Wood as a Construction Material

Wood as a Construction Material - 43 Wood as a Construction...

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© 2003 by CRC Press LLC 43 Wood as a Construction Material 43.1 Introduction What Is Wood? • Definitions • Wood Chemistry and Anatomy 43.2 Wood Defects as They Affect Wood Strength 43.3 Physical Properties of Wood Specific Gravity (SG) • Moisture Content (MC) and Shrinkage • Thermal Properties/Temperature Effects • Durability • Chemical Effects 43.4 Mechanical Properties of Selected Species Major Engineering Properties • Strengths and Weaknesses • Duration of Load Effects • Strength Variability • Age Effects 43.5 Structural Products and Their Uses 43.6 Preservatives 43.7 Grades and Grading of Wood Products 43.8 Wood Fasteners and Adhesives 43.9 Where Do Designers Go Wrong? Typical Problems in Wood Construction 43.10 Wood and the Environment 43.1 Introduction This brief introduction to wood as a material is written primarily to inform the practicing civil engineer about what wood is; its cellular makeup; and, therefore, how it may be expected to react under various loading conditions. Space limitations preclude much detail; instead, references are given to lead the reader to detailed cause-effect relationships. Emphasis is placed on those items and relationships that most often lead to wood misuse or problems of proper wood use in structural applications and that may provide useful, practical guidelines for successful wood use. What Is Wood? Next to stone, wood is perhaps the building material used earliest by humans. Despite its complex chemical nature, wood has excellent properties which lend themselves to human use. It is readily and economically available; easily machinable; amenable to fabrication into an infinite variety of sizes and shapes using simple on-site building techniques; exceptionally strong relative to its weight; a good heat and electrical insulator; and—of increasing importance—it is a renewable and biodegradable resource. However, it also has some drawbacks of which the user must be aware. It is a “natural” material and, as John F. Senft Purdue University
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such, it comes with an array of defects ( knots , irregular grain, etc.); it is subject to decay if not kept dry; it is flammable; and it is anisotropic. Definitions In order to understand how best to use wood as a structural material, a few terms must be understood. A tree is a marvel of nature; it comes in a variety of species, sizes, shapes, and utilization potentials. However, all trees have some basic characteristics in common: Growth ring: The portion of wood of a tree produced during one growing season. In the temperate zones this is also called an annual ring . Earlywood: The portion of a growth ring that is formed early in the growing season. It normally contains larger cells with thinner walls. Earlywood is relatively low in density and is followed by latewood as the growing season progresses.
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This note was uploaded on 02/11/2010 for the course ENGR CIVE 402 taught by Professor Thorton during the Spring '10 term at Colorado State.

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Wood as a Construction Material - 43 Wood as a Construction...

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