How long would the World Trade Center (1973-2001) have stood after the large commercial passenger aircraft impact if the columns had been made of concrete?

The perimeter columns were steel according to Wikipedia...

The framed-tube design, introduced in the 1960s by Bangladeshi-American structural engineer Fazlur Rahman Khan,[59] was a new approach that allowed more open floor plans than the traditional design that distributed columns throughout the interior to support building loads. Each of the World Trade Center towers had 236 high-strength, load-bearing perimeter steel columns which acted as Vierendeel trusses.[60][56] The perimeter columns were spaced closely together to form a strong, rigid wall structure, supporting virtually all lateral loads such as wind loads, and sharing the gravity load with the core columns.

The core columns were steel according to Wikipedia...

The core of the towers housed the elevator and utility shafts, restrooms, three stairwells, and other support spaces. The core of each tower was a rectangular area 87 by 135 feet (27 by 41 m) and contained 47 steel columns running from the bedrock to the top of the tower.

Edit... A quote from an answer below is...

A more approachable question might be 'how do steel frame skyscrapers compare to reinforced concrete skyscrapers in terms of fire resistance and dynamic impact resistance?'

Please think of this as the question. It is a superior expression of my intended inquiry. Additionally you should assume that the reinforced concrete buildings have an amount of capacity for office space and height similar to the actual WTC (1973-2001).

  • $\begingroup$ Columns are not made on concrete . They are steel rebar with concrete around the rebar. There are various amounts of rebar with various strengths depending on the strength needed for the column. The lower columns of the trade center ( the ones with gothic arches) were plain ordinary strength ASTM A36; I do not know about the higher steel columns. Concrete adds a valuable heat insulation factor protecting the steel which bears the primary load. $\endgroup$ Jul 25, 2022 at 21:10
  • $\begingroup$ Based on the info provided, whatever answer you may get from here is going to be a wild guess. Try refine your question with sufficient engineering data for people to act on. $\endgroup$
    – r13
    Jul 25, 2022 at 22:04
  • $\begingroup$ The back story got my interest. The Amoco bldg ( now Aon) perfected the tube in tube design for steel skyscrapers . Determined by the greatest number of square feet divided by the tons of steel. Fazlur Khan designed the Hancock Tower ( Chicago) , a tapered tube . Then the Amoco was built. Then Kahn designed the Sears tower ( now Willis) nine tubes together. They all use steel more efficiently than the Empire State bldg , but Amoco is the most efficient . ( Disclaimer - yes , I was an Amoco employee but had almost nothing to do with the building). $\endgroup$ Jul 25, 2022 at 23:43
  • $\begingroup$ And the Trade Center withstood the aircraft impacts. It was the fire that destroyed the steel buildings . You may have noticed the hijackers planned to use planes that were almost full of fuel. $\endgroup$ Jul 25, 2022 at 23:52
  • $\begingroup$ The reinforced concrete structures have one major disadvantage over steel structures - to reach the same strength, the concrete column will be much larger than steel, thus, the weight. When a building is damaged through dynamic means, the weight is not a friend you would like to have. $\endgroup$
    – r13
    Jul 27, 2022 at 3:36

1 Answer 1


As it stands this question is too open ended. If the exact same column positions and geometry were used but the material was concrete not steel, the structure would not stand up under its own weight and it would have not been possible to construct.

A more approachable question might be 'how do steel frame skyscrapers compare to reinforced concrete skyscrapers in terms of fire resistance and dynamic impact resistance?'

Engineering such structures is extremely complex, and of course there is huge variety even between different forms of steel frame structures or between reinforced concrete structural forms. Many structures are composite and use both structural steel as well as reinforced concrete. Note that unreinforced concrete is almost never used structurally.

There are a myriad of factors that affect the performance of concrete and steel structures, however to give two relevant although extremely general points; steel often has a larger ability to absorb impact energy through undergoing plastic deformation, and reinforced concrete may in certain circumstances have better fire resistance due to its greater thermal mass and insulating effect.


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