Harris-Structural
Civil/Environmental
- Apr 5, 2023
- 1
Hi everyone, we investigated OSB Truss Gusset plates and made a quick calculator for gusset plate design. The calculator has six different connections including the heel connection and various other typical truss connections. We are throwing this to the wolves to see what the engineering community thinks about it and see if they find any errors or missing design calculations or theories. The calculator checks the number of nails required in each member and OSB shear strength.
We based our design on several other Eng-Tips articles regarding OSB gusset plates. OSB strengths are based on the APA Panel Design Specification, and have variable strengths depending on the direction of force. We only specify Oriented Strand Board (OSB) because the shear values through-the-thickness are nearly double compared to plywood. Nail capacity is based on the online AWC Connection Calculator. OSB is placed on both sides and nails penetrate through all layers of OSB and wood and have crimped ends, thus providing double shear strength for the nails.
An article in the November 2008 Edition of the Structure Magazine by Steven E. Fox, titled Repair of Wood Trusses offers good guidelines for OSB shear strength. The idea behind it is similar to the Whitmore Section theory of steel gusset plate design, where forces concentrate based the required compression/tension width of the OSB. Combining this idea with Truss Plate Institute manual ANSI/TPI 1-2014, Section 8.5, in order to prevent shear buckling of the OSB in unsupported areas, the unsupported areas are considered to have no shear strength except for a triangular area a, which is equal to 27 times the thickness of the OSB. Shear lines are assumed to be parallel with all joint connections. Also see section 8.3.2.2 for a Heel Reduction Factor to help resist moment effects at Heel connections.
The calculator is not perfect, especially when it comes to calculating the number of nails in the connection. We found that it is best to draw each connection and find the number of nails based on the connection geometry.
Let me know if the file attachment link isn't working.
We based our design on several other Eng-Tips articles regarding OSB gusset plates. OSB strengths are based on the APA Panel Design Specification, and have variable strengths depending on the direction of force. We only specify Oriented Strand Board (OSB) because the shear values through-the-thickness are nearly double compared to plywood. Nail capacity is based on the online AWC Connection Calculator. OSB is placed on both sides and nails penetrate through all layers of OSB and wood and have crimped ends, thus providing double shear strength for the nails.
An article in the November 2008 Edition of the Structure Magazine by Steven E. Fox, titled Repair of Wood Trusses offers good guidelines for OSB shear strength. The idea behind it is similar to the Whitmore Section theory of steel gusset plate design, where forces concentrate based the required compression/tension width of the OSB. Combining this idea with Truss Plate Institute manual ANSI/TPI 1-2014, Section 8.5, in order to prevent shear buckling of the OSB in unsupported areas, the unsupported areas are considered to have no shear strength except for a triangular area a, which is equal to 27 times the thickness of the OSB. Shear lines are assumed to be parallel with all joint connections. Also see section 8.3.2.2 for a Heel Reduction Factor to help resist moment effects at Heel connections.
The calculator is not perfect, especially when it comes to calculating the number of nails in the connection. We found that it is best to draw each connection and find the number of nails based on the connection geometry.
Let me know if the file attachment link isn't working.
