OF STEEL STRUCTURES Lecture1 The steel sections manufactured in rolling mills and used as structural members are known as rolled structural steel sections The steel sections are named according to their cross sectional shapes ID: 1020133
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1. 1 CE – 318NDESIGN OF STEEL STRUCTURESLecture-1
2. The steel sections manufactured in rolling mills and used as structural members are known as rolled structural steel sections. The steel sections are named according to their cross sectional shapes. The shapes of sections selected depend on the types of members which are fabricated and to some extent on the process of erection. Many steel sections are readily available in the market and have frequent demand. Such steel sections are known as regular steel sections. INTRODUCTION
3. Some steel sections are rarely used. Such sections are produced on special requisition and are known as special sections.‘ISI Handbook for Structural Engineers’ gives nominal dimensions, weight and geometrical properties of various rolled structural steel sections.INTRODUCTION
4. Hot-Rolled Sections. Cold Formed Sections. Built-Up Sections.TYPE OF STRUCTURAL STEEL SECTIONS
5. In metalworking, rolling is a metal forming process in which metal stock is passed through one or more pairs of rolls to reduce the thickness and to make the thickness uniform., giving greater toughness, shock resistance and tensile (stress) strength .Rolling is classified according to the temperature of the metal rolled.If the temperature of the metal is above its recrystallization temperature, (temperatures over 1,000 degrees Fahrenheit ) then the process is known as hot rolling. If the temperature of the metal is below its recrystallization temperature, the process is known as cold rolling. ROLLED STRUCTURAL SHAPES
6. Larger sized materials that need to be in more distinct shapes should be created with the hot rolled steel process. Smaller products that need to be more durable and tolerant, should be created with the cold rolled steel process.
7. Rolled SectionsThe types of Steel Shapes rolled are described as follows. 1. Rolled steel I-Section 2. Rolled steel Channel Section 3. Rolled steel angle Section 4. Rolled steel T-Section 5. Rolled steel tube Section 6. Rolled steel bars 7. .Rolled steel flats 8. Rolled steel plates 9. Rolled steel sheets 10. Rolled steel strips
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9. IS Handbook No 1 published by BIS provides the dimensions, weights and geometrical properties 0f various section.Rolled Steel I – SectionsKnown as rolled steel joists or beams. Consists of two flanges connected by a web. The web resists shear forces, while the flanges resist most of the bending moment. CLASSIFICATION OF BEAMS/COLUMNS SECTIONS
10. The rolled steel beams are classified into following four series as per BIS : (IS : 808-1989) a) Indian Standard junior beams (ISJB)b) Indian Standard light weight beams (ISLB)c) Indian Standard medium weight beams (ISMB)d) Indian Standard wide flange beams (ISWB)Columns/Heavy Weight Beams are classified as follows:a) Indian Standard column sections (ISSC)b) Indian Standard heavy weight beam (ISHB)Designated- Beam, columns sections shall be designated by the respective abbreviated reference symbols followed by the depth and weight , for example: ISMB 200@ 735.8N/m means medium weight beam of depth 200 mm and the self weight is 735.8 N per metre length. CLASSIFICATION OF BEAMS/COLUMNS SECTIONS
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14. ISLB are used as roof Beam where load are relatively less, ISMB are used as floor beams. they have high moment of Inertia about x axix as compared with y axis. Lateral buckling strength of these beams is low, this disadvantage overcome by laterally restraining of each flange of the beamISWB have higher moment of inertia about yy axis so higher lateral buckling strength and so they are used as columns.
15. It is not effective as a beam or column. However, it is best to use for framing floor openings, stringers for steel stairs and stairwells. Efficient built-up members can be constructed out of channel assembled together with other structural shapes and connected by bolts or welds. Channelsa) Indian Standard junior channels (ISJC)b) Indian Standard light weight channels (ISLC)c) Indian Standard medium weight channels (ISMC)d) Indian Standard special Channels (ISSC)CLASSIFICATION OF CHANNEL SECTIONS
16. Channel sections shall be designated by the respective abbreviated reference symbols followed by the depth and weight , for example: a) ISSC 200@xx — for a column section of depth 200 mm and the self weight is xx N per metre length., b) ISMC 200@xx — for medium weight channel of depth 200 mm, DESIGNATION
17. c) ISMC 200@xx — for medium weight channel of depth 200 mm,
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19. Angles It’s legs may be equal or unequal and it is used for bracings, connections and trusses.a) Indian Standard equal leg angles (ISA)b) Indian Standard unequal leg angles (ISA)CLASSIFICATION OF BEAMS, COLUMNS, CHANNEL SECTIONS
20. Rolled Steel Angle Sections (ISA)Designated as ISA and width and length and thickness of legsAvailable asEqual angle sectionsTwo legs will be equal in lengthAvailable in sizes varying from 20mm x 20mm x 3mm to 200mm x 200mm x 25mm20
21. Unequal angle sectionsTwo legs will be unequal in length.Available in sizes varying from 30mm x 20mm x3mm to 200mm x 150 mm x 18mm21
22. Bulb angle sections ISBAExtensively used in structural steel works like roof trusses, and as connecting members for different structures. Bulb increases the stiffness of angles22
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24. Rolled steel Tee sections:Resembles the alphabet TConsists of web and flangeEach T section is designated by the series to which it belongs followed by depth eg ISNT 100Available in sizes varying from 20mm x 20mm x 3mm to 150mm x 150mm x 10mm.Widely used as members of the steel roof truss and form built – up sections.24
25. T SectionsISNT- Indian Standard Rolled Normal Tee section- having width of Flange equal to depth of sectionISHT- H Tee - having width of Flange equal to twice the depth of sectionISST (Short Tee)- having width of Flange shorter than the depth of sectionISLT- (Light T)- having light weightISJT- Junior TeeCLASSIFICATION OF BEAMS, COLUMNS, CHANNEL SECTIONS
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28. Structural steel sectionsRolled steel bar section:Indian Standard Round Bars (ISRO):Designated as ISRO 10 (round bars having diameter 10mm)Available in diameter varying from 6mm to 25mm. 28
29. Indian Standard square bars (ISSQ):Designated as ISSQ 10 (square bars of size 10mm)Used for grillwork, handrails for staircases etc.29
30. Rolled Steel Plate Section ( ISPL):Designated as ISPL 500 x 5 (500mm width and 5mm thickness)Used for construction of water tanks and other storage structures, built up beams, columns, base plate for foundations etc. 30
31. Rolled Standard Sheet Sections (ISSH):Plates having thickness less than 5mm.Designated as ISSH 1800 x 600 x 4 (sheet having length 1800mm, breadth 600mm and thickness 4mm).Used for construction of boxes and vehicle bodies.31
32. Indian Standard Strips (ISST):Mainly used as beedings.Designated as ISST 100 x 2 (steel strip with a width of 100mm and thickness 2mm).32
33. Indian Standard Flats (ISF):Designated as ISF 10 x 3(flat of width 10mm and thickness 3 mm).Available in suitable widths varying from 10mm to 400mmThickness varying from 3mm to 40mm.Used for steel grillwork for windows and gates.33
34. Rolled Steel Tubes:Inner diameter varying from 15 to 150mm.Thickness varying from 2 to 5.4mm.Efficient structural sections for formwork and trusses34
35. Built up sectionThese are members made up by a fabricator from two or more standard sections.Built-up members are specified by the designer when the desired properties or configuration cannot be obtained in a single hot rolled section.Such a situation arises when none of the standard rolled shapes are large enough; that is, the cross section does not have enough area or moment of inertia.Cover-plated rolled beams are used when the required bending capacity is not available in a rolled standard beam or when depth limitations preclude use of a deeper rolled beam or plate girder.
36. Built –up sections:Composed of a combination of available basic sections like plates, angles, channels etc.For increased strength and stabilityDifferent sections are joined by welding or riveting36
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38. Types of built – up sectionsTwo angles back to backTwo channelsI-sections with top and bottom platesPlate girderBuilt up column sections38
39. Light gauge sectionsMade from steel sheets of uniform thickness – process in cold stateCoated with zinc or aluminium Thickness normally less than 2mmYield stress ranging from 250MPa to 550 MPa.Normally have stiffening lips on flangesIntermediate stiffeners in wide flanges and webs39
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42. 42Plain C sectionLipped C sectionSwage beamSFS C sectionMultichannel Multibeam Zed sectionZeta sectionUltrazed section
43. Advantages of light gauge sectionsLightnessHigh strength and stiffnessEase of fabrication and mass productionFast and easy erection and installationHigh strength to weight ratioSubstantial elimination of delays due to weatherFormwork not neededUniform quality43
44. Choice of SectionIS:800 and IS handbook No.1 lists the properties Governed by the cross-sectional area, section modulus and radius of gyration and availability in market.Ease of connecting different sectionsIn IS 800:2007 there is no min. thickness requirements However better to use min. thickness of 6mm for the main members and 5mm for secondary members exposed to the atmosphere, especially in coastal areas44
45. Choice of SectionThe ideal beam is the one with the least cross-sectional area (and hence requiring the least material) needed to achieve a given section modulus. Since the section modulus depends on the value of the moment of inertia, an efficient beam must have most of its material located as far from the neutral axis as possible. The farther a given amount of material is from the neutral axis, the larger is the section modulus and hence a larger bending moment can be resisted.Column sections are governed by radius of gyration45
46. Beams need HIGH and Z in direction of bending Beams need high High modulusNeed stiffness in other direction to resist lateral buckling Some sections useful for both Columns usually need large value of r in both directions= better sections for beamsWhat Section to Use?27/28
47. Sections used for Beams
48. Selection of section which is safe and economical.Section is selected by(i) experience or(ii) by assuming certain stress valueA= Load/Axial StressSection Modulus= Moment/ Bending Stress= I/ySafety- Apply desired check for safetyEconomy- Minimum weight/unit weight, ease of fabrication.DESIGN OF STEEL STRUCTURES
49. I-SERIES N/m A(cm2) ry (cm) Zpz(cm3) ISMB 250 365.91 47.55 2.65 465.71 ISHB 200 365.91 47.54 4.50 397.23 For a beam z high and for a column r max lamda min to prevent bucklingλ=𝒍/𝒓r = sqrt (I/A)Z= M/f