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Wood Structural Design Data

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Wood Structural Design Data WOOD STRUCTURAL DESIGN DATA 1986 Edition with 1992 Revisions American American Wood Council American Wood Forest & Paper Association WOOD STRUCTURAL DESIGN DATA 1986 Edition with 1992 Revisions The American Wood Council (AWC) is the wood products division of the American Forest & Paper Association (AF&PA). AF&PA is the national trade association of the forest, paper, and wood products industry, representing member companies engaged in growing, harvesting, and processing wood and wood fiber, manufacturing pulp, paper, and paperboard products from both virgin and recycled fiber, and producing engineered and traditional wood products. For more information see www.afandpa.org. While every effort has been made to insure the accuracy of the information presented, and special effort has been made to assure that the information reflects the state-of-the-art, neither the American Forest & Paper Association nor its members assume any responsibility for any particular design prepared from this publication. Those using this document assume all liability from its use. Copyright © 1993, 2004 American Forest & Paper Association, Inc. American Wood Council 1111 19th St., NW, Suite 800 Washington, DC 20036 202-463-4713 [email protected] www.awc.org Copyright © American Wood Council. Downloaded/printed pursuant to License Agreement. No further reproductions authorized. WOOD STRUCTURAL DESIGN DATA r-II 1986 Edition with 1992 Revisions Recommended by AMERICAN FOREST 81 PAPER ASSOCIATION (ormerly National Forest Products Associatio Copyright © American Wood Council. Downloaded/printed pursuant to License Agreement. No further reproductions authorized. FOREWORD Wood in the form of lumber and timbers has been used as a major structural material for centuries. Originally the material of craftsmen, wood is now the material of the engineer who uses technical data to design todays’ sophisticated structures. Wood Structural Design Data, 1986 Edition, provides information relating to design of typical wood structural members. These data are augmented by reference to the National Design Specification for Wood Construction, particularly on the subject of design stresses. Wood Structural Design Data was first published in 1934, with revised editions issued periodically to take into account new data and developments in wood design. Tabular data in this volume are presented primarily as a convenient aid in design of the most frequently encountered elements of wood structural framing. Hence, certain subjects are only summarized in the text to indicate their relationships to the tabular data. More detailed information is available in other publications, many of which are listed as References. In preparation of this and previous editions, information from the regional lumber manufacturers associations provided valuable data. Reports and other publi- cations from the Forest Products Laboratory, U. S. Department of Agriculture, were important sources of fundamental information. Tabular data relate to dressed sizes conforming to the American Softwood Lumber Standard, Voluntary Product Standard 20-70, U.S. Department of Ccmmerce, National Bureau of Standards. Copyright © American Wood Council. Downloaded/printed pursuant to License Agreement. No further reproductions authorized. TABLE OF CONTENTS PAGE PROPERTIES OF STRUCTURAL LUMBER Physical Properties ................................................... 1 Mechanical Properties ................................................. 8 Design Values for Structural Lumber ....................................... 11 Adjustment of Design Values for Duration of Loading ............................ 13 Glossary of Lumber Terms ............................................. 16 Abbreviations of Lumber Terms .......................................... 19 Table of Board Measure ............................................... 21 Standard Sizes of Yard Lumber and Timbers .................................. 23 Properties of Standard Dressed Lumber Sizes .................................. 24 WOOD BEAMS General Design Information ............................................ 28 Design for Bending Movement ........................................... 30 Design for Bending and Axial Loading Combines ............................... 34 Design for Deflection ................................................ 35 Design for Horizontal Shear ............................................ 37 Design for Bearing on Supports .......................................... 40 Formulas and Diagrams for Static Loads ..................................... 41 Wood Beams .Load Tables ............................................ 58 WOOD COLUMNS General Design Information ........................................... 201 SolidColumns .................................................... 203 Spaced Columns. Connector Joined ....................................... 205 Combined Axial and Bending Loading ..................................... 207 Solution of Hankinson Formula ......................................... 208 Use of Tabular Column Data ........................................... 210 Unit Axial Stresses .Simple Solid Columns .t/d from 2 to 30 ...................... 211 Unit Axial Stresses .Simple Solid Columns .t/d from 30 to 50 ..................... 217 Unit Axial Stresses .Spaced Columns, Condition "a" .t/d from 2 to 46 ................ 223 Unit Axial Stresses .Spaced Columns, Condition "a" .P/d from 46 to 80 ............... 229 Unit Axial Stresses .Spaced Columns, Condition "b" .t/d from 2 to 46 ................ 235 Unit Axial Stresses .Spaced Columns, Condition "b" .t/d from 46 to 80 ............... 241 PLANK AND LAMINATED FLOORS AND ROOFS General Design Information ........................................... 247 Table of Uniform Loads .Type I11 ....................................... 253 Table of Uniform Loads .Type IV ....................................... 254 MAXIMUM SPANS FOR FLOOR JOISTS General Design Information ........................................... 255 Maximum Spans .50 psf Live Load ...................................... 256 Maximum Spans .60 psf Live Load ...................................... 257 Maximum Spans .70 psf Live Load ...................................... 258 Maximum Spans .80 psf Live Load ...................................... 259 Maximum Spans .90 psf Live Load ...................................... 260 Maximum Spans .100 psf Live Load ..................................... 261 REFERENCES ........................................................ 262 DECIMALEQUIVALENTS ............................................... 264 Copyright © American Wood Council. Downloaded/printed pursuant to License Agreement. No further reproductions authorized. 1 PROPERTIES OF STRUCTURAL LUMBER Physical Properties Wood Structure Wood is an aggregate of cells, essentially cellulose in composition, which are cemen- ted together by a substance called lignin. Although wood cells vary in shape and size ac- cording to their function, the greater number are elongated and are positioned vertically in the standing tree. Known as fibers in hardwoods and tracheids in softwoods, wood cells vary from about 1/25 to 1/3-inch in length and 1/100 of these dimensions in width. Hardwoods and softwoods have some horizontally positioned bands of cells called rays. These are usually evident on quarter-sawed surfaces and are more conspicuous in some species than others. They provide a pleasing pattern where visible. Hardwoods and Softwoods Native trees are divided into two classes-hardwoods which have broad leaves and softwoods or conifers, which have needlelike or scalelike leaves. Most hardwoods shed their leaves at the end of each growing season. Softwoods, except cypress, larch, and some exotic species are evergreen. The terms “hardwood” and “softwood” do not apply to the hardness or softness of the wood. In fact, some species of hardwoods have softer wood than some of the species of soft- woods while certain softwoods are as hard as the medium density hardwoods. Heartwood and Sapwood The end of a log shows three distinct zones, ‘the bark, a light-colored zone just beneath it called the sapwood, and an inner zone, often darker in color, called heartwood. At the structural center of the heartwood is the pith or “heart center” as it is called in the lumber trade. A tree increases in diameter by forming new layers of cells at the outer surface of the sapwood. Here a thin band of tissue called the cambium lays down new bark cells toward the outside and new wood cells toward the inner or sapwood side. The young tree is composed primarily of sapwood which functions in sap conduction and food storage. As the tree increases in diameter, inner sapwood cells cease their con- ductive function and form the inactive heartwood. Deposits in these inactive cells give the heartwood of many species a darker color than the sapwood. As all heartwood was once sapwood, there is no consistent difference between heart- wood and sapwood in weight when dry or in strength. Deposits in the cells, however, make heartwood inore durable when in contact with soil and under other conditions conduclve to decay. Where wood is to be treated with perservative. however. deeper and more effective penetration can be attained in sapwood. Copyright © American Wood Council. Downloaded/printed pursuant to License Agreement. No further reproductions authorized. 2 ~ PROPERTIES OF STRUCTURAL LUMBER Annular Growth Rings The activity of the cambium tissue in forming new wood is influenced in temperate zones by the growing
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