Quote:
Originally Posted by Changing City
No, I'm not an engineer, but in the past I read some of the engineering reports. Here's a link that includes a video that says the rehabilitation work is intended to be 'for decades to come'. It's certainly not intended that it should be replaced in a couple of decades, and it's also obviously one of the city's more important heritage landmarks (with all the lighting columns that were lost in the 1960s recently replaced, for example). as has been noted, if there was any suggestion that it wouldn't be retained for the long term the Senakw developers wouldn't waste their money designing and building a transit connection that will be adjacent to, but structurally separate from the bridge structure.
London isn't seismically active, but it doesn't need to be for bridges to need replacing, if they're poorly built. The 1831 London Bridge was sinking about 2.5 cm every eight years, and by 1924 the east side had sunk some 9 cm lower than the west side. The decision was taken to replace it in 1968, and it was dismantled and sold to an American who re-erected the 10,000 tons of facing stone on a new structure at Lake Havasu City, Arizona, which opened in 1971. |
Well,
"decades to come" is rather vague and a far cry from your originally suggested claim of 90 more years.
That's practically a century more, and again,....a far cry from
"decades to come".
Furthermore, you also brought up Pattullo bridge, which was built in 1937 - five years after Burrard - so presumably within the same time-frame level of technology and technological know-how, even if possibly not to the same standards.
Pattullo was
designed and built to have a 50 year lifespan, and thanks to the various maintenance efforts over the years, that 50 year lifespan was stretched by an additional 30 years before the engineering assessment report done on it found that it had only an additional 7 more years of usability in 2017 and recommended immediate replacement to mitigate to risk of any catastrophic failure despite any future retrofits.
Even if we assume that the 5 year older Burrard bridge was built and designed for a longer lifespan of double that of Pattullo and was designed for a 100 year usability,...
And if we further take it that the 20 or so odd years of retrofits it's had, and the structural maintenance and upgrades carried out on it have added another 30-40 years of usability to it's original mid-2030's end of natural lifespan timeline, it would still put it closer to needing replacement closer to when the Ironworks bridge own end date of about 2060-2070(-ish) is, rather than closer to the almost 100 years from now in the early 2100's.
Obviously this is all speculation on both our parts since there's a whole load of data that would need to be known to have a firmer idea on actual numbers, but going by what we already know of what already exists and the standards required for our zone, it's not an unreasonable speculation.
I know little of London's construction requirements and standards other than the fact as mentioned before that they're not in a seismically active zone, nor are in an area that experiences strong wind force and shear force pressure - both of which are not insignificant factors when it comes to how individual cities and locales set their standards and requirements for how buildings and structures are not only built, but should be maintained and also for how long their usability is determined.
Like for example the fact that Tokyo would naturally have higher structural design standards then even BC and the GVA given how much more seismically active a zone they're located in compared to ourselves, and as such it wouldn't be surprising to find that even though they construct structures (like bridges and overpasses) to higher standards, they also have shorter prescribed lifespans before needing replacement or just generally requiring more frequent maintenance retrofits.
It's part of the reason why I felt those examples from London weren't exactly useful.
I could give an example of a bridge constructed in a, for all intents and purposes, seismically inactive and dead zone, that's lasted for over 200 years.
Of what use is it to compare such a structure and its lifespan (and construction standards) to one that's built in a place like Florida that's perpetually hit by Hurricane gale wind forces, or one in Okinawa?
Or a bridge that's crossing sea water and perpetually exposed to corrosive brine versus one that crosses a freshwater river (like most of the Thames is)?
Different circumstances; different conditions; and ultimately different factors affecting how long it can be usable or needs replacing/maintenance and how often.
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