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Re: Positive connection

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The State of California Department of Highway Division (Bridge Department) held a meeting in the PG&E building on Market Street in San Francisco with the SEONC engineers after San Fernando and publicly stated that they had screwed up. The fellow's last name was Elliot (if my memory is accurate). At that time I don't remember that the State was participating much in the earthquake study world as it does today.

Neil

On 4/21/2014 1:45 PM, Larry Bryant wrote:
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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