Need a book? Engineering books recommendations...

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

RE: Increase of f'c over time

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Yes, you are right about not relying on "reasonable assumptions of
strength".  I am not doing that.  What I did not explain in my original
email was that there is another aspect of the client's job in which a
portion of the concrete structure is being demolished.  During this
demolition, the client will take cores and test them.  This is the procedure
that I have outlined the assumptions portion of my report to him.  However,
this will not be accomplished before he has to somewhat "commit" to his
superiors that the placement of the new equipment onto the existing concrete
slab can take place.  I have told him that I will not "commit" to the
concrete strength being what I have used in the calculations without backup
test data.  Granted, this is a dicey situation for him, so he would like to
have some kind of backup study showing this increase of strength over a long
period of time does occur.

F.Y.I.  Something else that I did not explain was that the "member" that I
am investigating is an unreinforced, 10" thick slab on grade, so I have also
had to make assumptions on the modulus of subgrade reaction.  Therefore, a
"failure" of the slab will not be a catestrophic failure.  However, the new
equipment the client is placing is VERY deflection sensitive.

Thank you for your reply Bill.

> -----Original Message-----
> From:	Bill Polhemus [SMTP:bill(--nospam--at)polhemus.cc]
> Sent:	Thursday, December 20, 2001 9:02 PM
> To:	seaint(--nospam--at)seaint.org
> Subject:	RE: Increase of f'c over time
> 
> Never, ever, ever rely on "reasonable assumptions of strength" when
> evaluating an existing structure. If you check the model building codes,
> for
> example, you will find that existing structures MUST be evaluated using
> empirical measurements. That's why, whenever I'm doing a
> renovation/retrofit
> job, and the contractor/owner tells me "oh, and I have the drawings right
> here," I tell him "that's nice, they'll serve as a good reference. But
> they
> will NOT be relied upon as the final word. I will take measurements
> including if need be assessments of the actual strength of the in situ
> materials.
> 
> What you did at the outset was fine, for a first approximation. But you're
> going to need material testing to back up your assumptions if you want the
> existing structure to sustain an appreciable increase in service loading.
> 
> This is where this game gets dicey, because contractors/owners don't want
> to
> hear that; they think we ought to know these things, I suppose by osmosis.
> 
> 
> 
> William L. Polhemus, Jr. P.E.
> Polhemus Engineering Company
> Katy, TX, USA
> Phone (281) 492-2251
> FAX (281) 492-8203
> email bill(--nospam--at)polhemus.cc
> 
> -----Original Message-----
> From: Barclay, George [mailto:GBarclay(--nospam--at)lgt.lg.com]
> Sent: Thursday, December 20, 2001 5:35 PM
> To: 'seaint(--nospam--at)seaint.org'
> Subject: Increase of f'c over time
> I am performing a job that involves the capacity of structural plain
> concrete.  The new (heavy equipment) demand exceeds the flexural capacity
> of
> the member using the original concrete strength given in the 1960
> construction documents.  The client obviously wants to avoid modification
> of
> the structure.  He has good reasons which I will not go into here, for
> length of the discussion.  I know that concrete strength increases over
> time.  I spoke with one of my grad school professors from whom I
> originally
> heard of this increase.  He said that he wouldn't be surprised if the
> strength of the concrete had as much as doubled over that amount of time.
> 
> 
> 
> ******* ****** ******* ******** ******* ******* ******* ***
> *   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 
> ******* ****** ****** ****** ******* ****** ****** ******** 
> 
> 
The information contained in this e-mail message and any attachments is
Lockwood Greene Technologies business information intended only for the use
of the individual or entities named above.  If the reader of this message is
not the intended recipient you are hereby notified that any dissemination,
distribution or copying of this communication is strictly prohibited.  If
you have received this communication in error, please notify us immediately
by e-mail at the originating address or at postmaster(--nospam--at)lgt.lg.com.



******* ****** ******* ******** ******* ******* ******* ***
*   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 
******* ****** ****** ****** ******* ****** ****** ********