The detail used for reinforcement might be quick and theoretically sound but the 4 tensors are quite difficult to equilibrate. Maybe some clamped thing can also work, and more difficult of get it out of the wanted work.
The four outside rods were likely to fail, as these were working as tension hangers subsituting for cracked eyebar. Being threaded, i.e. nicely notched make them prime candidates for fatique cracking, and a month seems about right as time frame for fatique built up.
The only way to prevent the fatique phenomenon was to pre-tension the whole assembly to make it behave as a block,reducing the stress range below the treshold.
I agree with both viktor and IFRs. The hinge seems to be seeing active excursions under the loading. Mere friction built from the degradation of the hinge must have meant bending action on the eyebar itself (intended a tension only member) and then be fatigued to failure. Reduction of friction at the hinge, greasing, substitution or whatever seems a right movement. Furthermore a coupon at the crack of the eyebar should show the fatigued surface.
Respect the rectangular outfit of the reinforcement it is clear that built friction by prestress of the rods must have derived as viktor implies rhomboidal configuration upon the hinge rotational excursions, then entailed very localized action upon likely significantly prestressed rods (to share the load from the start). So a purportedly indiferently stable equilibrium was not since 1st difficult to actually be equilibrated and then upon real small separation of the notional equilibrium concept falls apart from such intended state and becomes unstable upon growth of stresses not devised (it seems enough) on the solution.
More, an interesting observation about the commonality of languages. It could be said that friction here entails pinching action, in spanish would be said, implies "acción de entalla". Entails means to be drawn, "arrastrar" in spanish, and "acción de entalla" means the pinching action at cleavage points. So in the past some people must have seen many ropes to fail just on this grip-grip movement. Anyone, not only engineers, have much to learn about situations by only understanding how something is described in the most ordinary language. Words, apart of the generalized current meaning have usually 3 or more deep levels of meaning that convey in subtle ways in-built knowledge as pertaining to the related matters.
Hindsight is wonderful, and these guys here under a huge amount of pressure to re-open the bridge as soon as possible.
Having said that, it is true that the set-up seems poor to me and there is no way to guarantee an equal distribution of loads between the four rods. It would be interesting to know the stressing sequence and how the jacks were connected (parallel?).
Afer stressing anything as simple as sunshine in one side and not on the other would increase the stresses unevenly. I am not sure fatigue would be it. As complete elucubration, my bet would be for overstress on one of the rods.
Interesting observation about languages Ishvaaag. No two languages are alike. I am still seeking a good translation for 'accurate' in Spanish, somehow I feel 'preciso' does not have the same connotations.
Maybe for accurate the word is "fiel", someone or something with fidelity. Of course, fiel has that other main meaning; an accurate rendering of the situation would be "una representación fiel de lo que sucede (o pasa)". Lacks anyway the sense of measure, given by maybe "the more approximate representation".
It doesn't seem like a good setup to me either, kelowna. Is it possible to replace eyebars? Offhand, I can't see how it could be done. The repair done on the Labor day weekend looks like, if you'll pardon the expression a "Rube Goldberg" solution.
I would think traffic should be kept off the bridge until the eyebar has been replaced.
There was rust inside the crack, so it had been there for a while. The last inspection was two years ago and the crack was not found at that time. Seems to me there should be more frequent inspections.
Replacing an eyebar should be possible, but I do not think it is an 'off the self' item. I guess they tried to open the bridge as soon as possible.
Regarding the last inspection not detecting the crack, that does not mean it was not there. An visual inspection is just that, a good look at the bridge.
I agree the bridge should be closed until the eyebar is replaced. On the other hand I am sure there will be huge political pressure to open it as soon as possible.
Just a bit more about entails, "acción de entalla". It also means position, at the tail, at the end, and also, in the pinching action, the kite tail shape, strangled shape, at ends. The "talle" of a woman is the waist, again related to an hourglass shape. Not only position but shape is kept within these words, and when related to strength, a specific kind of failure related to both.
The cracked eyebar was found in September. This is not a problem of undetected eyebar cracks.
The cracked eyebar is still in place, even after the failure of the repair. This is not a question of "if only they'd found the crack in time".
The repair, as I understand it, was meant to be temporary while they figured out how to go about repairing the eyebar. It's 1930s steel, forged, unknown metallurgy. I asked someone smarter than me why they wouldn't just replace it with a new one, and it was pointed out that taking apart a joint like that is a serious engineering undertaking. So that means welding it, if they can. Or some other kind of bypass, along the lines of this repair they just did.
Since the forces at the 2 and 2 rods sides are equal, and now it is surmised both the anchors of the rods and seat on the pin are as frictionless as feasible, the detail is still susceptible to take rhomboidal shape for a small disturbing force, coming from, say, some friction developing, vibration dislocation and irregular tension loss at the rods. The scarce friction status means that even a small force can mean significant rhomboidal distortion and then contact with the allocated dimensionss of the cylindrical channels trugh which the rods pass at the seating device.
Rhomboidal distortion when both rods' sides present equal stiffness, and trapecial when one side comes to show less stiffness than the other upon relaxation. The trapecial distortion also may bring rod to seat contact.
