Concrete columns - rule of thumb sizes?
Greg Howland
10, 20, 40, and 80 story building? I'm assuming this is an office
building of 100 x 100 feet with 25 foot bays and 15 feet floor to
floor height (32 x 32 meters with 8 meter bays and 5 meter height).
Also, what would be the theoretical and/or practical limit of high you
can construct a building with these dimensions using concrete columns
and a simple straight forward building method (approximate)?
Thanks
Phil Scott
"Greg Howland" <gregory...@yahoo.com> wrote in message
news:be500925.04062...@posting.google.com...
10 story, 16" columns.. at the base
20 story 18" columns
40 story 32" columns
80 story 54" columns, smaller as you go up.
those are wild guesses based on typical conditions. + 30% for
a practical max. columns can go a lot smaller with cast in
diagonals. Post tensioning of various sorts will also affect
column dimensions as will the quality of the agregate (amount
of silicon added) and amount of steel in each column.
tapering or stepping the building in as you go taller also
reduces the size of the columns....that moves the center of
gravity down, and reduces leverage from the top of the
building on the base under seismic loads.
You could probably go to 80 stories if the top were just say
25% smaller than the base... that converts the seismic loads
on the columns from dominantly bending vectors to tension and
compression loads. (triangulation effects). See the
transamerica building in SF Calif for an extreme example of
that.
(the primary design flaw as I see it on the WTC were those
cheezy little clips they used to attach the floor trusses to
the perimeter frame. they could have spent an extra 1% on the
building and doubled the strength on those... a situation of
running the calcs and doing it by the numbers rather than
taking advantage of heavier steel at only slightly more cost.)
Ask yourself.. 'what little thing could I do to double the
strength'... not 'will my design meet the calculated max
stress criteria'.... do that math.. then ask yourself the
first question and then use the answer to violate your
calculated sizing and design.
Why? Because the math is only 3 or 4 dimensional at best, but
life and actuality is 90 dimensional or more. And its in
those 90 dimensions that your building or gizmo is going to
live.
Phil Scott
The height would be heavily dependent on seismic
considerations for the area and local ordinances. 40 stories
might be a max for many situations with a 100' square base.
You may be able to go taller with a flexible steel frame on
hydraulic dampered spring and roller isolated pads in some
areas.
A steel space frame is going to be more cost effective than
the straight steel reinforced concrete columns you are looking
at.
Phil Scott
>
> Thanks
Rico dJour
Bob K 207
>From: rico...@aol.computer (Rico dJour)
>Date: 6/29/04 5:57 AM Pacific Daylight Time
>Message-id: <20040629085744...@mb-m23.aol.com>
OP
Tower Burbank is a 31-story office building, & is the tallest (1989) concrete
building west of the Mississippi River (1989)
there must be a good reason, do some research on the web, read to get more than
"just the answer"
Google> "tall concrete buildings"; "history of concrete"
Eunoia Eigensinn
because of a strong steel lobby.
Most of the major concrete-framed towers in the US (and world-wide for that
matter) are built using Canadian consultants/technology. With the use of
"flying forms" and high-early cement, there's very little difference in
erection time between steel & concrete but obviously, the concrete frame will
be superior.
9m x 9m (30 ' x 30') bays with 4.5m (15') cantilevers around the perimeter
(developers like the marketability of column-free windowed exec offices) are
pretty much standard and the optimum floor plate size is about 200 m^2 (~20k
ft^2).
Obviously, the column size will be larger for those on the lower storeys.
Brian Belliveau
"Phil Scott" <phil...@philscott.net> wrote in message
news:cbqr8j$nvt$1...@news.tdl.com...
> Why? Because the math is only 3 or 4 dimensional at best, but
> life and actuality is 90 dimensional or more. And its in
> those 90 dimensions that your building or gizmo is going to
> live.
>
>
>
> Phil Scott
What color is the sky in your universe ?
Matt Whiting
Medium, Large, Extra-large, and Super-size.
Matt
Bob K 207
>Date: 6/29/04 9:48 AM Pacific Daylight Time
>Message-id: <1105_10...@news.vif.com>
>
>The primary reason that steel-framed towers are prominent on the US scene is
>because of a strong steel lobby.
>
I disagree.......
concrete is a good building material for certain situations, but its strength
to weight ratio is not great.
please explain how the "strong steel lobby" makes or convinces SE's to design
tall structures in steel rather than concrete
regards
Bob
Deepak Warad
When the building is more than 15 storey, column sizes increase
drastcally. SRC columns (composite sections made up of steel sections
encased with concrete) would be better. In India, we have
predominantly concrete buildings, the tallest being 28 storied at
Bombay. In this example, the floor to floor height is 15' which is
quite high. Slenderness of columns will be a major factor for upper
floors. Seismic load considerations will play a crucial role and a
size of say 18"x36" will be required even for 10 storey buildings. As
pointed out in this discussion, the important consideration should be
the overall geometry of the building which should be symmetrical and
reduction of size towards upper stories will give economical results.
Another consideration should be providing shear walls at key places
which will reduce the effect of lateral loads on surrounding columns,
thereby reducing their sizes.
Deepak
Matt Whiting <whi...@chilitech.net> wrote in message news:<cbsqv...@enews3.newsguy.com>...
Phil Scott
"Deepak Warad" <deepak...@yahoo.com> wrote in message
news:31936db5.04062...@posting.google.com...
Its been calculated that a 200 story concrete building
will be so heavy that it will punch its way though to the
center of the earth, loosing much of its retail space appeal.
Getting concrete up that high is a problem too,.. and you
still have to fit a couple of tons of rebar into a typical 16"
column.... not much savings there. Its all labor intensive.
Im surprised we see concrete to the degree we do at all... in
this area its rare. Even 3 story buildings are steel or wood
frame these days.
Phil Scott
Greg Howland
I'll just throw this out for comment. One idea I'm looking at is to see
if new buildings can be built using "old" methods. So for example, in
this same 100 x 100 foot building, what if the columns were built by
stacking solid concrete blocks on top of each other. The blocks would
be 3 feet x 3 feet x 4 inches (1 x 1 x 0.1 meters) and the columns
connected to each other with arches creating vaulted ceilings, so the
entire building would be built in compression. I'm thinking that rebar
would not be needed, and for that matter I'm wondering if mortar would
even be needed if the blocks were precision made for this with
interlocking grooves.
Each column of this size would weigh about 15,000 pounds per floor,
however columns of half this width, used for smaller buildings and
upper floors of larger buildings, would weigh only about 4,000 pounds.
Is this that much heavier than a conventionally built building? It
seems that the ceiling vaults could be made of lightweight concrete
since they are structurally efficient and since floor loads of an
office building are light. I guess the outside columns would need
buttressing, but would this be small or insignificant since the floor
loads would not be exerting that much outward pressure?
Other than a high labor cost, any other comments about this?
3D Peruna
used anymore. You might find some answers there that will inform your
current questions.
Tom C
You're describing women shoppers at WalMart!
Tom
"Matt Whiting" <whi...@chilitech.net> wrote in message
news:cbsqv...@enews3.newsguy.com...
Greg Howland
> used anymore. You might find some answers there that will inform your
> current questions.
That's what I'm getting at. Many of the reasons that they were
abandoned can be addressed today but solutions were not available at
the time they were abandoned. For example, the high labor costs of
stone cutters is addressed by mass producing preformed concrete blocks
in factories. Methods of delevery of material is greatly improved. The
sheer massiveness required is reduced with the use of lightweight
concrete. The architect as mastercraftsman was replaced by the
architect as designer. And the preferred visual style of buildings
changed. All of these issues can be addressed. What would be other
issues?
Rich Jones
Also, realize why there isn't more lightweight concrete out there.
Designers love it, contractors hate it - it is harder to batch.
Now, we have another modern lightweight option to massive concrete - steel.
Rich Jones
> Its been calculated that a 200 story concrete building
> will be so heavy that it will punch its way though to the
> center of the earth, loosing much of its retail space appeal.
> Getting concrete up that high is a problem too,.. and you
> still have to fit a couple of tons of rebar into a typical 16"
> column.... not much savings there. Its all labor intensive.
>
But the hoisting requirements are less.
You can pump all of the concrete from the ground, and all you have do lift
is forms and rebar cages. Besides, if you have a massive cage in a dinky
16" column, you ought to use a bigger column.
> Im surprised we see concrete to the degree we do at all... in
> this area its rare. Even 3 story buildings are steel or wood
> frame these days.
>
>
That can have to do with things completely unrelated to the structural
properties of concrete.
Examples:
In NYC, all rebar must be field bent from straight bar on site*, adding
tremendously to the cost. This gives structural steel an unfair advantage,
and is one of the reasons that steel is so popular there.
*This is according to the union rules. You _could_ try and work open shop,
but it would be amusing.
P. Fritz
"Eunoia Eigensinn" <Eige...@BVI.com> wrote in message
news:1105_10...@news.vif.com...
> The primary reason that steel-framed towers are prominent on the US
scene is
> because of a strong steel lobby.
Not true.
>
> Most of the major concrete-framed towers in the US (and world-wide for
that
> matter) are built using Canadian consultants/technology. With the use of
> "flying forms" and high-early cement, there's very little difference in
> erection time between steel & concrete but obviously, the concrete frame
will
> be superior.
Time is not the only issue. (Though I would argue that the time is near
te same) Cost is the primary one, second is space
>
> 9m x 9m (30 ' x 30') bays with 4.5m (15') cantilevers around the
perimeter
> (developers like the marketability of column-free windowed exec offices)
are
> pretty much standard and the optimum floor plate size is about 200 m^2
(~20k
> ft^2).
>
> Obviously, the column size will be larger for those on the lower
storeys.
Another reason developers favor steel
P. Fritz
"Greg Howland" <gregory...@fastmail.fm> wrote in message
news:2004070105241675249%gregoryhowland@fastmailfm...
Another is that is rather simple to reinforce a steel building as needed
for high localized loading.......it is much harder to do with concrete.
>
Eunoia Eigensinn
wrote:
>
> "Eunoia Eigensinn" <Eige...@BVI.com> wrote in message
> news:1105_10...@news.vif.com...
> > The primary reason that steel-framed towers are prominent on the US
> scene is because of a strong steel lobby.
>
> Not true.
>
>
> >
> > Most of the major concrete-framed towers in the US (and world-wide for
> that
> > matter) are built using Canadian consultants/technology. With the use of
> > "flying forms" and high-early cement, there's very little difference in
> > erection time between steel & concrete but obviously, the concrete frame
> will
> > be superior.
>
> Time is not the only issue. (Though I would argue that the time is near
> te same) Cost is the primary one, second is space
Time is a big issue for the developer.
Every day that the property sits there without occupied office space stacked
on top of it, his ROI is decreased. That is a cost.
Do you know how much futzing around is involved in fireprooofing a steel frame
? How much time (and cost) does that involve ?
What trades (and unions) are required to erect a steel frame ? Compare that
to the trades involved in doing a concrete frame. What's the incremental cost
of the former ?
With a concrete frame, 9m x 9m column bays can easily be accomplished with
two-way slabs, with no beams to interfere with the running of services.
This translates to lower floor-to-floor height, more useable building volume
and hence, lowered costs.
etc etc. When considering costs, it makes no sense to use a steel frame and
yet, see how much trouble you'll encounter in trying to get a concrete-framed
tower built. Yes Paul, as much as you may not want to know, the steel lobby
and unions in the US are very powerful and play a big role in the above.
> > 9m x 9m (30 ' x 30') bays with 4.5m (15') cantilevers around the
> perimeter
> > (developers like the marketability of column-free windowed exec offices)
> are
> > pretty much standard and the optimum floor plate size is about 200 m^2
> (~20k
> > ft^2).
> >
> > Obviously, the column size will be larger for those on the lower
> storeys.
>
> Another reason developers favor steel
If you're trying to tell me that the columns in a steel tower are the same
size at the base as those at the 50th or 60th floor then you obviously know
nothing about building.
P.Fritz
"Eunoia Eigensinn" <Eige...@BVI.com> wrote in message
> On Thu, 1 Jul 2004 08:29:40 -0400, "P. Fritz"
<paulfrit...@voyager.net>
> wrote:
> >
> > "Eunoia Eigensinn" <Eige...@BVI.com> wrote in message
> > news:1105_10...@news.vif.com...
> > > The primary reason that steel-framed towers are prominent on the US
> > scene is because of a strong steel lobby.
> >
> > Not true.
> >
> >
> > >
> > > Most of the major concrete-framed towers in the US (and world-wide
for
> > that
> > > matter) are built using Canadian consultants/technology. With the
use of
> > > "flying forms" and high-early cement, there's very little difference
in
> > > erection time between steel & concrete but obviously, the concrete
frame
> > will
> > > be superior.
> >
> > Time is not the only issue. (Though I would argue that the time is
near
> > te same) Cost is the primary one, second is space
>
>
> Time is a big issue for the developer.
Nobody said it wasn't.....it is NOT the primary issue.
> Every day that the property sits there without occupied office space
stacked
> on top of it, his ROI is decreased. That is a cost.
And you have yet to prove that concrete is any quicker to build.
>
> Do you know how much futzing around is involved in fireprooofing a steel
frame
> ? How much time (and cost) does that involve ?
Yup......just finished a 250,000 s.f steel building complete with spray
on......<YAWN>
>
> What trades (and unions) are required to erect a steel frame ? Compare
that
> to the trades involved in doing a concrete frame. What's the incremental
cost
> of the former ?
<snicker> for every point you make WRT the benfits of concrete
construction, I can point to others that are just as valid for steel.
>
> With a concrete frame, 9m x 9m column bays can easily be accomplished with
> two-way slabs, with no beams to interfere with the running of services.
So? you can span further with steel if desired, and using joists and
trusses eliminates the 'interference" non problem.
>
> This translates to lower floor-to-floor height, more useable building
volume
> and hence, lowered costs.
Nope
>
> etc etc. When considering costs, it makes no sense to use a steel frame
and
> yet, see how much trouble you'll encounter in trying to get a
concrete-framed
> tower built.
Just your speculation and conspiracy theories......Free hint to the
clueless......cost drives almost all construction. And the few points you
have mentioned are just a fraction of total costs that drive the
construction business.
>Yes Paul, as much as you may not want to know, the steel lobby
> and unions in the US are very powerful and play a big role in the above.
<YAWN> Another conspiracy nut obviously
>
>
> > > 9m x 9m (30 ' x 30') bays with 4.5m (15') cantilevers around the
> > perimeter
> > > (developers like the marketability of column-free windowed exec
offices)
> > are
> > > pretty much standard and the optimum floor plate size is about 200
m^2
> > (~20k
> > > ft^2).
> > >
> > > Obviously, the column size will be larger for those on the lower
> > storeys.
> >
> > Another reason developers favor steel
>
> If you're trying to tell me that the columns in a steel tower are the same
> size at the base as those at the 50th or 60th floor then you obviously
know
> nothing about building.
If you are trying to say that a properly sized steel column can be replaced
with the same size concrete one.....then you are a complete idiot.
BTW......anymore unsolicted private emails will result in a complaint to
your ISP
>
>
>
>
>
JTMcC
"Eunoia Eigensinn" <Eige...@BVI.com> wrote in message
news:1105_10...@news.vif.com...
is
> because of a strong steel lobby.
>
> Most of the major concrete-framed towers in the US (and world-wide for
that
> matter) are built using Canadian consultants/technology. With the use of
> "flying forms" and high-early cement, there's very little difference in
> erection time between steel & concrete but obviously, the concrete frame
will
> be superior.
>
> 9m x 9m (30 ' x 30') bays with 4.5m (15') cantilevers around the
perimeter
> (developers like the marketability of column-free windowed exec offices)
are
> pretty much standard and the optimum floor plate size is about 200 m^2
(~20k
> ft^2).
>
> Obviously, the column size will be larger for those on the lower storeys.
Us silly Americans, we don't know how to build things like sky scrapers,
bridges, thousand mile pipelines, space craft, ect. You are right, we need
to enlist the help of third world nations to truly show us the way! Of
course concrete is the superior material for hi rise building! Especially in
seismic zones! Show us the way oh great one! chuckle, chuckle.
JTMcC.
JTMcC
"Eunoia Eigensinn" <Eige...@BVI.com> wrote in message
Sure I do, I've seen it done many times. I haven't yet witnessed a bunch of
"futzing" as you say, it's mostly work, done by experienced contractors. Is
"futze" a technical term?
>
> What trades (and unions) are required to erect a steel frame ? Compare
that
> to the trades involved in doing a concrete frame. What's the incremental
cost
> of the former ?
OK, Steel frame = pile drivers,iron workers, carpenters,
pipefitters/plumbers, electricians, operating engineers. (these being the
main crafts involved).
Concrete frame = pile drivers, iron workers, carpenters,
pipefitters/plumbers, electricians, operating engineers.
How many years do you have on site in the commercial construction world? You
should know this.
>
> With a concrete frame, 9m x 9m column bays can easily be accomplished with
> two-way slabs, with no beams to interfere with the running of services.
>
> This translates to lower floor-to-floor height, more useable building
volume
> and hence, lowered costs.
>
> etc etc. When considering costs, it makes no sense to use a steel frame
and
> yet, see how much trouble you'll encounter in trying to get a
concrete-framed
> tower built. Yes Paul, as much as you may not want to know, the steel
lobby
> and unions in the US are very powerful and play a big role in the above.
Which unions? Really, I want an answer. The same iron workers that hang the
iron, place the rods in your concrete hi rise.
JTMcC.
Don Phillips
In the Unites States and in many parts of the world, the code for reinforced
concrete is ACI 318 and is typically referenced as a standard in most
building codes. The practical limit for concrete is purely monetary.
Sincerely,
Donald L. Phillips, Jr., P.E.
Worthington Engineering, Inc.
145 Greenglade Avenue
Worthington, OH 43085-2264
dphi...@worthingtonNSengineering.com
[remove NS to use}
http:\\worthingtonengineering.com
Don Phillips
news:20040630030335...@mb-m10.aol.com...
I agree. Until the advent of pozzolans and flyash into the cement allowing
compressive strengths into 10,000 psi and higher, the ehight of reinforced
concrete buildings was limited, financially. If I remember, there is a 60
or so building in Seattle using 10 ksi concrete and I think it was built in
the early 90's.
I am sure www.aci-int.org will provide a lot of literature, if interested.
Don Phillips
In addition to gravity loads, you have to consider wind and siesmic loads.
Some of the block will be in tension and you will need reinforcement since
grout and block is poor in tension. Block is also must weaker than concrete
so eventually, concrete would be more econimical than block.
Don Phillips
news:_OREc.13167$Ch.1638@okepread04...
> Phil Scott wrote:
>
> > Its been calculated that a 200 story concrete building
> > will be so heavy that it will punch its way though to the
> > center of the earth, loosing much of its retail space appeal.
> > Getting concrete up that high is a problem too,.. and you
> > still have to fit a couple of tons of rebar into a typical 16"
> > column.... not much savings there. Its all labor intensive.
> >
>
> But the hoisting requirements are less.
> You can pump all of the concrete from the ground, and all you have do lift
> is forms and rebar cages. Besides, if you have a massive cage in a dinky
> 16" column, you ought to use a bigger column.
I would think there is a limit how high you can pump concrete.
Eunoia Eigensinn
Fritz;
Complain away. It won't get you anywhere.
All anyone has to do is read the message to which you replied to see that you
did indeed solicit a response. I can easily ignore you from here on in though.
Not much point talking to a fencepost.
Now where did I say anything about equivalency of cross-sectional areas ?
That said, if you were to include the fireproofing, furring and finish
cladding of the steel column (we're talking about Class A office towers,
million+ sf BTW, as implied by the OP; not low-rise slums like the one you
refer to in your message) then I may very well say "yes" to the above.
Deepak Warad
Even after so much discussion, it still confuses me why steel is
considered better than concrete for high rise buildings. In India, we
have 95% of buildings made with concrete, except the industrial sheds.
What about other things like fire hazard? Is concrete not a better
material as compared to steel?
Under severe climatic conditions (exterme cold or hot), which material
will be better?
And what about lightening? If a lightening strikes on a building, will
a steel frame be better due to its high conductivity?
Regards,
Deepak
Eunoia Eigensinn
I would venture that those who argue that steel makes for better towers simply
don't know how to do concrete frames properly.
I would further venture that had the WTC towers been concrete-framed, the
events of 9/11 would have been far less devastating.
There is a reason that they don't build American embassies using steel frames.
Rich Jones
> Deepak;
>
> I wocompetitivehat those who argue that steel makes for better towers
> simply don't know how to do concrete frames properly.
>
> I would further venture that had the WTC towers been concrete-framed, the
> events of 9/11 would have been far less devastating.
>
> There is a reason that they don't build American embassies using steel
> frames.
>
OK, I'll bite -
1)
Maybe it's easier and cheaper to perform quality control of local aggregates
and import the rebar than to import structural steel.
Remember, Buy America legislation probably still applies to federal money
projects in foreign countries.
2)
How tall are these buildings? If I had to guess, they are mostly squat, 5
floors or less. Not really a tower.
3)
An embassy is a bunker, not a tower. Different functional requirements.
Finally, I would venture that those that build everything out of concrete
don't know how to design steel properly.