What is the relationship between the collapse and overload of 50 bridges that have collapsed in the past 10 years?

 What is the relationship between the collapse and overload of 50 bridges that have collapsed in the past 10 years?

Maybe if we take an example to perfect it, for example, a chopstick, a lot of people can break it, a bundle of chopsticks, we say it is certainly not easy to break, right? But I want to introduce another concept, axle load, wheelbase. Axle load is the concept of cumulative equivalent axle number used in pavement design. There are many kinds of vehicles on the highway. Different types of vehicles and different times of action have different impacts on the road surface. In order to facilitate road design, it is necessary to convert the mixed traffic volume composed of different types of vehicles into a uniform equivalent axle load. Equivalent axle number is based on equivalent principle of pavement damage. The number of axle loads acting on different types of vehicles and different axle loads is converted to the number of axle loads acting on the standard axle load BZZ-100. This unified axle load is called standard axle load. The wheelbase is the distance between wheels.

The incident in Harbin picked something up: It is known that the design bearing standard of Baihe Bridge in Baoshan Temple is Automobile-20 (the total weight of six-axle trucks and goods does not exceed 55 tons). Zhang Wenjun drives a truck with an actual load ceiling of 31.5 tons, while the truck loaded 145.5 tons of gravel and over 110 tons of overweight at the time of the accident. What bigger pickup trucks, SUVs, cars, millions of vehicles on the bridge surface every day, nothing at all. Why? Because the role of the road is too small, neglect, as long as it can pass, it is 24 hours a year and dust as well. But, if its a big truck, this fate, this fate, this fate, this fate, if its too much, its like a forging machine cutting metal, it has a strong shearing effect at both ends of the function. Generally speaking, it has a strong downward force, a large, gravitational direction, and a small action surface. This has a great destructive effect on the road surface, a few overloads. Ten tons of trucks are more serious than tens of millions of cars passing through the road at the same time (the action surface is very small, the damage is very fast). The structure that could have withstood decades has been destroyed centrally. Even a lot of thick chopsticks can not help but cut like you. Just like a lentil on the earth, you cant see the ground sinking. You try to put one on the ground. A neutron bomb, a black hole? The ground cant bear it at all. It must fall down. Its a must.

I dont want to say too much about the entanglement between rampant overload, high freight and bridge design. Here, I quote Marxs saying: If capital has 50% profit, it will take risks; if it has 100% profit, it will dare to trample all laws on earth; if it has 300% profit, it will dare to commit any crime, very much. To risk being hanged. Overloading is a big profit for transportation companies. Great! Great! The damage to the bridge is also great! Great! Great!

Citation Report

A schematic diagram of the rupture and collapse of ramp bridges in Heyuan City of Guangdong-Jiangxi Expressway

Chengnan Ramp Approach Bridge is an export built on the Guangdong-Jiangxi Expressway according to the design service life standard of 100 years. At present, the opening time is less than 10 years. But such a high standard design ramp approach bridge, unexpectedly collapsed in front of four trucks, which is the weight or quality caused by the accident?

On the site of the collapse of the Chengnan Ramp Approach Bridge, Ao Daochao, chief engineer of Guangdong Expressway Co., Ltd., introduced that the design and service life of the Ramp Bridge is 100 years. He believed that the bridge collapse was caused by several heavy trucks overloading at the same time, exceeding the design limit.

But some drivers who have been driving along the Guangdong-Jiangxi Expressway all the year round think that the quality of the ramp bridge is questionable. These drivers said that in the busy Guangdong-Jiangxi Expressway in Guangdong, on the approach bridge of the exit ramp, the close arrangement of large trucks is normal. If the truck wants to leave the ramp, it will slow down naturally. You cant always stipulate in the design that several trucks should not be on the ramp at the same time. Such a high-standard ramp bridge collapsed because of several overloaded trucks, which is also very abnormal.

After the incident, many people questioned the quality of bridge structure design and construction. For example, the two piers of the ramp bridge are all built on the swamp foundation. Are they solid? Is it reasonable to design only two piers for a bridge over 100 meters long?

Experts say

Its more appropriate to say collapse, not fracture.

Its more appropriate to say collapse, not fracture. Shan Chenglin, a bridge professor at the School of Civil Engineering and Communications, South China University of Technology, said that from the online picture, the bridge fell as a whole, and there were some bends on the plane of the bridge, which belonged to a curved bridge with a larger radius. He said that from the photos and information sent, the bridge fell from the connecting part of the pier, not from the middle of the break.

The girder of the bridge was removed

According to Shan Chenglin, bridge accidents are usually caused by the removal of its beams and less fracture. It can be divided into two categories: concrete fracture and steel bar fracture. Usually concrete is broken, if the steel bar is broken, it will be more serious. Highway bridges are constructed according to the first-class standard of highway. Generally speaking, it is a design method to replace the actual load with the waiting load. In the design, the actual bearing capacity of the bridge is greater than or equal to the design load combination. By analogy, you can pick 100 kilograms. The design should be greater than or equal to 100 kilograms. For example, the design should be 120 kilograms. But if you pick 150 kilograms, you may not be able to bear it. Of course, this is in theory. If the bridge itself is ill, it may even be difficult to pick up 80 jin.

Centralized driving is dangerous.

How many kilograms can a bridge load? Shan Chenglin said that its design standard is the specification before 2004, that is, cars exceed 20, trailers 120. Vehicle over 20 means that when more than one vehicle passes, the heaviest vehicle load is 55 tons, allowing other sub-heavy vehicles to pass as a fleet. But if the trailer is 120 class, the maximum load is 120 tons, and only one trailer can be allowed to pass through the bridge. Shan Chenglin stressed that the distance between four trucks should also be paid special attention. If its clustered, its much more dangerous than driving separately.

How long does a healthy bridge last? In theory, 100 years! This is a world problem, like fortune telling, its hard to say. Shan Chenglin said that if the design specifications, quality is good, and does not exceed the design load, according to the normal traffic volume, use time is 100 years of life. He said that if the bridge itself had quality problems, or exceeded the design load, it would depend on the degree of damage.

Shan Chenglin said that a bridge to pass, first of all, the design to meet the requirements, whether the construction meets the requirements, mainly through the completion of acceptance to determine. Including appearance, load test and so on. In the load experiment, a truck loaded with heavy objects will be used to drive on it and load it at the same time until it is equal to its designed load weight. The test passes the acceptance test. This requires all tests. The experimental data are true, accurate, and can not be false, so they are qualified. Shan Chenglin said that, generally speaking, the acceptance unit is responsible for the quality supervision station under the Ministry of Communications of the industry.

Expert Analysis of Bridge Collapse Process

Experts from the Department of Bridge Engineering of Tongji University have analyzed that the design of single-column piers of curved bridges has hidden dangers of small probability, and the vehicle condition in China is complex or the accident probability is increased.

In the early morning of June 19, the ramp bridge in Heyuan City of Guangdong-Jiangxi Expressway broke and collapsed, and four heavy-duty trucks fell down. The collapsed bridge deck is about 73 meters long and contains two piers. The distance between the piers is about 24 meters. The maximum height between the collapsed bridge deck and the ground is about 11 meters.

A professor in the Department of Bridge Engineering, Tongji University, who asked not to be named, told Nandu that the reason for the collapse of the expressway bridge was similar to that of the Shangyu Chunhui overpass in Zhejiang Province in the early morning of February 21, 2011. For the Shangyu Bridge Collapse incident, the professor has done research in the subject study and formed a complete project report.

It is difficult to restrain torsion of single-column pier

For the specific reasons of the incident, the professor made a detailed analysis to Nandu reporters. He said that for continuous curved bridges, i.e. multi-span girder bridges with a curved shape, theoretically all piers can use single-column piers. Generally, the abutments at both ends are equipped with torsional bearings which can resist the bias load caused by vehicles walking along one side of the bridge. Generally, two bearings are used, and single-column piers can be used in the middle support pillars.

The bridge of Guangdong-Jiangxi Expressway and Shangyu Chunhui Overpass are all single-column piers in the middle. The use of single-column piers in the middle of continuous curved bridges can not only save the cost of construction, but also improve the vision under the bridge, so it is widely used in the ramps of overpasses. He said that the analysis showed that there was no possibility that the main girder would be crushed because of the design of single pier, which is why the main girder of the bridge and Shangyu Bridge fell from the pier and did not stop.

The professor went on to explain that when the bridge is not bending well, that is, when it is relatively straight, there is a clear difference between the use of single-column piers and double-column piers in the middle and when the car is all on one side. When the bending is not severe, the cumulative torsion effect of eccentric load is greater. If there are single piers in the middle, most of the torsion produced by eccentric load of automobiles will be transmitted to the abutments at both ends, and the torsion of all the middle holes will eventually accumulate on the double supports at the end of the beam. Large torque will make the end bearing on one side produce pull-up force, if there is no special measures, it will make the bearing out of space.

Therefore, in his opinion, when the radius of curvature is large, it is not appropriate to design multi-span continuous beams with single pier in the middle, especially in the wider straight bridge, multi-span single pier in the middle should not be installed. This is why a bridge over 70 meters, although there are two piers in the middle, it seems very stable, but the middle is a single-column pier, in fact, it is easy to roll over.

The Professor further analyzed that in recent years, curved bridges with single-column piers often suffer from roll accidents. The main reason is that the single-column in the middle can not restrain the torque, and all the torque is transferred to the end of the beam, resulting in the void of one end of the support. According to the hypothesis of small displacement, as long as the center of gravity of the whole beam does not run out of the connection between any two peripheral piers, the void of the pier will not cause the lateral inclination of the beam. However, under eccentric load, the main girder torsion occurs. When the rotation angle reaches a certain degree, the sliding force of the support reaction will exceed the lateral restraint capacity of the support. At this time, the main girder will slide, and the horizontal component will also push the pier and column side down. Therefore, the pier of single-column bridge needs to be specially checked for lateral resistance.

The bridge of Guangdong-Jiangxi Expressway is very similar to the collapse of Shangyu Chunhui overpass. This bridge is also a single-column pier in the middle. Because of the large torsion angle of the main girder, the pier was pushed down laterally, so the girder collapsed.

Publishing the Truth and Promoting Design Optimization

The professor told Nandu reporters that the optimal design of single pier is a problem that is generally not well understood. Most engineers do not know that the pier will eventually be pushed down from one side.

In his view, in recent years, this kind of accident happened many times, which has gradually made people realize the problem. But because the real cause of the accident is difficult to fully disclose, so not everyone knows.

The professor went on to explain that some vehicles are overloaded and do not follow the rules anymore. Many large or overweight vehicles are on the side of the road. This is a small probability event in the original road and bridge design theory, but in China where traffic is chaotic, the probability is greatly increased.

Many carts are on one side of the road, and the single pier in the middle can not bear excessive bias load, which is why the ordinary people do not understand why such a small span bridge will collapse. The professor said that it was not necessarily a tofu dregs project, but a cognitive problem in engineering design circles.

As for the solution, the simplest is not to design single pier in the middle, but this will greatly increase the cost of the project, and it is estimated that China will take this road in the future. For designers, no one wants to fall over their own bridge. The design of single pier is a technical problem, which requires many special considerations. If we do not change the system, it is difficult to solve the problem fundamentally by upgrading technology alone. The professor said.

According to the professor, the correct solution should be to fully disclose the real causes of the full investigation to the public, accept the social test, and urge the industry authorities to formulate more reasonable design specifications according to the causes of the accident, so as to enable all engineers to design more scientifically in future engineering design, and let those who drive according to the rules know how to avoid launching. Such an accident happened.

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