Keywords: double-sided nail plate, embedding strength, finite element, sensitivity, stiffness.

Punched metal plate wood fasteners with projections on one side were invented and patented in the United States of America in 1952 by Carroll Sanford [1]. At that time, as is mostly the case at the present moment, they were primarily intended for roof and floor truss joint fabrication. The invention brought about a revolution in the trussed roof construction industry. The process of punched metal plate fastener manufacture was automated making it possible to punch out the teeth and shear the plate to the required dimensions at the same time, thereby driving down the cost of production. If the product range of punched metal plate fasteners is diversified, their benefits can be extended to other prefabricated wood structure components.

The wider scope of this study deals with the development of a prototype strip-type punched metal plate fastener, with projections on both sides. This type of fastener is referred to as "double-sided" to distinguish it from the conventional punched metal plate fasteners with projections on one side. Prior to this study, research on double-sided punched metal plate fasteners had been conducted in Poland and Germany and the fasteners were licensed in Poland [2]. These fasteners offer two distinct potential advantages over their single-sided counterparts, and these were identified as (1) improved joint fire resistance since the metal fasteners are sandwiched between the wood members connected, and (2) better joint aesthetics since the metal fasteners are concealed by the timber members connected.

However, product development of these fasteners is largely based on destructive joint testing. Dominance of this approach can be attributed to the limited capability for implementing fastener performance optimization using modeling approaches most commonly adopted for wood joints. Significant development cost savings can be realized by adoption of more appropriate modeling techniques to replace some of the joint tests. During the current studies, a finite element method-based inverse modeling technique was proposed for optimization analysis of a prototype double-sided fastener. The non-unique nature of the inverse model solutions makes assessment of model sensitivity to input material properties imperative. This paper uses parametric studies for sensitivity analysis of the joint modeling output. Joint stiffness is most sensitive to wood elastic moduli. Ultimate strength is significantly influenced by steel yield strength and wood embedding and shear strengths. The coefficient of friction, steel yield strength, wood shear and embedding strengths have significant effects on joint slip.

1

Wolfe R.W., Stahl D.C., Cramer S.M., "Experimental assessment of wood trusses with square-end webs", Research Paper FPL-RP-544, Forest Products Laboratory, USDA, Madison WI, USA, 1996.

2

Malinowski C., "Untersuchung mit Nagelübeln als Holzverbindungsmittel - Teil 1: Versuche zur Ermittlung einer günstigen Formgebung und geeigneter Anwendungsbereiche", Bauen Mit Holz, 1/85, 1985. (Translated by Riederer J. as: "Research about nail dowels as timber fastener - Part 1: Experiments to examine a promising design and suitable fields of application", July 2004.

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