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Re: Escalator Drifts[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: Re: Escalator Drifts
- From: "Gerard Madden, SE" <gmse4603(--nospam--at)gmail.com>
- Date: Mon, 16 Apr 2012 22:26:00 -0700
The commentary is clear, it is the Elastic Displacement with R = 1, but ASCE 7-05 leaves out the part about R=1... so since I have a SMRF, my R is 8. Cd factor is 5.5 and my building has an I=1.25, so I've scaled up my elastic drifts by 4.4 and designed my frames to stay just under the 2% limit giving a drift of 4.7", which is fairly typical of SMRF design (Drift governs, not strength) as you know.
I agree with you both and it's clear to me....I'm battling an Escalator company saying I'm way off and ASCE 7-05 unfortunately seems to support their argument.
I'll check out the commentary. Thanks as always Harold !
Joe, regarding building separations, the code in california has been clear since the 97 UBC, pounding/building separation is SRSS of each buildings' INELASTIC (Delta_M) drifts, so you are on solid ground there. There was an equation showing the SRSS in UBC, then that got removed in ASCE 7-05 I believe with a simple statement saying buildings shall be separated so as not to collide, but I read the equation would be put back in in ASCE 7-10
-gmOn Mon, Apr 16, 2012 at 7:58 PM, Harold Sprague <spraguehope(--nospam--at)hotmail.com> wrote:
Unless you are designing to an R of 1, you must anticipate that you will have a nonlinear response.
The ASCE 7-05 has a commentary, but it is not all contained in the ASCE 7. Go to the BSSC 2003 NEHRP Commentary and look at section 6.2.7 Seismic relative displacements. The ASCE 7-10 pulled the 2009 NERHP Commentary into the ASCE 7 so you don't have to go looking for it. The ASCE 7-05 had some commentary, but it was not complete. We left most of it in the 2003 NEHRP.
You can get the 2003 NEHRP commentary (which fed the 2005 ASCE 7) from:
We frequently use elastic analysis design. The 1.5 factor is intended to give you a ballpark inelastic drift. The inelastic drift you cited does not appear to be excessive for a 20 ft floor to floor.
Regards, Harold Sprague
Subject: RE: Escalator Drifts
Date: Mon, 16 Apr 2012 21:24:35 -0400
I have debated similar issues with adjacent buildings and expansion/seismic joints in buildings. I would strongly lean towards the inelastic drifts. And I explain the advantage to my clients, for it is their dollar that will replace the items if elastic drifts meet the intention of code but this event was bigger than we expected. The cost savings to do it better now and the peace of mine usually works with clients. The elevator manufacturer will skate by with code minimums and be nowhere in sight if a problem arises.
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Question on Drift of Escalators and the seismic movement the connection needs to be able to handle.
ASME 17.1-2004 (Code for Elevator and Escalators) section 126.96.36.199.2 reads as follows:
188.8.131.52.2 At the sliding end or ends, the width or widths of the beam seat shall be capable of accommodating, without damage, at least 1.5 times the story drift as obtained by either of the following:
(a) through engineering calculations
(b) by using the maximum code allowed story drift per the NEHRP 1997 Table for Allowable Story Drifts. This table allows story drifts of 0.0375 hsx where hsx is the building story height.
I provided the inelastic drifts for my building in the specifications which at 2% drift for a 20 foot story height is about 4.8" (I'm very close to this limit). I'm being told that this is way too high by the elevator people. Their experience is 2.375" of movement (1 3/16 each way) is the most they've ever done in San Francisco or California (my project is in SF)
So my response so far has been that since 184.108.40.206.2 says "WITHOUT DAMAGE" they want an INELASTIC DRIFT to be accommodated in the bearing slip . In option B they want 1.5 x 3.75% story height which again leads me to think INELASTIC DRIFT.
The numbers quoted by the elevator people seem like elastic drifts. ASCE 7-05. ASCE 7-05 13.6.10 tells you to follow ASME A17.1 (quoted above) bu then says "except as modified in the following text". There is no following text, just another code section (220.127.116.11) which goes on to say "Escalators .... shall be designed to meet the force and displacement requirements of sections 13.3.1 & 13.3.2)
13.3.2 SEISMIC RELATIVE DISPLACEMENTS uses ELASTIC DRIFTS.....
So, which one do I use?
Thanks Everyone...who may be there still....
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