Some high-altitude bridges are poured in small sections, and the construction requirements and difficulty must be very high.

In railway engineering, the use of prefabricated box girder construction can indeed effectively improve the construction quality of bridges and speed up the progress of bridge construction. The common railway prefabricated box girder is about 32 meters long, as for the weight, you might as well guess......

It is understood that a total of 1,199 box girders need to be erected on the Suqian section of the Weisu high-speed railway. The first box girder successfully erected this time is huge in volume and complex in process, with a length of 32.6 meters, a width of 12.6 meters, and a weight of 719.8 tons. 

Yes, you read that right, a piece of prefabricated box girder weighs more than 700 tons.

What is this concept?

We know that a family car weighs about 1.5 tons, so the weight of a prefabricated box girder is about the same as 480 family cars, doesn't it feel exaggerated?

Don't worry, there are more exaggerations. ^ ^

When railway bridges cross urban roads or highways, a span of 32 meters (i.e., the distance between two adjacent piers) is far from sufficient.

In order to be able to cross the road smoothly, railway bridges need to have a larger span, usually the span of the bridge across the road ranges from tens of meters to hundreds of meters.

We can make a visual comparison of prefabricated box girders and bridges across the road from the figure below. Among them, the area pointed by the orange arrow is erected with prefabricated box girders, and the red area is a continuous beam spanning the highway, with a total length of 223.48 meters and a maximum span of 100 meters.

So, how heavy should a bridge cross the road?

We still take the Weisu high-speed railway mentioned in the above answer as an example.

17,000 tons, which is about the weight of 24 prefabricated box girders, or the weight of 11,333 family cars!

At present, the known super-large lifting equipment in China, such as Zoomlion's world's largest 4,000-ton all-terrain crane, cannot lift this bridge across the highway.

Since there is no such thing in China, is there any larger lifting equipment abroad?

Yes.

For example, the Sarens SGC 250 crane produced in Belgium has a lifting capacity of an astonishing 5,000 tons, but it is still unable to lift this concrete beam.

Perhaps, you may think that concrete beams are too heavy, if you change to steel box girders, won't the weight be greatly reduced?

Then we might as well take a look at an engineering case - the Ningbo-Xiangshan Urban (Suburban) Railway Xiangshan Port Cross-Sea Bridge Project.

The steel beam erected this time is 107.5 meters long, weighs about 1779 tons, and has a total weight of 2182 tons with spreaders, which is equivalent to the weight of 1,500 family cars, and the maximum height from the bridge deck to the sea surface is 53 meters (nearly 20 floors high), and the steel beam erection area is adjacent to the existing Xiangshan Port Highway Bridge, and the ship station is close to the main channel. 

It should be pointed out that the above-mentioned steel box girder is only 107.5 meters long, and the lifting weight has reached 2,182 tons, and if the steel box girder is extended to 272 meters of the continuous beam of the Weisu high-speed railway to Qingdao connection line across Shenhai, its weight may exceed 5,500 tons, and the existing large-scale lifting equipment is still difficult to meet the hoisting requirements.

To sum up, the construction plan of large-scale projects is rigorous and complex, and it must not be taken for granted and patted on the head, otherwise it will become a "castle in the air". ^ ^

At this stage, considering many aspects such as construction technology, economy, and operability, the continuous beam is still the best solution for sectional cantilever pouring.