Treesearch

Fire-retardant-treated (FRT) plywood used as roof sheathing has exhibited strength degradation in some situations. The cause appears to be certain fire retardant chemicals that are activated under environmental conditions of high temperature and moisture content. This report describes how fire retardants are made, how they work, and what causes strength degradation of FRT wood. We present guidelines for selecting and using FRT wood and precautions to follow when designing roof systems with FRT plywood.

For 65 years, the Forest Products Laboratory (FPL) in Madison, Wisconsin, has had a continuous and extensive program of research on finishing wood for outdoor use. The research has stressed the fundamental aspects of wood weathering and the interactions of pretreatments and finishes on wood surfaces. This report outlines the history of the FPL wood finishing research program, including the perspective of Dr. Frederick L. Browne, the program’s leader during the strategic years from 1922-1963. We describe the early research that established the important role of the wood substrate in finish...

This report presents national measures of forest productivity for timber. These measures reveal trends in the relationship between quantity of timber produced by forests and the quantity of forest resources employed in timber production. Timber production is measured by net annual growth of timber and annual timber removals. Measures of timber productivity include annual growth per acre and indexes of growth/inventory and removals/inventory. Information is presented separately for softwood and hardwood timber. National timber data are obtained from national compilations of Forest Service...

Plywood manufacturing costs have increased over the years with inflation. In recent years, new technologies that improve productivity and reduce costs have become available. Cost data published by the American Plywood Association (APA) show moderating rates of increase by 1983. New data from a sample of western U.S. mills show that nonwood manufacturing costs have decreased since the 1983 APA estimates. Costs for sanded-plywood mills declined by 12 to 17 percent between 1983 and 1988, while sheathing costs declined by 8 to 9 percent. Sheathing mills were not included in this analysis....

The first report of a three-part series that covers results of a full-scale roof assemblies research program. The focus of this report is the structural performance of truss assemblies comprising trusses with abnormally high stiffness variability and critical joint strength. Results discussed include properties of truss members and connections. individual truss stiffness and strength. and the structural performance of two full-scale truss roof assemblies. Findings support the use of linear models to predict the behavior of trusses used in residential roof assemblies. linear superposition...

An analysis of elastic buckling in beam-columns was undertaken to develop a general interaction equation for use in timber design. The derivation of a general buckling criterion and the determination of moment modification factors following the method of Southwell (1922) are presented. Biaxial bending, axial compression. and water ponding on flat roofs are all considered. Simple support is assumed. but results may be applicable to other support cases. The results are of interest to code developers and to designers of space frames, towers, and trusses, where biaxial bending and axial...

Two equations are presented that may be used to estimate a maximum investment limit and working capital requirements for the FPL low-cost solar dry kiln systems. The equations require data for drying cycle time, green lumber cost, and kiln-dried lumber costs. Results are intended to provide a preliminary estimate.

Electric moisture meters for wood measure electric conductance (resistance) or dielectric properties, which vary fairly consistently with moisture content when it is less than 30 percent. The two major classes of electric moisture meters are the conductance (resistance) type and the dielectric type. Conductance-t ype meters use penetrating electrodes that measure in a small volume, so moisture gradients may be deduced by repeated measurements at increasing depths. Dielectric-type meters use surface electrodes that do not puncture the wood surface, and can measure the moisture content of...

This report contains suggested dry kiln schedules for over 500 commercial woods, both temperate and tropical. Kiln schedules are completely assembled and written out for easy use. Schedules for several thicknesses and specialty products (e.g. squares, handle stock, gunstock blanks) are given for many species. The majority of the schedules are from the world literature, with emphasis on U.S., Canadian, and British publications. Revised schedules have been suggested for western U.S. and Canadian softwoods and for the U.S. southern pines. Current thinking on high- temperature drying (temperatu...

Current shear design technology in the United States for lumber or glued- laminated beams is confusing. This report summarizes shear stress and strength research including both analytical and experimental approaches. Both checked and unchecked beams are included. The analytical work has been experimentally verified for only limited load conditions and span-to- depth ratios. Future research is required to better define the effects of beam size, load configuration, checks, and combined stresses on shear design.