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RE: Positive connection

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That was pushing the limits of my memory, but yes, 1971 San Fernando and 
1994 Northridge had examples, I believe.  I believe there were some examples 
 in Miyagi-ken-oki Japan, as well, but no money on that one! I'm no seismic 
 designer, but I believe we never expected (or designed for) vertical 
accelerations as high as was seen in 1971 and 1994.  I think unintended 
support motion due to any cause is a reason to provide positive connections 
 in some cases.

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 nma [nma(--nospam--at)nma-se.com] Sent: Monday, April 21, 2014 4:25 PM
To: seaint-seaosc(--nospam--at)mail-list.com
Subject: Re: [SEAINT-SEAOSC] Positive connection

San Fernando EQ and Northridge EQ

Neil
On 4/21/2014 12:03 PM, Steve Gordin wrote:
> Larry,
> 
> Could you please provide references to the case(s) of the bridges
> actually uplifting and then missing the shifted abutments on the way
> down? Such
> reference would be of great importance, and I would highly appreciate it.
> 
> Thanks,
> 
> 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
> 
> On Apr 21, 2014, at 11:37 AM, Larry Bryant<lbryant(--nospam--at)ara.com>  wrote:
> 
>> 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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