Screw Buckling Values for Compression Perpendicular to Grain Reinforcement
This white paper addresses the challenges faced by engineers and designers in North American mass timber design in selecting efficient members, particularly in relation to compression reinforcement perpendicular to grain using self-tapping screws. The current design standards in the US and Canada lack comprehensive methodologies for this specific application, necessitating the adaptation of European design equations and the development of new approaches tailored to North American mass timber construction.
The article highlights the limited literature and standardization available regarding screws loaded in compression in wood, especially in comparison to the extensive research on their tension, shear, and withdrawal applications. To fill this gap, the study conducts a series of tests on fully threaded ASSY screws in glulam specimens. These tests focus on screws installed at 90 degrees to the grain direction in various wood species, including Black Spruce, Douglas-Fir, and Southern Yellow Pine.
The findings of the tests serve as the basis for establishing allowable screw buckling values and factored design values for LRFD/LSD through ASTM D5457.
North American standards often require empirical test results for acceptance, and the European equations used for screw buckling may not be recognized by authorities having jurisdiction. The study’s contributions lie in providing engineers and designers with practical guidance backed by empirical data and derived design values specifically for screws loaded in compression as compression reinforcement perpendicular to grain. It fills the existing literature gap, offering valuable insights into the behavior of self-tapping screws under compression loads. The design values provided here can be referenced when following the Reinforcement Design Guide.
In conclusion, this study aims to optimize member selection efficiency by offering reliable data for incorporating self-tapping screws as reinforcement in bearing connections in glulam or CLT. By addressing the limitations of current design standards and providing practical guidance, the research supports engineers and designers in North America in achieving efficient and effective mass timber connection designs.