Need a book? Engineering books recommendations...

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

RE: 1930's Poured in Place Concrete Building - Scott's Comments

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Scott
Here are the results of the six core tests; however, there is a note
from the testing lab that the sixth test is invalid due to the aggregate
size:
Test #1 Corrected PSI (Conical break): 1060 psi
Test #2 Corrected PSI (Shear): 440 psi
Test #3 Corrected PSI (Shear): 2430 psi
Test #4: Crumbled upon removal of the core - 0 psi
Test #5 Corrected PSI (Shear): 580 psi
Test #6 Corrected PSI (Shear): 1740 psi - considered invalid due to
aggregate size.

Not a good test result, but if you consider a solid 50' long or 40'-long
wall, the shear from the structure and the wood framed addition above
would probably (my intuition only) result in a lower shear per linear
foot than the interpolation of the test #2 (eliminating test 4 and 6).
Where it is critical is the front and rear of the building which is
definitely an open-front (and soft-story rear) of the building that can
be strengthened by moment frame or Gunnite. 

I have to revise my date on the building. The original engineer noted
that square rebar was commonly used in the 1920's so we are dealing with
a building that is about 10 years or more older than I originally
thought.

I will ask for the City to meet with us next week to see what they will
negotiate on the methodology to be used on the design of "Their"
building. Remember, the City owns this building and it is necessary to
keep the cost of retrofit or repair to the building within a reasonable
cost to allow the structure to be used within their federally funded
empowerment zone.

Dennis

-----Original Message-----
From: Scott Maxwell [mailto:smaxwell(--nospam--at)engin.umich.edu] 
Sent: Thursday, November 20, 2003 7:32 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: 1930's Poured in Place Concrete Building

Dennis,

As Jake and Gerard pointed out, you might be in a position of having to
satisfy more than UCBC guidelines/requirements due to either a change in
occupancy and/or an addition.  In theory, your apparent change in
occupancy (from your post at least) would lessen the loads, but then
there
is the "temporal" shift from a 1930's code (or lack of one) and the
current 1997 UBC.  While the occupancy might be going from an
"essential"
facility (an old firestation from your post) to a "normal" building, if
the local jurisdiction still calls it a change of occupancy an makes you
meet the current requirements for the "normal" building, then it is
likely your loads will increase anyways, not to mention the ductile
detailing requirements.  Regardless, the addition of the mezzanine
should
require you to bring much, if not all, of the building up to current
code,
unless you isolate the mezzanine from the original building.  Thus, I
agree with both Gerard and Jake...you are likely facing a requirement to
"bring" it up to current code.  Although, I have to admit that I don't
see
the "upgrade" type provisions in the UBC that I am used to in the
BOCA/IBC
(but then I am not too terribly familiar with the UBC).

As to the concrete walls, have you had compressive tests done on the
cores
or were they just for visual inspection/observation?  You mention the
"too
much aggregate and local desert sand", but do you have an idea how that
translates into actual current concrete strength?  How "bad" is the
concrete (i.e. if lightly hit/tap with a hammer does it crumble, etc)?
Just from your minimal description, I would say that your first
inclination for the long sidewalls makes sense to me.  My gut (without
testing or other information) is that those walls would likely be
basically OK.  You have a nice long stretch of wall, so you probably
have
much more shearwall than you need...meaning the load per foot should be
rather small.  Your only problem can be what you choose to use for R in
determining seismic loading (see above).  If you use the code value of
4.5
(bearing wall system with concrete shearwalls), then your shearwalls
would
have to met ductile detailing requirements, which is rather unlikely
(all
assuming that you must meet current code requirements).  You might want
to
look into a lower R value so that the system behaves in a more elastic
way.  This would obviously increase the loads but could eliminate the
need
to follow prescriptive ductile detailing requirements.  This is a method
that is "permitted" (at least to my knowledge) and used in my area when
dealing with steel moment frames (if you use R=3 or less, then some
ductile detailing requirements for steel aren't required, like a lot of
the requirements that came about due to Northridge).

As to the from of the building, you might want to look into a concrete
moment frame rather than a steel one, if it will fit in the design.  A
concrete moment frame should be "naturally" more stiff than a steel
moment
frame, which will help with the relative rigidity issue.  This in
combination with reinforcing the rearwall with shotcrete or
cast-in-place concrete could work.  Your other option would be to
"abandon" the rear wall as a shearwall (would require isolating it) and
putting a moment frame at the rear as well as at the front, making the
system in that direction a pure moment frame system rather than a dual
system.

As to the deterioration of the concrete on the sidewalls, similar
questions from above come to mind.  Can you be more specific as to what
you mean by deterioration?  Is the concrete spalling, meaning the cover
to
the rebar is falling away, but the main part of the wall is still intact
with reasonably good concrete?  If so, then all you would really need is
something to protect rebar, as that is all the cover really is there for
(assumes two layers of bars, not one in the center).  Or is the concrete
actually crumbling, including concrete inside the "core"?  If this is
the
case, then you might have to consider something more drastice like
shotcrete (in otherwords, you concrete walls might be bad enough that
they
need reinforcement).

As to your mezzanine plan, it sounds reasonable to me...just keep in
mind
that it might mean that you have to bring the parts (if not all) of the
existing building up to current code.  If that becomes the case, then
you
might want to isolate the mezzanine from the existing building, creating
a
new, completely seperate "sub" structure (that would have to meet
current
code).

HTH,

Scott
Ypsilanti, MI


On Thu, 20 Nov 2003, Jake Watson wrote:

> Dennis,
>     Remember to consider relative rigidities of materials.  If you put
a
> moment frame on the front, how far will it move before it does resists
much
> force?  Will the masonry along that line fail before the frame takes
over?
> If the masonry fails in shear, will it still carry gravity loads or is
there
> an alternate gravity load path?
>     Also, I second Gerard's comments about change in occupancy.  I
would
> review the new occupancy with the municipality before proceeding too
far.
> If you are increasing the "public hazard" significantly, you may need
to be
> fully code compliant.
>     As for the concrete, you might look a FEMA 356.  It might give you
a
> better procedure to deal with the concrete.
>
> Best of luck,
> Jake Watson, P.E.
> Salt Lake City, UT
>
>   -----Original Message-----
>   From: Dennis Wish [mailto:dennis.wish(--nospam--at)verizon.net]
>   Sent: Wednesday, November 19, 2003 11:52 PM
>   To: seaint(--nospam--at)seaint.org
>   Subject: 1930's Poured in Place Concrete Building
>
>
>   A local empowerment zone redevelopment agency is leasing a 1930's
concrete
> wall building from a local city. The building was a high bay fire
station
> and since the original construction, a second story wood frame
structure has
> been added. The walls were cored and while the cores were tested for
> compression, the reinforcement was found to be the old square rebar
used in
> that period of time.
>
>   A firm from outside the area was brought in by an Architectural firm
> representing a bank that wishes to sub-lease the building. I was
recommended
> by the local testing agency as a second opinion based on my knowledge
of old
> Unreinforced Masonry buildings.
>
>
>
>   Even if there is minimum rebar, the walls that pose the least threat
are
> the side walls which are long and solid. The shear transferred from
the wood
> frame addition above is not a threat to these walls. There ends of the
> building pose another problem. The front is where two large doors were
> placed to allow fire trucks in and out. The rear wall is inaccessible
at the
> time the testing lab inspected the building, but I would assume that
the
> wall which the Architect shows on his plan is concrete, but too short
and
> possibly too weak to be used as an appropriate shearwall - especially
due to
> the shear from the second story wood frame addition. This rear wall is
> concealed by a wood one story addition added sometime after the
building was
> constructed. This portion of the building will be removed by the bank
and a
> new structure will be built in its place.
>
>
>
>   For those in California, here are my questions:
>
>
>
>     1.. I don't know of any Hazard Mitigation program in California
that
> would require retrofit of the existing roof (floor of the second
story) to
> the concrete walls. UCBC Appendix Chapter One does not address
reinforced
> concrete buildings. Is this building exempt from retrofit rules in
> California?
>     2.. The concrete is not the best - some good cores, others that
have too
> much aggregate and local desert sand in the mix. Still, the length of
the
> walls and the minimum reinforcement would resist lateral loads. I
would plan
> on a steel moment frame in the front of the building connected by
welding to
> the steel lintel above the doors. The new design pops the front out
two or
> three feet which makes the frame an ideal solution as there is enough
room
> for the grade beam and erection pads in proximity to the property
line. The
> rear wall can be strengthened with Gunnite for shear and additional
> foundations added or replaced as needed. What choices do I have to
reduce
> further deterioration of the concrete on the exterior face of the
sides
> (long sides) of the building?
>     3.. A mezzanine is to be added by the bank. I believe this
mezzanine
> (which will induce additional shear) can be supported on a wood stud
wall
> and the floor joists (TJI) supported by these walls. The mezzanine can
be
> used to brace the walls from buckling, The bearing stud walls below
can also
> be used to run utilities with minimum loss to leasable space. Does
this
> sound like a reasonable plan?
>
>
>   The tough part is that the Empowerment zone has limited funds and I
have
> no idea how to calculate the retrofit or upgrade portion of the
project. If
> the mezzanine is used to brace the walls then the cost is absorbed by
the
> bank as an improvement and does not come from the Empowerment Zone.
This
> leaves me only the moment frame, a Gunnite wall at the rear and any
coating
> or covering of the concrete that can improve or reduce further
deterioration
> of the walls. The building is probably about 2000 square feet and the
walls
> are 8-inch thick with joints at 8-feet horizontal as the this was the
height
> of the lifts.
>
>
>
>   Another firm figured the reconstruction to bring the building into a
safe
> zone would be close to $90,000.00 which seems very high to me. It is a
> prevailing wage project but I would think that at the worst case
scenario,
> we would be talking between $50K and $60K.
>
>
>
>   I could use some advice as how I might approach this type of
structure. My
> experience, besides wood, is URM and Structural Clay (Unreinforced).
I've
> also done some Adobe but have not worked on this type of Concrete
structure.
> Finally, the building is not on a state historic registry and not
protected
> except by the allowances of the city Building And Safety division.
>
>
>
>   Please let me know what you think.
>
>
>
>   TIA
>
>   Dennis S. Wish, PE
>
>
>
>   PS. We have not done a Pachometer test yet and I am waiting for
options
> before recommending spending any more of their money on this building.
I was
> not involved in the original testing or preliminary plan development -
I was
> brought in to offer a second opinion to another engineers report.
While his
> report appears valid, his approach to solving the problem is to
attempt to
> bring the building up to compliance. My approach would be similar to
URM
> buildings - identifying their weakness and designing to the failure of
the
> weakest element but providing sufficient secondary support to get
people out
> of the building. After that there would be no guarantees.
>







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


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