Steal Framed Buildings 1

[Mbrooke]

Question- are steal framed buildings less likely to pancake or have a total collapse? Why weren't the Champlain towers framed out of steal? Would the incident been less likely to have occurred? Why is concrete chosen over steal?

 

[Ingenuity]

Steel...NOT steal!

You can also say the opposite ==> Hard Rock Hotel in New Orleans, for example, was constructed in structural steel that 'pancaked' whilst under construction, however , the 6 levels of concrete (actually post-tensioned concrete) framing survived.

Steel vs concrete is very local market dependent. However, concrete is very common for mid and high-rise residential construction where floor-to-floor height and reduced structural framing thickness is important to developers where height restrictions are in place by local authorities etc.

 

[Mbrooke]

Thanks. The thing is I picture concrete as being brittle, while I see steel as strong yet flexible. Of course my knowledge of structural engineering is limited so I'm just going by preconceived notions.

 

[LittleInch]

Steel CAN be a little more resistant to sudden failure and can yield more than concrete which tends to fail at lower strain, but a good reinforced concrete frame is equally "strong" as a steel framed building.

But under design, errors, corrosion, sudden failure, can happen in both.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[hokie66]

Another factor is fire resistance, in which concrete holds the edge.

 

[Mbrooke]

True, concrete does hold better to fire.

With that said, does code require fire proofing in steel buildings?

 

[1503-44]

Fire proofing is for steel buildings. Concrete is basically its own FP.
Concrete structures are designed to fail in a ductile manner by ensuring that steel reinforcing controls the failure mechanism, i.e. it fails in ductile manner in tension before the concrete fails from "explosive" compressive crushing. Typical beams have tops in compression and bottoms in tension, hence the bottom region is designed so that the steel essentially fails before the concrete in the upper portion of the beams reaches a compressive failure. "Brittle" rapid failures occur when the bottom section has too much steel, thereby allowing the concrete to fail first. Same for columns, although they can have more complicated tension and compression stress patterns.

 

[Ingenuity]

"Brittle" rapid failures occur when the top section has too much steel, thereby allowing the concrete to fail first.

When there is TOO much tension-steel (i.e. over-reinforced) you will get brittle, compression (flexural) failure. Added top steel (in compression zone) would assist in ductility increase.

 

[1503-44]

Too much steel in the sense of that being added after concrete reached failure wouldnt add any helpful ductility. It would increase the load carrying capacity, but concrete still fails when it hits f'c. But I can change that to bottom steel and everyone can be happy.

 

[Mbrooke]

Question. If the Champlain tower was made out of steel, would it still have collapsed? For some reason I fear concrete, but imagine steel as being able to hold up.

 

[EdStainless]

If there was uneven settling, possible corrosion from leakage, and then whatever other issues any building will give up at some point.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[phamENG]

Considering we don't know the cause of the Champlain tower collapse yet, that's an impossible question to answer.

But if the issue has to do with corrosion of the rebar due to leaks and chemical exposure...then a poorly maintained steel building may have failed earlier.

 

[Mbrooke]

I see. But would steel at least have some indications prior to global failure?

 

[phamENG]

Maybe, maybe not. Concrete - properly designed, detailed, and constructed - will fail in such a way that you have indication. Major cracks in beams, etc. will give ductile failure modes and, in some cases, buildings like this one can be detailed such that a column or beam failure can be absorbed by the structure to give everyone ample time to get out, the site secured, and the building repaired or demolished in a controlled fashion With steel, if you don't proportion the connections right and you have a tear-out failure in shear or tension you won't know until you're on your way down.

All structural materials have their pros and cons, but no one material is better than the others in the generic sense you seem to be going after. In a particular set of circumstances one will be more advantageous than the others, but you can't say "steel is always better than concrete."