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Re: Question about Shear wall aspect ratio[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: Re: Question about Shear wall aspect ratio
- From: "erik gibbs" <erik.gibbs(--nospam--at)gmail.com>
- Date: Wed, 6 Feb 2008 12:29:59 -0800
The code requires the shear walls to meet the aspect ratio of table 2305.3.4. The manufactured shear walls – Simpson, hardy frame – as used in most design, does not meet this requirement. Is this an issue some of you are facing and how do you go around the building department that is requesting that the code aspect ratio requirement be met. The code does not waive the aspect ratio requirement for walls tested for dynamic loads.
From: Benjamin Maxwell [mailto:enginerd666(--nospam--at)yahoo.com]
Sent: Wednesday, February 06, 2008 10:54 AM
Subject: Re: WARNING against using Staples in shear walls/diaphragms
To speak to your questions regarding the CUREE tests I had the following thoughts:
The deformation issues described most likely relate to the differences in nonlinear deformation capacity of the two systems. The CUREE tests indicate that the stapled diaphragms do not have the same inelastic deformation capacity as a nailed diaphragm - meaning the stapled diaphragm would see a significant reduction in strength at a lower drift than the nailed diaphragm - independent of span ratios and plywood gaps and what have you. This implies less available ductility in the system and less robust hysteretic damping, i.e. reduced or nonequivalent performance.
May be true that a stapled diaphragm is harder to rip apart from its supporting framing, but this strength is not a complete picture of the system's intended seismic performance. Strength alone does not make the system work as needed.
Adding more staples to diaphragm would certainly make it stronger, but it seems from the information Thor passed along that it may not make it more capable of dissipating the additional absorbed energy in a meaningful way. Added strength and stiffness will help you absorb more elastic energy, but not necessarily the capacity to dissipate it.
What seems to me to be the case with the stapled diaphragm performance is that the size (diameter) of the individual connectors at the interface between the plywood and stud framing has a profound, and possibly yet unconsidered, affect on the overall system seismic performance.
Your final comments regarding the tests as SJSU underscore the complexity of plywood shear wall lateral load-resisting systems. The inter-related nonlinear behaviors of the plywood diaphragm and the tensile yielding (hopefully not pull out) of the hold down anchors is surely a difficult challenge to properly capture, especially without creating code-required design practices that could push the economy of wood-framed design into an undesirable place.
My first impression of stapling plywood is that it may be a better system than nails. Design factors may need to be re-considered. My strongest concern is corrosion of the staple, not its resilience in a seismic event. A water repair should include a review of the staples.
Following are what I intend to find answers for and these are followed by some facts that can help.
What spans are the drift values for?
When is the drift limited by the gaps between the panels edges?
If drift exceeds 1", how probable is it to not witness a permanent deflection? Is a nailed diaphragm allowed to remain if there is evidence of a 1" drift?
Over the shorter distance of the staple drift could the staple demonstrate a higher resistance than the nail and absorb more energy? Could more staples develop this equivalent energy absorption?
What are the COLA/SEAOSC and CUREE test methods as they relate to the above questions.
I have talked to a contractor who I had remove a stapled diaphragm. The stapled plywood, was twice as difficult to remove than a similar nailed system. That suggests that when panel edges bind it might be more likely for a nailed panel to separate, out of plane, from the framing.
Like gypsum, there might need to be more staples. Gypsum, with the proper design penalties and correctly installed, can out perform the equal plywood option.
Lately I have heard of testing of shear walls, at SJSU. Inadvertently, they discovered the shear wall nails were not yielding before the hold-downs failed. That probably results in little energy absorption. Could it be that we cannot rely on the code design benefits of nail yielding when brittle hold-downs trump the energy absorbing capacity?
David B Merrick, SE
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- WARNING against using Staples in shear walls/diaphragms
- From: mrkgp
- Re: WARNING against using Staples in shear walls/diaphragms
- From: Benjamin Maxwell
- RE: Question about Shear wall aspect ratio
- From: Gautam Manandhar
- WARNING against using Staples in shear walls/diaphragms
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