designofsteelstructures1-170401120327.pptx

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1. DESIGN OF STEEL STRUCTURES INTRODUCTION

2. CE3601 DESIGN OF STEEL STRUCTURAL ELEMENTS L T P C 3 0 0 3 COURSE OBJECTIVE To introduce the students to limit state design of structural steel members subjectedto compressive, tensile and bending loads, including connections and to provide the students the tools necessary for designing structural systems such as rooftrusses and gantry girders as per provisions of current code (IS 800 - 2007) of practice . UNIT I INTRODUCTION TO STRUCTURAL STEEL AND DESIGN OF CONNECTIONS 9 General -Types of Steel -Properties of structural steel - I.S. rolled sections - Concept of Limit State Design - Design of Simple and eccentric Bolted and welded connections - Types of failure and efficiency of joint – prying action - Introduction to HSFG bolts UNIT II DESIGN OF TENSION AND COMPRESSION MEMBERS 9 Behaviour and Design of simple and built-up members subjected to tension - Shear lag effect- Design of lug angles - tension splice - Behaviour of short and long columns - Euler's column theory- Design of simple and built-up compression members with lacings and battens - Design of column bases - slab base and gusseted base

3. UNIT III DESIGN OF BEAMS 9 Design of laterally supported and unsupported beams - Design of built-up beams - Design of plate girders UNIT IV INDUSTRIAL STRUCTURES 9 Design of roof trusses – loads on trusses – purlin design using angle and channel sections – truss design, Design of joints and end bearings–Design of gantry girder - Introduction to pre-engineered buildings UNIT V PLASTIC ANALYSIS AND DESIGN 9 Introduction to plastic analysis - Theory of plastic Analysis - Design of continuous beams and portal frames using plastic design approach TOTAL: 45 PERIODS COURSE OUTCOMES: Upon completion of this course, students will be able to: CO1 Recognize the design philosophy of steel structures and identify the different failure modes of bolted and welded connections, and determine their design strengths CO2 Select the most suitable section shape and size for tension and compression members and beams according to specific design criteria CO3 Apply the principles, procedures and current code requirements to the analysis and design of steel tension members, columns, column bases and beams CO4 Identify and compute the design loads on Industrial structures, and gantry girder CO5 Find out ultimate load of steel beams and portal frames using plastic analysis

4. 1. What are steel structures In steel structures, structural steel is the main load carrying material to transfer the load within them and to transfer load to the ground Ex: - I-Beam, Tee section, [ - Channel section, Steel plate etc.., Steel concrete composite structures are also used in high-rise buildings but we are only going to study about steel structures in this paper

5. 2.Common Steel structures Roof truss in factories, cinema halls, railways etc., Crane girders, columns, beams Plate girders, bridges Transmission towers, water tank, chimney etc.,

6. Old Arch Bridge

7. Framed Building

8. Framed Building

9. Industrial Building

10. Industrial Building

11. Truss Bridge

12. Suspension Bridge

13. Cable Stayed Bridge

14. Advantages High comp. & tensile strength per unit weight hence low construction weight, saves space Good aesthetic view Good quality and durability Very high speed of construction Reusability and scrap value – env. Friendly Better solution to cover large span and tall structures Disadvantages Highcost – Initial Corrosion Low fire resistance 2. Adv. & Disadv.

15. 3. Steel Steel making First iron is extracted from iron ores like haematite, limestone, magnetite in furnace Oxygen is passed through molten iron to remove carbon and impurities to make steel. Magnese is added to strengthen the steel Adding chrome, nickel, phosphorous can impart special properties in steel

16. Co n t…. Semi finished products from the machine is hot rolled to different sections like bars, plates, angles, sections etc.., Adding carbon increases the tensile strength and hardness but lowers ductility and toughness In building we use structural steel which has low carbon of upto 0.1% to have ductility and yield.

17. - Manganese - Ferrite -- C a rb o n -Ferrite

18. Ingot slab bloom Billet Basic shapes and their relative proportions Primary rolls for plates

19. 4.Properties of steel Physical properties (IS800:2.2.4) 1. r = 7850 kg/m3 = 78.5kN/m3 2. E = 2x105 N/mm2 3. Poison ratio µ = 0.3

20. Type l Desi g n - ation UTS (M Pa ) Yield strength (Mpa) Thickness (mm) <20 20-40 >40 Standard st r uct u r a l steel Fe 410A 410 250 240 230 Fe 410B 410 250 240 230 Fe 410C 410 250 240 230 Hi g h t en s i l e structural steel St58HT 580 360 0.05 1.00 ST55-HTW 550 360 .05 1.00 Mechanical properties FE 410 A W I R ON GRADE WELDABLE U L TIM A T E TENSILE STRENGTH

21. Tensile test specimen before rupture F Area=S - F F Standard tensile test specimen F r t d L Area=S 0- L

22. Duct i li t y Ability of material to change its shape without fracture Mild steel – high ductility High carbon steel – low ductility Toughness & brittle fracture Ability of material to resist (absorb) impact load like earthquake load, machine load etc.., Requires both strength and ductility At low temp. steel fails on impact loading due to reduction in ductility and toughness called brittle fracture Temp At high temp strength reduces Corrosion Steel corrodes in moist air, sea water and acid. Adopt Painting, metallic coating, plastic coating, using corrosion resistant steel to resist corrosion

23. Hardness Resistance of the material to intentions and scratching Brinell harness, rockwell hardness number are used to measure hardness Fatigue Damage of material to cyclic loading Occurs due to moving loads, vibration in bridge Residual stress Latent stress present in the steel sections due to uneven heating and cooling during steel making Stress concentration Under loading, stress is concentrated at places at abrubt change in geomentry like holes bolts

24. 5. STEEL SECTIONS

25. Steel sections Steel is rolled to a required shape during fabrication. Commonly available I section – I Tee section – T Channel sections – Angle sections – l - Steel bars , tubes, plates, sheets, strips Refer structural engg handbook or steel table for sectional details

26. Common Steel members

27. Rolled steel I - section ISJB – Indian standard junior beam ISLB – “ Light beam ISMB - “ Medium beam ISWB - “ Wide flange beam ISHB - “ Heavy beam

28. Rolled steel I - section Example = ISMB 500 & 0.852 kN/m Depth Weight per Unit length 500 mm

29. Beam – Column construction

30. Rolled steel Channel - section ISLC, ISMC, ISLC, ISSC(Indian standard special section) Example ISMC 300 & 0.351 kN/m 300 mm

31. Rolled Steel Angle section ISA Equal angle – ISA 150 x 150 x 12 ISA unequal angle – ISA 150 x 115 x 12 Thickness

32. Rolled Tee- section ISNT – Indian standard Normal beam d ISHT – “ Heavy beam ISLT - “ special legge ISLT - “ Light beam

33. Other Sections Steel bars ISRO – Round bars ISSQ – Square bars Steel Tubes Steel plates

34. Braced frame Moment resisting frame Core and suspended floors

35. Py lon Lattice girder Tapered portal Knee brace Cable stayed bridge Suspension bridge

36. Choice of sections Governed by sectional properties and availability Popular in India – ISMB, ISMC, equal angles Channels are used in purlins, Tee and angles in truss, I section in beam and column Other forms of sections Built-up, stepped, wide flange, hybrid, cold formed (formed from light gauge steel strips)

37. 6. Loads on Structures DL = Dead load – self weight and perm load (IS875 - part 1) LL = Live load - changes from time to time – person ,furniture etc.., ( part 2) WL = Wind load – IS875 part 3 AL = IS875 part 5 EL = Earthquake load – IS1893

38. Design philosophy Working Stress method Stress at which the material starts to yield is taken as permissible stress of the section. All sections are designed not to exceed the permissible stress Permissible stress = Yield stress / F.O.S Since steel can resist load after yield point, following this principle results in bulky, uneconomical sections Ultimate Load method (plastic design method) Permissible load is a load when all the fiber in the steel is yielded This method does not ensure serviceability

39. Limit State Method (IS800 : 2007) It takes both strength and serviceability to account Limit state of Serviceability Minimum deformation, deflection, crack, vibration, corrosion to ensure aesthetic view, functionability and safety to partitions etc., Limit state of strength Structure should be stable and not collapse under load γf = partial safety factor for load (table 4) γm = partial safety factor for material (table 5)

40. Questions ??? Next Class: Connection