Comprehensive survey of structural hollow sections
HSS stands for hollow section (metal) structures that are produced in round, square and rectangular shapes and in a wide range of sizes.
These sections are a type of steel profile with a hollow cross-section, which has a closed geometry, without sharp corners and with an attractive appearance.
Hollow structural sections (HSS) are high-strength welded steel tubes that are used as a load-bearing member in buildings and other structures and manufactured products.
Due to industrial production, these sections have a much higher quality than the traditional handmade sections, both in terms of welding quality and in terms of distortion and tolerance. HSS corners are round and have a radius almost twice the wall thickness of hollow structural sections. This wall thickness is the same throughout the cross section.
The geometric shape of these sections is such that it facilitates the efficient use of materials in the construction industry and other applications, and the proper use of these sections leads to the construction of more affordable and lighter structures that have better speed and quality than other sections which made with the traditional method follow.
In recent years, the use of hollow construction sections has made great progress due to its appearance and mechanical properties. These materials have been dubbed the “material of the 21st century” by architects due to their unique and remarkable properties.
The volume of welding in the conventional method due to having 4 welding lines and the need to install stiffeners is more than 4 times that of welding in the H.S.S production method, which has only one welding seam and is made without stiffeners.
The higher strength-to-weight ratio of HSS compared to sections produced in the traditional way means that less material is used to create the same strength. Compressive strength, load bearing characteristics and high torsional strength have provided the application of HSS for different types of columns.
Due to the requirement to install the internal stiffener in the production of the column in the usual way, it is practically not possible to do these sections with concrete. But there is no such limitation in using construction sections (H.S.S).
By filling the HSS sections with concrete, which leads to the production of CFT composite columns, the characteristics of concrete and steel can be used simultaneously in the structure.
HSS has a higher strength-to-weight ratio than wide-wing and HP-shaped sections. HSS has a higher strength-to-weight ratio than wide-wing and HP-shaped sections.
In response to the growing demand for these sections, the HSS production process has been continuously developed with high quality.
This process involves the production of HSS with fully automatic machines that receive the metal sheet from the coil at the beginning of the line and pass it through a cold rolling process through a set of rollers to form the sheet into a tube.
Today, in order to reduce the residual stress caused by welding in these sections and prevent the transformation of the steel properties, advanced welding methods such as electric resistance welding (ERW) are used for the longitudinal welding of sheet edges. Then the closed sections are produced to complete the form processes. The pieces are passed through a set of rollers to finally become completely round, square or rectangular sections.
Electric resistance welding (ERW)
, a high frequency welding machine, is able to weld the prepared edges of the sheet longitudinally and continuously, without using an electrode. This weld boasts superior quality and is classified as Electric Resistance Welding (ERW), known for its exceptional electrical resistance properties.
Resistance welding (ERW) is a type of welding in which the two edges of the sheet are welded by simultaneous action and pressure. In this method, a continuous electric current is established on the surface of the steel sheet, the high amount of electric current in the welding area due to the electrical resistance causes the metal to melt in the welding area and it is forged well by pressing the two edges of the sheet together.
Types of HSS are produced in round shapes (circular hollow sections, CHS), square (SHS) and rectangular (RHS).
Hollow structural steel (HSS) sections are widely used in residential and commercial building structures (as columns or bracing members), stadiums, bridges and aerospace structures.
Also, these sections are used in the construction of car chassis, marine platforms, subway stations, airport halls, petrochemical industries, amusement parks, smart parking structures, etc. Hollow round sections can also be used for water pipes in accordance with the relevant standards.
Engineers, designers, builders and contractors today are looking for new applications for hollow structural steel (HSS) sections due to the following advantages:
01. It is affordable
02. It is used in light structures.
03. It is more resistant to twisting.
04. Its resistance to weight ratio is higher.
05. Create more space
06. It makes optimal use of materials.
07. The possibility of producing sections of desired length
and customized length.
08. Continuous and non-stop production is possible.
09. The best option is for the column.
- The use of HSS greatly reduces the need for manpower, time and cost to make composite sections and makes its use more affordable.
- Since these sections have 33 to 50% less cross-sectional area than open sections, it saves paint, fireproofing materials, protection costs and manpower.
- It can be said that the most important advantage of using these construction sections is the reduction of expenses. With the increasing production costs, the use of construction sections instead of columns made of four-sided sheet has an undeniable effect on the finished cost of the skeleton.
- Due to its higher strength-to-weight ratio, HSS has made it possible to build lighter structures.
- In addition to the direct economic and environmental benefits, lighter structures create less seismic forces, which makes them more economical to design.
- Also, these sections are used in the construction of structures with larger free openings.
- HSS has the best resistance to twisting compared to other materials or other shapes because it has a closed section with a thin wall.
- Hollow sections (HSS) can also be used as beams, although wide flange flanges and I-beams are in many cases more efficient structures for this application, however, hollow sections have better resistance to they have lateral twisting and buckling.
- The torsional strength of HSS (the torsional constant of HSS is about 200 times that of open sections) makes it an excellent choice for strapping and perimeter members.
- The quality of welding in the traditional way is much lower than the welding used in the production of S.S. construction sections (ERW welding) due to the sub-powder welding (SAW) or manual (CAW) welding.
- As a result, the amount of residual stress in members is significantly reduced. In addition, as a result of a complete quality control process, the final product produced in this way will have a much higher quality than the traditional method.
- Eliminate stress in the corners
- In the conventional way of building the column, four longitudinal welding seams in the corners of the column connect the plates, which causes tension in the section, especially in the 4 corners of the column. In the S.S production process, there is only one welding seam in the middle of one of the sides, which creates the least amount of stress in the section.
- Since the steel materials in HSS profiles have the greatest distance from the axes passing through the center of the surface compared to other steel profiles, the hollow shape of HSS is inherently more resistant and efficient.
- In addition, all parts of HSS sections based on AISC and Iran standards have both supporting edges that delay their local buckling.
- Therefore, HSS has a higher strength-to-weight ratio even compared to other construction materials.
- It is natural that less weight makes construction easier, reduces the forces caused by earthquakes, reduces the costs of installing the structure and transporting materials, and also makes other parts of the building, such as the foundation, be designed more economically. This advantage makes HSS a suitable option for increasing the floors of existing buildings without imposing excessive load on the foundation.
- Hollow structural sections occupy less space compared to wide wing sections, and instead of large I and H (wide wing) sections, smaller steel boxes (HSS) can be used to create more space.
- The higher strength-to-weight ratio of HSS compared to sections produced in the traditional way means that less material is used to create the same resistance.
- Additionally, all HSS cross-section members have restrained edges parallel to the load, which significantly reduces the likelihood of localized buckling.
- Therefore, the steel used can usually bear more than its yield strength and it can be assured that all the capacity of the material has been fully and optimally used.
- Industrial production of HSS makes it possible to produce sections of any length (as long as it can be transported). This feature of HSS reduces the need to cut profiles and patch them together to produce sections with the required length.
- Since the existing sheets are usually 6 meters long, producing longer columns traditionally requires cutting, strapping, and welding several pieces together.
- As a result, it is not possible to produce long integrated columns. But in the S.S method, due to the use of a roll in the production process, it is possible to produce an integrated column of the desired size.
- It takes 2 days for 5 skilled workers to assemble a 40 x 40 cm square column 18 meters long in the traditional way. In the HSS industrial production method, the same column is produced in less than 2 minutes.
- In addition, according to the amount of work required to cut and prepare sheets and perform electrode welding, it is clear that HSS production is more useful from the point of view of using resources, has less economic and social negative effects, and also has a more continuous production process.
- HSS with having two or more symmetrical axes and a large radius of gyration, is the most suitable option as a column or column beam in structural systems that perform the main task of bearing gravity and lateral loads.
- Compressive strength, load bearing characteristics and high torsional strength have provided the application of HSS for different types of columns.
- Hollow structural sections, especially rectangular sections, are usually used in welded steel structures as the main load-bearing member in different directions. Also, square and circular sections are also very efficient for this multiaxial loading. Due to having uniform geometric properties of these sections along two or more axes, they have very great strength and this characteristic makes these sections good options for columns. They also have good resistance to rotation.
- More space without braces and thus more flexibility for structural design
- Reducing the overall weight of the structure and thus lower cost for engineering buildings
- Less cross section: Less side cost (painting and cleaning)
- High seismic ductility
- tall buildings
- Bridges with long spans
- Structures located on soft ground
- structures located in earthquake-prone lands; which performance is the result of the force from the earthquake in proportion to the weight of the structure.
Many structural engineers are aware of the advantages of HSS in construction, but since the production of these hollow sections in Iran was limited in the past, engineers had no choice but to use sections made with sheets instead of using these sections.
Although traditionally made sections are similar in appearance to HSS sections, often, the welding process and low quality of their construction Substantially impact the final quality of the products. On the contrary, the amount of damage caused by welding and residual stress in HSS is significantly less.
It can be said that the most important advantage of using these construction sections is the reduction of expenses. With the increasing production costs, the use of construction sections instead of columns made of four-sided sheet has an undeniable effect on the finished cost of the skeleton.
Hollow structural steel (HSS) sections have various advantages for industrial and construction applications.
The geometric shape of these sections is such that it facilitates the efficient use of materials in the construction industry and other applications, and the proper use of these sections leads to the construction of more affordable and lighter structures that have better speed and quality than other sections which made with the traditional method follow.
In addition, the appearance of HSS is more eye-catching than most other steel sections, and as a result, it can be used in the construction of elegant structures that provide both structural safety and an architectural appearance. In recent years, the use of sections Hollow construction has made significant progress due to its appearance and mechanical properties. Architects have called these materials the material of the 21st century because of its special properties.
The use of HSS has other important advantages, such as increasing the speed of construction, reducing the risk of human error, and reducing the need for specialized labor.
Eliminate stress in the corners
In the conventional way of building the column, four longitudinal welding seams in the corners of the column connect the plates, which causes tension in the section, especially in the 4 corners of the column. In the S.S production process, there is only one welding seam in the middle of one of the sides, which creates the least amount of stress in the section.
Many structural engineers are aware of the advantages of HSS in construction, but since the production of these hollow sections in Iran was limited in the past, engineers had no choice but to use sections made with sheets instead of using these sections.
Although the traditional made sections are similar in appearance to the HSS sections, but often, the welding process and their poor manufacturing quality Significantly impact the final quality of the products. On the contrary, the amount of damage caused by welding and residual stress in HSS is significantly less.
The first choice of designers of advanced countries
Simultaneously with the advancement of HSS production technology, the production and use of these sections becomes more affordable day by day and this advantage has made HSS in advanced countries to become one of the first choices of designers in the construction of strong and safe structures as well as use in industries and sustainable development
In developing countries, due to the increasing need for safe and economical construction techniques in recent years, This issue has been duly considered., especially in structures that are affected by critical loads such as floods, storms, and earthquakes.
It is affordable.
Construction using steel is naturally faster than construction with concrete or masonry, which results in lower labor costs and a faster return on investment.
Its resistance to weight ratio is higher.
Compared to other building materials such as concrete or wood, steel is known among engineers as a material with the highest strength-to-weight ratio due to its greater resistance.
The advantages of steel are so significant that it is even used in construction with other types of building materials, such as steel reinforcements in concrete structures and joints in wooden structures.
It is used in stylization of structures.
Due to greater resistance, structures made of steel are usually lighter than structures made of other materials such as concrete or masonry.
It has a higher quality.
Due to the high quality of steel construction compared to building materials and concrete, steel is usually chosen by engineers to build more important and high-quality structures. On the other hand, several workshop factors can adversely affect the quality of building materials and concrete.
It lasts a long time.
If designed and protected correctly, steel is considered one of the most durable construction materials.
It is reusable.
Steel components are among the few building materials that can be reused after the building is destroyed.
It can be recycled.
In addition to being resistant, durable, versatile and reusable, steel is also recyclable. In fact, a significant part of all steel components is obtained from the recycling of other steels.
It is environmentally friendly.
Since construction steel is reusable and recyclable and has very little waste, it is the most compatible with the environment. In addition, the construction using steel is cleaner, dust-free and relatively quiet. Also, due to the need to transport a smaller amount of materials and the speed of construction processes, it reduces the adverse effects on the surrounding environments of the construction site.
It has the ability to build smaller structures and create more open space.
Due to the high resistance of these sections, in general, construction using structural steel creates more open space, which is desirable in terms of architecture and beautification.
High failure resistance
Due to its high ductility, steel undergoes a high deformation before failure, so it has high resistance to failure, which is an important property for impact forces such as explosions and earthquakes.
Predictability of section behavior
The homogeneity and isotope of the steel has made the behavior of these sections to be expected and also reduced the amount of errors in static calculations.
The properties of steel can be predicted with a high degree of confidence.
