mininamib said:
150 years doesn't seem that long, especially when you consider how old many of the houses in places like Europe, North Africa, and some parts of the Middle East (Yemeni "skyscrapers" in Shibam Hadramawt) are.
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Unreinforced masonry is great for avoiding corrosion. It's not great because when an earthquake happens, basically everyone dies.
 
FastidiousHack said:
It's really hard to say how long our new skyscrapers will last, as modern reinforced concrete construction techniques haven't been around long enough. 100 year old concrete buildings today were designed and constructed much differently than buildings going up today.

There's a number of things that would warrant demolition. Freeze/thaw exposure, the salt for deicing, and just general time are all things that cause rebar corrosion. There's also the possibility of a design level wind or earthquake event, in which case the building would likely need to be demolished.

In the absence of those factors, let's say the structure is contained inside the envelope, GFRP bars are used, and no earthquakes - theoretically it would last "forever" (i.e. longer than humanity). The chances of nothing bad ever happening are pretty small, so people usually say somewhere between 100-200 years.

Ultimately, I'd expect these buildings to be torn down for social or financial reasons over structural. that is unless an earthquake hits Toronto. In which case I could rant for a while about design codes, structural performance, and the unpreparedness of our infrastructure for such events.
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Due to the relatively low fundamental frequency of tall buildings, skyscrapers typically perform very well in earthquakes so I think we can likely eliminate that risk.
 
FastidiousHack said:
GFRP bars are used
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Speaking of GFRP... Is fiberglass-polymer rebar ever used in Toronto for skyscraper construction? I don't seem to remember seeing anything other than good ol' rusted steel rebar at the construction sites. Is it cost-prohibitive to put into building construction? Does it require special skilled labor to install? (i.e. you can't just weld the damn thing)
 
Taken 30 November.

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Full Metal Junkie said:
Speaking of GFRP... Is fiberglass-polymer rebar ever used in Toronto for skyscraper construction? I don't seem to remember seeing anything other than good ol' rusted steel rebar at the construction sites. Is it cost-prohibitive to put into building construction? Does it require special skilled labor to install? (i.e. you can't just weld the damn thing)
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It's being used more often recently, there are some examples in North York. It's advantages are more pronounced in transportation infrastructure. As for why, mostly just cost.
Civdis said:
Due to the relatively low fundamental frequency of tall buildings, skyscrapers typically perform very well in earthquakes so I think we can likely eliminate that risk.
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I generally agree, wind will dominate lateral load cases, however that doesn't mean tall buildings are immune from damage due to earthquakes.

A ~300m building will have a fundamental period of around 6 seconds, and the spectral acceleration does decrease as the height increases, but that's not the end of the story. Maintaining the weight of a ~4m transfer slab that high off the ground requires extremely high lateral stiffness of the elements below it, which when the ground starts moving, will incur monumental forces.

The building certainly won't collapse, but there will be quite a large amount of damage sustained due to the stiffness irregularity the transfer slab imposes. Of course all of this depends on the severity of the earthquake, but if meaningful damage is sustained between the ground and the transfer slab, it'd very difficult to repair a structure with tensioned lateral systems and deem it safe for reoccupancy.
 
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Full Metal Junkie said:
Fascinating to see Canadian construction industry measure concrete in cubic meters. It's almost like we live in a metric country. How did we ever move away from measuring concrete in foot-yard freedom units?
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A true Canadian would measure it in cubic metres. A meter is a tool to measure. A metre is a measurement.
 
FastidiousHack said:
It's really hard to say how long our new skyscrapers will last, as modern reinforced concrete construction techniques haven't been around long enough. 100 year old concrete buildings today were designed and constructed much differently than buildings going up today.
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I would say modern construction techniques can be employed due to high fidelity computer stress modelling, allowing for better design life predictability. I would agree with you that there are many other reasons why a building may deteriorate beyond economic repair, well before it reaches its intended structural design life.
 
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