Why I - Section used for connecting rods and railway rails?
What is an I-beam?
An I-beam, also known as H-beam, W-beam (for "wide flange"), Universal Beam (UB), Rolled Steel Joist (RSJ), or double-T (especially in Polish, Bulgarian, Spanish, Italian and German), is a beam with an I or H-shaped cross-section. The horizontal elements of the "I" are known as flanges, while the vertical element is termed the web. I-beams are usually made of structural steel and are used in construction and civil engineering.
Why do we use I Beam, instead of rectangular beam?
On the left side we have a simple rectangular beam, whereas on the left hand side on the above image, we have an I section beam.
The question that is most commonly asked as to why do I section beam most frequently used in construction as compared to simple rectangular beam. And also why only I beam is used and not a beam of any other shape.
When a beam is subjected to stresses, the outer layer is compressed, with the inner one undergo tension.
The middle layer is a neutral layer, which do not experience either tension or compression.
Now, as we move away from Neutral Axis, the stresses due to bending moment increases proportionally, according to bending moment equation-
As you can see in this picture, the positive and negative maximum of bending stress occurs at the extreme fibres.
I-Section is preferred to rectangular section for resisting Bending Moment (BM) because, in I-Section more than 80% of the bending stress is resisted by the flanges itself!
For a given cross sectional area (i.e. A=constant), the distribution of that area (i.e. Moment of Inertia) matters in resisting Bending Moment, as section modulus (Z) depends on I and y.
I-Section has higher moment of resistance (MoR) because the areas of flanges is away from the neutral axis (N.A.)
In a beam of I-Section, more material is positioned near the outer fibres representing the regions of greatest stress and hence is stronger than a beam of rectangular cross section
Moreover deeper the flange part, more the shear stress it can resist
To conclude, a beam of fixed length and for a given weight of material, I-Section provides the greatest possible moment of resistance, hence it is widely used in Beam design!
For Beam "SECTION MODULUS" is a measure of beam strength. For I shape beam section modulus value is higher in comparison to other sections (ex. circular, rectangular, triangle), that's why "I" beams are mostly preferred.
SECTION MODULUS (Z)-:
Z=I/Ymax.
where, y= distance from neutral axis.
from above expression it;s clear that section modulus is dependent upon second moment of inertia (for beams of equal depth).
taking example of I beam since most of area is distributed away from centroidal axis (Neutral Axis) hence it's moment of inertia is larger relatively to other available section.
Section modulus is basically a measure of how much load it can carry prior to moment of stress in it's farthest fiber reaches it's yielding or ultima
te value
In the case of I section, the web resists shear forces, while the flanges resist most of the bending moment experienced by the beam. Beam theory shows that the I-shaped section is a very efficient form for carrying both bending and shear loads in the plane of the web. On the other hand, the cross-section has a reduced capacity in the transverse direction, and is also inefficient in carrying torsion, for which hollow structural sections are often preferred. But it is more complicated and expensive to manufacture hollow beam, so for this reason it is not used practically.
The image below shows how the web resists most of the shear force.
An I-beam, also known as H-beam, W-beam (for "wide flange"), Universal Beam (UB), Rolled Steel Joist (RSJ), or double-T (especially in Polish, Bulgarian, Spanish, Italian and German), is a beam with an I or H-shaped cross-section. The horizontal elements of the "I" are known as flanges, while the vertical element is termed the web. I-beams are usually made of structural steel and are used in construction and civil engineering.
Why do we use I Beam, instead of rectangular beam?
On the left side we have a simple rectangular beam, whereas on the left hand side on the above image, we have an I section beam.
The question that is most commonly asked as to why do I section beam most frequently used in construction as compared to simple rectangular beam. And also why only I beam is used and not a beam of any other shape.
When a beam is subjected to stresses, the outer layer is compressed, with the inner one undergo tension.
The middle layer is a neutral layer, which do not experience either tension or compression.
Now, as we move away from Neutral Axis, the stresses due to bending moment increases proportionally, according to bending moment equation-
I-Section is preferred to rectangular section for resisting Bending Moment (BM) because, in I-Section more than 80% of the bending stress is resisted by the flanges itself!
For a given cross sectional area (i.e. A=constant), the distribution of that area (i.e. Moment of Inertia) matters in resisting Bending Moment, as section modulus (Z) depends on I and y.
I-Section has higher moment of resistance (MoR) because the areas of flanges is away from the neutral axis (N.A.)
In a beam of I-Section, more material is positioned near the outer fibres representing the regions of greatest stress and hence is stronger than a beam of rectangular cross section
Moreover deeper the flange part, more the shear stress it can resist
To conclude, a beam of fixed length and for a given weight of material, I-Section provides the greatest possible moment of resistance, hence it is widely used in Beam design!
For Beam "SECTION MODULUS" is a measure of beam strength. For I shape beam section modulus value is higher in comparison to other sections (ex. circular, rectangular, triangle), that's why "I" beams are mostly preferred.
SECTION MODULUS (Z)-:
Z=I/Ymax.
where, y= distance from neutral axis.
from above expression it;s clear that section modulus is dependent upon second moment of inertia (for beams of equal depth).
taking example of I beam since most of area is distributed away from centroidal axis (Neutral Axis) hence it's moment of inertia is larger relatively to other available section.
Section modulus is basically a measure of how much load it can carry prior to moment of stress in it's farthest fiber reaches it's yielding or ultima
te value
In the case of I section, the web resists shear forces, while the flanges resist most of the bending moment experienced by the beam. Beam theory shows that the I-shaped section is a very efficient form for carrying both bending and shear loads in the plane of the web. On the other hand, the cross-section has a reduced capacity in the transverse direction, and is also inefficient in carrying torsion, for which hollow structural sections are often preferred. But it is more complicated and expensive to manufacture hollow beam, so for this reason it is not used practically.
The image below shows how the web resists most of the shear force.
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