI/NFoPA who have suggested changes in the content of the NDS-1991 with an approval date of October 16, 1992. Specification. AWC invites and welcomes comments, In 2010, AWC was separately incorporated, re- inquiries, suggestions, and new data relative to the chartered, and accredited by ANSI as a standards provisions of this document. developing organization. The current edition of the It is intended that this document be used in con- Standard is designated ANSI/AWC NDS-2018 with junction with competent engineering design, accurate an approval date of November 16, 2017. fabrication, and adequate supervision of construction. In developing the provisions of this Specification, AWC does not assume any responsibility for errors the most reliable data available from laboratory tests or omissions in the document, nor for engineering and experience with structures in service have been designs, plans, or construction prepared from it. carefully analyzed and evaluated for the purpose of Those using this standard assume all liability aris- providing, in convenient form, a national standard ing from its use. The design of engineered structures of practice. is within the scope of expertise of licensed engineers, It is intended that this Specification be used in architects, or other licensed professionals for applica- conjunction with competent engineering design, tions to a particular structure. accurate fabrication, and adequate supervision of American Wood Council construction. Particular attention is directed to Sec- Copyright © American Wood Council. Downloaded/printed pursuant to License Agreement. No reproduction or transfer authorized. AMERICAN WOOD COUNCIL iv NATIONAL DESIGN SPECIFICATION FOR WOOD CONSTRUCTION Copyright © American Wood Council. Downloaded/printed pursuant to License Agreement. No reproduction or transfer authorized. AMERICAN WOOD COUNCIL NATIONAL DESIGN SPECIFICATION FOR WOOD CONSTRUCTION v TABLE OF CONTENTS FOR THE NDS Part/Title Page Part/Title Page 1 General Requirements for Structural 7 Prefabricated Wood I-Joists ...............47 Design.....................................................1 7.1 General 48 1.1 Scope 2 7.2 Reference Design Values 48 1.2 General Requirements 2 7.3 Adjustment of Reference Design 1.3 Standard as a Whole 2 Values 48 1.4 Design Procedures 2 7.4 Special Design Considerations 50 1.5 Specifications and Plans 3 1.6 Notation 3 8 Structural Composite Lumber ............51 8.1 General 52 2 Design Values for Structural 8.2 Reference Design Values 52 Members ................................................9 8.3 Adjustment of Reference Design 2.1 General 10 Values 52 2.2 Reference Design Values 10 8.4 Special Design Considerations 54 2.3 Adjustment of Reference Design Values 10 9 Wood Structural Panels ......................55 9.1 General 56 3 Design Provisions and Equations ......13 9.2 Reference Design Values 56 3.1 General 14 9.3 Adjustment of Reference Design 3.2 Bending Members – General 15 Values 57 3.3 Bending Members – Flexure 15 9.4 Design Considerations 58 3.4 Bending Members – Shear 17 3.5 Bending Members – Deflection 19 10 Cross- Laminated Timber ....................59 3.6 Compression Members – General 20 10.1 General 60 3.7 Solid Columns 21 10.2 Reference Design Values 60 3.8 Tension Members 22 10.3 Adjustment of Reference Design 3.9 Combined Bending and Axial Loading 22 Values 60 3.10 Design for Bearing 23 10.4 Special Design Considerations 62 4 Sawn Lumber .......................................25 11 Mechanical Connections ....................63 4.1 General 26 11.1 General 64 4.2 Reference Design Values 27 11.2 Reference Design Values 65 4.3 Adjustment of Reference Design 11.3 Adjustment of Reference Design Values 28 Values 65 4.4 Special Design Considerations 31 12 Dowel-Type Fasteners .........................73 5 Structural Glued Laminated Timber ...33 12.1 General 74 5.1 General 34 12.2 Reference Withdrawal Design Values 76 5.2 Reference Design Values 35 12.3 Reference Lateral Design Values 83 5.3 Adjustment of Reference Design 12.4 Combined Lateral and Withdrawal Values 36 Loads 89 5.4 Special Design Considerations 39 12.5 Adjustment of Reference Design Values 89 6 Round Timber Poles and Piles ............43 12.6 Multiple Fasteners 93 6.1 General 44 6.2 Reference Design Values 44 13 Split Ring and Shear Plate 6.3 Adjustment of Reference Design Connectors .........................................119 Values 44 13.1 General 120 13.2 Reference Design Values 121 13.3 Placement of Split Ring and Shear Plate Connectors 127 Copyright © American Wood Council. Downloaded/printed pursuant to License Agreement. No reproduction or transfer authorized. AMERICAN WOOD COUNCIL vi TABLE OF CONTENTS Part/Title Pag Part/Title Page 14 Timber Rivets .....................................133 Appendix ....................................................157 14.1 General 134 A Construction and Design Practices 158 14.2 Reference Design Values 134 B Load Duration (ASD Only) 160 14.3 Placement of Timber Rivets 136 C Temperature Effects 162 D Lateral Stability of Beams 163 15 Special Loading Conditions ..............145 E Local Stresses in Fastener Groups 164 15.1 Lateral Distribution of a F Design for Creep and Critical Concentrated Load 146 Deflection Applications 169 15.2 Spaced Columns 146 G Effective Column Length 171 15.3 Built-Up Columns 148 H Lateral Stability of Columns 172 15.4 Wood Columns with Side Loads and I Yield Limit