Evaluation of Extended Wall OSB Sheathing Connection: Combined Uplift and Shear Loading for 24-inch Heel Trusses

A new study has been published, Evaluation of Extended Wall OSB Sheathing Connection under Combined Uplift and Shear Loading for 24-inch Heel Trusses, by Vladimir Kochkin and Andrew DeRenzis from the Home Innovation Research Labs, Upper Marlboro, Maryland, and FPL’s Xiping Wang.

According to Norbord, Inc. (Toronto, Ontario), home builders in high-wind areas are increasingly frustrated by the large number of metal hold down devices (hurricane straps) required between floors on exterior walls. In addition to the expense and additional labor required to install such devices, they often experience nailing interference problems with the wood structural panel sheathing or siding, or both. Wood structural panels can be used to resist both shear and uplift.

The present study was designed to evaluate the performance of the extended wall structural panel connection in resisting combined uplift and shear forces at the roof-to-wall interface with a focus on a truss heel height of 24 inches to address the expected increases in the depth of attic insulation used in Climate Zones 5 and higher. Five full-size roof–wall assemblies were constructed with extended oriented strandboard (OSB) wall sheathing and each was tested under a different loading combination.

fig_01

Test specimen and setup.

The test results indicate that using extended wood structural panel wall sheathing as the primary connecting element (without additional connecting hardware) at the roof-to-wall interface of energy trusses can provide a continuous load path in both the shear and uplift directions and can be considered a viable option for residential construction in most areas of the country. The overturning effects caused by increased truss heel heights up to 24 inches can be offset by additional face nails that attach the extended wood structural panel wall sheathing to the energy truss heel.

This study was Phase 3 of a test program that responds to the new requirements for roof-to-wall connections in the 2012 International Residential Code (IRC) and expands upon the previous phases that evaluated innovative roof-to-wall connection systems. The new IRC provisions specify complex details for attachment of rafters and trusses to the supporting walls. These new requirements, which apply to high-heel energy trusses even in the low-wind areas, are labor intensive and add cost to construction of light-frame wood buildings. A previous testing project conducted to evaluate optimized structural roof-to-wall attachment solutions demonstrated the effectiveness of wood structural panels in restraining high heel (i.e., energy) trusses against rotation. Further testing in Phase 2 confirmed the ability of oriented strandboard (OSB) wall sheathing panels extended over the roof heel to resist combined uplift and shear forces without additional roof-to-wall hardware.

Phase 3 builds upon previous testing by evaluating the performance of the extended wall structural panel connection in resisting combined uplift and shear forces at the roof-to-wall interface with a focus on a truss heel height of 24 inches to address the expected increases in the depth of attic insulation used in Climate Zones 5 and higher. The results of this study are expected to further expand prescriptive construction solutions optimized for performance from the standpoint of structure, energy, and ease of construction.

The specific objective of the Kochkin and others study was to develop an uplift-shear capacity interaction curve for extended wood structural panel wall sheathing used as the primary connecting element at the roof-to-wall interface with 24-inch-high energy truss heels.

Curve

This figure shows the uplift versus shear capacity interaction curve based on the test results. For comparison, the figure also includes a linear interaction.