https://www.nsia.no/Road/Investigations/22-441
It does not state why they conclude the cause was overload, only that "Uncovering the technical causal factors for the collapse of the Tretten bridge has been challenging. The expert group has worked its way through several hypotheses to be able to exclude non-relevant fracture mechanisms, by connecting findings to computational analyses. There was significant consequential damage to the bridge structure, both from the collapse itself, the impact with the ground and the salvage work, and it has been challenging to separate these from each other."
Personally I would think that a bridge should be able to handle "A passenger car and a truck with trailer loaded with lime were on the bridge when it collapsed".
[1]https://www.researchgate.net/figure/The-Perkolo-bridge-after...
>"... An overview of capacity models derived using the yield limit equations and following the European Yield Model (EYM) approach is provided in [20]. Major examples of structures collapse led by brittle failure in dowelled slotted-in-plate connections are the two trusses of the Siemens Sports Arena in Denmark [21] and the truss of the Perkolo bridge in Norway [22]. Uncertainty in the evaluation of connections' deformability is responsible for local damage in connections, and change of force transfer mechanisms compare to those considered in the design. ..."
The Norwegian Safety Investigation Authority seems to agree. https://www.nsia.no/Road/Investigations/22-441?iid=35881&pid...:
“Checked according to the recommended calculation methods in today's current regulations for the design of wooden structures, the degree of utilization in the connections on the relevant diagonals was around 200%. That is to say, the capacity of these connections was half of what they should have been when calculating the bridge's failure limit state, where safety factors for both loads and strength of materials were taken into account”
Most sophisticated structures are engineered using load factors in combination rather than traditional strength design methods because it leads to more efficient use of materials and hence lower cost.
Yes, strength design might require a 4x safety factor. That’s why engineering practice employs statistical methods and combined loads.
Keep in mind that the safety factors are never supposed to be the difference between stability and failure. If the structure relies on safety factors there’s a problem.
They are mostly on rarely used roads in farm country (as in a handful of cars per week cross), so a truck with lime is one of the more likely potential loads, but of course the local farmers know that bridge can't handle the weight of a truck and plan their deliveries to take a different route (which often more than doubles the trip time vs if the bridge could handle the weight)
Are these bridges you are referring to from your area really old and poorly maintained bridges?
He did a an episode on this bridge. It is excellent, and it provides some context about other timber bridges that is not discussed in this article.
I thought you linked to B1M or something.
My dad is a retired civil-engineer and he displays the same type of mockery (and worse) when he sees badly built stuff. Because he very well knows that badly built stuff can cause people to, well, die. It's not "they made an ooopsiee, let's not make it worse by denigrating the designers/builders", it's "they really f.ed things up, people could have died, they're morons (and worst)".
You don't say...
[0] https://triblive.com/local/frick-park-bridge-collapses-natur...
It just doesn't really go anywhere except a couple thousand homes.
The big bridges on the three rivers, on the other hand! It seems to me that they're always always under repair.
I'm much more worried about like, a random 40 foot bridge outside of the second largest suburb of the third largest city in a southern state or whatever. A short fall into icy water or just getting bonked by a piece of the falling bridge at the bottom is less dramatic but you'd be just as dead. And I'm pretty sure those bridges haven't seen an attentive engineer since whenever they were finished.
Various ancient bridges near my rural home have been "saved" by local morons (here they might be called "hillbillies") who organize elaborate campaigns to demand that the highway department not close them despite their ill repair. In some cases an alternative bridge has been built nearby at vastly increased expense, in other cases it just means that only morons use the existing rusted-out (or in the case of the "swinging" variety, multiple-broken-planked) bridge, carefully driving so they don't drop a tire into the holes.
How a utilitarian object riveted together out of commodity steel in 1910 is such a triumph of human will that it must be imposed on posterity forever, surpasses understanding.
I say novel design, but it's more like some novel techniques for combining wood and metal together. The basic bridge design is fairly common but typically built using all wood or all metal. When you look at it it's fairly similar to train bridges from last century.
This type of bridge needs every beam - so when one broke, the whole thing fell.
The mystery really is why it didn't collapse sooner - that's still under investigation.
