The viaduct piers are large, but the part that really comes into contact with the bridge deck is small. Why is that?

If notRubber bearin, or other types of bearings, but are connected into a whole, such as our two-span highway bridge above. So what are the problems? Or why do you have to put a bearing between the bridge deck and the pier?

Imagine the small truck in our picture driving on the bridge deck, what impact will the weight of this truck have on the bridge?

When the truck is on the left span, the bridge will become like this; after a while, it will drive to the right span, and the bridge will become like this below.

Of course, I drew a very, very exaggerated schematic diagram, just to make it easier for everyone to understand. In fact, bridges do have such deformation, but the amplitude is very small, and it may not be possible to distinguish with the naked eye, but the bridge deck and piers will indeed be bent and deformed. Or simply put, the bridge deck is swinging up and down, and the piers are swinging left and right.

Similarly, we know that materials will expand and contract. What effect will external temperature changes have on such a bridge?

When expanded by heat, the bridge deck tends to become longer outward, causing the outer piers to bend outward. When contracted by cold, the bridge deck tends to become shorter inward, causing the outer piers to bend inward. Under the temperature changes throughout the year and day and night, the piers are also repeatedly bent and swinging.

We know that axial tension of piers is better than bending. Similarly, it is easy for you to break chopsticks, but it is difficult to break or crush chopsticks. If you are interested in this question, you can refer to this answer: Why is it easier to break than to pull a wooden stick, iron rod, etc.?

Because it is difficult to break and relatively easy to break, we should try to avoid the piers being "broken". The bridge above us, under the action of changes in vehicle weight and temperature, the piers have been swinging left and right, or in other words, they have been "bent" to the left or right. And this situation is exactly what we want to avoid.

So how to avoid it? Why not try the following one?

The bridge deck and piers are separated, separated by bearings in the middle. The triangular bearings on the middle piers mean that the bridge deck can rotate freely here, but cannot be moved; The circular bearings on the piers on both sides represent that the bridge deck can rotate freely here, plus it can be moved left and right.

Why don't all three of them be rounded? Because if all three are round and all three places can move left and right, then the bridge deck will slide down to the left or right.

At this time, when the truck comes up again, will the pillar still swing? Because the bridge deck can rotate freely at the bearing, it will no longer deform along with the piers. To put it simply, no matter how the truck drives, the piers remain almost vertical and no longer swing greatly from side to side.

Let's look at the temperature change. Similarly, because the bridge deck at the circular bearing can move freely, only the bridge deck becomes longer or shorter horizontally, and the pier remains vertical. Such temperature changes have little effect on the piers.

This official said, is it really fake? Are such big bridges all placed on such circular supports?

True, and in the early days, it was a truly literal "round" support.

What do you think? I didn't lie to you, did I?"

This is also a true round bearing.

What about the triangular support?

Look at this, this kind of support is really like this, or it means a bit triangular. You can understand it as a hinge of a door, which can be rotated but cannot be moved.

The same pier supports the left and right decks. The one on the left is a triangular bearing, and the one on the right is a round bearing. You can see it from the picture, it is very obvious.

With the development of technology and the emergence of new materials,Cast stee, rubber has been used in the field of bridge bearings one after another, replacing these antique bearings in our photo above, but the role is similar.

Rubber bearings are layers of rubber and steel plates superimposed on each other, and there are various types of bearings that can meet different displacement conditions. At the same time, the rubber bearing separates the bridge deck and the pier, which not only allows the deformation of the bridge deck to affect the pier as little as possible, but also allows the seismic waves from the ground to affect the bridge deck as little as possible, which plays a certain roleSeismic isolatio. In addition, industrialized and standardized rubber bearings are relatively economical and reasonable, so rubber bearings are more and more widely used in the field of bridges.

The officer also said that since the bending is so bad, it needs to be avoided as much as possible, so after using the support, the piers are not bent much, and the bridge deck is still bending? What to do?

To solve this problem, please move on to this answer: Why is the suspension bridge so strong in crossing?

Many times, we may be able to intuitively feel the transmission of vertical forces, such as thick piers transmitting the weight of the bridge to the earth. But this is only one aspect of the structural system. Other aspects, such as bending resistance, or ratherLateral force resistance syste, may be just as important, if not more important.

For example, this is the machinery pavilion of the 1900 Paris World Expo, which is obviously a steel structure pavilion, representing the high and new technology of the time. It is noticed that it is very large in scale, which can refer to the height of the person in the distance in the photo. Unlike the thick masonry pillars in the past, this steel pillar is smaller the closer it is to the ground, why do you think this is?

Maybe you think that the weight of the car, along with the heavy bridge deck itself, including asphalt, ends up falling on the small rubber bearing, which sounds a bit unreliable. However, there are reasonable reasons and reasons for this.

Finally, I ended my answer with a more unreliable joke that the professor told us in class.

This paragraph said that he was doing research on carbon fiber bridge decks, and it happened that the bridge decks of the highway were broken, and the State Transportation Bureau cooperated with him to prepare a pilot project to replace the carbon fiber bridge decks. In a sense, you could say that carbon fiber is also a type of plastic. On the day of construction, the police directed the traffic to the opposite lane, and the crane came up here, replaced the prefabricated carbon fiber board, and it was done in less than half an hour. Then the police resumed traffic, where state officials and media reporters waited.

After a while, a buddy came up in a big pickup truck. When he got there, the police told him to stop, and then the state officials went up and shook his hand, saying, "Congratulations, you're the first American to drive on a "plastic" bridge!" Then the reporter took a photo. This buddy was frightened and dumbfounded, looking blank, and stuck his head out of the car window for a while, "What? Are you kidding？！」

The government official handed over a glass of champagne, "Dude, let's take a photo!" The buddy looked at the police officer next to him and said, "What are you doing? Do you want to cheat me on drunk driving?" The person next to me said, "We're all ready, don't worry, this is all non-alcoholic champagne."

This guy suddenly had a sudden realization, and then said, "I understand, are you making funny videos on the Internet?!"