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Fw: Concrete vs. Steel

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>     I'm not saying that R/C won't work.  I'm saying that the better choice
>(IMO) is steel.  Supporting arguments:
>
>1.  To a point as with any material, concrete works fine in bending.  But,
>in cyclic shear + tension it fractures one side at a time until all that is
>left is two cone shaped ends with rebar holding them together and no
>frictional surface.  Steel is ductile and concrete is brittle.


That really is the WHOLE point of ductile detailing - to take a relatively
brittle material (concrete) which is good in compression, combine it with
steel which is good in tension, then keep the composite together while it
undergoes plastic deformation through the use of properly designed
transverse reinforcement.  If you look at literature reporting testing of
ductiley detailed R/C members, you would see that you can obtain rotational
ductility capacities which are more than adequate for accomodating expected
rotations and displacements.

The failure that you are (generally) describing above would be applicable to
an IMPROPERLY designed R/C member, NOT to a ductilely designed one.



>2.  The bay bridge failed in shear (I SAW the joints) at d/2 to d below the
>knee.

Again, getting back to PROPERLY designed R/C, I think you will find that the
Cypress structure (to which you seem to be referring) to have been designed
back in the 50's before proper detailing was really known about.  If you are
going to compare older structures in order to point out how poorly concrete
performs, you may just want to go ahead and throw in the Acropolis on to the
list.

>3.  You can't fix wrongly detailed concrete.

Simply untrue.  The structure AS A WHOLE can be retrofit, and I think you
will find numerous examples of such projects if you care to look.  If you
wish to make an issue of the fact that it is difficult (NOT IMPOSSIBLE) to,
say, retrofit an improperly constructed R/C beam column joint, then I would
agree.  But through the addition of shear walls, or stiff frames, the
expected displacements (and hence rotations in the subject joint) can be
reduced to the point where the joint can be expected to perform adequately.
Would it be all that much different from choosing to retrofit a STEEL
structure by adding bracing instead of addressing deficient welds on the
numerous beam column joints?


>4.  In the event of collapse, with concrete people get buried and steel
>maintains a space (better)(~).

With proper design and construction I think this becomes a moot point.

>5.  With n=9(+) and weight per unit vol. =3.3 for steel/concrete the
>strength to weight ratio makes steel a better material where mass is a
>critical factor.

What about where mass is helpful?  Granted, here on Guam with 155mph winds
we have a somewhat unique case, but the actual structural weight is very
much beneficial when resisting uplift/overturning under wind loading.  The
increased mass due to concrete doesn't pose much of a problem as far as I
have seen.


Greg - I would really suggest that you read up a bit on R/C and earthquakes
(recent information that is).  I think you will find that It is certainly
possible to design R/C structures (shearwall AND frames) to undergo severe
seismic action and come out just fine.

T. Eric Gillham PE
GK2 Inc.
PO Box 3207  Agana, Guam  96932
Email - gk2(--nospam--at)kuentos.guam.net
Ph:  (671) 477-9224
Fax: (671) 477-3456
>
>So much for that ACI Fellowship,
>(no offense to ACI)
>Greg
>
>
>-----Original Message-----
>From: Mark T. Swingle <mswingle(--nospam--at)earthlink.net>
>To: seaint(--nospam--at)seaint.org <seaint(--nospam--at)seaint.org>
>Date: Monday, October 25, 1999 3:19 AM
>Subject: Re: Concrete vs. Steel
>
>
>>Dear Greg in OK,
>>
>>Please don't come to California to design until
>>you do some more
>>homework! :-)
>>
>>Well-designed and -constructed concrete is a very
>>viable and ec-
>>onomical solution in all areas of high
>>seismicity.  This type of
>>structure has been proven safe in many
>>earthquakes.
>>
>>The problems in Turkey were apparently due almost
>>entirely to two
>>factors: 1) poor detailing, and 2) poor material
>>quality.
>>
>>In Kobe, steel buildings were affected as much, if
>>not more, than
>>concrete buildings.
>>
>>If you drive over the Bay Bridge, the only
>>"obvious" thing is that
>>it is made of steel, not concrete.  It was steel
>>connections
>>that failed.
>>
>>By your reasoning, perhaps we should prohibit the
>>use of steel
>>connections (in buildings as well as bridges) in
>>earthquake country,
>>based on the experience with the Bay Bridge and
>>Northridge.
>>
>>Mark Swingle, SE
>>Oakland, CA
>>
>>
>>Greg Smith wrote:
>>
>>>  To be in charge of a project and prescribe the wrong material
>>> (even for economical reasons) is like a doctor prescribing the
>>> wrong medicine because the patient can't afford the right one.
>>> In engineering as with medicine, this can lead to death.
>>
>>> I believe that concrete has been WRONGLY prescribed ANYWHERE in a
>>> high seismic risk zone.  The EQ's in Turkey, Bay Bridge, Japan etc.
>>> are obvious proof of this.  Yes, it is possible to construct a
>>> concrete structure that will withstand a Richter 10 but THAT would
>>> be UNeconomical.  Granted that Northridge revealed problems with
>>> steel and brittle fracture, it will be easier to overcome this
>>> than to take the mass out of concrete.  Concrete has it's
>>> advantages but only in a compatible location.
>>>
>>> Greg in Oklahoma
>>
>
>
>