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Use of Hollow section in modern constructions

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As steel is having very high tensile and compressive strengths and much better performance than concrete in terms of bending, deflection, shear, torsion, resilience and flexibility. However steel has high susceptibility to environment exposure effects, if not maintained properly.

Steel structural members are preferred for constructing larger, heavily loaded structures and structures subject to dynamic loads. To optimise on shape and size of structural members, keeping intact or improving on their sectional properties, often we play with the geometric shape of steel sections used in construction. All the steel design and construction codes worldwide identify a few common shapes, to be used as a steel member. These sections are noted by their cross-section shape profile. Below mentioned are a few commonly used sections.

Common SECTION TYPEs

  • I Shape / H Shape joists
  • C Shape / Channels
  • L Shape / Angle
  • T Shape, and Square, Rectangular, and Round Hollow Structural Section (HSS)

After going through the above list, one might wonder, why do we need to mold the steel sections into different shapes, instead use solid shapes (rectangular, square, circular or other polygons)? In order to know the reason, we need to understand a little about the load applications, structural phenomena subjected on member, parameters that control the structural capacity of a member. Most common load applications that are encountered in the construction includes one or combination of below:

  • Vertical or inclined / Point Loads (PL)
  • Uniformly distributed loads (UDL)
  • Composite loads ( combination of PL and UDL)
  • Dynamic / moving loads
  • Horizontal /wind loads
  • Moment / bending
  • Torsion / Rotation

Depending on type of the load application/s, any member is subjected to one or combination of structural phenomena such as:

  • Compression
  • Tension
  • Shear
  • Flexure
  • Torsion

In order to assess a member against the above-mentioned phenomena, the sectional properties - few parameters that indicate the resistance offered such as:

  • Cross section area
  • Total Depth
  • Thickness of Web, Flange/s, and Legs
  • Moment of Inertia and/or Section modulus
  • Torsion Constant

Square, Rectangular, and Round Hollow Structural Section (HSS)

A hollow section is a type of metal profile which gives greater flexibility in use and large strength-to-weight ratio than conventional sections. This enhances efficiency and reduces cost. In construction, Advantages of hollow sections, pipes are build lightweight, sustainable and aesthetically appealing structures.

The Hollow Structural section (HSS) is obtained by steel tubing in the shapes of Square, Rectangular and Round/Circular. Hollow Structural Sections are cold-formed, welded steel tubes used for welded or bolted construction of buildings, bridges, and other structures as well as a wide-range of manufactured products. They are produced in square, round, and rectangular shapes to meet structural design requirements. 

Hollow Structural Sections add strength and beauty to any steel structure. From cost savings to flexibility, using HSS for construction and structural applications offers several advantages compared to using normal structural steel.

These sections are highly applicable for point loads and rotation. These sections provide high structural capacity against compression and torsion. Most common usages of this section are structural column, shafts, truss, composite beams and many forms of custom designed configurations.

Benefits

  • Provides high torsion resistance compared to I, C, L, and T shapes.

  • Provides high structural capacity in both directions (X-X and Y-Y) compared to I, C, L, and T shapes.

  • Can be used as a jacket for concrete column for increased axial capacity.

  • Relatively beneficial weight : capacity ratio (in case of axial loading)

 

Disadvantages

  • Connections such as bolting is hard to install, since the section is closed.

 

Conclusion

Other sections that are very frequently used as steel members, these days, are Pipe section, Based on the above discussions, we can now understand the differences between different shape sections, their relative benefits, their structural strengths etc.

 

Relative evaluation of efficiency under different load conditions

Subjected force / load

Joist

Channel

Angle

Tee

Tube / RHS / SHS

Axial

Good

Moderate

Moderate

Moderate

Good

Flexure X-X

Poor

Poor

Moderate

Poor

Good

Flexure Y-Y

Good

Moderate

Poor

Moderate

Good

Buckling

Poor

Poor

Poor

Poor

Moderate

Tortion

Poor

Poor

Poor

Poor

Good

Shear

Good

Moderate

Moderate

Moderate

Good

The advantages are clear from the table above table

The practical and aesthetic benefits of using steel Hollow Structural Sections make it an ideal material choice for structural applications in buildings and other structures such as bridges, architecturally exposed buildings, fencing, railings and many more. 

 

1.Benefits in Design Aspects.

 design element provides the following advantages :-

  • it is lighter.
  • It can be very long with fewer joints.
  • It has more crystalline purlins & trusses with a high possibility of closeout transversal bracing.
  • It provides more slender supports.
  • There are some sections that can be dismissed even more with the use of tubular sections filled with concrete.
  • Highly economical in the complete process of using it.
  • Easily executed direct joints reduce construction cycle time.
  • Convenient in maintenance.
  • Can be delivered on schedule date.
  • Absence of sharp edges, etc.

 

2. Strength Element:

Compression – For the same load and under identical conditions tubular members perform better due to its improved sectional properties attributed to it’s configuration and profile.

Torsion – Their hollowness is the most amazing of all business steel segments. Hence, for this reason, their act is unbreakable in case of parallel swelling.

Tensile – The utilization of welded joints all throughout the steel implies that the resistance area in the joints is utilized completely, unlike bolted joints.

Fatigue – The widespread variety of mechanical applications in which we can discover steel tubular areas are proof of their ideal behavior in these conditions.

 

3. Cost Savings 

 In every construction project, keeping the costs down, is crucial. Using Hollow Structural Sections yields significant weight savings that then lead to significant material cost savings. It simply takes less steel to do the same job. When working with HSS, less steel is required to support any given load, which translates directly to material cost savings. Lastly, if unpainted weathering steel is specified along with the Hollow Structural Section, you receive a double benefit of cost savings on the initial construction and additional life cycle cost savings due to the very limited ongoing maintenance costs when compared to a painted structure. Also, when there is less weight involved, you will save money in transportation, handling and erection costs. 

 

Aesthetics And Flexibility 

 

Hollow members provide increased aesthetic appeal and flexibility for architects, engineers, and contractors.

Advanced researches are on for replacing solid steel bars with steel tubes in roof slabs and other suitable RCC members with remarkable initial success – both in terms of cost and performance, with a reduction in structure load and enhancement on sustainability front. Very soon we are going to witness a paradigm shift in usage of construction steel with great economy and flexibility. In fact, it has already started, but requires spread of awareness and acceptability from the construction fraternity for a faster switch over.

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