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With the progress of the times, steel structures have become the main form of building structures. With their high strength, lightweight, anti-seismic, uniform material, and durability, steel structures can effectively meet the design requirements of buildings.

Introduction to steel structure:

Steel structures are one of the main types of buildings.
A steel structure mainly comprises steel beams, columns, trusses, and other components made of steel sections and plates connected through welds, bolts, or rivets.

Steel structures are strong, lightweight, high strength, deformable, rigid, and reliable. Using steel structures in construction projects can improve performance and save costs. Replacing concrete structures with steel structures can reduce the use of sand, stone, and cement and minimize damage to non-renewable resources.

With the rapid development of the construction industry, steel structures stand out for their high strength, lightweight, and plasticity. These characteristics of steel make it possible to build large-span, high-rise, and heavy-duty buildings, while its modularity, prefabrication, and rapid construction improve construction efficiency. In addition, steel structures are environmentally friendly and recyclable, which aligns with sustainable development.

Selection of building structure system:

Choosing the right structural system according to the building requirements and site conditions is crucial. Steel building systems include portal steel frames, steel frames, and truss structures. The choice of structural design depends on building requirements, site conditions, and budget.

Portal steel frames suit large-span buildings, such as industrial plants and stadiums. They usually have rectangular structures of equal height and width, good stability, and load-carrying capacity.

Steel frame structures are suitable for small and medium-sized buildings, such as commercial buildings and residences. They usually consist of horizontal and vertical steel members, which can form a mesh structure with good seismic and load-bearing capacity.

Truss structures are suitable for building roofs or bridges. They usually consist of diagonally intersecting steel members that form a triangular structure with good stability and load-carrying capacity.

What should be considered when designing steel structures in different steel buildings?

1. High-rise buildings:

Steel structures are usually used in high-rise buildings to support the building frame. The design of a steel structure needs to consider the overall stability of the building, wind load, earthquake load, and other factors. For example, Shanghai Center Tower is a super high-rise building with a steel structure. By optimizing the cross-section design, adopting advanced connection technology, and using high-performance steel, the safety and economy of the structure are ensured.

2. Bridges:
In bridge design, steel structures are widely used in main girders, piers, towers, and other parts. Steel structure design must consider the bridge’s span, load, fatigue calculation, and stability. For example, the Golden Gate Bridge is a famous steel suspension bridge. The designers ensure the long-term safe operation of the bridge by accurately calculating the cross-section dimensions, optimizing the node structure, and taking anti-corrosion measures.

3. Industrial plant:
Industrial plants often use steel structures to support the roof frame, columns, beams, etc. The steel structure design must consider the span, load, equipment arrangement, fire prevention, and other plant factors, such as how some large-scale iron and steel enterprises use steel structures. The designers ensure the safety and productivity of the plant through reasonable support column arrangement, adoption of fireproof coatings, and other measures.

4. Stadiums:
Steel structures are often used in sports stadiums to support roofs, stands, facilities, etc. The design of a steel structure needs to consider the number of spectators, equipment arrangement, safety, comfort, and other factors. The Bird’s Nest (Beijing National Stadium) is a sports stadium with a steel structure. The designers ensure the safety and aesthetics of the stadium through innovative structural forms, optimized cross-section design, and efficient construction methods.

Steel Structure Features:

Seismic resistance
Most of the roofs of low-rise villas are sloped. The roof structure adopts the triangular roof frame system made of cold-formed steel members. Structural boards and gypsum boards seal the light steel members to form a solid “plate rib structure system,” which can more effectively resist earthquakes and horizontal loads and is suitable for areas of 8 degrees or above seismic intensity.

Wind Resistance
A steel structure is lightweight and has high strength, good overall rigidity, and strong deformation ability. Its self-weight is only one-fifth of that of a brick-concrete structure. Thus, it can withstand hurricane winds of 70 meters/second and effectively protect the safety of life and property.

Durable
The light steel residential structure adopts a cold-formed, thin-walled steel component system. The steel frame is made of super anti-corrosive high-strength cold-rolled galvanized sheet, which effectively avoids the corrosive effects of steel sheets during construction and use and increases the service life of light steel components, with a structural life of up to 100 years.

Thermal insulation
The thermal insulation material is mainly glass wool, which has an excellent thermal insulation effect. Using thermal insulation panels on the external wall can effectively avoid the phenomenon of a “cold bridge” within the wall and achieve a better thermal insulation effect. 100mm thick R15, thermal insulation cotton, can be equivalent to the thermal resistance value of a 1m brick wall.

Sound insulation
The sound insulation effect is an essential index for evaluating a residence. All the windows installed by the light steel system adopt insulating glass, which has a good sound insulation effect and can reach more than 40 decibels. The sound insulation effect of walls with light steel keel and gypsum board insulation material can be as high as 60 decibels.

Healthy
Dry construction reduces waste pollution. The house’s steel structure and most other supporting materials can be recycled 100%, which is in line with today’s environmental awareness; all materials are green building materials that meet the requirements of the ecological environment and are beneficial to health.

Comfortable
The light steel wall adopts an energy-efficient system with a breathing function, which can regulate the dryness and humidity of the indoor air; the roof has a ventilation function, which can form a flowing air space above the interior of the house to ensure the ventilation and heat dissipation needs inside the roof.

Environmentally Friendly
The materials are 100% recyclable, genuinely green and pollution-free.

Energy-saving
All the walls are energy-efficient, with good heat preservation, insulation, and soundproofing effects, and can reach 50% energy-saving standards.

Steel Structure Information: Fabrication.

Step 1: Cutting
The first step in processing is cutting the steel plate. A CNC cutting machine, such as a plasma, laser, or flame cutter, is often necessary to make them into specific sizes and shapes. These machines utilize advanced CNC technology to efficiently and accurately cut the material into the desired shape and size.

Step 2: Assembly and welding
Once the steel plate is cut into the appropriate shape, it must be assembled by automated equipment and automatically welded. According to the requirements of processing drawings, automatic welding can weld steel plates into various shapes, such as H-shape and box-shape. However, some parts that cannot be welded automatically, such as connecting plates and reinforcement bars, must be welded manually.

Welding is a critical part of the manufacturing process as it ensures the strength and durability of the structure. The welding process must be carried out with great care and precision to avoid structural defects or weaknesses. Therefore, stringent quality control and testing are required before welding to ensure that the quality of the weld meets the requirements.

Step 3: Surface Preparation
After the steel structure is welded, a surface treatment must be carried out. This step involves removing rust and painting the steel to prevent corrosion and other forms of damage. Depending on the project’s requirements and characteristics, surface preparation methods can include different processes, such as shot blasting, painting, or galvanizing.

Step 4: Quality Inspection
Steel components must undergo rigorous quality checks before leaving the factory, including visual inspection and dimensional measurements, to ensure they meet the design requirements. In addition, for some unique features, non-destructive testing is required to ensure their structural strength meets standards.

Quality inspection is critical to the steel component fabrication process to ensure the quality and performance of the final product. Only after a thorough inspection can steel components be sent to the site for erection and use.

Steel Structure Installation

Preparation: Preliminary preparation work must be carried out before installation of the steel structure.

First, an on-site investigation is necessary to determine the location and precise dimensions of the steel structure installation and simultaneously develop the installation program and construction plan. In addition, the tools and equipment required for installation, including cranes, spreaders, welders, and so on, must be prepared.

Foundation construction: Excavate the foundation, pour concrete bedding and backfill, and do tamping to ensure a solid foundation.

Preparation and acceptance of components: Before the steel structure installation, all incoming steel components, including quality certification, geometric dimensions, etc., must be accepted to ensure they meet the design requirements.

Installation of steel columns: Lift them to the predetermined position, make preliminary corrections, and fix them. During the installation process, pay attention to the control of verticality and horizontality to ensure that the position of the steel column is accurate.

Installation of steel beams: After installing steel columns is completed, install the steel beams. The installation sequence and method of steel beams should be determined according to the specific design and can generally be lifting or splicing.

Installation of secondary components: This includes installing secondary elements such as horizontal support, inter-column support, tie bars, and tie rods. These components improve the steel structure’s overall stability and load-bearing capacity.

Installation of roof and wall panels: After the main structure is installed, roof and wall panels are installed. During installation, attention should be paid to the fixing and sealing treatment of the panels to ensure waterproof performance.

Connection and fixing: The connection and fixing between the components are crucial in the steel structure installation process. Generally, welding and bolting are adopted to ensure a firm and reliable connection.

Inspection and acceptance: Comprehensive inspection and approval are required after the steel structure installation. This includes checking whether each component’s installation position, verticality, and level meet the design requirements, whether the connection is firm and reliable, and whether the waterproof performance is up to standard.

In conclusion, installing steel structures requires careful preparation and following specific steps. In addition, the installation must be carried out strictly with relevant standards and requirements to ensure its quality and safety.

Steel versus concrete structures: which one dominates?

There are two main methods of building structures: steel and concrete. Each method has advantages and disadvantages, and deciding which form to use is complex.

1. Graphic design:

Steel structure: large span can be 20 meters
Concrete: 10 meters span

For a three-story steel office building, a column-free interior space, i.e., a single-bay steel frame structural system, was adopted to realize the building plan’s more flexible functional division. This design allows for a beam span of 13.5 meters, which is relatively easy to achieve using H-shaped solid web steel beams in conjunction with cold-formed rectangular steel tube columns. Steel-framed buildings can thus provide more open space and a freer functional layout. In contrast, concrete structures are challenging to realize this combination of span and clear height.

2. Column dimensions:

Steel’s high strength and uniform properties allow smaller section sizes to be used. In the three-story office building mentioned above, for example, the width of the steel columns is only 40 cm, compared to a significantly wider column width of at least 65 cm with reinforced concrete.

3. Beam height

The minimum height-to-span ratio for concrete beams is 1/18, and the maximum is 1/20 for steel structures. In conventional design, the height-to-span ratio for steel beams is usually 1/20.

This ratio can be reduced to 1/30 for steel beams in light roofs but generally not less than 1/40. This difference in beam height affects not only the clear height of the building and space utilization but also the overall structural rigidity.

Steel structures, with their smaller beam heights, allow for more flexible placement of piping and equipment and larger spans. However, designers need to be careful to control the deflection of steel beams to ensure the structure’s performance and comfort during the use phase.

4. Self-weight of building

Steel structure: 0.6-0.8 tons/m2
Concrete structure: 1.0-1.5 tons/m2

Proportionally, the deadweight of a building with a steel structure is usually reduced by more than 40%. A study of a 50-meter high-rise office building comparing different structural systems showed even more dramatic results. The office building had an upper floor area of 10,400 square meters, and using steel, the structural weight per square meter was reduced by 56%, and the foundation cost was reduced by 7.5%.

This weight reduction affects the building’s overall loading and favors structural design and construction methods. For example, the lighter deadweight reduces inertial forces under seismic action.

5. Foundation

Steel structure: The upper part is lightweight so that the foundation construction will be simple.
Concrete structures: the weight is high, and the foundation work is more expensive.

Despite the lighter weight of the steel structure, if the concrete structure is also all on independent foundations, the percentage of cost reduction is relatively small, around 7%.

However, if it is possible to change the form of the foundation due to the reduced weight – for example, concrete structures require a raft foundation, whereas steel structures can be converted to free-standing foundations – then the proportion of cost reduction can be considerable, estimated at around 15%.

6. Reliability of components

Steel structures: components are manufactured in the factory with high accuracy.
Concrete structures: A lot of work is done on-site, and human errors are unavoidable in several dimensions, especially in the protective layer of reinforcement.

The difference is quite apparent. Although high-quality concrete structures may be more accurate than steel structures, this situation does not represent a universal level. Typically, the varying skill levels of on-site construction workers, the harsher working environment, and the prevailing time pressure to meet deadlines make it difficult to match the quality of construction with factory-prefabricated elements. Even if the concrete is prefabricated in factories, the cost does not have an absolute advantage over steel structures.

7. Durability

Steel structure: can be used for a long time if rust prevention treatment and finishing layer are done indoors.
Concrete structure: Shrinkage cracks are unavoidable, so preventive control should be taken to prevent the carbonization of concrete and the rusting of steel reinforcement.

In general, in an indoor, non-humid environment, the rusting speed of steel structures is prolonged even without special protection.

In actual projects, a decorative surface layer will be added in addition to anti-rust treatment so the steel structure can be used safely for a long time without frequent maintenance. However, in daily use and renovation, care must be taken not to damage the corrosion protection layer of the steel structure.

In contrast, concrete structures need to focus on preventing and controlling cracking. Once the cracks exceed the allowable range of the code, the steel reinforcement loses the reliable protection of concrete and is prone to corrosion. In short, the durability of a steel structure depends largely on the design of the external protective measures. In contrast, the durability of a concrete structure depends on the design of the concrete itself.

8. Fire resistance

Steel structure: steel has a short fire resistance time and generally needs fire protection.
Concrete: comes with fire protection and generally does not require additional fire protection measures.

The fire resistance of steel structure is poor, firstly, because the heat conduction coefficient of steel is substantial, and the steel member warms up very quickly under fire; secondly, because the strength of steel decreases instantaneously with the increase of temperature so that the steel structure can not withstand the external loads and fails to be damaged. The fire resistance time of steel structures without fire protection is usually only 15-20 minutes. Therefore, to prevent and reduce the fire hazards of building steel structures, it is necessary to carry out fire protection design for steel structures.

The fire resistance limit of a concrete structure depends on three key factors. Taking concrete columns as an example, to achieve a fire resistance limit of 3 hours, the thickness of the concrete protective layer of the force reinforcement needs to be not less than 35mm in the case of multi-face fire, the axial compression ratio (μ-value) needs to be 0.5, and the column width needs to be 65cm.

9. Construction period

Generally speaking, steel structures can shorten the construction period than reinforced concrete structures. This is mainly because in the construction of the foundation, the steel structure can be synchronized with processing in the factory, and no wet work on-site needs to be like concrete as time-consuming maintenance.

However, in practice, several factors influence the ability to reduce the total construction period. First, the transportation and lifting of steel structures require precise planning and coordination to ensure the components arrive at the construction site and are accurately positioned. Second, key processes such as on-site welding and high-strength bolting require high technology and quality control. Finally, fire protection and anti-corrosion treatment of the steel structure are also essential factors affecting the schedule and must be fully considered in the construction plan.

10. Beam perforation

Steel structure: the diameter of steel beam perforation shall not exceed 1/2 of the beam height.
Concrete structure: The hole in the frame beam should not exceed 40% of the beam height.

11. Floor Height

Steel structure: beam height + 35cm (floor finish + floor slab + fire protection layer + ceiling) + clear interior height.
Concrete structure: beam height + 45cm (floor lose sleep + ventilation ducts + ceiling) + net indoor height.

Under the same indoor clear height requirement, reducing the structural beam height can reduce the overall floor height, thus reducing the construction cost. Not only does it reduce the amount of building materials used, but it also reduces the area of exterior walls, which in turn reduces energy consumption and overall construction costs. For buildings with a sufficient number of stories, reducing the height of each story may increase the usable area of one story for a fixed total building height.

12. Recyclability

Steel has the highest recycling rate of any material on the planet. By weight, 81% of steel products in the U.S. are recycled at the end of their useful life. Specifically, 85% of automobiles, 82% of appliances, 70% of containers, 72% of rebar, and 98% of structural steel are recycled.

13. Processes

Significant differences exist in the design and construction processes used to manage the entire construction process for steel and concrete structures.
Steel structures rely heavily on factory prefabrication and on-site erection, requiring precise dimensional control and connection design.
In contrast, concrete structures focus more on on-site pouring and maintenance, with higher requirements for formwork and bracing systems. These differences directly impact project schedule, quality, and cost management.

14. Design

Compared with the design of a concrete structure, the design of a steel structure differs more in thinking, knowledge system, and skill requirements.

Specifically, it is mainly reflected in understanding materials, component design, connection node design, overall and local stability analysis, and construction technology. All these aspects require designers to have rich professional knowledge and practical experience, and they also need to have innovative thinking to cope with various problems that may be encountered in steel structure design.

15. Different material properties:

The materials of steel structures are homogeneous and isotropic.
Concrete structures comprise concrete and steel composites with non-uniform and anisotropic material properties.

16. The focus of calculation and analysis is different:

The steel structure design emphasizes the ability to consider the elastic phase of the material force and plastic development, focusing on overall stability, local buckling, and plasticity analysis.

The design process of concrete structure mainly focuses on the bearing capacity and durability, emphasizing the rationality of reinforcement and cracking control of concrete.

17. Different connection methods:

The connection mode of steel structure design is complicated, and the design needs to consider the force situation and implementability of the connection entirely. The connection quality has a significant impact on the overall structural stress.

The connection of a concrete structure is mainly realized by on-site casting, usually monolithic casting, which requires special consideration of the node location reinforcement and the shear resistance and anchorage performance.

Summary:

Although steel structures have many advantages over concrete and are absolute winners in industrial and public buildings such as factories, large stadiums, exhibition halls, etc., their share is still minimal in civil construction.