When the superstructure supports, the steel that supports the road bed fails, the roadbed takes on significant stress. The stress will be distributed in that sheet as tension and compression.
The roadbed is a sheet of reenforced concrete. Where there's tension, and the stress rises to the breaking point, the concrete simply cracks and the rebar yeilds. Where there's compression, and the stress hits the failure limit, the concrete "explodes". It pulverizes and shoots out with all the energy that was contained in the concrete at that location, prior to the failure. IOWs, the static potential energy contained in those portions of the sheet that were under compression, was released as kinetic energy in the form of flying concrete dust and the shock wave created by that release. Those areas that failed in tension, simply crack, with the energy going into movement of the large broken sections and the shockwave created by the propagation of the crack.
In this case, the steel had yielded prior to the catastrophic failure. Regardless of what the rat politicos said in the various interviews. The engineering reports noted cracks in the steel. Cracks in the steel are never simply cosmetic. Cracks in the steel only occur when stress is applied. Cracks in mild steel, as is the case here, indicate fatigue, which is a microscopic rearrangement of atoms that aligns and separates grain boundaries in the steel "along the crack". That means the steel can not support what it originally could and the roadbed, the reenforced concrete sheet, now contains a considerable stress pattern that the sheet was never intended to contain.
The various interviews all say the roadwork was simply cosmetic resurfacing. That was not the case. The concrete sheet was being hammered and cut. That action caused the stress contained at those points to be redistributed to other intact areas of the sheet, so that those areas hit their failure limit. Once the sheet gave, it redistributed the forces on the fatigued steel of the superstructure, which was already stressed close to breaking(it had already began to crack), and the whole thing went down.
Neither the engineers that inspected the bridge, or the ones hired to do the repairs had any appreciation for what they were working on. The proof is in the water.
“Neither the engineers that inspected the bridge, or the ones hired to do the repairs had any appreciation for what they were working on.
The proof is in the water.”
Well said!
“he various interviews all say the roadwork was simply cosmetic resurfacing. That was not the case. The concrete sheet was being hammered and cut. That action caused the stress contained at those points to be redistributed to other intact areas of the sheet”
Your latter statements do not contradict the former. Just because actions RESULTED in failure does not mean they INTENDED anything beyond “cosmetic” resurfacing.
Otherwise, I liked your summary. ;-)
Great explanation!
How can cracks in steel beams be ignored? I went to engineering school, and I remember cracks being a veeeery bad thing.