5 ms·

Sure they don't, but they also do not last for eternity (without maintenance or repairs). The theme is more about whether to build "massive" (and expensive) mo

by jaclaz 4y ago

Sure they don't, but they also do not last for eternity (without maintenance or repairs). The theme is more about whether to build "massive" (and expensive) more lasting structures or build more economical but less lasting structures and how to properly evaluate the expected lifetime of these structures. We know empirically that many (reinforced concrete) structures built 70/80 years ago (some even less than that) start showing a number of issues (that often require "heavy" repairs) besides the few that made it to the news. We don't have that many examples of earlier constructions of this kind (pre-stressed concrete is relatively recent as a technology), but we do know that in many countries a large number of bridges were built in the '60's and '70's so they are nearing the time they will reach the age we already found to be critical.

bluGill 4y ago
In short the system of inspections is working.
- jaclaz 4y ago
  >In short the system of inspections is working. Actually no, it isn't working because it cannot possibly work, at least not with decades old structures (that however do not collapse because they were often over-engineered, because after all they weren't built so shoddily and for a thousand other possible reasons). A bridge inspection more often than not amounts to a visual inspection, to detect cracks, check bearings, but while some elements of the structure are visible (as said bearings and concrete surface) the state of internal cables is hard or impossible to check, though there are some new techniques that look promising (though they are not yet AFAIK properly documented/standardized), as an example, JFYI: https://www.youtube.com/watch?v=pKWxpHsLBRk https://www.youtube.com/watch?v=pKWxpHsLBRk And there is another key point, norms have obviously changed a lot in the several decades since the construction, original calculations and drawings may have been lost, and there is the need to re-do the calculations with the new standards of loads and check whether the current loads/frequency of traffic is compatible with those the original project took into account.

by jaclaz 4y ago

bluGill 4y ago

In short the system of inspections is working.

jaclaz 4y ago
>In short the system of inspections is working. Actually no, it isn't working because it cannot possibly work, at least not with decades old structures (that however do not collapse because they were often over-engineered, because after all they weren't built so shoddily and for a thousand other possible reasons). A bridge inspection more often than not amounts to a visual inspection, to detect cracks, check bearings, but while some elements of the structure are visible (as said bearings and concrete surface) the state of internal cables is hard or impossible to check, though there are some new techniques that look promising (though they are not yet AFAIK properly documented/standardized), as an example, JFYI: https://www.youtube.com/watch?v=pKWxpHsLBRk https://www.youtube.com/watch?v=pKWxpHsLBRk And there is another key point, norms have obviously changed a lot in the several decades since the construction, original calculations and drawings may have been lost, and there is the need to re-do the calculations with the new standards of loads and check whether the current loads/frequency of traffic is compatible with those the original project took into account.