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Huge traffic bridge in Italy collapses...

Step

I am with you on this "prestressed concrete cable stays" concept. I have some vague remembrance of discussion of prestressed concrete from my undergrad days - layout wires in a form and stretch them (love the Braveheart reference). Pour the concrete and allow it to set up to a point, then release the cable tension and allow the steel to relax and transfer the tensile load into the hardening concrete - the concrete is actually stressed in compression which must be "overcome" by the tensile loading in the final bridge configuration.

The slenderness of the prestressed concrete "cable stay" is not critical during the process due to the formwork - but what about after the forms are removed and the "prestressed concrete stay" must handle the compression load by itself? Once erected and connected in to the structure, the primarily loading on the stay is tension which really alleviates the prestressed compressive loading - do I have this correct?

There could be ways to temporarily fasten stiffening components to the prestressed cable stay that would reduce the slenderness ratio of the actual member - those temporary members would remain attached until the stay was erected and assumed the normal tensile load in the bridge.

Any type of cracking (not necessarily visible to the eye) that occurs (think vibration from traffic loading and wind stresses) provides an avenue for moisture and then potential corrosion of the prestressing cables. Now I start to reminisce about the Silver Bridge and it's sudden demise due to a small construction flaw that created a different fatigue category in a fracture critical member.

It seems that there has been some sort of structural retrofitting on this bridge's stay members - don't know enough about it to comment. Somebody was aware of something happening.

I anxiously await the expert's report on the cause of this catastrophe - my prayers for the victims, their families and the brave recovery workers in this even.

Today, these cable stays would be steel cables made from galvanized wires and the stays would be sheathed with fiberglass wrap with attention to allowing any moisture that entered the assemble to drain.
 
I anxiously await the expert's report on the cause of this catastrophe - my prayers for the victims, their families and the brave recovery workers in this even.
You appear to be a wonderful gentleman, Mr. Dibbs. Thank you much for sharing your thoughts on this tragedy.

Yes, I believe you are correct on both of your observations. Prayers for the innocent that were involved in this and their loved ones.

I have this terrible feeling that the investigation will reveal an erroneous engineering concept needlessly causing the deaths of so many.

I'm at Lehigh University today for a few PDH classes. At 2pm we have a short lunch break, maybe other structural guys will have opinions.

Have fine day MrDibbs
 
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