# Steel frame vs reenforced concrete.



## Jerry666 (Jan 11, 2012)

Kanto said:


> ^^ So many things I didn't know, thanks for your post :cheers:
> 
> Btw I have a small question, you said the structure of a skyscraper costs 3-5% of the total cost, what elements of a skyscraper cost the most?


 
The fabrication and the erection of a structure is between 2 to 5 times the cost of the material, 2 if it is a simple structure to 5 if it is highly complex.
The finishings + cladding are the main component of the price.


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## Jerry666 (Jan 11, 2012)

dfiler said:


> Does this analysis take into account the shape of steel and concrete columns?
> 
> The reason I ask is that steel columns are not solid cross sections. This means that while steel is stronger, there is a smaller difference in tems of area required for a column. A steel column with a hollow square or H shaped cross section will occupy more space than indicated in a direct strength comparison.
> 
> Either way, thanks for the write-up! It is a fascinating read.


You are right ,theroretically, the best structural choice is a tube. It gives you the highest moment of inertia with the minimum amount of material as you put the steel far away from the neutral axis. 
Steel tubes are usually more expensive per ton than rolled sections. Connections between tubes and beams are more complex to achieve, and you are transporting a lot of air during shipment. 

In the US, they are using more rolled bared H sections as columns fire protected with spray (vermiculite) or encased H columns into concrete to get a composite effect with automatic fire protection. The net area is much greater than with concrete, the fabrication costs are minimal and the erection speed is the highest. 
In China, they are using today more built-up sections made of plates (a lot of "poor" fabrication) also encased into concrete or they are using tubes filled-in with concrete for medium size buildings. 
After a huge earthquake, it will be very difficult for them to check/repair the concrete inside the tubes.


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## Kanto (Apr 23, 2011)

^^ Thanks for the info :cheers:


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## Highcliff (May 4, 2006)

can anyone answer my question?
in brazil the most of buildings are made in concrete, not in steel








why this?


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## China Hand (Jun 11, 2012)

What is inside those columns?



Jerry666 said:


> You are right ,theroretically, the best structural choice is a tube. It gives you the highest moment of inertia with the minimum amount of material as you put the steel far away from the neutral axis.


This would explain the current super-column trend. They look to be square tubes, curved steel for this not yet feasible for 700 m structures.

What about the combined materials? Do they have greater strength/stress handling/deformation tolerance compared to only steel or only concrete?


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## Jerry666 (Jan 11, 2012)

Mega columns in high-rise are made of steel surrounded by concrete. Steel is 5 to 7 times stiffer than concrete. The columns are optimized to limit their overall cost.

In Bazil, they are using more concrete than steel because there are many rebars producers. Small sections are available but large sections needs to be imported. It is possible to import them but it takes a few months. So for small fast track projects, concrete is the fastest solution. For high-rises, steel will become the best solution to reduce the sizes of the columns


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## Jim856796 (Jun 1, 2006)

delete post.


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## Airman Kris™ (Feb 22, 2014)

Kanto said:


> ^^ So many things I didn't know, thanks for your post :cheers:
> 
> Btw I have a small question, you said the structure of a skyscraper costs 3-5% of the total cost, what elements of a skyscraper cost the most?


I would say the glass and electrical components. You have to remember for a 50 level you would need several AC units, transformers,etc. and not to mention _miles_ of insulated wire.


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## Airman Kris™ (Feb 22, 2014)

Jerry666 said:


> Mega columns in high-rise are made of steel surrounded by concrete. Steel is 5 to 7 times stiffer than concrete. The columns are optimized to limit their overall cost.
> 
> In Bazil, they are using more concrete than steel because there are many rebars producers. Small sections are available but large sections needs to be imported. It is possible to import them but it takes a few months. So for small fast track projects, concrete is the fastest solution. For high-rises, steel will become the best solution to reduce the sizes of the columns


Interesting! Great information.:cheers:


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## Jerry666 (Jan 11, 2012)

Something to think about!
Yearly consumption of concrete is 7.5 billions of cubic meters (more than 1 cubic meter per capita). This is the second commodity after water.
Buildings are normally built for 100 years. After that, they have to be demolished or renovated at huge expenses. The most common way to recycle concrete is to crush it and use it for building foundations of roads.
If the concrete production stays stable, in 100 years, we will have to recycle 7.5 billions tons of concrete every year.
If we consider a 10 cm slab of crushed concrete to be dumped, every year we will be able to cover 75 billions of square meter = 75.000 square km of land with a slab of 10cm of crushed concrete. 
The total surface of the land on earth being about 150.000.000 square km, it means that in 150.000.000 / 75.000 = 2.000 years (2 thousands years only), the whole surface of the earth will be covered by a 10 cm of crushed concrete! 
Steel is 100% recyclable and it is recyclable for ever. Let's go steel.


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## Jim856796 (Jun 1, 2006)

"Buildings are normally built for 100 years. After that, they have to be demolished or renovated at huge expenses." I think this will be problematic for the cities and countries who have to build all of their skyscrapers out of reinforced concrete rather than steel just because it reinforced concrete is cheaper than steel?


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## ciaochiao (May 15, 2014)

Jerry666 said:


> Mega columns in high-rise are made of steel surrounded by concrete. Steel is 5 to 7 times stiffer than concrete. The columns are optimized to limit their overall cost.
> 
> In Bazil, they are using more concrete than steel because there are many rebars producers. Small sections are available but large sections needs to be imported. It is possible to import them but it takes a few months. So for small fast track projects, concrete is the fastest solution. For high-rises, steel will become the best solution to reduce the sizes of the columns


Hi @Jerry666,

Your answers are very helpful. Same as Brazil, China uses mostly concrete. I was wondering if it is due to the same reason or is there other consideration? Thanks.


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## Jerry666 (Jan 11, 2012)

China is producing more than 50% of all the steel produced today!
Thus, they are using a lot of steel to build tall buildings and for fire protection, they encase the steel into concrete, this is maybe the reason why you think that they have only concrete buildings.


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## ArchGuy1 (May 17, 2019)

Chapelo said:


> Not to mention the Twins only had sheetrock (drywall) protecting the core columns. Good for small fires, but in a fire like the one seen on 9/11, no real protection. You didn't see many buildings with reinforced concrete cores before 9/11, but it seems like everything that's going up these days has a concrete core.


Have any other skyscrapers been built with only sheetrock surrounding the core columns besides the Twin Towers.


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