Determination of Net Section Properties of Metal Truss Plates

The only load carrying material between two pieces of wood butted at the bottom chord splice is the perforated metal plate. In the design of any metal truss plate, the determination of the net section properties should be one of the first areas of investigation. A method of physical testing combined with an analytical approach was used in determining the effective net section of the TECO Fibre Grip Truss Plate. A series of tests were performed on truss plates having teeth punched out of the center section of the plate. These specimens were pulled in direct tension to determine the load capacity for each specimen. Solid section plates were also pulled in direct tension to determine their load capacity. A ratio was then formed by using the perforated plate ultimates stress as the numerator and the solid plate ultimate stress as the denominator. The drop of the beam method for determining yield point load was ineffective, so it is recommended that the divider method (ASTM A-370) be used as a fast accurate method of determining yield point on similar future tests. Determination of a ratio based on perforated plate stress over solid plate stress is an effective and realistic way of determining the net section properties of light-gauge metal truss plates. For the widths of plates tested, it does not appear that plate width is an influencing factor in net section properties. This may not be the case if different sheets of steel are used since there may be more variation between sheets than within sheets.

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