Construction Materials - Steel -

1. Prof. Ghassan ChehabFaculty of Engineering and ArchitectureDep. of Civil and Environmental EngineeringAmerican University of Beirut Construction Materials - Steel -

2. Introduction • The steel is formed of iron and carbon. • The use of Iron, the basic constituent of steel, goes back to 1500 BC. • Iron forms about 4-5% of earth crust. • The steel production started in the mid 1800s. • The steel technology advanced in the second half of the 19th century with the development of the basic oxygen furnace and continuous wasting methods. • New technologies increase the efficiency and the reduces the cost of steel production.

3. Introduction

4. Introduction: Steel in the Circular Economy

5. Introduction Steel products Miscellaneous products Applications: forms and pans… Structural steel Applications: vertical columns, plates… Fastening products Applications: structural connections, bolts, nuts… Reinforced steel Applications: rebars, concrete reinforcement… Cold-formed steel Applications: trusses, decking…

6. Steel Production

7. Steel Alloys • Alloy metals can be used to alter the properties of steel. • About 250000 alloys are used for steel production. Around 200 alloys are used for civil engineering application. • Alloy agents are used to add one or more of the below properties: • Hardenability • Corrosion resistance • Machinability • Ductility • Strength

8. Steel Alloys

9. Steel Alloys • By varying the carbon and the alloy content using different heat treatments, steel can be produced with different characteristics. • Low alloy • Low carbon • Medium carbon • High carbon • High alloy • Tool • Stainless • The steel used in construction projects are usually low and medium carbon steel.

10. Definitions of some basic properties: • Stiffness :property by which a material can resist deformation. Measure of stiffness is E. • Ductility :ability of the material to withstand considerable plastic deformation without breaking when subjected to the action of tensile stress beyond the yield point. Measure of ductility is % elongation before fracture (steel is ductile) = ℓf - ℓ0/ℓ0 • Malleability:same as ductility but under compression • Brittleness:is the absence of ductility or malleability; small plastic deformation leads to rupture. The ultimate strength is the fracture strength or yield strength whichever is higher. • Hardness:is the ability of a material to resist abrasion or indentation. • Toughness:property of a material to absorb energy at high stress (usually above the elastic limit) without fracture. Measure of toughness is amount of energy that a unit volume of the material has absorbed after being stressed up to fracture point. Measure of toughness is area under stress.

11. Heat Treatment of Steel • Steel properties depend on the carbon content. • The properties of steel can vary depending on the heat treatment. • The response of steel to heat treatment depends upon its alloy composition. • Process of heat treatment: heat the steel to a specific temperature, hold this temperature to a specific period of time, then cool the material at a specific rate Steel heat treatment Tempering Annealing Normalizing Hardening

12. Tension Test • ASTM E8 • To determine: the yield strength, yield point, ultimate tensile strength, elongation and reduction of area. • Performed at T= 10-35ºC • An axial load is applied to the specimen at a specific rate.

13. Tension Test • Tension Test

14. Tension Test • Tension Test •  = stress = force per unit area (N/m2 = Pa) •  = P/A • = strain = L/L = (L-L0)/L0 = deformation per unit length • L0 = gage length • L = observed length under a given load • L = gage elongation or shortening • 1 MPa = 106 N/m2 • 1 Gpa = 109 N/m2

15. Reinforcing Steel • Structural concrete members subjected to tensile and flexural stresses must be reinforced since concrete is weak in tension. • Conventional or prestressed concrete can be used depending on the design situation. Conventional reinforcing steel Deformed wire fabrics Plain bars Plain wire fabrics Deformed bars

16. Reinforcing Steel Grades: 40, 60, 75, and 90 For grade 60: • fy= yield strength = 60,000 psi (4200 kg/cm2) • Es= modulus of elasticity = 29,000 ksi (2 x 106 kg/cm2) • ℰy = yield strain = Es/ fy = 0.002 • ℇsh= strain corresponding to strain hardening = 0.008 to 0.01 • fsu= ultimate stress = 1.35 to 1.6 fy Density of Steel: 7850 kg/m3

17. Reinforcing Steel Hanger Bars Tension Reinforcement Stirrups for shear reinforcement

18. Structural Steel Structural Steel Used in hot-rolled structural shapes, plates, and bars. Used for different applications: columns, beams, bracings, frames, trusses, bridges girders....

19. Structural Steel • Structural steel grades • Steel is designed based on grade, type and class. • The yieled strength of steel is also referred to as the steel’s grade i.e. a steel with a yield strength of 50 ksi is called grade 50 • Common systems for identifying and designing steel: • ASTM : American Society for testing and materials

20. Structural Steel Commonly Used Sections

21. Structural Steel Commonly Used Sections

22. Structural Steel Commonly Used Sections

23. Structural Steel Commonly Used Sections

24. Structural Steel Commonly Used Sections

25. Structural Steel Commonly Used Sections

26. Structural Steel Commonly Used Sections

27. Structural Steel Commonly Used Sections

28. Structural Steel Member Connections: Welds vs Bolts

29. Steel Corrosion • Corrosion is an electromechanical reaction to the environment. For steel, it can be defined as the destruction that can be detected by rust formation. • Corrosion requires 4 elements: • An Anode: the electrode where corrosion occurs • A cathode: the other electrode needed to cover corrosion cell • Conductor: a metallic pathway for electrodes to flow • Electrolyte: a liquid that can support the flow of electrons

30. Steel Corrosion • Methods of Corrosion Resistance: • Barrier coating: works solely by isolating the steel from moisture. These coatings have low water and oxygen permeability. • Inhabitive primer coating: it contains passive pigments. They are low-solubility pigments that migrate to the steel surface when moisture passes through the film to passivate the steel surface. • Sacrificial primers (cathodic protection): it contains pigments such as elemental zinc. A close contact between the steel and sacrificial primers should exist to have an effective corrosion protection.→ Hot dip galvanizing example: Z90, Z180, Z275….

31. Mechanical Testing of Steel • Bend Test • ASTM E290 • To check the ductility to accommodate bending • To evaluate the ability of steel or a weld to resist cracking during bending. • A transverse force is applied to the specimen in the portion that is being bent (usually at midlength).

32. Mechanical Testing of Steel • Torsion Test • ASTM E143 • To determine the shear modulus of structural materials. • A cylindrical or tabular specimen is loaded either incrementally or continually by applying an external torque to cause a twist within the gauge length.

33. Mechanical Testing of Steel • Charpy V Notch Impact Test • ASTM E23 • To measure the toughness or the energy required to fracture V-notched simply supported beam specimen. • Test used for structural steel in tension members.

34. Mechanical Testing of Steel • Charpy V Notch Impact Test • ASTM E23 • Toughness is a function of temperature, it increases with increasing the temperature. • The fracture surface consists of a dull shear area (ductile) at the edges and a shiny cleavage area (brittle) at the center.

35. Reference: Mamlouk, M., Zaniewski, J., Materials for Civil and Construction Engineers, Third Edition, Pearson Education