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Re: Flat Bottom Tank Anchorage

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Yi,

The following comment is not entirely accurate.  The provisions against the
use of friction from gravity loads in resisting seismic loads are contained
in section 1632, which is for equipment supported by structures.  If you are
designing a tank on grade the applicable section would be 1634, non-building
structures.

The provision against friction from gravity loads is one of the worst
defined code provisions in the UBC.  I suggest you read the SEAOC Blue Book
commentary to understand the intent of this section and how it should be
applied.  For instance, friction resulting from the seismic overturning
forces acting on the tank are not excluded.

Paul Feather
----- Original Message -----
From: "YI" <YI(--nospam--at)summit-sr.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Thursday, October 18, 2001 9:49 AM
Subject: RE: Flat Bottom Tank Anchorage


> I don't think all those conditions are really relevant to my questions,
> except that the tank is located in Zone 4, UBC does not allow you to
resist
> seismic load with any kind of friction, that's why all the anchor bolts
need
> to resist all the lateral load in shear, plus uplift of course, but that's
> another subject.
> As far as shear is concerned, the very bottom ring of the tank wall should
> have a unit shear stress tangent to the ring along the entire
circumference
> of the ring (picture a horizontal shear flow through a ring). My real
> question is to figure out the maximum shear on any particular anchor bolt,
> since the lateral force could be from any direction.  That's why I assumed
4
> bolts for simplicity.  The unit shear stress in the bottom tank ring is
not
> uniform along the entire ring, it's at maximum where it's 90 degrees from
> the the direction of the load, and minimum at where it's in line with the
> direction of the lateral load.  Therefore the distribution of the lateral
> load into each anchor is not uniform.  If it is assumed that there is no
> shear stress at all for the anchor bolts located in line with the
direction
> of the lateral load, then the combined tensile and shear stress is not an
> issue, since that's where the maximum tension would be.  However if that
> assumption is incorrect, that might become a problem because of the
conbined
> stress ratio, since the bolt would be designed for tension only based on
> that assumption.
>
> If there are 50 anchor bolts for the tank, and you divide the lateral
force
> by 50 to get the shear force on each anchor, I think that would be
> insufficient because some anchor bolts will have more than 1/50 of the
> lateral force and some will have less than that, the maximum shear on each
> anchor must be more than 1/50 of the total.
>
> Yi Yang
>
>
> -----Original Message-----
> From: bob.ross(--nospam--at)wgint.com [mailto:bob.ross(--nospam--at)wgint.com]
> Sent: Wednesday, October 17, 2001 6:43 PM
> To: seaint(--nospam--at)seaint.org
> Subject: Re: Flat Bottom Tank Anchorage
>
>
> Is your design an API or AWWA tank?
>    Is it a tank supplying a supply during an emergency?
>    In what Seismic Zone is the tank?
>    Where is the tank location and distance in relation to the nearest
> known active fault(s)?
>    When anchor shear bolts are provided, (which do damage during an
> event), each should be assigned an equal share in resisting the seismic
> lateral and vertical loads.
>
> Pax e Gratia
> Bob Ross
> Robert P. Ross, P.E.
> Principal Project Manager
> Washington Group International,Inc.
> Industrial Processes
> 17320 Red Hill, Suite 300
> Irvine, Ca. 92614
> Mobile 562-254-4604
> Office 949-222-3978
> FAX 949-222-3985
> E-mail: Bob.Ross(--nospam--at)WGINT.com
>
> ----- Original Message -----
> From: YI <YI(--nospam--at)summit-sr.com>
> Date: Wednesday, October 17, 2001 6:05 pm
> Subject: Flat Bottom Tank Anchorage
>
> > I have question regarding the design the anchor bolts for a
> > circular tank
> > with bottom fully supported on concrete pad.
> > When a lateral load is applied to the tank, assume no fiction
> > between the
> > tank and the pad, the lateral load is resist by the shear capacity
> > of the
> > anchor bolts.  The maximum shear force per anchor bolt is occured
> > on the
> > bolt located 90 degres from the direction of applied load, and
> > minium  shear
> > on anchor bolts occure on the bolts that are in line with the applied
> > lateral load.  Consider the situation where there are only 4
> > anchor bolts on
> > the ring of the tank base, will there be any shear force at all on the
> > anchor bolts located in line with the direction of the applied lateral
> > force?  Are all the lateral force resisted by the 2 anchor bolts
> > located 90
> > degrees each side of the load direction?
> >
> > Thanks in advance.
> >
> > Yi Yang
> >
> >
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