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

RE: seaint Digest for 14 Mar 2002

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Thanks for the comment Conrad.  Yes I will be using PVC water stops in
the cold (construction) joints, between slab and walls, and between wall
pours.  I am more concerned about the possibility of major cracks
developing if I go with the multi-cell approach of joining the 3 cells
together.

Last night I found some interesting stuff on predicting crack spacing
due to shrinkage and temperature effects in the chapter by B.P.Hughes
that I mentionned.  

He explains the mechanism of cracking through slipping at the interface
between of the re-bar and the concrete.  The critical time is right at
the end of the period of initial heating-up due to hydration, as the
concrete cools down but is still very weak (low bond strength and low
tensile strength).  This occurs within about 3 days after the pour.

So it will be important to keep the concrete cool and wet during the
first few days.

I understand that the British code BS 5337 allows 3 options for this
type of structure:
1. Continuous design with full restraint (no joints, except maybe
expansion joints at wide spacings for walls exposed to the sun).
2. Semi-continuous design with partial restraint (with contraction
joints at various spacings depending on whether the steel is interrupted
at the joint)
3. Close movement joints design for freedom of movement. (Close
contraction joints at spacings depending on calculated crack spacing).  

Option 1 uses the most steel, but saves a certain number of joints which
also have a price to consider, especially if they leak.

Kevin Below
Génécor inc., experts-conseils


-----Original Message-----
From: "Conrad Guymon" <conrad(--nospam--at)karren.com>
To: <seaint(--nospam--at)seaint.org>
Subject: Re: Water reservoir - joints, wall ties, and alternate pours


Have you considered using cast in place a neoprene water stop at cold
joints?  Greenstreak makes one that we have used on occasion.  I think
they have a website, and they are not the only manufacturer out there.

Conrad Guymon, P.E.

  ----- Original Message -----=20
  From: Kevin Below=20
  To: seaint(--nospam--at)seaint.org=20
  Sent: Thursday, March 14, 2002 3:47 PM
  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
  Genecor 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
******* ****** ****** ****** ******* ****** ****** ********