Treesearch

Covered wooden bridges once dotted the landscape of the United States numbering 14,000 at one time as reported in the Federal Highway Administration’s Covered Bridge Manual. Today there are only 500 to 600 covered bridges remaining in the country, having survived hundreds of years largely as result of the roof structure which kept the bridge timbers dry. This paper reports on select number of existing covered bridges and current efforts to preserve and restore these historic structures. It provides an overview of the National Historic Covered Bridge Preservation (NHCBP) Program administered...

Several changes relating to timber bridges have been incorporated into the AASHTO-LRFD Bridge Design Specifications recently. In addition, the Federal Highway Administration is strongly encouraging an LRFD-based design approach for all new bridges in the United States. The Bridge Design Code in Canada was one of the first to adopt the limit states design philosophy, doing so many years ago. This paper presents an overview of the United States and Canadian bridge design codes, highlighting similarities and differences that relate to the design of timber bridges.

This paper discusses the effects of size and moisture content on stress wave properties of wood and evaluates the feasibility of using stress waves to E-rate Douglas-fir dimension lumber in green condition. Six size groups of Douglas-fir lumber were tested using both stress wave and static bending methods at different moisture levels, ranging from green to dry conditions. Stress wave speed increased continuously as moisture content decreased through the whole moisture range studied. General speed moisture relationships were developed to adjust stress wave speed values from one moisture...

Many timber trestle railroad bridges in Wisconsin have experienced deterioration and are in need of rehabilitation. In addition, the railroad industry is increasing the weights of cars. The combined effect of heavier loads and deterioration threatens to cut short the service life of timber bridges. One of the most critical problems that has been identified was the overloading of timber piles in bridges, which can be remedied by creating a stiffer pile cap. The goal of this investigation was to show that fiber reinforced polymer (FRP) strips fastened to timber with screws can be used to...

The goal of this study was to find the environmental impact of hardwood lumber production through a gate-to-gate Life-Cycle Inventory (LCI) on hardwood sawmills in the northeast and northcentral (NE/NC) United States. Primary mill data was collected per CORRIM Research Guidelines (CORRIM 2001). Lifecycle analysis is beyond the scope of the study.

Accurate determination of corrosion rates for threaded fasteners hinges on the ability to determine the surface area on which corrosion is occurring. Currently, no general analytical expression of surface area exists for the threaded fastener types. A recent voluntary withdrawal of chromated copper arsenate as the primary, long-standing preservative treatment for wood resulted in the need to determine the corrosion rates of threaded fasteners. This paper developed general analytical surface area equations for a wedge-shaped thread and the area between the threads for three cases: (1) an...

The Intergovernmental Panel on Climate Change (IPCC) provides guidelines for countries to report greenhouse gas removals by sinks and emissions from sources. These guidelines allow use of several accounting approaches when reporting the contribution of harvested wood products (HWP) under the United Nations Framework Convention on Climate Change. Using extensions of methods suggested by the IPCC and a software model called WOODCARB II in Microsoft Excel, this paper presents estimates of the U.S. HWP contribution to annual greenhouse gas removals in the agriculture, forestry, land use, and...

The anisotropy of wood creates a complex problem requiring that analyses be based on fundamental material properties and characteristics of the wood structure to solve heat transfer problems. A two-dimensional finite element model that evaluates the effective thermal conductivity of a wood cell over the full range of moisture contents and porosities was previously developed, but its dependence on software limits its use. A statistical curve-fit to finite-element results would provide a simplified expression of the model’s results without the need for software to interpolate values. This...

Forest products from improved trees grown on managed plantations and harvested in short rotations will contain higher proportions of juvenile wood than in current harvests. More information is needed on the influence of juvenile wood on lumber properties. Most information developed to date has concentrated on ultimate tensile stress, modulus of rupture, and modulus of elasticity. This paper shows for this sample of loblolly pine three-dimensional surfaces fit to test results for shear stress parallel to the grain, compression and tension stress perpendicular to the grain, and mode I...

Much of the research on wood-plastic composites (WPC) has focused on formulation development and processing while high biological durability of the material was assumed. The gap between assumption and knowledge in biodeterioration of WPC needs to be reduced. Although some information on the short-term resistance of WPC against biological degradation is available, long-term data are required in order to adequately evaluate the performance of these relatively new materials and to enable use of WPC for structural applications. The influence of abiotic factors on material performance also has...