Why can overload + unbalanced load become an unbearable burden for single-column pier bridges?

 Why can overload + unbalanced load become an unbearable burden for single-column pier bridges?

According to the information released by Wuxi Audit Bureau, the 312 National Highway Wuxi, which belongs to the accident section, had undergone an expansion and transformation from 2003 to 2005. The collapsed viaduct belongs to the newly built bridge and culvert, which means that the bridge has been completed for less than 15 years.

This viaduct is designed with single pier bridge structure, while other viaducts using this kind of bridge also have many rollover accidents. After sorting out the past records of Peng Mei News, it is found that at least six similar accidents have occurred since 2007.

Single-column pier bridge is a common bridge structure in China and even in the world. Thoughts on the collapse of Yangmingtan Bridge in Harbin mentions that the Viaduct with continuous box girders generally adopts single-column piers and double-column piers. For narrow bridges under three lanes, single-column piers are generally used. This kind of bridge has many advantages: simple structure, small area, strong adaptability and good economy.

Overload is one of the important causes of bridge collapse or overturning.

According to the preliminary analysis of the accident investigation team, the serious overload of the truck or the direct cause of the Wuxi viaduct accident. Pengchao reporters had previously learned from people familiar with the situation that, after investigation, the truck involved was limited to 40 tons, but at that time it had been overloaded four times.

It should be noted that according to the current national compulsory standard GB1589-2016 Automobile, Trailer and Train Outer Size, Axle Load and Quality Limit Value, even if the longest six-axle truck plus a longest three-and-a-half-week trailer, the maximum allowable total mass is 89 tons.

According to the audit announcement of Wuxi Audit Bureau, the new bridges and culverts in Wuxi section of 312 National Highway adopt the construction standard of Qichao-20 and Hanging-120. That is to say, on this road, cars should not exceed 20 tons and trailers should not exceed 120 tons.

Coincidentally, in the past two accidents, the accident vehicles are not only overweight, but also mostly exceed the design load of the bridge itself.

Shangyu Chunhui Overpass in Zhejiang Province in 2011

Bridge Design Load Limitation: 55 Tons per Vehicle

Accident Vehicle Load: The four vehicles are 28.52 tons, 124.44 tons, 125.6 tons and 110.73 tons respectively.

Yangmingtan Bridge in Harbin in 2012

Bridge Design Load Limitation: 55 Tons per Vehicle

Accident Vehicle Load: Four vehicles are 18.62 tons, 153.29 tons, 163.59 tons and 149.68 tons respectively.

However, the article Thoughts on the Collapse of Yangmingtan Bridge in Harbin published in 2012 mentioned that the design safety factor of general bridges is relatively large, even if the weight exceeds 2.45 times the design value, it is not necessarily able to crush the bridge.

However, if the bridge encounters unbalanced loads at the same time, the possibility of accidents will increase. For example, in the Yangmingtan Bridge accident in Harbin in 2012, the expert group confirmed that the direct cause of the accident was that three overloaded trucks were driving on the right side of the bridge at the same time within the long beam body of 121.96 meters, resulting in partial load on one side of the bridge and serious overload, thus overturning.

(2) partial load

In a paper published this year in Sichuan Building Materials, the author restores the common scene of single-pier bridge accidents in recent years: Severe overloaded trucks or heavy vehicles traveling along the single-pier Bridge side together, resulting in serious partial load of the bridge, resulting in unilateral void of the bridge support and lateral rollover of the bridge girder.

The popular explanation is, On a boat, a very heavy fat man sits on the outermost side of the boat, and on the other side sits a thin man, then the boat will roll over. Yang Rui, who has been engaged in bridge design and construction for many years, told the cover story figuratively.

Compared with linear bridges, the force of curved girder bridges is more complex because of the unique bending-torsion coupling effect of the latter, i.e. under the dual effects of overload and unbalanced load, the bridge girder will produce torsion and torsion. At first, the weight of the bridge can resist the torsion of this part, but with the increasing load, the bearing will be void, and when the load reaches the limit, the bridge will overturn.

As shown in the figure below, the Southern Metropolitan Daily made a three-dimensional picture of the collapse of the Guangdong-Jiangxi Expressway in 2015. All three trucks were driving outside the bend, and finally the pressure caused the bridge to overturn.

In addition, the paper in Sichuan Building Materials also mentions that the overturning and collapse of single-pier bridges is a phased and continuous process, but the destruction occurs instantaneously, and there are no obvious signs before the overturning. Source: Wang Ning_NB12468, responsible editor of Peng Mei News

In addition, the paper of Sichuan building materials also mentioned that the collapse of single pier bridge is a periodic and continuous process, but the destruction is instantaneous, and there is no obvious sign before the collapse.