Recent discussions about studrail design refers.
Note that Ram Concept has the ability to design studrails according to the provisions of the ACI 318-08 (or previous versions if you're so inclined) . Previous codes had "speed bumps" allocated such that
The issue is this: The Decon Studrail ICC report limits the Vc to =< 1.5(f'c)^0.5...!!!! WTH... That means that we could conceivably design stud rails all the way at 3(f'c)^0.5 - when in fact the product to be installed (including all look-alikes) are limited to 1.5(f'c)^0.5 by approved ICC docs. ICC claims that this limit is inherent in the ACI 421 code which references that limit in relation to earthquake loads... not sure of the context... do not have a copy of this doc...!
So given the lack of clarity and direction on this issue at this point (i called Decon and ICC - no real direction coming from any of them!) - we have decided at CTE to limit our studrail designs to the 318-05 version - which includes the 2* and 6* limits...
Note that Ram Concept has the ability to design studrails according to the provisions of the ACI 318-08 (or previous versions if you're so inclined) . Previous codes had "speed bumps" allocated such that
- Vc =< 2(f'c)^0.5 (Concrete strength) and,
- Vn =< 6(f'c)^0.5.
- Vc =< 3(f'c)^0.5 and
- Vn =< 8(f'c)^0.5.
The issue is this: The Decon Studrail ICC report limits the Vc to =< 1.5(f'c)^0.5...!!!! WTH... That means that we could conceivably design stud rails all the way at 3(f'c)^0.5 - when in fact the product to be installed (including all look-alikes) are limited to 1.5(f'c)^0.5 by approved ICC docs. ICC claims that this limit is inherent in the ACI 421 code which references that limit in relation to earthquake loads... not sure of the context... do not have a copy of this doc...!
So given the lack of clarity and direction on this issue at this point (i called Decon and ICC - no real direction coming from any of them!) - we have decided at CTE to limit our studrail designs to the 318-05 version - which includes the 2* and 6* limits...
3 comments:
As it turns out, we do have a copy of ACI 421R99... Someone (Pete) should look into it...!
So the latest is:
We are still having issues. The latest ICC acceptance criteria (AC395) was revised in May 2011. The ICC appear to have revised their AC criteria, and now i cannot find a reference to the ACI421-99 - that was the genesis for the 1.5(f'c)^0.5 in the first place. Instead, the AC refers to ACI 318-08, and references 3.5.5, 7.7.5, 11.11.5, 21.3.6.8, 31.13.6(b) and table 12.12-1 of this code.
I remain flabergasted that the code is CONTINUING (this issue has been around for over 5 years as far as i can tell)to be subverted in favor of a status quo - even though this issue has been challenged repeatedly (i am led to understand).
To repeat the basic point: The ACI421 points out in chapter 8 how stud rails perform well in seismic situations - even at drift limits in the 3% - 7% range - they perform in a ductile fashion without failure! In this context, the Vc =1.5(f'c)^0.5 is used - my interpretation is to use a reduced Vc when drift is excessive.
Our situations are generally concrete or CMU shearwalls where drift is pertty close to 0! In this case very little (induced) moment is generated, and the requirement for the 1.5* appears moot!
The ACI 318-08 seems to handle this (drift issue) in the 21.3.6 - where it essentially required a min Vs requirement AND a requirement that the stud rails extend out AT LEAST 4xslab-depth - UNLESS your shear ratios are manageable OR your drift is not a problem... DUH...!
Do we REALLY need more than this...!
Feel free to ping back in the comments.
So i discovered today that there is an update to the ACI421.1 - it is revision R-08.
Since this aspect of our PT design has been prominent and is generating signficant discussion and insterest, we should be sure to have the latest copy in our office and pay attention to it.
I'll ask Andre (or someone) to get us a record copy.
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