Steel structures are made from combinations of structural steel members designed to carry loads and provide rigidity. Common steel structures include buildings, bridges, and towers. Steel comes in various grades depending on carbon content, including low carbon steel (mild steel), medium carbon steel, and high carbon steel. Steel structures offer advantages like strength, light weight, and ease of fabrication but require maintenance to prevent corrosion. Common steel sections used in construction include I-beams, channels, angles, and hollow sections. Connections between steel members can be welded, bolted, or riveted.

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WHAT ARE STEEL STRUCTURES ?
 structure which is made from organised combination of structural STEEL members designed to carry loads and provide adequate
rigidity
 Steel structures involve a sub-structure or members in a building made from structural steel.
 Some famous steel structures are-
WALT DISNEY CONCERT HALL, US TYNE BRIDGE, UK HOWRAH BRIDGE, INDIA
OBJECTIVE
THE OBJECTIVES OF STRUCTURAL DESIGN IS TO DESIGN THE STRUCTURE FOR STABILITY, STRENGTH AND SERVICEABILITY. IT MUST
ALSO BE ECONOMICAL AND AESTHETIC.
The design of a structure must satisfy three basic requirements :
1) STABILITY to prevent overturning, sliding or buckling of the structure, or parts of it, under the action of loads
2) STRENGTH to resist safely the stresses induced by the loads in the various structural members; and
3) SERVICEABILITY to ensure satisfactory performance under service load conditions – which implies providing adequate
stiffness and reinforcements to contain deflections, crack-widths and vibrations within acceptable limits, and also providing
impermeability and durability (including corrosion-resistance), etc.
PROPERTIES OF STRUCTURAL STEEL
• The major constituent of structural steel is Iron.
• There are three commonly available commercial forms of steel namely Low Carbon Steel, Mild Steel (M.S.), High carbon steel which are
based on the amount of carbon content in it.
1. Low Carbon Steel (Mild Steel): Typically contain 0.04% to 0.30% carbon content. This is one of the largest groups of Carbon
Steel. It covers a great diversity of shapes; from Flat Sheet to Structural Beam. Depending on the desired properties needed, other
elements are added or increased.
For example: Drawing Quality (DQ) – The carbon level is kept low and Aluminum is added, and for Structural Steel the carbon
level is higher and the manganese content is increased.
2. Medium Carbon Steel: Typically has a carbon range of 0.31% to 0.60%, and a manganese content ranging from .060% to 1.65%.
This product is stronger than low carbon steel, and it is more difficult to form, weld and cut. Medium carbon steels are quite often
hardened and tempered using heat treatment.
3. High Carbon Steel: Commonly known as “carbon tool steel” it typically has a carbon range between 0.61% and 1.50%. High
carbon steel is very difficult to cut, bend and weld. Once heat treated it becomes extremely hard and brittle.
 mechanical properties for steel are:
• Hardness
The ability of a material to withstand abrasion; carbon content determines the maximum hardness obtainable in steel,
or hardenability.
• Strength
The amount of force necessary to deform a material. Higher carbon content and hardness result in steel with higher
strength.
• Ductility
The ability of a metal to deform under tensile stress. Lower carbon content and less hardness result in steel with higher
ductility.
• Toughness
The ability to withstand stress. High ductility is associated with better toughness.
• Corrosion resistance
The resistance to oxidization (rusting).

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• Machinability
The ease with which the steel can be shaped by cutting, grinding, or drilling. Machinability is influenced by hardness,
strength, thermal conductivity, and thermal expansion.
• Weldability
The ability of steel to be welded without defects. Weldability is primarily dependent on chemical composition and heat
treatment.
 ADVANTAGES & DIS-ADVANTAGES OF STEEL
 ADVANTAGES
• Lightness
• high strengTh and stiffness per weight
• Ease of fabrication and mass production
• fast and easy erection and installation
• Substantial elimination of delays due to weather
• More accurate detailing
• Non shrinking and non creeping at ambient temperature
• formwork unneeded
• Termite proof and rot proof
• Uniform quality
• Economy in transportation and handling
 CLASSIFICATIONS OF STEEL-SECTIONS
 Dis-ADVANTAGES
1. Maintenance cost of a steel structure is very high.
Due to action of rust in steel, expensive paints are
required to renew time to time. So that resistance
against severe conditions increases.
2. Steel has very small resistance against fire as
compared to concrete. Almost from 600-700C half
of steel strength reduced.
3. Steel cannot be mold in any direction you want. It
can only be used in forms in which sections
originally exists.
4. If steel loses its ductility property, than chances of
brittle fractures increase.
5. If there are very large variations in tensile strength
than this lead steel to more tension. Due to which
steel tensile properties graph falls down.

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I-SECTIONS TEE-SECTIONS CHANNEL SECTIONS ANGLE
SECTIONs HOLLOW SECTIONS BOX-CHANNEL SECTIONS ZED SECTIONS
OMEGA (TOP HAT) SECTIONS h-sections, etc.
I-SECTIONS : The core of the I-beam, better known as the web, will ensure that resistance against shear forces is provided. Except for
the web, the I-beam also consist of flanges, taper or parallel flange, on either side of the web and at both ends. The flanges provide
resistance to bending moments.
I-beams are used as cross sections providing strengths to girders, it also provides support to joists which in turns support ceilings and/or
floors. They are also widely used in the construction industry as a support for buildings to ensure that the structure is strong enough.
Even though I-beams can resist bending.The size of I-beams are determined by the weight it should be able to support and will
differ from application to application and structure to structure.
TEE-SECTIONS : Tee Section, also known as T beam or T bar, is a structural beam with a “T” shaped cross
section. Tee section is generally made of plain carbon steel. Manufacturing methods of “T” sections are hot
rolling, extrusion and plate welding. T bars are often used for general fabrication
HOLLOW SECTIONS: A hollow section shall be designated by its outside dimensions and its thickness in
millimetres and shall be further classified into CF or HF depending
upon whether it is cold formed or hot formed.
ANGLE SECTIONs : Mild Steel Angle Iron is suitable for making
structures and general fabrications . Mild steel angle has many practical uses including the
construction of fences or trailers, and is often used as fence posts. It provides a reliable and
sound structure and will also be widely recycled, making it a very ‘green’ choice of material.
Strong, versatile and easily formed Widely recycled
Often used to construct frames and structures Available cut to size

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WHERE & WHEN USE STEEL
STRUCTURES?
1) Long-span structures
2) Multi-storey & high-rise buildings
3) Buildings of heavy duty plants
4) Tower & mast structures
5) Portal frames
6) Bridges
7) Infrastructures
8) Deployable structures
9) Generalized structures: mechanical
 CONNECTIONS
Connections are the devises which are used to join
elements of a structure together at a point such
that forces can be transferred between them
safely.
 TYPES OF CONNECTIONS…
 BASED ON MEANS OF CONNECTION
WELDED CONNECTIONS
RIVITED CONNECTIONS
BOLTED CONNECTIONS
 BASED ON FORCES TO BE TRANSFERED
TRUSS CONNECTIONS
FULLY RESTRAINED CONNECTONS
PARTIALLY RESTRAINED CONNECTIONS
SPLICES
BARCKETS
 BASED ON PLACEMENT OF PARTS TO BE JOINED
LAP JOINTS
BUTT JOINTS
WELDED CONNECTIONS: the welding process uses
an electric arc to generate heat to melt the parent
material in the joint. A separate filler material supplied as
a consumable electrode also melts and combines with the
parent material to form a molten weld pool. As welding
progresses along the joint, the weld pool solidifies fusing
the parent and weld metal together. Several passes or
runs may be required to fill the joint or to build up the
weld to the design size.
STRESS STRAIN CURVE

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 Positions of the welds:
 Horizontal
 Vertical
 Overhead
 Flat
 Advantages:
 Economical – Cost of materials and labors.
 Efficiency is 100% as compared to rivets (75- 90%)
 Fabrication of Complex Structures – Easy – like Circular
Steel pipes.
 Provides Rigid Joints – Modern Practice is of Rigid Joints.
 Disadvantage:
 No provision for expansion or contraction therefore
greater chances of cracking.
 Uneven heating and cooling - member may distort - may
result in additional stresses.
 Inspection is difficult and more costlier than rivets
 BOLTED CONNECTIONS:
Bolted joints are one of the most common elements
in construction and machine design. They consist of fasteners that capture and join other parts, and are secured with the
mating of screw threads.
Connection classification: Classification based on
the type of resultant force transferred: The bolted
connections are referred to as concentric connections (force
transfer in tension and compression member), eccentric
connections (in reaction transferring brackets) or moment
resisting connections (in beam to column connections in
frames).

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 RIVITED CONNECTIONS:
A rivet is a permanent mechanical fastener.
Before being installed, a rivet consists Of
smooth cylindrical shaft with a head on one end.
The end opposite to the head is called the tail. On
installation the rivet is placed in a punched or
drilled hole, and the tail is upset, or bucked (i.e.,
deformed), so that it expands to about 1.5 times
the original shaft diameter, holding the rivet in
place.
 Installation:
 Heating of the rivet
 Inserting it to an oversize hole pressure to the head.
 Squeezing the plain End by Pneumatic driver Round
head.
 On Cooling Reduces in Length–Clamping Force.
MILD STEEL: - Mild steel consist of iron alloyed with less than 0.3% carbon, most commonly between 0.1
to 0.25%. The building industry frequently uses mild steel in construction because of its ductility and malleability.
MILD Steel frame usually refers to a building technique with a "skeleton frame" of vertical steel columns and
horizontal beams, constructed in a rectangular grid to support the floors, roof and walls of a building which are all
attached to the frame. The development of this technique made the construction of the skyscraper possible
PROPERTIES:
1. Ductile & malleable
2. More tough and more elastic than cast iron and
USES:

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Wrought iron
3. More prone to rusting than wrought iron
4. Corrodes quickly
5. Easily forged, welded & riveted
6. Withstands shocks & impacts well
7. Not much affected by saline water
8. Equally strong in tension, compression and in shear
9. Difficult to harden and temper
10. Sp. Gravity 7.8
STAINLESS STEEL:-
Stainless steel is an iron-based alloy with a significant chromium content; in many cases, together with chromium,
other special chemical elements are intentionally added, such as nickel and molybdenum. The main characteristics of
this family of steels is resistance to wet corrosion, or electrochemical corrosion, in aggressive environments such as
fresh water, sea water, contaminated water based solutions, acid and base environments, industrial environments, etc.
 Strength: Duplex stainless steels are much stronger than regular stainless steels.
 Toughness and ductility: Duplex stainless steels have better toughness and ductility than ferritic grades but not as
good as austenitic stainless steel.
 Corrosion resistance: corrosion resistance is nearly similar to normal stainless steel (austenitic/ ferritic)..
 Stress corrosion resistance:( corrosion at increased rate under stress) Duplex stainless steels show very good stress
corrosion cracking (SCC) resistance like ferritic steel
 Cost: Duplex stainless steels have lower nickel and molybdenum contents than their austenitic counterparts (of similar
corrosion resistance)..This reduces the alloying costs.