Structural steel 8768

A presentation on

Structural Steel

By: Vinod Singh

Steel ď Ž

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Man made metal derived from iron- which is its major constituent Remaining components are small amounts of other elements Added to improve the quality of steel

Used as: ď Ž

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Basic products of steel mill such as plate, section and bars From this members are fabricated viz. beams, girders, columns, struts, ties etc.

Steel vs. Cast Iron  

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Up to 1.5 % Carbon combines with iron More than 1.5 -4.5 % present as free graphite – known as cast iron Properties vary with the varying carbon content Increasing carbon content produces increase in shear strength & hardness Decreases the ductility and toughness

Comparison between Cast Iron, Wrought Iron & Steel Cast Iron Wrought iron Steel composition

Crude form containing Purest 2-4% carbon Contains up to 0.25% carbon

Midway

Melting point

1200 degree Celsius

1500 degree Celsius

1300-1400 degree Celsius

Hardness

Hard, hardened by heating & sudden cooling

Cannot be hardened or tempered

Can be hardened & tempered

Strength

Comp. strength 6.37.1 tonnes/sq cm Ultimate tensile strength 1.26 to 1.57tonnes/sq cm.

compressive strength is 2.0 tonnes/sq cm and ultimate tensile strength 3.15 tonnes/sq cm

Comp strength 4.75 -25.2 tonnes/ sq cm Ultimate tensile strength is 5.51 to 11.02 t /sq m

Comparison between Cast Iron, Wrought Iron & Steel

Rusting

Cast Iron

Wrought iron

Steel

Does not rust easily

Rusts more than Cast Iron

Rusts easily

Malleability&Duct Brittle & cannot Tough, Tough, malleable ility be welded or malleable, ductile & Ductile rolled into sheets & moderately elastic Reaction to sudden shock

Does not absorb shocks

Cannot stand heavy shocks

Absorbs shocks

Forging & Welding

Brittle and cannot be welded or rolled into sheets

Easily forged or welded

Rapidly forged or welded

Comparison between Cast Iron, Wrought Iron & Steel

Uses

Cast Iron

Wrought iron

Steel

For parts that rust easily like water pipes, sewers, drain pipes etc.

Making such parts of machines as are not likely to be subjects to shocks or tension Lamp posts, columns and railings

Costlier than mild steel so being replaced by the latter Withstand shocks without permanent injury so used in chains, crane hooks and railway couplings

Used as reinforcemen t in R.B. & R.C.C. Used in making St. members, bolts, rivets and sheets (plain and corrugated) Making cutlery, files & machine tools

Types of Steel:

(According to varying

Carbon Content)  

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Dead Mild Steel (Less than 0.15 % Carbon ) Mild Steel (0.15 – 0.30 % Carbon) Medium Carbon Steel (0.30 -0.80 % Carbon) High Carbon Steel (0.80 -1.50 % Carbon) Cast Steel / Carbon Tool Steel (More than 1.50 % Carbon)

Mild Steel          

Ductile & malleable More tough and more elastic than cast iron and wrought iron More prone to rusting than wrought iron Corrodes quickly Easily forged, welded & riveted Withstands shocks & impacts well Not much affected by saline water Equally strong in tension, compression and in shear Difficult to harden and temper Sp. Gravity 7.8

Mild Steel : Uses 

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Used as rolled structural sections like Isection; T-section; channel Section; angle irons. Plates round and square rods M.S. Round bars Used as reinforcement in R.C.C. M.S. tubes are used in structures Plain and Corrugated M.S. Sheets are used in roofing

Medium Carbon Steel    

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Granular structure More tough & elastic than M.S. Easier to harden & to temper More difficult to to forge and to weld Stronger in compression than in tension or in shear Withstands shocks and vibrations better

Medium Carbon Steel : Uses ď Ž

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For making tools such as dills, files, chisels Used for making those parts that ae hard , tough and durable and capable of withstanding shocks and vibrations

High Carbon Steel 

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Increased tensile strength leads to less weight of it being used as compared to M.S. Structure becomes lighter Resists corrosion better Tougher and more elastic More brittle and less ductile than mild steel

High Carbon Steel : Uses ď Ž

In reinforcing prestressed concrete structures

Types of Steel: (according to elements used) ď Ž

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Steels that owe their properties due to carbon are called Carbon Steels Steels with properties due to elements other than carbon are termed as Alloy Steels

Alloy Steels 

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The elements that impart distinctive characteristics to steel are added to iron to produce an alloy steel named after the element added Prepared to increase strength, hardness, toughness, resistance to corrosion and thermal and electrical conductivities

Divided into two categories:  Ferrous alloys ( chromium, nickel, vanadium, tungsten, molybdenum and manganese )  Non Ferrous alloys

Stress strain curve

Hot rolled sections

Structural steel sections

Tolerances in structural steel It is not possible in rolling process to produce sections to the exact dimensions specified.

Allowances for:  Slight variation in member length  Inaccurate location of holes  Out of squareness of member ends  Variation in depth of welded girders  Other dimensional variations 

bolting Most common method in joining structural is bolting:

welding There are 3 different type of welds  Butt weld  Fillet weld  Lap weld

Properties of a structural steel frame In design:  Large spans  With columns of small sections  Great building heights and high loadbearing capacity  Combined with low dead weight of the structure  Structural systems in which openings can be easily provided  To simplify installation of services

Properties of a structural steel frame In construction:  Prefabrication and erection of components  Shorter construction time  Close dimensional tolerances  Ease in fixing and cladding  Erection independent of weather conditions  Modest demand on space on the site  Dry construction

Properties of a structural steel frame In use:  Greater flexibility  Limited no. of internal supports  Adaptibility of frame work to change of use  Increasing effective life of building  Ease in dismantling or demolition

Applications

1. Portal Frame - Rafter 2. Portal Frame - Column 3. Wind bracing 4. Purlins 5. Wall Rails 6. Roof panels 7. Wall panels 8. Astrotherm insulation 9. Eave gutter 10. Monovent

11. Circular vent 12. Vehicle door 13. Pedestrian door 14. Window 15. Roof light 16. Canopy 17. Parapet 18. Crane beams and rails 19. Bridge crane 20. Mezzanine or Structural Floor

Applications: Wind Bracing ď Ž

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Wind bracing provides the longitudinal stability of the building.

It consists of cross bracing located in roof and sidewalls, in one or more bays depending on loadings and the length of the building.

If it is not possible to have cross bracing in the sidewalls, it can be replaced by wind portal frames or by fixed base wind columns, located adjacent and connected to the mainframe columns.

Applications: Roof Lights 

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Roof Lights can be of dome construction as shown here or as profiled sheets replacing steel roof panels.

Function Continuous natural light General Characteristics Insulated roof curb A framed opening of double skin metallic roof curb, to match the profile of the roof sheet and its location. Class-fibre insulation is installed on job site.

Applications: Astrotherm insulation ď Ž

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Astrotherm insulation consists of fibre glass blanket complete with a laminated facing vapour barrier Optionally, isoblocks are supplied to minimise thermal bridges and Alustrip to improve the overall appearance of any exposed insulation joints.

Eave gutter ď Ž

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Gutters are often an afterthought and can spoil the appearance of a building The gutters are large capacity and colour coated to compliment the building. Alternatively internal gutters can be provided

Monovent Used On the peak in the roofs  Function Ventilation of the building at the ideal peak position, where large movement of air is required.  General Characteristics Steel operating cable, cable guides (instead of standard type pulleys), hook and cable stop.  Stainless steel screws and aluminium rivets. 

Roof Panels

Wall Panels

Mezzanine

Purlins

Bridge crane

Circular Vents

Pedestrian door

Structural steel in buildings

Airport terminal complex

A steel joist and king post truss system provide support for the 650,000sq. ft. roof.

This framing system creates wide-open, column-free spaces king post trusses form the lateral-force resisting system, eliminating the need for bracing and further increasing flexibility of the interior space.

Steel buildings- stadium

The upper tier, cantilevering 46' over the suite and club Levels supported by column groupings consisting of four massive steel HSS placed at the midpoint alternating structural bays.