Why did the Wuxi viaduct collapse? How to evaluate the collapse of the Wuxi viaduct?

The collapse of the Wuxi viaduct is currently the focus of attention of netizens. No one can understand why a good viaduct would collapse for no reason. Many people speculated on the cause. The official answer has been given that it was caused by an overweight train on the bridge. Let's take a look at the detailed introduction below.

Why did the Wuxi viaduct collapse?

Some people say it was caused by "resonance". I personally think that unless you are a top expert, it is generally difficult to confirm that the cause is "resonance" in a short period of time. In history, there have indeed been cases of bridge collapses caused by resonance, such as wind vibration and soldiers crossing the bridge, but that is really different from this. If there is resonance, it can be seen with the naked eye.

From the pictures posted by netizens, some of the bridge piers are single piers. Single piers have poor robustness and one side is overloaded, just like a seesaw. Now they are gradually being phased out. Although the structure has certain limitations, as long as the load is within the design range, there should be no problem. So it is too early to say that it is shoddy because we don't know.

It is speculated that the root cause is still overloading. Of course, it is too early to draw a conclusion now. Let's wait for further investigation.

Some people ask: Why don't we consider overload when designing structures? Actually, we do consider it. We always leave a margin, and leave enough margin through load adjustment coefficient and safety factor. What is "enough"? This is related to the level of economic development and technology. In the past, when we were poor, we couldn't leave enough. Now that we are not so poor, we can cover more risks. But this defense is not infinite, it is always limited. When the Pentagon designed it, it would not be "enough" to prevent an aircraft collision.

How to evaluate the collapse of Wuxi viaduct

1. This bridge is a three-span continuous beam with a single support at the middle point, and its anti-overturning capacity is relatively poor (it is only worse than the double-support solution, which does not mean that it cannot withstand the overturning load required by the specification).

2. This bridge has no transverse block. Once the fixed support that constrains the transverse displacement is damaged, the transverse sliding of the box girder as a whole will not be restricted. (Under normal circumstances, the fixed support can meet the transverse force requirements and prevent transverse displacement, provided that the support is not damaged)

There are anti-vibration stops to prevent lateral sliding to a certain extent

No lateral stop, cannot prevent sliding after support failure

3. Judging from the video, the fall of the bridge was not a typical overturning, but more like a lateral sliding beam fall.

4. From the video, we can see that the overloaded 180-ton vehicle is located near the side pier on the side span. If it is a typical rollover, the rollover may have occurred before the vehicle reached this position.

In summary:

Possible cause of the accident 1: When a heavily overloaded truck drove near the side pier support on the left side of the bridge, it crushed the support on the left side. The support on the right side was higher than the left side, causing the entire beam to slide to the left and fall.

Possible cause of the accident 2: When a seriously overloaded truck was driving on the left side near the side pier support, the right side support became vacant, causing the beam to overturn around the left side support.

The cantilever of this bridge is not large, and the vehicle was located at the side pier of the double support when it overturned. Personally, I prefer the first reason.

The above is a technical discussion from a personal perspective. The information comes from the Internet. The true reason is subject to the final official report.

If the vehicle is not overloaded, there should be no problem. If the vehicle is driving in the middle of the bridge, the load is shared by two supports, and I think this accident will not happen. In fact, when designing the bridge, we have left enough room to deal with general unexpected situations, but the room is not endless.

Finally, I would like to say that if the designers design according to national standards, the drivers operate according to national laws and regulations, and everyone acts in accordance with the law, I believe that similar accidents will never happen.

Kind tips

All elevated roads under the jurisdiction of the municipal government in Wuxi City are indeed not accessible to trucks, and all entrances have clear signs prohibiting trucks from entering. However, the section of road where the accident occurred was not a municipal elevated road, but a section of an overpass on the national highway, and it is legal for trucks to drive on it (let's not discuss whether the regulations are reasonable). If the truck wants to take the national highway to Shanghai, that section is also a must-go road, and there is no ground road for it to pass.