A presentation on Structural Steel

By:Vinod Singh

Steel 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:

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 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 & SteelCast Iron Wrought

ironSteel

composition Crude form containing 2-4% carbon

Purest 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 6.3-7.1 tonnes/sq cmUltimate 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

Cast Iron Wrought iron

Steel

Rusting Does not rust easily

Rusts more than Cast Iron

Rusts easily

Malleability&Ductility

Brittle & cannot be welded or rolled into sheets

Tough, malleable, ductile & moderately elastic

Tough, malleable & Ductile

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

Cast Iron Wrought iron Steel

Uses 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 tensionLamp posts, columns and railings

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

Used as reinforcement 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)

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 Used as rolled structural sections like I-

section; 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

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

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 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

In reinforcing prestressed concrete structures

Types of Steel:(according to elements used)

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 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

Structural steel sections

Hot rolled 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

11. Circular vent12. Vehicle door13. Pedestrian door14. Window15. Roof light16. Canopy17. Parapet18. Crane beams and rails19. Bridge crane20. Mezzanine or Structural Floor

1. Portal Frame - Rafter2. Portal Frame - Column3. Wind bracing4. Purlins5. Wall Rails6. Roof panels7. Wall panels8. Astrotherm insulation9. Eave gutter10. Monovent

Applications: Wind Bracing

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 Roof Lights can be of dome construction as

shown here or as profiled sheets replacing steel roof panels.

FunctionContinuous natural lightGeneral 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

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

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 systemprovide support for the 650,000sq. ft. roof.

This framing system createswide-open, column-free spaces

king post trusses form the lateral-force resistingsystem, eliminating the need for bracing and further increasing flexibilityof the interior space.

Steel buildings- stadium

The upper tier, cantilevering 46' over the suite and clubLevelssupported by column groupings consisting of four massivesteel HSS placed at the midpoint alternating structural bays.