Although steel has been used for structural purposes for decades, aluminum alloys are increasingly being considered nowadays for various applications such as building facades, curtain wall glazing, building cladding system etc. due to their unique properties. While construction is very important to ensure safety, durability, and cost-effectiveness of a project. Aluminum alloys can be a very good choice in terms of these properties. In this article we will discuss how it compares with structural steel.
Key Points
| Aluminum Alloys | Structural Steel | |
| Strength | Moderate strength compared to steel. Some alloys can achieve strength like mild steel. | Carbon steel can achieve very high strength |
| Modulus of Elasticity | Less; deflect three time more than steel with the same cross section | High; can resist three times more deflection compared to aluminum section |
| Weight | Lightweight; nearly three times less than steel with same cross section | Heavyweight; weigh three times more with the same cross section of aluminum |
| Cost | Very costly compared to steel construction | Low cost |
| Corrosion Resistance | High resistance to corrosion | Low resistance to corrosion; Can easily corroded over time |
| Finishing | Excellent material finishes. Aesthetically appealing. Can easily be done powder coating and PVDF coating | Not very good compared to aluminum finish. |
| Design Flexibility | Can be extruded into complex shapes | Less flexible in terms of extrusions |
| Joint Connection | Bolted connection is preferred as welding likely to reduce strength | Bolt bolted and welded connection is suitable for steel joint |
Strength
Aluminum Alloys:
Aluminum alloys can achieve high strength through heat treatment and alloying. But they generally do not match the tensile strength of steel. However, some aluminum alloys can achieve the strength of mild steel. For example, aluminum alloy 6061-T6 strength is similar to ASTM A36 steel.
Structural Steel:
Steel is renowned for its high tensile and compressive strength, making it ideal for load-bearing structures.
Weight and Young Modulus
Aluminum:
Aluminum alloys are about one-third the weight and modulus of elasticity of steel. This significant weight reduction can lead to lower dead loads and easier handling and transportation, making them ideal for structures where weight is a critical factor. Due to the less weight, the amount of material is less. Hence, sometimes they cost less than the steel structure.
Also, due to the lower modulus of elasticity, the section will be larger to resist the same amount of deflection with steel. Which again may require more cost. This also needed to be considered.
Steel:
The higher density and higher modulus of elasticity of steel means it is much heavier than aluminum, almost three times heavier, which can be a disadvantage in applications where weight reduction is essential. On the other hand, the higher modulus of elasticity can resist more deflection which is advantageous where deflection is more critical.
Corrosion Resistance
Aluminum Alloys:
Aluminum naturally forms a protective oxide layer that provides excellent resistance to corrosion. This makes it suitable for use in harsh environments, such as marine or industrial settings, where steel might require protective coatings and frequent maintenance.
Structural Steel:
Steel is susceptible to corrosion, especially in environments with high humidity, salinity, or industrial pollutants. Protective measures such as galvanizing, painting, or the use of weathering steel are necessary to enhance its durability.
Design Flexibility
Aluminum Alloys:
Aluminum is highly malleable and can be extruded into any complex shapes, allowing for innovative and aesthetically pleasing designs. This flexibility is beneficial for creating intricate architectural features and lightweight structures.
Structural Steel:
Steel offers excellent design flexibility through various forms such as rolled sections, plates, and built-up shapes. However, the complexity of shapes achievable with steel is generally less than with aluminum due to steel’s higher density and lower malleability.
Recyclability
Aluminum Alloys:
Aluminum is 100% recyclable without losing its properties. The recycling process consumes only a fraction of the energy required to produce primary aluminum, making it an environmentally friendly choice.
Structural Steel:
Steel is also highly recyclable and can be reused multiple times. Recycling steel requires significantly less energy than producing new steel, but it still consumes more energy compared to aluminum recycling.
Joint Connections
Joint connections are a critical aspect of structural engineering, influencing the overall integrity and performance of the structure. Both aluminum alloys and structural steel present unique challenges and advantages in this regard.
Aluminum Alloys:
Welding: Welding aluminum can be more challenging than welding steel due to aluminum’s higher thermal conductivity and lower melting point. Specialized techniques, such as TIG (Tungsten Inert Gas) welding, and welders trained in aluminum welding are necessary.
Bolted Connections: Bolting aluminum requires careful consideration of galvanic corrosion, especially when in contact with steel or other metals. Insulating materials or protective coatings are often used to prevent this.
Fatigue Resistance: Aluminum has lower fatigue resistance compared to steel, which must be considered in the design of joints in dynamic or cyclic loading conditions.
Structural Steel:
Welding: Steel is easier to weld using conventional welding techniques, and the material’s higher melting point makes it more forgiving in terms of heat management.
Bolted Connections: Bolting steel is straightforward, with a wide range of standard bolts, nuts, and washers available. Steel structures are less prone to issues like galvanic corrosion when bolted.
Fatigue Resistance: Steel generally exhibits better fatigue resistance than aluminum, making it more suitable for applications subjected to repetitive loading.
Applications and Considerations
Aluminum Alloys:
Applications: Ideal for lightweight structures such as building facades, large-span roofs, marine structures, and transportation infrastructure where weight reduction and corrosion resistance are critical.
Considerations: Higher material cost, specialized joint connection techniques, and lower fatigue resistance are key factors to consider.
Structural Steel:
Applications: Suited for high-load structures such as skyscrapers, bridges, and industrial buildings where high strength and durability are paramount.
Considerations: Requires corrosion protection in harsh environments, and the higher weight can be a disadvantage in certain applications.
Conclusion
Both aluminum alloys and structural steel have distinct advantages and challenges in structural engineering. The choice between the two depends on the specific requirements of the project, including weight, strength, environmental conditions, design complexity, and sustainability goals. By understanding the properties and joint connection considerations of each material, engineers can make informed decisions to optimize the performance and longevity of their structures.