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Re: Positive connection

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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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