Nailed Mortised-Plate Connections for Small-Diameter Round Timber
Keywords:Small-diameter round timber, connections, power-driven nails, design value, failure mode
AbstractIn an effort to encourage the development of value-added engineered applications for smalldiameter round timber, research is being conducted at the US Forest Products Laboratory to develop and verify design guidelines for connections with specific application to round timbers. The objective of this study is to provide potential users with a number of viable connection options applicable to the fabrication of engineered, round-timber structural components and systems. Target uses include trusses, built-up flange beams, and space frames. This article presents information on a mortised steel-plate connection fabricated using power-driven nails in 150-mm-dia ponderosa pine. The article discusses methods used to determine per nail load capacity and to develop design procedures that incorporate that value in the determination of a multinail connection design value. These connections offer the advantage of low labor and material cost, ductile failure modes, and strengths in the range of 4.7 kN/nail. The failure of the connections was mode III nail failure and wood block shear failure. Joints that failed in block shear appeared to have roughly the same strength as those that failed from nail yield. The National Design Specification yield model for nails provides accurate predictions of joint capacity for nail yield-type failures and overestimates strength of joints that exhibit wood failure. Block shear capacity can be estimated on the basis of clear-wood strength and effective tensile and shear area of the connection.
AF&PA (2005) National design specification for wood construction. American Forest and Paper Association. Washington, DC.nASTM (1998) D2555. Standard test method for establishing clear wood strength values. American Society for Testing and Materials, West Conshohocken, PA.nASTM (2003) F1575. Standard test method for determining bending yield moment of nails. American Society for Testing and Materials, West Conshohocken, PA.nFPL (1999) Wood handbook—Wood as an engineering material. USDA For Serv Forest Products Laboratory, Madison, WI.nShim K-B, Lee D-S. (2005) The tensile properties for power-driven-nail connections for Japanese Larch small round timber. J Korean Wood Sci Technol 33(2):8-16.nWolfe R (2000) Research challenges for structural use of small-diameter round timbers. Forest Prod J 50(2): 21-29.n
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