Steel Structure
A steel structure is a construction system in which the primary load-carrying framework is made from structural steel sections such as I-beams, channels, angles, and hollow sections connected by bolts, rivets, or welds. Steel structures offer high strength-to-weight ratios, predictable material properties, rapid erection, and the ability to span large distances, making them ideal for high-rise buildings, industrial sheds, bridges, and towers. Design follows limit-state or allowable-stress methods specified by standards such as IS 800 (India) or AISC (USA).
Key Formula
σ = M·y / I
LaTeX: \sigma = \frac{M \cdot y}{I}
| Symbol | Meaning | Unit |
|---|---|---|
| \sigma | Bending stress at a fibre | Pa (N/m²) |
| M | Applied bending moment | N·m |
| y | Distance from neutral axis to fibre | m |
| I | Second moment of area (moment of inertia) | m⁴ |
Worked Example
Problem
An ISMB 300 steel beam (I = 8603 cm⁴, depth = 300 mm) spans 6 m and carries a central point load of 40 kN. Calculate the maximum bending stress in the beam (assume simply supported).
Solution
Maximum moment: M = W·L/4 = 40,000 × 6 / 4 = 60,000 N·m = 60 kN·m. Distance to extreme fibre: y = 300/2 = 150 mm = 0.150 m. Convert I: 8603 cm⁴ = 8603 × 10⁻⁸ m⁴. Bending stress: σ = M·y / I = (60,000 × 0.150) / (8603 × 10⁻⁸) = 9000 / (8.603 × 10⁻⁵) ≈ 104.6 × 10⁶ Pa.
Answer
σ_max ≈ 104.6 MPa (well below fy = 250 MPa for Fe 250 steel)
Common Structural Steel Sections and Their Uses
| Section Type | Symbol | Primary Use | Strength in |
|---|---|---|---|
| I-beam / Universal Beam | ISMB / UB | Beams, girders | Bending |
| I-column / Universal Column | ISSC / UC | Columns | Axial + bending |
| Channel Section | ISMC | Purlins, bracing | Bending, shear |
| Angle Section | ISA | Trusses, bracing | Tension, compression |
| Hollow Square/Rectangle | SHS / RHS | Columns, frames | Axial, torsion |
| Circular Hollow Section | CHS | Towers, masts | Torsion, axial |
Interactive Tools
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Related Terms
Reinforced Concrete
Reinforced concrete is a composite construction material in which steel reinforcement bars (rebars), plates, or fibers are embedded within concrete to improve its tensile strength. Concrete alone is strong in compression but weak in tension; the steel reinforcement carries tensile stresses and prevents cracking under load. This combination is fundamental to modern structural construction, enabling the building of beams, slabs, columns, foundations, and entire structures.
Bridge Design
Bridge design is the engineering discipline concerned with planning, analysing, and sizing all structural and non-structural components of a bridge to carry specified traffic, wind, seismic, and thermal loads safely and economically over its design life. The process involves selection of bridge type (beam, arch, truss, cable-stayed, suspension), site investigation, load calculations to relevant codes (IRC in India, AASHTO in the USA), structural analysis, material design, and consideration of aesthetics, constructability, and durability. Bridge design integrates structural mechanics, geotechnical engineering, hydraulics, and materials science.
Seismic Design
Seismic design is the process of designing structures to resist the dynamic forces imposed by earthquakes, ensuring they do not collapse and allow safe evacuation even under strong ground shaking. It involves determining design seismic forces based on a site's seismic zone, soil type, and building importance; modelling dynamic structural response; and detailing ductile connections and structural systems that can absorb and dissipate seismic energy. In India, seismic design follows IS 1893 (Part 1), which classifies the country into four seismic zones (II–V) of increasing hazard.
The word 'steel' derives from the Proto-Germanic 'stahlaz' (firm, rigid). 'Structure' comes from the Latin 'structura' (a fitting together of parts), from 'struere' (to build). The use of wrought-iron and later Bessemer-process steel for structural frameworks became widespread after the 1850s, with the first all-steel-framed skyscraper (Home Insurance Building, Chicago) completed in 1885.