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Re: Positive connection

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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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