Post
by v12 » Tue Aug 21, 2018 11:25 am
The Koh Pich disaster was electrocution, doesn't have anything to do with rust and/or concrete/iron strength.
Many concrete based bridges do suffer from 2 aspects:
- Chemical additives originally added to the concrete to "enhance" the concrete, turning out to rust the rebar from the inside out, effectively demolishing the concrete structure in 20-30 years.
- Overload, the bridge being designed for a 50+ years lifespan on load xyz though nowadays getting double or more of the daily load in traffic as well as significantly heavier loaded trucks passing the bridge.
For Cambodia, my biggest "bridge" worries would be the washing away of a pylon foundation.
The Genua cause has yet to be established. It could easily be a foundation problem instead of rust and everything associated with that. Let a bridge pylon move 10 cm (down or horizontally) and the whole strength calculation is completely off. The collapsed Genua bridge pylon was located pretty close to the river and the collapse happened during an extreme downpour, signaling something of the bridge has been moving, etc. and the downpour day was just the latest straw that broke. A bridge is unlikely to go down due to a downpour, no matter how rusty the whole thing is.
My understanding of the Genua bridge collapse, is the middle bridge segment between the remaining pylon and the collapsed pylon tore off on the remaining pylon side and hanged "down" the collapsed pylon, which got out of balance and subsequently simply collapsed. That tearing off, of the middle bridge segment is not something caused by rust, though due to movement of the bridge layout/foundation. In the end, something will give way, when that happens ......
Added: A picture has appeared from just before the collapse, showing some (non bridge structural) cabling dangling down the bridge, around the connection between the remaining pylon and the middle bridge segment, suggesting the "gap" between the remaining pylon and middle bridge segment got bigger and some cabling tore off.