STRUCTURAL STEEL
INTRODUCTION
• 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 & Steel
Composition
Melting point
Hardness
Strength
Rusting
Malleability & Ductility
Reaction to sudden shock
Forging & Welding
Uses
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
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 forge and to weld
• Stronger in compression than in tension or in shear
• Withstands shocks and vibrations better
Uses
• For making tools such as dills, files, chisels
• Used for making those parts that are 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
USE
In reinforcing pre-stressed 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
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
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
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
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
Roof Lights
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.
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
Circular Vents
Examples
A steel joist and king post truss system provide support for the 650,000sq. ft. roof
This framing system creates wideopen, column-free spaces
king post trusses form the lateralforce resisting system, eliminating the need for bracing and further increasing flexibility of the interior space.
Steel buildings- stadium
