Return to index: [Subject] [Thread] [Date] [Author]

RE: Water reservoir - joints, wall ties, and alternate pours

[Subject Prev][Subject Next][Thread Prev][Thread Next]
I've done above grade liquid-containing structures in the 150-175-ft range
(45-53 meters) without crack control joints but using heavier reinforcement
as recommended for liquid-containing structures and providing construction
joints at a spacing of about 40-ft (12- meters). Since your structure is
buried, that may help to reduce temperature and moisture changes, so you may
be able to justify going longer without contraction or expansion joints.
Walls have a tendency to crack near the base of wall due to restraint from
the slab, so we sometimes increase our reinforcement just above the base
slab. If you use a low water-cement ratio and good curing techniques, that
will also help. 
 
 -----Original Message-----
From: Kevin Below [mailto:kevin.below(--nospam--at)sympatico.ca]
Sent: Thursday, March 14, 2002 3:48 PM
To: seaint(--nospam--at)seaint.org
Subject: Water reservoir - joints, wall ties, and alternate pours


I am designing my first water-retaining structure - a series of 3
underground rectangular tamks, each 20m x 20m x 2.5m deep with 355mm (14")
wall thickness. We have 60 degrees Celsius range of temperature here in
Quebec.  
The total length is thus 60m, which is a long way to go without joints.  But
I would like to avoid joints like the plague, so I have elected to use a
separate structure for each tank.  So I have a double-wall between the
tanks, with the intention to pour the walls of one tank, apply a
bond-breaker on the face of the common wall, and then pour the second tank,
and so on.
I don't like it, because it complicates the wall ties for the second wall of
the double-wall section.  And then I have to cover the joint with flashing
to keep out the water in our freeze-thaw climate.  But the experts in my
books seem to agree that no joint is a good joint,... well maybe
construction joints are a necessary evil and can be done well.  
 
What do you think?  Is it better to separate the tanks as I have proposed,
or to simplify the construction and add a joint or two ?
 
What do you do with the wall ties ?  Do you use conical ends, and patch the
holes?  Will non-shrink grout do the trick?
 
What about pouring the wall in alternate sections, leaving short sections to
infill after a week or two?  Is it worth it?  
 
I have been researching this and doing my calcs for 3 days now, and I have
accumulated a lot of notes from my references, but they can't answer
everything I guess...
I have heard horror stories of engineers in court because of leaky tanks, so
I am very wary.  One reference I use is in a chapter on water-retaining
structures by B.P. Hughes at the University of Birmingham.  He mentions the
importance of limiting crack widths to 0.1mm (0.004"), which usually
controls the design.  And so it does in this case.  Steel stresses are way
down at about 50 MPa (7,000 psi).  Interesting.  It's very different from
buildings.
 
Kevin Below
Génécor inc., experts-conseils

******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
*
*   This email was sent to you via Structural Engineers
*   Association of Southern California (SEAOSC) server. To
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
*   send to the list is public domain and may be re-posted
*   without your permission. Make sure you visit our web
*   site at: http://www.seaint.org
******* ****** ****** ****** ******* ****** ****** ********