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Gu

Sorry I haven't replied.  My own comments were simple opinion and I do not have
any direct references that I can recommend to you.  It just seems reasonable
that as soon as concrete "sets" that only the residual pressure will remain and
that as the concrete cures it shrinks and therefore even that pressure comes off
partially or completely.  I suggest that the time drop of pressure is directly
proportional to the rate of curing and shrinking.  Which is why I get concerned
when concrete placers seem to ignore the on-going setting when they are pouring.
 This often results in "cold joints" or, conversely, in higher formwork
pressures than allowed for.  This implies that placing concrete is an art!

Thor A Tandy P.Eng
Victoria BC
Canada
e-mail: vicpeng(--nospam--at)vtcg.com
  ----- Original Message -----
  From: Gu Jianzhong
  To: seaint(--nospam--at)seaint.org
  Sent: Monday, May 29, 2000 9:50 PM
  Subject: Re: Time-dependent lateral pressure on formwork


  Mr Vicpeng,

  I am glad to have the same idea with you. I am studying the effect of
composite structure of steel and concrete. And the time-dependent pressure is
important for the structure. The question has  puzzled me  for a long period.
Could you kindly recommend me with some references? Even basic expriemental data
or prelim reports are useful for me.

  Accoring to a paper,  lateral  pressure on formwork will reduce to 1/4  of
initial one. But it is written in Chinese and not detail enough to draw
conclusion.


  Best regards,

  Gu Jianzhong

  Graduate student of Civil Engineering Dept.

  B9810091,Shanghai Jiao Tong Uinversity

  Shanghai ,P.R.China

  Email: jz_gu(--nospam--at)263.net

  >If the concrete has hardened enough to remove the lateral pressure how do you
avoid a cold joint, on a repeat pass, without serious vibration of the "set"
surface, interfering with that set, and re-introducing lateral pressures?  How
about designing for the full height and then run the pour, full height, with a
running "active" face along the length of the wall.  I am always uncomfortable
with repeat passes especially if I have no control on the length of time between
passes. 
  >

  >If the wall is so high that repeat passes are necessary, shouldn't there be
allowance for a proper construction joint between lifts?
  >

  >Thor A Tandy P.Eng, MCSCE
  >Victoria BC
  >Canada
  >e-mail: vicpeng(--nospam--at)vtcg.com