The (approximate) rule of the thumb is that anything in reinforced concrete calculated by "hand" has an "implied" additional safety factor of 5-10%, mainly due to roundings by excess in the calculations, at least this has been my experience in the mid 1990's, when for a couple of bridges existing hand made calculations had been re-made with computers.
It is a small (but good) thing, though it would have IMHO not been enough to save this particular bridge, here the issue is evidently a wrong static model, or - less likely - a wrong assessment of loads.
Besides the initial (huge) calculation error, what is really preoccupying is that they didn't consider as serious the cracks, which as seen in the video/photos on youtube are the typical (severe) shear cracks, that should have been ringing all alarms.
The poor structure, as often happens, did all it could to "signal" the issue, what I find bordering being criminal is ignoring or severely underestimating those clear signals.
It is a small (but good) thing, though it would have IMHO not been enough to save this particular bridge, here the issue is evidently a wrong static model, or - less likely - a wrong assessment of loads.
Besides the initial (huge) calculation error, what is really preoccupying is that they didn't consider as serious the cracks, which as seen in the video/photos on youtube are the typical (severe) shear cracks, that should have been ringing all alarms.
The poor structure, as often happens, did all it could to "signal" the issue, what I find bordering being criminal is ignoring or severely underestimating those clear signals.