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Re: '97 UBC and Proprietary Shearwalls[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: Re: '97 UBC and Proprietary Shearwalls
- From: Seaintonln(--nospam--at)aol.com
- Date: Sun, 15 Aug 1999 14:56:05 EDT
In a message dated 8/15/99 11:23:34 AM Pacific Daylight Time, chuckuc(--nospam--at)dnai.com writes: << Dennis -- Why not tell the architect we now need a minimum aspect ratio of 2:1 for shearwalls. >> Chuck, When an owner pays a million or more for a custom home on a golf course, the last thing they are willing to accept is a shearwall that will block their view. The public is uneducated in the importance of structural engineering. This is where the creativity of the engineer comes into play. It is simply an uphill battle with the engineer losing as he tries to restrict the creativity of the architectural industry. I've used Hardy Frames on five homes now. On each project where plywood shear walls were used, the contractors simply disregarded the plywood wall's integrity and thought nothing of cutting through sole plates to install stacks, plumbing, electrical or drains. It was not a matter of what was noted on the plans as there were sufficient notes on every detail and sheet to prevent this type of damage. Care was taken to double stud plumbing walls to prevent damage to shearwalls and much more. Besides, there were simply not enough walls to relocate the plywood shearwalls so that stacks and protrusions could be considered. The fact is that the Hardy Frames are more consistently constructed and predictable than plywood shear walls. Considering the limitations in width and heights, the stiffness is also predictable (if interpolation is acceptable). <Sheathed shearwall's have a multitude of virtues: a long history of good performance, great redundancy, excellent damping characteristics, some idea about appropriate design load values, good economics, and the carpenters know how to build them (more or less). You cannot say the same for Hardi-frames.> I don't think you need to ignore a new product simply because it does not have a historic track record. The fact is that it has more tests to support it's performance (I believe the tests were done at U.C. Irvine) than is possible with plywood shearwalls due to the number of materials and variables to consider. Regardless of all of the good values for plywood, the practical side is that the contractors destroys most of its value by overdrilling and overnailing. It did take contractors in my area time to get used to the Hardy Frame, but once they did, they believed that the installation was easier and cleaner than plywood - with less hassle from the building inspector. Yes, there are other opinions on proprietary shear walls, but only time will really tell on these. As long as the test reports are supported in approved ICBO reports and City approvals, I see no reason why they should perform any worse than historical, conventional plywood walls. I might be out in left field here, but I simply don't see where the holddown deflection (other than if installed incorrectly) makes much difference from one connector to another. I think that the nail elongation and wall racking has much more effect on the wall's deflection than the difference between 0.0625" and maybe 0.09" for da. What do the tests that Simpson has done show. Is the largest deformation in the deflection formula from holddown elongation? Dennis
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