Steel Lecture Notes PDF

Introduction to Steel OVERVIEW OF STEEL AS AN ESSENTIAL MATERIAL IN CIVIL ENGINEERING. Learning Objectives Understand Discuss Highlight Explore Discuss Understand Discuss stress- Highlight Explore fatigue Discuss brittle structural ste...

Introduction to Steel OVERVIEW OF STEEL AS AN ESSENTIAL MATERIAL IN CIVIL ENGINEERING. Learning Objectives Understand Discuss Highlight Explore Discuss Understand Discuss stress- Highlight Explore fatigue Discuss brittle structural steels. strain advantages/dis failure. fracture and fire relationships. advantages. performance.  Steel is an alloy of iron and carbon, often with other elements to - ~95% iron improve properties. It What is contains: Steel? - Trace elements - 1–2% carbon like manganese, nickel.  High strength Ductility Properties of Steel Resistance to wear make Malleability steel suitable for structural applications.  1. Low Carbon (Mild) Steel 2. Medium Carbon Steel Types of Steel 3. High Carbon (Tool) Steel 4. Cast Iron  Contains 0.05–0.32% carbon. - Used in nails, Low Carbon screws, and structural - Tough, ductile, easily joined. Steel components. - Poor corrosion resistance.  Contains 0.35–0.50% carbon. Offers higher Medium strength/hardness. Carbon Steel Less ductile and malleable. Applications: structural steel, rails.  Contains 0.55–1.50% carbon. High Very hard Carbon but less ductile. Steel Applications: hand tools, chisels, saw blades.  Contains 2–4% carbon. - Hard, brittle, strong Cast Iron under compression. - Applications: engine blocks, machine parts. Structural Steel Applications Steel is widely used in:  Multi-story building skeletons  Industrial buildings  Transmission towers  Railway bridges  Reinforced concrete rebar.  1. High 2. Lightweight strength-to- for transport. weight ratio. Advantages of Steel 4. Ductile— 3. Long provides lifespan with failure maintenance. warning. More Advantages  Easy to alter/extend.  Fast construction.  High scrap value.  Reusable upon demolition. Disadvantages of Steel SUSCEPTIBLE TO NEEDS FIREPROOF FATIGUE REDUCES CORROSION TREATMENT. STRENGTH UNDER (REQUIRES COATING). REPEATED STRESSES.  Steel deforms elastically before yielding. Stress-Strain Relationship Beyond the yield point, plastic deformation occurs permanently.  Common grades: S275, S355, S460. Yield Grades strength ranges of Steel from 275– 460 N/mm². Grade indicates strength. Fatigue in Steel Cause Avoid Use Repeated stress Avoid abrupt Use bolted can cause changes in instead of gradual cracking section. welded joints. and failure.  Occurs at low temperatures or stress concentrations. Brittle Avoid abrupt changes in design. Fracture Use grades resistant to brittle failure.  Steel loses strength at high temperatures. Fire Yield stress drops by Performance ~30% at 550°C. Use fireproofing measures like coatings or concrete encasing. Corrosion of Steel Corrosion occurs in the Protection methods: presence of moisture/oxygen. Galvanization Paint coatings Specialized alloys.  Carbon is the primary alloying element. Carbon Steel Higher carbon increases strength but reduces ductility.  Contains other elements like chromium, nickel, molybdenum. Alloy Steel Improved toughness, hardness, and wear resistance.  Known for its hardness and ability to hold edges. Tool Steel Applications: cutting tools, dies.  Contains >10.5% chromium. Stainless Resistant to rust and staining. Steel Applications: kitchens, architecture, and medical tools. Structural Steel Design  Relies on:  Yield strength  Ductility and weldability  Impact resistance. Hot Rolled Sections  Examples:  Universal beams (UB), channels, tubes.  Used in large frameworks. Cold Rolled Sections  Examples:  Corrugated steel roofs, wall panels.  Lighter and easier to handle. Fabricated Sections  Built-up sections (I-beams, box girders) for high-strength applications. Future of Steel  Emerging trends:  Advanced alloys.  Sustainable practices (recycling).  Smart materials for adaptive construction. Conclusion Steel is integral to modern construction, balancing versatility, strength, and sustainability.