Structural Steel
Structural steel is a category of steel used as a construction material for making structural elements like beams, columns, and trusses that form the skeleton of buildings and infrastructure, offering high strength-to-weight ratio and excellent ductility.
Composition
Iron alloyed primarily with carbon (typically 0.05-0.25% for structural grades), along with small amounts of manganese, phosphorus, sulfur, silicon, and other elements depending on the specific grade. Common structural grades include ASTM A36 (general purpose), A572 (high-strength), A992 (building framing), and A588 (weathering steel).
Properties
Yield Strength (A36)
36,000 psi (250 MPa)
The stress at which the material begins to deform plastically; higher grades offer yield strengths up to 100,000 psi.
Tensile Strength (A36)
58,000-80,000 psi (400-550 MPa)
The maximum stress the material can withstand before failure.
Density
490 lbs/ft³ (7,850 kg/m³)
Relatively high density compared to other structural materials like wood or aluminum.
Modulus of Elasticity
29,000,000 psi (200 GPa)
Measure of stiffness; consistent across most structural steel grades.
Ductility
Elongation 20-30%
Excellent ability to deform under tension without failure, providing warning before collapse.
Thermal Expansion
6.5 × 10⁻⁶ in/in/°F
Expands and contracts with temperature changes, requiring consideration in design.
Applications
Building Frames
Forms the primary structural system in many commercial, industrial, and high-rise buildings, supporting floors, walls, and roofs through beams, columns, and bracing.
Long-Span Structures
Used in convention centers, sports arenas, and hangars where large column-free spaces are required, often in the form of trusses, space frames, or arches.
Bridges
Essential material for various bridge types including beam, truss, arch, cable-stayed, and suspension bridges, offering strength and durability for spanning obstacles.
Industrial Structures
Forms frameworks for industrial facilities, power plants, refineries, and manufacturing facilities, often supporting heavy equipment and dynamic loads.
High-Rise Buildings
Enables the construction of tall buildings through moment frames, braced frames, or tubular systems that resist gravity and lateral loads.
Composite Construction
Combined with concrete in composite floor systems and columns to optimize the properties of both materials.
Advantages
- Exceptional strength-to-weight ratio compared to many construction materials
- Consistent and predictable material properties
- Excellent ductility providing warning before failure
- High durability with proper corrosion protection
- Allows for long spans and column-free spaces
- Rapid construction through prefabrication
- Adaptable through various connection methods
- Highly recyclable with minimal loss of properties
Limitations
- Vulnerable to corrosion without proper protection
- Reduced strength and stiffness at high temperatures requiring fire protection
- High thermal conductivity leading to thermal bridging
- Relatively high embodied energy and carbon
- Requires specialized fabrication facilities and equipment
- Connections require careful design and execution
- Transportation limitations for large members
- Potential for fatigue failure under cyclic loading
Sustainability Profile
Moderate sustainability profile with significant recycling benefits. Steel production is energy-intensive and generates substantial CO₂ emissions, primarily from the reduction of iron ore with coke in blast furnaces. However, structural steel has excellent end-of-life recyclability, with recycling rates exceeding 90% in many developed countries. Steel can be recycled indefinitely without loss of properties, and modern structural steel contains 90-98% recycled content when produced via electric arc furnaces. Innovations in production, including hydrogen-based direct reduction and electric arc furnaces powered by renewable energy, are reducing environmental impacts. Steel's durability, adaptability for reuse, and efficient material use through optimization also contribute to its sustainability profile.