MECHANICAL PROPERTY ASSESSMENT FOR ESTABLISHING DESIGN VALUES OF WESTERN JUNIPER
Abstract
Western juniper (Juniperus occidentalis) is a conifer that is native to Oregon, California, Washington, Nevada, and Idaho. Juniper is highly decay resistant and, therefore, is a popular choice for fence posts and landscape timbers. Forest management practices over the past 100 yr have resulted in an immense population increase in western juniper stands, transforming the grasslands/sagebrush biome into juniper forests. Landowners have been encouraged to cut back western juniper to restore grassland habitat, but there is no major market associated with juniper lumber. This study assessed the mechanical properties of western juniper to develop its design values for inclusion in the National Design Specification. Small clear samples were prepared from juniper harvested from three locations in eastern Oregon, one location in northeast California, and one location in southwest Idaho according to ASTM D143 for compression, bending, and shear. Average strength values were calculated and compared with similar wood species. Most properties were similar to those of other species, but modulus of elasticity was significantly lower. Compressive properties of western juniper also differed, with compression parallel-to-grain being lower and compression perpendicular-to-grain being relatively higher. Differences between species might be attributed to cell wall structure and distribution of lignin in the cells. Design values for western juniper were calculated using the strength values to establish allowable properties for visually graded lumber.
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