Steel is a major component in bridge construction, which explains its ever-increasing usage in long, medium, and short span bridges, railway bridges, and even footbridges. Steel is known for its versatility, strength, and ductility, features that allow bridges to resist dead and dynamic loads effectively. So, what are the main types of steel used in bridges?
The main types of steel used in bridges include carbon steel, heat-treated carbon steel, stainless steel, and weathering steel. The steel used in bridges often depends on the bridge type. Steel’s versatility allows it to be used as a primary member or in safety components.
In this article, we’ll examine the main types of steel used in bridge construction while also discussing some of the benefits of using steel as a construction material. Continue reading.
Steel: A Brief Overview
Steel has been a mainstay in both large and small-scale construction due to its ductility and tensile strength, which allow it to deform and bend considerably before breaking. The higher the yield strength, the harder it will be for the steel to break.
1. Carbon Steel
Carbon steel is a type of steel with a higher concentration of carbon than other types of steel. As revealed by Monroe Engineering, carbon steel’s carbon content goes up to 2.5%, which is considerably higher than other types of steel whose carbon content ranges from 0.05-0.3%. While a 2.5% carbon content might sound insignificant, it furnishes carbon steel with several advantages.
Advantages of Using Carbon Steel in Bridges
- Durable: Carbon steel is shock resistant and extremely strong, making it ideal for construction use.
- Environmentally friendly: Carbon steel is recyclable, which makes it environmentally friendly and great for use.
Disadvantages of Using Carbon Steel in Bridges
- High carbon content makes carbon steel brittle: While the high carbon content makes steel stronger, it also makes the steel material brittle and more susceptible to breakage. This explains why carbon steel is rarely used as a primary member in bridge construction.
- Not as versatile as other types of steel: Carbon steel isn’t easy to manipulate, cut, or molded into different shapes and sizes, limiting its usage in modern bridge constructions.
- Susceptible to rust: Carbon steel is more likely to rust compared to stainless steel. The lack of chromium (which makes stainless steel) means carbon steel doesn’t have a layer that protects against moisture and eventually rust.
2. Heat Treated Carbon Steel
Heat-treated carbon steel has incredible strength that’s derived from altering steel’s physical properties through strategic heating and cooling. This type of steel is widely used in bridge construction and other large projects due to its increased ductility and tensile strength.
Below are some of the types of heat treatments that carbon steel undergoes to alter its properties:
- Full annealing
- Process annealing
- Isothermal annealing
Advantages of Using Heat-Treated Carbon Steel in Bridges
- Enhances ductility and flexibility: Heat treated carbon steel is an integral component of most bridges due to its flexibility and ductility. The increased flexibility of heat-treated carbon steel allows architects and construction engineers to develop and implement unique designs during construction.
- Reduces the risk of breakage due to brittleness: Heat treated carbon steel is ideal for bridge construction due to its reduced brittleness. This means the steel can adjust better to increased loads without the risk of breaking.
- Easy to weld and mold: Heat treating carbon steel is a great way to make it easier to cut and mold without compromising structural strength. As a result, more construction engineers tend to prefer using heat-treated carbon steel in bridge construction.
- Heat-treated carbon steel is more durable: It’s crucial to use durable material in heavy construction projects like bridges. Fortunately, heat-treated carbon steel gives engineers the assurance that they won’t need to make any replacements in the near future.
3. Stainless Steel
Stainless steel is known for its strength, aesthetic appeal, and corrosion resistance properties. These features have played a pivotal role in the widespread use of stainless steel in bridges. Long-span bridges, highway bridges, pedestrian bridges, and even railroad bridges have become increasingly reliant on stainless steel.
The increased usage of stainless steel is due to its durability and ability to maintain a neat appearance despite long term usage.
Initially, stainless steel was primarily used on safety components such as handrails and guardrails. Over the years, the role of stainless steel in bridge construction has increased exponentially, which explains their use in structural components like decks, suspension systems, or tie-rods.Stainless steel is also used in bridges to fabricate bearings and other parts that are susceptible to corrosion. The main disadvantage of using stainless steel is its relatively high cost, which often limits its use in primary parts of the bridge.
Advantages of Using Stainless Steel in Bridges
Stainless steel has several advantages that allow for its usage in the construction of bridges. Below are some of the main advantages of stainless steel.
- Durable: Stainless steel is known for its anti-corrosive properties, meaning it’s highly unlikely to succumb to exposure to pollutants or rust. Stainless steel can be placed in bridges located in acidic or alkaline environments and resist corrosion and rusting, provided it’s regularly maintained.
- Has a high strength-to-weight ratio: Stainless steel’s high strength-to-weight ratio allows for less material to be used without compromising the bridge’s structural integrity. This consequently reduces the overall cost of production, especially since not too much stainless steel will be needed in construction.
- Aesthetically appealing: Besides its ability to resist rust and gradual corrosion, stainless steel is known for its attractive appearance that enhances structural beauty. A stainless steel bridge will maintain its beauty over time without needing too much maintenance work.
4. Weathering Steel
Weathering steel is a type of steel with enhanced resistance to elements of corrosion. This steel has a rustic appearance that allows it to blend seamlessly with the immediate environment. The impressive resistance to gradual corrosion and rust has seen the increased usage of weathering steel in bridges located in acidic or alkaline conditions.The use of weathering steel in the construction of bridges is tipped to continue increasing in the future, especially in saltwater environments where most metallic structures are prone to rust.
Advantages of Using Weathering Steel in Bridges
- Corrosion-resistant: Weathering steel has a unique chemical makeup that allows for the formation of protective rust called patina. Patina prevents corrosion and helps bridges to maintain their structural integrity and form with minimal maintenance.
- Blends well with outdoor environments: Weathering steel’s unpainted appearance blends well with parks, cliffs, and outdoor environments with bridges. Initially, weathering steel usually has an orange-brown appearance, which gradually transforms into a rich brown coloration after the patina continues to form over time.
- Requires minimal maintenance: No replacements will be needed if weathering steel is installed correctly in bridge members. The only form of maintenance needed is periodic inspection and cleaning to ensure the steel maintains its form and appearance. This feature makes weathering steel appropriate for bridges located in hard to access locations.
Bridge construction requires high-quality steel that can withstand corrosion, rust, and other forces that come into play once-dynamic loads are introduced. The most commonly used steel in bridges includes carbon steel, heat-treated carbon steel, stainless steel, and weathering steel.
Stainless steel and weathering steel bridges are ideal for bridges constructed in acidic or alkaline conditions as they’re corrosion and rust-resistant. Heat-treated carbon steel is also great for use on bridges, more so due to its moldability, durability, and strength.
- Wikipedia: Chromium
- Wikipedia: Ductility
- Wikipedia: Annealing
- ResearchGate: The Concept Of Brittleness And Its Applications
- Central Steel Service: Weathering Steel Bridges
- Springer: Effect of Heat Treatment
- Monroe Engineering: Pros And Cons Of Carbon Steel
- Usbridge: Best Material Bridges Steel
- About Civil: Materials Used In Bridges
- Designing Buildings: Types Of Steel For Construction
- Fedsteel: Carbon Steel Advantage