by Robert J. Leichti and Robert L. Ethington
This is an abridged version of a paper by David Green, Robert Ethington, Edward King, Jr., Brad Shelley, and David Gromala
that will appear in Forest Products Journal, 2004, vol. 54, no. 9, pp. 8-18.
The United States is the worlds leading producer and consumer of wood products. This demand for (mostly) construction material has led to better utilization of wood, the development of improved grading practices, and improved engineered wood products. Solid-sawn lumber continues to provide the bulk of structural lumber products used in construction, but, in addition, engineered wood products such as laminated veneer lumber and parallel strand lumber are being substituted for solid-sawn lumber. Large-diameter timbers are increasingly difficult to obtain, and products from them are often replaced by prefabricated wood I-joists and glued laminated, or glulam, beams. Plywood once replaced solid-sawn wood for sheathing material, and oriented strandboard has now largely replaced plywood. Compared to 100 years ago, the use of forest resources in the United States includes a more diverse array of species and trees with smaller diameters.
Wood was a useful material long before Europeans set foot in North America. By 1900, commerce in wood products had developed, in both sophistication and geographic reach, to the degree that standardization promised better consumer satisfaction and buyer/seller understanding. Since the early 1900s, a system of codes and standards has been developed for lumber and wood products to assure quality and reliability. ASTM International Committee D07 on Wood has played a vital role for 100 years in this system.
The Beginning: 1904 - 1929
At the 1904 annual meeting of the then-six-year-old American Society for Testing and Materials, a motion was adopted for the formation of a committee on specifications for the grading of structural timber.
In the spring of 1905, a group of 12 men met to organize ASTM Committee Q on Standard Specifications for the Grading of Structural Lumber, the seventh technical committee to be formed. A report on the activities of Committee Q was presented by Herman von Schrenk at the eighth annual ASTM meeting. The report read in part:
- It is believed that the time has come for a comprehensive study and analysis of the grading of structural timbers, so as to arrive at a general understanding of the qualities of the various woods used for structural purposes, in order to standardize as far as possible, for the use of lumber manufacturers on the one hand, and architects and engineers on the other hand, the various grades and qualities of wood.
In September of 1907 the first standard developed by Committee Q, D 9, Specification for Structural Timbers, was approved by Society ballot. The standard contained a definition of structural timber, definitions of standard defects, a list of standard names for structural timbers, and specifications for bridge and trestle timbers.
The year 1910 brought a name change for Committee Q to Committee D07. A Standard Specification for the Grading of Yellow-Pine Bridge and Trestle Timbers was approved, and work on similar standards for Douglas fir and western hemlock were in progress. Committee activities were changing to meet other challenges, especially with respect to preservative treatment of railroad ties and structural timbers. Some of the enduring standards approved over the next few years included a specification on the physical characteristics of round timber piles, standard methods of sampling and analysis of creosote oil, wood paving blocks for exposed pavements, and determination of the flashpoint of hazardous liquids under laboratory conditions. In the 1920s, several key standards emerged that focused on sampling, testing and analysis to derive design properties for sawn timbers.
Wood products standardization in the early years of the 20th century was not the exclusive domain of ASTM. Rather, there was close cooperation between Committee D07 and other organizations promoting standardization, such as the Department of Commerces Central Committee on Lumber Standards, the American Wood Preservers Board, and the American Wood Preservers Institute. Many members of D07 were also members of these other organizations. World War I brought a great deal of attention to the benefits of standardization.
Great Depression and War: 1930 - 1954
As time passed, some standards were modified and improved; others disappeared altogether. The decade of the 1930s is probably most recognized for the Great Depression and the prelude to World War II. As the decade opened, Committee D07 had developed four standards related to wood preservation, which are still in print, and five standards related to solid wood. The preservative standards dealt largely with creosote measurement and quality. The other standards dealt with wood terminology, testing small clear specimens, testing timbers in structural sizes, visual stress grading (that is, sorting lumber by quality classes with associated allowable properties), and specifications for round timber piles.
The research that underpinned the standards continued, perhaps at a reduced level, during this quarter century, and some research programs were concluded and published during the 1930s. But the slow business climate probably kept the industry component of D07 mostly on the sidelines, and with that minimal participation no new ASTM wood standards were promulgated until 1949, well after WWII. The focus for D07 standards through WWII, then, was on solid-sawn lumber and wood preservation.
However, the existing standards were used increasingly during that period. It was possible to classify structural timbers into grades that had reasonable uniformity and fairly definite minimums of strength. In turn, engineering principles could be used in design, although this prerogative was probably not practiced to any extent because most lumber was sold in yard grades for which no allowable property claims were made. The lumber industry had created the first national lumber standard in the United States. This standard relied heavily on the existing standards of D07 and in turn provided guiding principles for published trade association grading rules.
Evolution and Growth: 1955 - 1979
Standards on Mechanical Properties of Wood
Post-WWII demand fostered a rapid increase in lumber and plywood production, and the Federal Housing Administration required that lumber in houses meet ASTM D 245, Practice for Establishing Structural Grades and Related Allowable Properties for Visually Graded Lumber, if built to FHA standards. As more species were used for products in order to meet demand, a controversy developed about derivation of design properties for wood products. This set in motion at least two decades of research and development, much of it focused on sampling and analysis methods. Committee D07 was the center for codifying many of the results, and reorganized to meet this challenge. Some existing standards were extensively modified, and new standards on clear wood properties and statistical methodology were created.
Standards Development Takes Off
Forty-three new standards were developed by the committee after 1960, almost all of which continue to be published in updated form. This remarkable burst of activity occurred as regulatory agencies and user groups sought greater assurance that commodity wood products would provide satisfactory performance in service.
The 1970s saw the introduction of the first standards for deriving allowable properties for round timber piles. Lamination grades and species combinations and related design values were described for glued-laminated timber. Nineteen new specifications and test methods covering the content, analysis, evaluation, and treatment process for wood-preserving chemicals were introduced, including waterborne salt treatments, marking a time of accelerating demand for these clean treatments in construction. One of the most significant standards related to preservation issued in the history of Committee D07 is D 1760, Specification for Pressure Treatment of Timber Products. This standard is a virtual handbook of treatment and penetration/retention information of importance to manufacturers and users of treated wood products.
Test methods related to the properties of fire-retardant chemicals were developed in the 1970s. These include the durability of fire-retardant treatments of wood products under accelerated weathering and the use of interior fire retardant-treated lumber in roof systems.
The remaining 15 standards issued in this productive 25-year period deal with mechanical, physical, chemical, and machining test methods; simulated service testing for flooring; and terminology. Seven standards involve test procedures for evaluating individual properties of plywood. Another provides testing procedures for evaluating the withdrawal and lateral load resistance of nails, screws, bolts, and other types of connectors.
Rounding Out the Century
Committee D07 was spawned from a need for standardization of sawn lumber products, but wood and wood-based products are used in many products and assemblies. In the last half of the 20th century, the committee necessarily expanded its scope with the changes in the wood building products industry. As a result, relationships have been built with ASTM Committees D01 on Paint and Related Coatings, Materials, and Applications, D14 on Adhesives, D20 on Plastics, and E06 on Performance of Buildings.
In 1984, D07 was reorganized into six subcommittees: D07.01 on Fundamental Test Methods and Properties, D07.02 on Lumber and Engineered Products, D07.03 on Panel Products, D07.04 on Pole and Pile Products, D07.05 on Wood Assemblies, and D07.06 on Treatments for Wood Products. D07.07 on Fire Performance of Wood was added in the 1990s.
Standards developed during the last 25 years reflect the trend to define product sufficiency in terms of performance-based criteria. In some cases, these changes have resulted in new performance-based standards. In the same time frame, new engineered lumber-like products such as parallel laminated veneer lumber, oriented strandboard, and structural I-joists arrived on the scene. These products did not fit easily into the older prescriptive models for assigning allowable properties; they could be more easily accommodated by standards that set minimum product or test performance criteria.
At times, Committee D07 has been required to develop standards quickly in response to an urgent need. In the 1980s, some fire retardant treated lumber and panel products used in multi-family residential roof systems began to fail. Committee D07 quickly began to develop standards to evaluate the effects of fire retardant treatments on the structural properties of wood and wood-based products. In response to the urgency of the situation, the Test Method for Evaluating the Flexural Properties of Fire-Retardant Treated Softwood Plywood Exposed to Elevated Temperatures (now D 5516) was first approved and published as an emergency standard. Emergency standards (which are no longer used in ASTM) were a seldom-used option in the long history of D07, but it was clearly necessary in this case. Three additional standards dealing with fire-retardant-treated products were created by 2000.
During the 1980s, the wood products community also developed design methodologies that reflect the trend toward reliability-based design concepts. The adopted protocol is referred to as load and resistance factor design. In conjunction with the effort, Committee D07 created a new standard, D 5457, Specification for Computing the Reference Resistance of Wood-Based Materials and Structural Connections for Load and Resistance Factor Design, that provides a means for translating allowable properties developed according to earlier standards of D07 to an appropriate value and format for use with LRFD.
During this period a number of new standards were also adopted relating to the performance of connectors used for wood. These address metal shear plates, bolted connections and dowel fasteners and reflect major changes in the design of fasteners and the determination of connector performance.
Meeting the Challenges of the Future
As Committee D07 enters its second century, what are the prospects for the future? When we asked this question of people at the cutting edge of business, technology, and new product development, they identified four trends.
Multinational standards developing committees must assess the compatibility of standards from different countries. Differences in technical requirements, expressed in different terms and different languages, must be reconciled. The indirect implications of globalization are more profound. Manufacturers will continue to grow and consolidate. The needs of internationally focused companies will drive changes in U.S. standards development. These companies generally employ more sophisticated quality management systems than do smaller companies with a purely domestic focus.
When is a glulam beam no longer a glulam beam? The provisions of ASTM D 3737, Practice for Establishing Allowable Properties for Structural Glued Laminated Timber (Glulam), include hundreds of years of collective technical knowledge and manufacturing experience. However, even today, Committee D07 is testing the boundaries of this knowledge and experience. Is a glulam beam still a glulam beam when the tension ply on the outer face is laminated veneer lumber rather than sawn lumber? What if the entire tension zone is replaced with fiber-reinforced laminations?
In a more general sense, are there hidden limitations within our basic testing standards that make them unsuitable for use with composite products? These questions are already in the pipeline for D07s consideration. In addition, as the range of new products containing new combinations of materials continues to expand, we must be prepared to answer increasingly tough questions in this regard.
Standard Products vs. Product Standards
In the early days of Committee D07, the development of standard designations for commercial grades of lumber was a key goal. In a time when lumber was produced by thousands of small mills, it was in the best interests of both manufacturers and consumers to have standard grades and sizes available to the marketplace. This concept was carried over into standards for glulam and wood structural panels. However, when the next generation of engineered lumber-like products was presented to ASTM for standardization, companies were looking for something dramatically different. The companies introducing these products had invested heavily in their development. Patents typically covered many aspects of the products and their manufacturing techniques. Because of the many variables in manufacturing processes, it was generally accepted that each manufacturer should be responsible for evaluating the performance characteristics of its own production. This is in stark contrast to the approach used for visually graded lumber, in which fewer manufacturing variables impact structural performance.
The development of standards to cover engineered wood products presented D07 with a unique challenge achieving a balance in maintaining minimum safety levels and providing the manufacturer flexibility to optimize product performance. The difference between the old and new approaches is often contrasted as: The old system defines a standard product, while the new system establishes a product standard.
Some current standards are limited by the technology of the time in which they were developed. As testing hardware continues to evolve and data acquisition systems become more sophisticated, standards must evolve accordingly.
Historically, some conservatism was embedded in traditional designs as a result of the limitations of hand-based engineering calculations. As software-based designs continue to become more sophisticated, many structures will be designed with less conservatism, implying the need to review safety factors.
There seems little doubt that as electronic devices shrink in size, and capabilities increase, the impact on standardization will be dramatic in ways not currently obvious.
Committee D07 will continue to be challenged by product innovations, new materials, new technologies, and new regulations. Some future issues can be anticipated, and some will be thrust upon us. At stake in these issues will be public safety, economic vitality, efficient utilization of forest resources, and the competitive position of the U.S. economy. D07 has successfully faced these types of challenges in the past and is poised for the future. //
Copyright 2004, ASTM International