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RE: Positive connection

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I would consider a connection to be positive if it does not rely on friction 
 OR gravity.  We learned decades ago what happened when unexpectedly large 
vertical accelerations accompanied horizontal accelerations.  Bridges moved 
 up, supports moved laterally, and then bridges went down much further than 
 they went up!

Larry M. Bryant, PhD
Principal Engineer
Applied Research Associates, Inc.
(678) 342-5471 (Atlanta)
(601) 638-5401 (Vicksburg)

________________________________________
From: seaint-seaosc(--nospam--at)mail-list.com [seaint-seaosc(--nospam--at)mail-list.com] on behalf 
of Steve Gordin [sgordin(--nospam--at)sgeconsulting.com] Sent: Monday, April 21, 2014 
1:38 PM To: seaint-seaosc(--nospam--at)mail-list.com
Subject: Re: [SEAINT-SEAOSC] Positive connection

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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