News
Recent information on the field
ISANTA Clipped-Head Nail Study
Researchers who tested clipped-head and casing nails at Virginia Polytechnic University found
that clipped-head nails perform just as well as full round-head nails. They tested plywood
specimens nailed to lumber and loaded in shear, which reflects how nails connecting shear
panels to wood framing would be loaded.
The following is from the Conclusions section of their study:
It should be noted that the results of these tests go against what common engineering judgment would predict. Without further knowledge of the testing procedures and results, we recommend using full round-head nails.
You may e-mail ISANTA at Isanta@Ameritech.net or telephone them at (708) 482-8138 and request a copy of the study, which is titled "Cyclic Tests of Casing and Clipped Head Nail Connections."
The following is from the Conclusions section of their study:
"...there is not a satistically significant difference between the clipped-head and full-head
nails, regardless of the orientation of the clipped edge with respect to the load or plywood
face-grain direction."
It should be noted that the results of these tests go against what common engineering judgment would predict. Without further knowledge of the testing procedures and results, we recommend using full round-head nails.
You may e-mail ISANTA at Isanta@Ameritech.net or telephone them at (708) 482-8138 and request a copy of the study, which is titled "Cyclic Tests of Casing and Clipped Head Nail Connections."
"Green" Framing Lumber used in Shear Walls
Section 3.1.3 of the Shear Wall Construction Guide mentions that the strength of nails driven
into green lumber (lumber with a moisture content of 19% or more--usually "S-Grn" appears in the
grade-stamp) will have less strength than nails driven into dry lumber. The APA tested eight shear
walls, six framed with green lumber and two with seasoned lumber. They report that the ultimate
strength of the walls was not significantly different. However, they say that the stiffness of the
shear walls built with green lumber was less than the walls built with dry lumber. Remember that
stiffness is very important in preventing damage to building finishes.
For more information, see APA's Technical Bulletin TT-075 and APA Report T21002-53
For more information, see APA's Technical Bulletin TT-075 and APA Report T21002-53
Shear Walls with Sloping Top Chords
Appendix B of Wood-Framed Shear Wall Construction--an Illustrated Guide discusses the correct way
to analyze an isolated shear wall that is taller at one end than the other. Since sloping shear
walls are rarely isolated, other parts of the structural system will usually help keep the shear
wall from failing if it is not designed properly.
One structural engineer and researcher in the field of earthquake design had this to say: "What you are showing is one small part of a folded plate diaphragm system that I do not think any of us really understand at this point.... Because roof diaphragms are not a significant source of earthquake damage, they are not currently a high priority for testing, so we remain trying to develop mehcanics-based models without really knowing."
Engineers do analyze wood-framed systems by making many simplifications. But the shear wall will suffer more damage than the roof diaphragm because the forces in the roof diaphragm get "concentrated" at shear walls.
Until someone comes forward with a more accurate analytical model or some test results that show how sloping shear walls really behave, engineers should analyze sloping shear walls in way that best reflects reality. This is the method presented in Appendix B of Wood-Framed Shear Wall Construction--an Illustrated Guide
Engineers and other brave technical types can find even further discussion in the "Appendix to the Appendix". This is included at the end of APPENDIX B.
One structural engineer and researcher in the field of earthquake design had this to say: "What you are showing is one small part of a folded plate diaphragm system that I do not think any of us really understand at this point.... Because roof diaphragms are not a significant source of earthquake damage, they are not currently a high priority for testing, so we remain trying to develop mehcanics-based models without really knowing."
Engineers do analyze wood-framed systems by making many simplifications. But the shear wall will suffer more damage than the roof diaphragm because the forces in the roof diaphragm get "concentrated" at shear walls.
Until someone comes forward with a more accurate analytical model or some test results that show how sloping shear walls really behave, engineers should analyze sloping shear walls in way that best reflects reality. This is the method presented in Appendix B of Wood-Framed Shear Wall Construction--an Illustrated Guide
Engineers and other brave technical types can find even further discussion in the "Appendix to the Appendix". This is included at the end of APPENDIX B.
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