Treesearch

When sawn, a log yields round timber, ties, or lumber of varying quality. This chapter presents a general discussion of grading, standards, and specifications for these commercial products. In a broad sense, commercial lumber is any lumber that is bought or sold in the normal channels of commerce. Commercial lumber may be found in a variety of forms, species, and types, and in various commercial establishments, both wholesale and retail. Most commercial lumber is graded by standardized rules that make purchasing more or less uniform throughout the country. Round timbers and ties represent...

Round timbers, ties, and lumber sawn from a log, regardless of species and size, are quite variable in mechanical properties. Pieces may differ in strength by several hundred percent. For simplicity and economy in use, pieces of wood of similar mechanical properties are placed in categories called stress grades, which are characterized by (a) one or more sorting criteria, (b) a set of properties for engineering design, and (c) a unique grade name. The most familiar system is that for lumber. Sorting criteria have also been established for round timbers and ties. This chapter briefly...

The strength and stability of any structure depend heavily on the fastenings that hold its parts together. One prime advantage of wood as a structural material is the ease with which wood structural parts can be joined together with a wide variety of fastenings—nails, spikes, screws, bolts, lag screws, drift pins, staples, and metal connectors of various types. For utmost rigidity, strength, and service, each type of fastening requires joint designs adapted to the strength properties of wood along and across the grain and to dimensional changes that may occur with changes in moisture content.

Wood structural panel sheathed shear walls and diaphragms are the primary lateral-load resisting elements in wood-frame construction. The historical performance of light-frame structures in North America are very good due, in part, to model building codes that are designed to preserve life safety, as well as the inherent redundancy of wood-frame construction using wood structural panel shear walls and diaphragms. As wood-frame construction is continuously evolving, designers in many parts of North America are optimizing design solutions that require the understanding of force transfer...

Past timber bridge evaluation and maintenance efforts in the USA have principally focused on the internal integrity of timber components using various non-destructive evaluation tools to supplement visual inspection data. This project is part of a comprehensive effort to develop smart structure concepts for improving the long-term performance, maintenance, and management of timber bridges. This comprehensive effort focuses on developing an integrated turnkey system to analyze, monitor, and report on the performance and condition of the most commonly constructed timber bridge type in the...

In June 2009, the authors conducted a comprehensive on-site evaluation of the timber crib foundation at Alaska’s Historic Kennecott Mine Concentration Mill Building. The primary goal of the 6-day inspection was to assess the physical conditions of the existing timber crib foundation and identify timber members and areas that have structural deficiencies. The inspection process included visual assessment, species identification/confirmation, moisture content determination, stress wave scanning test, resistance micro-drilling, and core-drilling. Extensive deterioration was noted in the...

Covered wooden bridges proliferated in the United States in the mid-nineteenth century. Today an estimated 800 covered bridge structures remain, but they are nevertheless cherished links to the technological heritage of the United States. The through-truss designs vary from the Kingpost trusses built in the craft tradition to the engineered Burr arch and Paddleford trusses. Covered bridges are our links to the past and the pioneering bridge-building efforts, and as such, are considered important early American transportation structures to preserve for posterity. This paper provides an...

The specific gravity (SG) of wood is a measure of the amount of structural material a tree species allocates to support and strength. In recent years, wood specific gravity, traditionally a forester’s variable, has become the domain of ecologists exploring the universality of plant functional traits and conservationists estimating global carbon stocks. While these developments have expanded our knowledge and sample of woods, the methodologies employed to measure wood SG have not received as much scrutiny as SG’s ecological importance. Here, we reiterate some of the basic principles and...

Wood specific gravity is the single best descriptor of wood functional properties and tree life-history traits, and it is the most important variable in estimating carbon stocks in forests. Tropical pioneer trees produce wood of increasing specific gravity across the trunk radius as they grow in stature. Here, we tested whether radial increases in wood specific gravity were dependent on a tree’s diameter or its age by comparing trees of different diameters within cohorts. We cored trunks of four pioneer species in naturally regenerating, even-aged stands in the lowland, wet forests of...

Color, odor, and natural durability of heartwood are characteristics imparted by a class of chemicals in wood known collectively extractives. Wood is converted by the tree from sapwood to heartwood by the deposition of extractives, typically many years after the growth ring undergoing this change was formed by the tree. Extractives are thus not a part of the wood substance, nor do they play a major role in the mechanical strength of wood, but rather are additional materials added as a part of the natural aging process of the tree. Most commercial species that are valued for their appearance...