"...breaking ground on 2009 December 5th, and completed and opened to traffic on 20122 November 6th."
Wonderful Journalism.
I noted that one of the bloggers commented that the trucks must have been overloaded in that they had to trust the design, or something to that effect. This has got to be the epitomy of the problem of "saving face" - the propensity to ignore the underlying problem.
I think it was the color of the trucks. Everyone knows that blue trucks shouldn’t follow red trucks on a bridge like that, or is it the other way around. Also, the middle two piers were to pointy, had kinda small pier caps, without much vert. reinforcing running through the horiz. joint, at the top of the pier. Finally, it is obvious that they should have reverse engineered that span in the other direction. I think that’s a north/south spanning member on an east/west span. If the govment would only let them use Google, they could have Googled torsional loading.
From the photos, it is very clear that the whole span of the bridge was intact even after it had fallen. The falling seems to have been from an overturning effect. photo
And as such the news is that the 4 large overloaded cargo trucks were all on one side of the bridge girder leading to overturning of the girder. I would not put the blame on the overloaded cargo trucks. I am thinking that the designers must have been aware of designing with this in mind.
It's more clear the an overturning girder has largely to do with its geometric design which subsequently defines the position of the bearings (where those pot bearings?).
A pot bearing has a capacity of nearly 500tons which is already more than the 4overloaded trucks combined (~200tons).
So in essence, I am looking at the problem having been more from the geometry of the cross-section of the girder not being able to sustain those overturning moments (induced by the 4 truks) in relation to the positioning of the bearings.
I am in agreement with the geometry problem, but also point out that the dramatic changes in China have resulted in much heavier loadings because of the construction of freeways and not much experience of historical problems. The Harbin area (I think it was earlier called Manchuria) is growing almost as quickly as the southern China and the different provinces do have very structured rigorous standards requirements that are slow to change in comparison with the explosion of the country regarding roads and structures.
When I was in Harbin, I had a discussion with one of the heads of the Technical Institute. He expressed concern that the national/provincial/local standards have not kept up to pace with the progress of the actual development of the country and there is reluctance to automatically accept other concepts because of the cultural, geographical, material and climate difference with other parts of the world. When I was in China, I saw a car stuck in fresh concrete on an off ramp of a new freeway because the warning construction signs had not been posted. Two or three hour traffic jams are common in many areas.
Regarding the loads from trucks, the concept of maximums permitted are not enforced from a practical standpoint, especially in the wee hours of the day where traffic and loadings were not monitored while design and construction is 24/7.
It is a dynamic, growing country flexing its muscles on the short track. I have never met so many engineers so hungry for information and resources. - It is a "work in progress".
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
This was a ramp onto the bridge, designed and constructed by different companies than those who designed the bridge proper. China has the expertise or can hire it, but it is very inconsistent. No one should be surprised...failures happen in all countries, and even more so when there is rapid growth.
The failure is clearly due to shearing of the hammerhead pier, next to the pot bearing clearly presented in the photograph 7 in the linked article.
The reason for failure will be likely counting on the shear capacity of the concrete and provision of the reinforcing steel for excess shear.
AASHTO allows for similar sizing of shear reinforcement, while most European codes call for sizing shear rebars for full force when the stresses in the concrete are exceeded.
This was a three span section of the ramp, with hammerhead piers only at the ends. The two intermediate supports provided little resistance to overturning, so it all depended on the end supports.
I wouldn't find a reason not to trust the bridge proper, as this failure was to a ramp approach, designed and constructed by different firms than designed and built the bridge. Entirely separate structures. If you just don't trust anything about construction in China, then...
