Bridges are vital and important components of cities, and on the other hand, they are more at risk of damage than other structures. For example, weather factors are the main cause of bridge destruction and corrosion. The constant movement of heavy machinery and cars usually causes damage to these structures. For this reason, bridge strengthening should be considered. There are different methods of strengthening bridges that we will discuss in this article.
Methods of strengthening bridges
Various methods are recommended for strengthening urban bridges. Each of these methods has advantages and disadvantages, which we will discuss in more detail. In general, bridge strengthening methods are done in different ways, such as strengthening with concrete jacket, with FRP, with seismic isolators, with frictional isolators, and dampers. Below we explain all these methods.
Reinforcing the bridge with a concrete jacket
The use of concrete jacket is one of the common methods of strengthening bridges. Concrete jacket is actually a type of coating made from steel reinforcement and concrete materials. These jackets are made and concreted in a reinforced mesh of rebar.
The homogeneity of the concrete jacket with the structural components and the lack of need for fire-resistant cover components such as a concrete cover are among the most important advantages of this method of strengthening the bridge. Of course, the difficulty of building these structures lies in the biggest drawback of the bridge’s strengthening.
Reinforce the bridge with FRP
But the most common way to strengthen the bridge is to use FRP. This method is considered more modern than other methods and is used nowadays more than other methods due to its ease and speed. Also, this method can be used in the best way in cases where there is a possibility of increasing the dimensions of the structure or the bridge is placed below the water level.
In reinforcement with FRP, firstly, the upper and lower parts, which are called plastic, are surrounded by FRP fibers and strengthen the axial force of the bridge. Using this method, the axial force of the bridge increases and the flexibility of the bridge becomes easier and more flexible. Also, this method prevents breakage and warping of the longitudinal reinforcement.
The advantages of using FRP fibers to strengthen bridges are numerous. For example, the use of these fibers increases the speed of construction and makes your work easier. These fibers are also highly resistant and will not erode or be damaged easily due to environmental factors.
Strengthening the bridge with seismic isolators
Another way to strengthen the bridge is to use seismic isolators. In this way, transmission of strong ground movements such as earthquakes to the bridge is prevented. Insulators used in bridge reinforcement are usually used in two forms, elastomeric or elastomeric and frictional.
In bridge reinforcement, due to the presence of a large amount of inertial force on the structure, as well as the ease of implementation on site, seismic isolators are usually placed between, above and below the structure. This causes, for example, during an earthquake, the period of free vibration of the bridge increases, and at this time destructive forces cannot cause serious damage to the bridge.
Plastic insulators used as seismic insulators in bridges are made of synthetic plastic or natural plastic.
Plastic insulators reduce seismic force by increasing the period of the structure. These insulators must be able to withstand 3 times their thickness in lateral movement and remain firmly in place.
Strengthening bridges with friction insulators
As we said, the other type of seismic isolators were friction isolators. This method is one of the old and common ways to improve and strengthen bridges. In this method, the isolators will stabilize the bridges by causing slippage during the earthquake and will not allow destructive forces to destroy the bridge. The mechanism of use and installation of these isolators is the same as vibration isolators.
Reinforce the bridge with a damper
Dampers can also increase the resistance of bridges against strong vibrations and shocks. Dampers are actually seismic strengthening systems that work against vibrations caused by earthquakes. It is interesting to know that the material is only able to create 5% of the critical damping of the structure.
But using a seismic damper can ensure that you increase the damping of the structure by more than 50%. Therefore, dampers can be the best choice to save the bridge from earthquake damage.
Strengthening the bridge foundation
Another common way to increase the strength of a bridge is to strengthen the bridge foundation. Bridge foundations are usually concrete, which connects the bridge to the ground. On the other hand, bridge foundations are usually at risk in many places. For example, in many cases the foundation of a bridge is in water, and for this reason it may be at risk of corrosion, rust, or any other condition that reduces the life of the structure.
Since strengthening in water is a complex and delicate work, retrofitting a bridge foundation is a very delicate and specialized process. FRP composites are usually used for this purpose. Also, by applying FRP around the screw or all around, the ductility and bending strength of bridges can be increased a lot.
Using this method, the shear resistance of the bridge increases. In this method, FRP fibers must be applied horizontally and throughout the column. Of course, FRP fibers can also be applied in the direction perpendicular to the crack in concrete in the bridge foundation.
But in this case, if the loading direction changes, the crack direction will also change. If we do not see such an event in the horizontal implementation. For this reason, experts and specialists recommend using the screw method to strengthen the foundation and columns of bridges, which is actually the same as the horizontal method.
Strengthening concrete bridges
Strengthening concrete bridges has its own solutions. Given that there are many bridges in the cities and roads of the country, which are concrete bridges, strengthening them and knowing their strengthening methods has become very important. These bridges are usually more vulnerable to weather and environmental factors than other types of bridges. For this reason, various measures must be taken to reduce the useful load capacity of these structures.
One of the most common ways to strengthen concrete bridges is to use FRP. As we explained, by using these fibers, concrete bridges can easily be saved from the dangers of destruction. Also, using these fibers will help you easily repair the essential parts of these bridges, which are especially underwater, and prevent their destruction.