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Re: Positive connection

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Joe,

With all components adequately designed, it is a positive connection as it 
properly restricts the structure movement and does not rely on friction.

Thanks,

______________________________
V. Steve Gordin PhD
Licensed Structural Engineer
SGE Consulting Structural Engineers
2081 Business Center Drive #105
Irvine CA 92612
949-552-5244
sgordin(--nospam--at)sgeconsulting.com

On Apr 21, 2014, at 10:01 AM, Joseph Gmail <jrgrill55(--nospam--at)gmail.com> wrote:

> So, after reading all that, would you consider the shear key a "positive"
> attachment?
> 
> Joseph Grill
> 
> On Apr 21, 2014, at 11:49 AM, Steve Gordin <sgordin(--nospam--at)sgeconsulting.com>
>> wrote:
>> Good morning,
>> 
>> The question arose during a plancheck for one of my designs, and was 
>> related to the issue of whether a concrete shear key (or similar component) 
>> can be classified as a positive connection for a pedestrian bridge - even 
>> though it is not a steel attachment and allows some movement.
>> 
>> I got the reply from AISC Solution Center (below) this morning. Apparently, 
>> they did quite a research…
>> 
>> At the end of the day, the term appears to directly correlate to the
>> Merriam-Webster's definition of "positive:" formally laid down or imposed; 
>> fully assured;
>> independent of changing circumstances;
>> relating to or constituting a motion or device that is definite, unyielding, 
>> constant, or certain in its action; not fictitious;
>> directed or moving toward a source of stimulation.
>> Evidently, some smart engineer once coined the term - but forgot to define 
>> it...
>> 
>> They way I see it now, the definition for the positive connection should
>> be something like: "A structural connection against all applicable forces 
>> that is fully assured without the consideration of friction."
>> 
>> Have a good week,
>> 
>> Steve
>> 
>> ______________________________
>> V. Steve Gordin PhD
>> Licensed Structural Engineer
>> SGE Consulting Structural Engineers
>> 2081 Business Center Drive #105
>> Irvine CA 92612
>> 949-552-5244
>> sgordin(--nospam--at)sgeconsulting.com
>> 
>> Begin forwarded message:
>> 
>>> From: "Solutions Center" <Solutions(--nospam--at)aisc.org>
>>> Subject: RE: Positive connection
>>> Date: April 21, 2014 5:38:02 AM PDT
>>> To: <sgordin(--nospam--at)sgeconsulting.com>
>>> 
>>> 
>>> Steve,
>>> 
>>> 
>>> It does not appear that the AISC Specification, or the IBC define 
>>> “positive connection”.  In fact, the only place that I found that 
>>> provided a definition is in the FEMA E-74 document “Reducing the Risks 
>>> of Nonstructural Earthquake Damage, Section 6.6.1 Positive Connections. 
>>> There it states: “The objective of nonstructural anchorage or restraint 
>>> details is to provide what engineers refer to as a positive connection 
>>> between the item and a hard attachment point, such as a structural wall, 
>>> braced partition, concrete floor, or built-in countertop. Positive 
>>> connections generally consist of some combination of screws, bolts, 
>>> cables, chains, straps, steel angles, and other steel hardware that 
>>> transfer seismic loads to structural framing. Positive connections do 
>>> not rely solely on the frictional resistance produced by the effects of 
>>> gravity. Frictional resistance between the base of an object and the 
>>> floor or mechanical friction connections such as C-clamps or thumbscrew 
>>> clamps are not considered positive connections. The most common nonstructural 
>>> connection details for wall attachments, floor or ceiling attachments, 
>>> countertop attachments, and attachments between adjacent items are 
>>> discussed below. GENERAL INTEREST SIDEBAR Earthquake Forces Keep in mind 
>>> that although heavy objects are hard to move by hand, their weight (mass) 
>>> interacts with the shaking (accelerations) of an earthquake to produce 
>>> large inertial forces. Those forces mostly act sideways to make the 
>>> object slide or tip, and there are also vertical motions in earthquakes 
>>> that temporarily "lighten" an object and reduce frictional resistance.” 
>>> You can find this online at <http://cirrus.mail-list.com/seaint-seaosc/09421005.html> 
>>> Also, the term positive connection is sometimes used in relation to the
>>> OSHA regulations related to rigging and lifting, though I was unable to
>>> find a definition supplied by OSHA or even the use of this exact term 
>>> in the regulations – though I may have missed it. It can be inferred 
>>> from the context in which the term is used that a positive connection 
>>> is one which cannot accidentally become disengaged (i.e. slide off). For 
>>> instance OSHA seems to deem a shackle through a lifting lug to be a 
>>> positive connection, but a sling around a trunnion is not a positive 
>>> connection. I suspect the term is typically not used in conjunction with 
>>> the regulations related to steel erection since bolts provide a positive 
>>> connection and regulations relative to their use in steel erection are 
>>> pretty explicit. This definition of positive connection is also used 
>>> informally in other applications. The term positive connection can also 
>>> refer to electrical continuity and is also used this way in OSHA 
>>> documents.” I hope this helps.  Please let me know if you have any 
>>> additional questions. Sincerely, Carlo Lini, P.E., LEED AP BD+C Staff 
>>> Engineer American Institute of Steel Construction 866.ASK.AISC lsm/eng 
>>> How did we do? Your opinion matters to us: www.aisc.org/TellAISC for 
>>> your chance to win a free Steel Construction Manual! This document has 
>>> been prepared in accordance with information made available to the 
>>> American Institute of Steel Construction at the time of its preparation. 
>>> While it is believed to be accurate, it has not been prepared for 
>>> conventional use as an engineering or construction document and should 
>>> not be used or relied upon for any specific application without competent 
>>> professional examination and verification of its accuracy, suitability, 
>>> and applicability by a licensed engineer, architect or other professional. 
>>> AISC disclaims any liability arising from information provided by others 
>>> or from the unauthorized use of the information contained in this document. 
>>> 

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