This is the arch bridge I was trying to remember, in which the arch splits into 'wishbones' at the ends. Perhaps not a proximate reason for that collapse, but a weak point nevertheless.
There appears to be a significant gap at the apex of the arches with a simple, single bolt connection. I can't yet imagine how the guy wire mounts were included but the mount for the lower arch came away clean (as seen in previous images laying on the deck) and the mount for the upper arch appears still fixed to the west weldment but there is no damage to the east weldment. I guess the guy wire for the upper arch can pass through the gap in the lower arch connection.
That pin connection looks awfully flimsy ^. The pin holes in the clevis plates have almost no edge distance. The plates appear very thin. Was this really holding the whole arch together??
The area circled in green appears to have been torn out. Could this tear-out failure of the pin have caused the arch to collapse? Alternatively, the other side of the clevis appears to have collapsed at its base, which is not surprising considering how thin it is. Could this have initiated the pin to become dislodged and tear out of the other side?
I would image that under wind loading, one side of the clevis would have been in tension and the other in compression. Perhaps this bending through the connection was overlooked, because it might have been thought that the guy wires would eliminate such an effect. But the guy wires appear to be awfully flimsy as well and not in a particularly effective arrangement as I mentioned in my first post.
The structure likely experienced buffeting during its entire life. It is a large sail of significant mass so any movement would likely work over the joints pretty good.
That was the purpose of those huge cable stays on the Florida pedestrian bridge that collapsed, too. No one seems to want to take really clear photos of the connections, it would appear. That top 'pinned' connection is really strange looking and really flimsy by the look of it.
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
"Wow! If this "connection" isn't the cause of the collapse, I will eat my hat."
When I look at the pictures of the completed decoration, I don't see a connection as shown in that photo.
The connection you are referring to appears to have been temporary and long gone. If so, it's kind of hard to see how it could cause a collapse, since it didn't exist anymore.
I was able to see the news article... had to set my VPN to the US to see it. Hokie's correct in the the material is incised, so it's PT and not likely good firewood. The manner of repair seems flaky. I don't know what failed, but adhesives and clamps with self tapping screws seems a little odd.
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
agree Hokie... the similarity is that they, too, were decorative only, like the cables in this one. I don't know their function (even if only decorative) and what affect they had, if any, on the collapse. The Florida stays had the capability of supporting a load of several hundred kips... they weren't detailed as decorative... and they had nothing to do with the Florida failure.
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
Are the knuckle connections supposed to be rigid, ie designed as rigid? Would that be the design intent? The dont look very rigid. Yet I can’t see how it could ever be stable without them being rigid.
dik,
The Florida bridge stays may not have been detailed as decoration, but that was the intent, according to the project description. But the whole wooden monstrosity in NC was a sculpture, not a load bearing span. The cables may have been intended for lateral stability...maybe as an afterthought.
Tomfh, agreed. I would say that a traditional 3-hinge arch turned itself into a 5-hinge arch with the failure of those 'knuckles' at the top of the wishbones, and that is not a stable structure.
That may have been the intent, but had the structure 'stood up', whether it wanted to or not, the cable stays would have had a real impact on the strength and behavour of the structure. Just because you label them as decorative, unless you detail them as such, they may not be.
As I noted earlier, "I'm not sure what the cables are for... if to provide support of something below, they might have been OK. If to provide lateral support at the top, not so good. Any horizontal load at the top would greatly increase the force in the cable because of the 'steep slope'. We'll have to wait and see why it 'broke'."
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
I don't know... if they were for dynamic response, it would likely be lateral since that's the weak direction. The steep slope would increase cable loads substantially, and the vertical loading on the arches. The arches had been subjected to greater wind loads earlier this year. We'll have to wait to find out the cause from some other source. I'm still curious about what the earlier failure was and the manner of repair. That, too, might have bearing.
Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?
