WOOD handbook: Wood as an engineering material By Forest Products Laboratory Forest Service U.S. Department of Agriculture Agriculture Handbook No. 72 Revised August 1974 Library of Congress Catalog Card No. 73—600335 U.S. Forest Products Laboratory 1974. Wood handbook: Wood as an engineering material —(USDA Agr. Handb. 72, rev.) Summarizes information on wood as an engineering material. Properties of wood and wood-base products of particular concern to the architect and engineer are presented, along with discussions of designing with wood and some pertinent uses of wood. KEYWORDS: Wood structure, physical properties (wood), mechanical properties (wood), lumber, plywood, panel products, design, fastenings, wood moisture, drying, gluing, fire resistance, finishing, decay, sandwich construction, preservation, and wood-base products. Oxford 81/85 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402. Price $7.85 stock Number 0100^3200 11 PREFACE Forests, distinct from all their other services Purpose and benefits, supply a basic raw material— wood—which from the earliest times has fur- This handbook provides engineers, architects, nished mankind with necessities of existence and others with a source of information on the and with comforts and conveniences beyond physical and mechanical properties of wood, number. and how these properties are affected by varia- tions in the wood itself. Practical knowledge One major use has always been in struc- of wood has, over the years, resulted in strong tures, particularly in housing. But despite and beautiful structures, even though exact wood's long service in structures, it has not engineering data were not always available. always been used efficiently. In these days when Continuing research and evaluation techniques the Nation is trying to utilize its resources promise to permit wider and more efficient more fully, better and more efficient use of the utilization of wood and to encourage even more timber crop is vital. advanced industrial, structural, and decora- Authorship tive uses. As an aid to more efficient use of wood as Organization a material of construction, this handbook was Individual chapters describe not only the prepared by the Forest Products Laboratory, wood itself, but wood-based products, and the a unit of the research organization of the principles of how wood is dried, fastened, Forest Service, U.S. Department of Agricul- finished, and preserved from degradation in ture. The Laboratory, established in 1910, is today's world. Each chapter is climaxed with maintained at Madison, Wis., in cooperation a bibliography of allied information. A glos- with the University of Wisconsin. It was the sary of terms is presented at the end of the handbook. first institution in the world to conduct general The problem of adequately presenting infor- research on wood and its utilization. The vast mation for the architect, engineer, and builder accumulation of information that has resulted is complicated by the vast number of tree spec- from its engineering and allied investigations ies he may encounter in wood form. To prevent of wood and wood products over six decades— confusion, the common and botanical names along with knowledge of everyday construc- for different species mentioned in this volume tion practices and problems—is the chief basis conform to the official nomenclature of the for this handbook. Forest Service. Ill ACKNOWLEDGMENT The Forest Products Laboratory appreciates the cooperation of other elements of the Forest Service, and representatives of many universi- ties and segments of industry, in preparing this document. The number of such examples of assistance prevent the mentioning of in- dividual contributions, but their assistance is gratefully acknowledged. A special "thank you" is due to the organiza- tions that provided illustrations. These include the Acoustical and Insulating Materials As- sociation, American Hardboard Association, American Institute of Timber Construction, J. H. Baxter Wood Treating Company, Bell Lumber and Pole Company, California Red- wood Association, Forest Products Division of Koppers Co., Inc., National Forest Products Association, and National Particleboard As- sociation. IV Chapters No. Page 1 Characteristics and Availability of Woods Commercially Important in the United States 1-1 2 Structure of Wood 2-1 3 Physical Properties of Wood 3-1 4 Mechanical Properties of Wood _ _ 4-1 5 Commercial Lumber 5-1 6 Lumber Stress Grades and Allow- able Properties 6-1 7 Fastenings 7-1 8 Wood Structural Members 8-1 9 Gluing of Wood 9-1 10 Glued Structural Members 10-1 11 Plywood 11-1 12 Structural Sandwich Construction 12-1 13 Bent Wood Members 13-1 14 Control of Moisture and Dimen- sional Changes 14-1 15 Fire Resistance of Wood Construc- tion 15-1 16 Painting and Finishing 16-1 17 Protection from Organisms That Degrade Wood 17-1 18 Wood Preservation 18-1 19 Poles, Piles, and Ties 19-1 20 Thermal Insulation 20-1 21 Wood-Base Fiber and Particle Panel Materials 21-1 22 Modified Woods and Paper-Base Laminates 22-1 Glossary 23-1 Index 24-1 V The use of trade, firm, or corporation names in this publication is for the information and convenience of the reader. Such use does not constitute an official endorsement or approval of any product or service by the U.S. Department of Agriculture to the exclusion of others which may be suitable. Mention of a chemical in this handbook does not constitute a recommenda- tion; only those chemicals registered by the U.S. Environmental Protection Agency may be recommended, and then only for uses as prescribed in the registration—and in the manner and at the concentration prescribed. The list of registered chemicals varies from time to time; prospective users, therefore, should get current information on registration status from Pesticides Regulation Division, Environmental Protection Agency, Washington, D.C. 20460. Illustration Requests Requests for copies of illustrations contained in this handbook should be directed to the Forest Products Laboratory, USDA Forest Service, P.O. Box 5130, Madison, Wis. 53705. VI FS-351 Chapter 1 CHARACTERISTICS AND AVAILABILITY OF WOODS COMMERCIALLY IMPORTANT TO THE UNITED STATES Page Timber Resources and Wood Uses 1-2 Hardwoods and Softwoods 1-3 Commercial Sources of Wood Products __ 1-4 Use Classes and Trends 1-5 Commercial Species in the United States 1-5 Hardwoods 1-5 Softwoods 1-13 Imported Woods 1-22 Bibliography 1-38 1-1 CHARACTERISTICS AND AVAILABILITY OF WOODS COMMERCIALLY IMPORTANT IN THE UNITED STATES Through the ages the unique characteristics has diminished as new concepts of wood use and comparative abundance of wood have made have been introduced. Second-growth timber it a natural material for homes and other (fig. 1-1), the balance of the old-growth forests, structures, furniture, tools, vehicles, and dec- and imports continue to fill the needs for wood orative objects. Today, for the same reasons, in the quality required. Wood is as valuable wood is prized for a multitude of uses. an engineering material as it ever was, and All wood is composed of cellulose, lignin, in many cases technological advances have made ash-forming minerals, and extractives formed it even more useful. in a cellular structure. Variations in the charac- The inherent factors which keep wood in teristics and volume of the four components and the forefront of raw materials are many and differences in cellular structure result in some varied, but one of the chief attributes is its woods being heavy and some light, some stiff availability in many species, sizes, shapes, and and some flexible, some hard and some soft. conditions to suit almost every demand. It has For a single species, the properties are rel- a high ratio of strength to weight and a re- atively constant within limits; therefore, se- markable record for durability and perform- lection of wood by species alone may some- ance as a structural material. Dry wood has times be adequate. However, to use wood to its good insulating properties against heat, best advantage and most effectively in engineer- sound, and electricity. It tends to absorb and ing applications, the effect of specific char- dissipate vibrations under some conditions of acteristics or physical properties must be con- use, yet is an incomparable material for such sidered. musical instruments as violins. Because of Historically, some woods have filled many grain patterns and colors, wood is inherently purposes, while others which were not so readily an esthetically pleasing material, and its ap- available or so desirable qualitatively might pearance may be easily enhanced by stains, serve only one or two needs. The tough, strong, varnishes, lacquers, and other finishes. It is and durable white oak, for example, was a easily shaped with tools and fastened with highly prized wood for shipbuilding, bridges, adhesives, nails, screws, bolts, and dowels. cooperage, barn timbers, farm implements, rail- When wood is damaged it is easily repaired, and road crossties, fenceposts, flooring, paneling, wood structures are easily remodeled or altered. and other products. On the other hand, woods In addition, wood resists oxidation, acid, salt such as black walnut and cherry became primar- water, and other corrosive agents; has a high ily cabinet woods. Hickory was manufactured salvage value; has good shock resistance; into tough, hard resilient striking-tool handles. takes treatments with preservatives and fire Black locust was prized for barn timbers and retardants; and combines with almost any treenails. What the early builder or craftsman other material for both functional and esthetic learned by trial and error became the basis uses. for the decision as to which species to use for a given purpose, and what characteristics TIMBER RESOURCES AND WOOD USES to look for in selecting a tree for a given use. In the United States more than 100 woods It was commonly accepted that wood from are available to the prospective user, but it is trees gown in certain locations under certain very unlikely that all are available in any one conditions was stronger, more durable, and locality.