What Is A Bridge Abutment & Which Types Are There?

The next time you find yourself crossing a bridge, either as a pedestrian or as a driver, I want you to ask yourself one thing. How much do you actually know about these constructions that are designed to help us get from point A to point B while avoiding an obstacle, such as a water surface, in the process? Sure, you know their purpose and you know that they are sturdy and resistant, but that’s probably about it, isn’t it?

Well, I think it’s high time you learned a bit more about this particular construction, starting with the bridge abutments which are an integral part of every bridge that successfully fulfills its purpose. Depending on your particular field of expertise, you might have already heard about these, or this might be the first time you are hearing the word “abutment” at all. In any case, this construction does require our special attention, so keep on reading in order to get properly acquainted with it.

What Is A Bridge Abutment?

Let us start with the most basic things here. Every single bridge you see is made of a superstructure and a substructure. If “superstructure” sounds like something that you would hear in a superhero movie, let me assure you that it has its application in the real world. Although, when you think about it closely, it wouldn’t be that weird to compare bridges to some kinds of superheroes.

Anyway, we shouldn’t get lost in those fantasies. Basically, the superstructure is that part of the bridge that provides the horizontal span. In other words, it’s the part that supports people and traffic. To make things even more clearly, it’s what you get to walk or drive across. As you can see, this has nothing to do with superheroes, does it?

Now, on the other side of it all, there’s the substructure. I suppose that you could guess all on your own what the substructure is, especially after superstructure has been explained above. Let me explain it anyway. This is the below part, which is responsible for supporting the superstructure and making it safe for everyone to walk or drive across. The abutment, as you can see here, is a part of the substructure.

This particular construction is responsible for providing support to the one terminus of the superstructure, while at the same time supporting the soil, or the embankment on which the bridge is located. It is an integral part of a bridge that makes it not only safe, but also sturdy and durable. Simply said, you wouldn’t want to hear that the bridge you are walking across doesn’t have an abutment.

How Is It Made?

Usually, reinforced concrete or masonry plain concrete is used for the making of an abutment. It can, however, be made in various different ways, depending on the actual type of the abutment. The first thing that you should know is that there are integral and semi-integral types, differing in one simple, yet important thing. The integral one is made to move together with the bridge, while the semi-integral type allows the abutment and the superstructure to move independently.

The integral type is certainly the most common one used today and there are quite a few reasons for that. Given the way it is made and integrated with the whole bridge, the use of joints over piers and abutments is avoided, which provides for a more durable overall constructions, since joints are prone to leaks that can cause damage. There is one more thing you need to know when it comes to the process of making abutments.

Integral abutments can be made with piled foundations that usually incorporate steel H piles oriented in a way that allows the bending to occur about their weaker axes. On the other hand, there are those with spread footings. The truth is, however, that these are not so widespread, since they cannot be used in most of the areas where a bridge is actually necessary.

Learn more about abutments: https://www.sciencedirect.com/topics/engineering/abutments-bridge

Which Types Are There?

Now that you have, hopefully, understood what these constructions are, what their purpose is and how they are usually made, it’s time to talk about the types. The important thing to understand is that there certainly are a lot of different types out there and they all have their own purpose. Additionally, you should remember that I have mentioned the integral and semi-integral constructions above, meaning that I will now be focusing on other types. So, pay attention now and you’ll be able to brag with your knowledge later.

First of all, we have to mention the closed abutment. I’m sure you have seen it, but you probably didn’t know what it was called. Simply said, this is the full-height wall that has wings on the sides. This type is popular because it minimized the required span length of the overall bridge. As any other type, though, this one comes both with advantages and disadvantages. Namely, the closed abutment isn’t really suitable for embankments on soft foundations or for high embankments.

A perched abutment is the one that is created after the embankment has been completely done. It can be supported on spread footings on the embankment or perhaps on piles of drilled shafts. This type allows for a relatively small lateral earth pressure, but the downside is that it might require longer bridge spans than, for example, the full-height closed abutment I have mentioned above.

Pedestal abutments, as the name says it, are constructions supported by columns or pedestals that extend to the natural ground. This one has to be constructed before the embankment and a fill is placed on both sides of the columns, so that the unbalanced earth pressure is minimized. The downside of it all might lie in the fact that it can be rather difficult to compact the fill properly. Plus, it can be extremely susceptible to erosion, which is another disadvantage of this particular type.

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