Steel structures
Definition- it is combination of members which is designed for specific purpose.
Structural steel
Structural steel is a material used for steel construction.Steel is an alloy of iron and carbon.Apart from carbon by adding small percentage of manganese, sulphur, phosphorus,chrome nickel and copper.
Note .
Cast iron- percentage of carbon varies 2%-4%
Wrought iron - percentage of carbon 0.15%
Steel - percentage of carbon 0.15%
Mild steel- percentage of carbon 0.15%-0.30%
Physical properties of structural steel.
(1)- Density- 78.5kN/m3 (7.85gm/cc)or (7850 kg/m3).
(2) Co-efficient of linear expansion- 12x10^6/°C.
(3)-Young's Modulus-2.04x10^5 Mpa or 2x10^5 N/mm2.
(4)-Modulus of Rigidity- 0.84x10^5 - 0.98x10^5 N/mm2
Types of steel structure
(1)- Frame building
(2)- Plate girder used for bridges.
(3)- Steel arch bridge .
(4)- Industrial building.
(5)- Transmission line tower and mobile tower.
Advantages of steel over R.C.C structure.
(1)- Strength of steel structure >>>> R.C.C structure.
(2)- less time consuming for construction of steel structure .
(3)- Area occupied by the structure is less as compared to R.C.C. structure .
(4)- Ultimate strength is high.
(5)- Yield Strength is high..
Disadvantages of steel structure
(1)- Steel structure may be more costly than other types of structures.
(2)- The strength of steel is reduced substantially when heated at temperatures commonly observed in building fires.
(3)- Steel structures exposed to air and water, such as bridges are susceptible to corrosion and needs regular maintenance.
Rolled Steel Sections
(1) Beam and column section
(2) Channel section
(3) Rectangular hollow section.
(4) Circular hollow section
(5) Single angle section
(6) Double angle
(7) Built up section
(6) Tee section
Loads
(1)- Dead loads
(2) Imposed loads
(3) Wind loads .
(4) Earthquake loads.
(5) Erection loads.
(6) Accidental loads.
(7) Secondary effect (Temperature effect).
(1)- Dead loads
Dead load is due to the weight of every element of component within the structure .It is calculated from the member sizes and estimated material densities.
For example- weight of walls ,beams, columns, footings,floor slabs,roof slabs.
(2) Imposed loads
Following loads are grouped as imposed loads.
* Live loads
* Crane loads.
* Snow loads.
* Dust loads.
* Hydraulic and earth pressure.
* Impact loads.
(3) Wind loads
The force exerted by the horizontal components of wind is to be considered in the design of buildings, tower and other massive structures.
Note upto a height of 30 meter ,the wind pressure is considered to act uniformly,above 30 m height the wind pressure increases.
(4) Earthquake loads.
The earthquake loads on the structure during an earthquake result from inertia forces which were created by ground acceleration .
(5) Erection loads
Construction loads produced during the handling operations of heavy component erection ,govern the design of all elements of the rigging and handling system ,and affect both the existing infrastructure and the respective component being erected.
(6) Accidental loads.
The accidental loads arising out of human action includes the following.
(a)- Impact and collision
(b)- Explosion
(c)- Fire
(7)- Secondary Effects
The following types of secondary effects should be looked into the design
(a) Differential settlement of foundation
(b)- Differential shortening of columns
(c) Eccentric connections
(d) Rigidity of joints differing from design assumption.
See.....Specific gravity
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