Bridges are important structures that help to span physical obstacles like water masses, roads, and valleys. And since the sole purpose of a bridge is to provide passage over an obstacle, it must be strong enough to withstand both static and dynamic loads. So what are the best materials for building bridges?
The best materials for building bridges depend on the type of bridge under construction. However, the most commonly used materials include concrete, steel, stone, and composite material. Concrete and steel are usually used in the construction of the superstructure members of a bridge.
This article will discuss the best materials for building bridges while also shedding more light on each material’s specific roles. Ready? Then let’s jump right into it.
Concrete is arguably among the most important materials used in bridge construction. Concrete gives bridges a high level of versatility and flexibility, making it perfect for weight absorption and distribution. The use of concrete allows construction engineers and architects to develop a wide range of practical structural forms.
Despite being great for use in large construction projects, concrete has a relatively low tensile strength. However, to address these issues, civil engineers opt to use reinforced concrete to construct bridges.
Reinforced concrete has a similar coefficient of thermal expansion to that of steel, which helps eliminate internal stresses resulting from contraction or thermal expansion. Concrete also helps to absorb structural stress, allowing the load to be transmitted efficiently across different materials. This usually occurs when the cement paste inside the concrete hardens and conforms to the surface details and shape of steel.
A popular alternative to reinforced concrete is using prestressed concrete. Prestressed concrete is usually lighter compared to reinforced concrete that’s often bulky and heavy. Therefore, when constructing bridges and structures meant to absorb shock and impact, prestressed concrete is the most preferred option.
Unlike RCC that usually neglects the pressure below the neutral axis, prestressed concrete is highly effective in load resistance. Civil engineers also prefer prestressed concrete for heavily loaded structures since the reduced weight and cross-section translates to more savings in terms of materials used.
Benefits of Using Concrete in Bridge Construction
Concrete is a popular construction material that helps maintain the structural integrity of buildings and large construction projects. Below are some of the benefits of using concrete in constructing bridges.
Drawbacks of Using Concrete in Bridge Construction
It’s difficult to discuss bridge construction without mentioning steel. The strength, ductility, and versatility of steel make it a fantastic option for constructing bridges. You’ll find steel in railway bridges, long-span bridges, and even short and medium span bridges.
Normal construction steel usually has a compressive and tensile strength of an impressive 370 N/sq mm, which is considerably higher than concrete’s compressive and tensile strength. One of steel’s most remarkable features is its ductility. The ductility allows the steel to deform considerably before breaking when exposed to stress beyond its structural capabilities.
The Main Categories of Steel Bridges Used in Construction
Steel is a super material when it comes to large-scale or small-scale constructions. Besides responding well to both static and dynamic loads, steel is strong enough to distribute weight and hold other members in place, especially in massive constructions.
Below are the main categories of steel used in bridge construction.
Advantages of Using Steel in Bridge Construction
High Strength to Weight Ratio
Steel’s high strength to weight ratio helps minimize overall construction costs by eliminating the need for substructures. Moreover, steel comes in handy when used in long-span bridges due to its lightweight nature. Steel also minimizes mechanical plants’ overall costs since it reduces the required counter-weight size, especially in swing and lift bridges.
High-Quality Construction Material
Steel is readily available (in various certified grades, sizes, and shapes). Steel can be prefabricated, and the trial assembly can be quickly done at the fabrication centers to eliminate the risk of fit-up problems on the construction site. The ease of prefabrication and fitting makes steel ideal for use in both large and small construction projects.
The prefabrication of steel means that construction will be fast, especially in hostile environments. And since steel bridges can be installed fast, roads and railway lines won’t be closed for too long before the public can use them again. Steel’s lightweight nature allows the smooth erection of large members, which consequently reduces the overall duration of the project.
There’s usually no limitation to how steel is installed in bridges. Depending on the project’s size, steel can be installed by slide-in techniques, launching, cranes, and even transporters. The erection contractor will have the much-required flexibility when installing the steel.
Repair, Modification, and Demolition
Steel is highly preferred in bridge construction due to its adaptability and ease of repair. Engineers can widen (and strengthen) the steel bridges to accommodate additional traffic lanes. Even better, steel girders can be cut into manageable pieces and recycled when the bridge is no longer in use.
The ease of repairing steel also makes it ideal for use in high-risk areas. All that needs to be done is cutting out the affected areas before welding in the new steel. Girders are also repairable by heat straightening.
Compared to concrete that can easily crack without any signs, steel is predictable due to its easily visible and accessible structural elements. The ease of visibility ensures that civil engineers won’t need to conduct extensive research to determine affected areas. And in case corrosion occurs over time, repainting the problematic areas will be enough to solve the problem.
Steel is among the best materials to use in bridge construction due to its ease of modification. You can modify the steel to look heavy or light, while the possibility of sculpturing further gives engineers and welders the freedom to come up with different shapes and trims.
Steel is also used in the construction of trusses, which, besides distributing loads across the bridge, also contributes to the construction’s overall beauty. Therefore, the flexibility that comes with steel allows engineers and welders to implement their creative designs.
Stone has been used in the construction of bridges for several centuries. Although not as popular as before, bridges built from stone are arguably among the strongest and most durable types of bridge.
However, in modern bridges, stones are usually used on the surfaces. This explains why you’ll likely find stones used as facing for piers, abutments, or arches. When choosing a stone for bridge construction, it’s crucial to ensure it’s weather-resistant to neutralize the negative effects of rain, salty winds, and even snow.
Best Stones to Use in Bridge Construction
Due to their role of absorbing and distributing both static and dynamic loads, bridges require heavy stones with high specific gravity. Below are some of the best stones to use in bridges.
Benefits of Using Stone in Bridge Construction
Drawbacks of Using Stones in Bridge Construction
4. Composite Material
Composite material helps in the construction of new bridges and also comes in handy when making repairs. Fiber-reinforced plastic, for instance, is usually reinforced with either carbon or glass fibers. The resulting material is usually durable, lightweight, strong, and ductile.
Reactive powder concrete (RPC) is also becoming popular in the construction of slim columns in long-span bridges. You can also use composite material to repair or reconstruct columns and other supportive elements in a bridge. Epoxy impregnated fiberglass also helps to cover non-ductile columns, thus making them more resistant to external forces.
Basic Parts of a Bridge
Typical bridges are usually made up of the foundation, decking, and additional components like girders, bearings, trusses, and abutments. Please note that supplemental components usually vary depending on the type of bridge being constructed.
Below is a brief discussion of the main parts of a bridge and the ideal materials to use.
Also referred to as a pile, the foundation serves as the main support or legs of the bridge under construction. Foundations preserve the structural integrity of buildings and bridges by absorbing and distributing the total loads on the bridge.
Modern civil engineers prefer to use on-site piling where holes are deeply bored into the earth. Reinforced steel is then installed before concrete is poured on the perforations. Bridge foundations are usually the first to be constructed as their installation often determines the structure’s overall stability and strength.Concrete and steel are the most frequently used materials on foundations due to their strength and ability to handle varying types of loads.
The decking is usually the most used (and viewed) section of a bridge since it serves as the usable surface for vehicles and people to travel on. In reinforced concrete bridges, the decking is usually made from concrete that’s poured over a sturdy metal framework to strengthen the entire structure.
The girder normally acts as the arms of the bridge, ensuring the entire deck is fully supported. Girders are usually installed over caps to receive and distribute the weight to the foundation. A girder can be made from either steel or concrete, depending on the immediate environment.
Bearings help to absorb the pressure and stress resulting from vehicles and environmental factors. By absorbing pressure before it spreads to other parts, bearings are able to maintain the bridges’ structural integrity.
Some architects prefer using elastomeric bearings in bridges. These bearings are usually composed of quality steel plates fused with rubber or elastomer material. The increased elasticity allows the bridge to resist movements that could damage the steel-concrete structures.
Abutments connect a bridge to the land, thus providing support for the entire unit by absorbing the pressure caused by both static and mobile loads. Abutments should be stable and robust enough to receive loads from a bridge’s superstructure while also neutralizing the pressure emanating from earth movements.
Concrete is commonly used in the construction of abutments due to its ability to withstand heavy loads.
Trusses help to distribute loads across the entire bridge structure. Besides their important role in load distribution, trusses also help to make bridges more attractive. The beams and bars used in the construction of truss networks are often made from steel due to its weather and corrosion-resistant properties.
There are several materials that can be used in constructing bridges. The best materials, however, should suit the type of bridge that’s being constructed.
Over the years, concrete has emerged as an essential material for constructing short, medium, and long bridges. Another important material is steel, which is vital in helping a bridge maintain its structural integrity.
Stones also play a pivotal role in bridge construction, more so in the surfaces of piers, arches, or abutments. And since bridges need to be strong and sturdy enough to resist loads, using high-quality construction material is highly advised.