CFT (Concrete Filled Tube) structure is one of the new technologies in construction. This structure has unique features and its execution method is different from other structures. CFT structure is considered better than metal and concrete structures by using new methods, and nowadays many constructions are done based on this type of structure.

Introduction of CFT structure

Today, the construction of CFT structures is much more than in the past. To properly define CFT structures, you should know that mixed columns are filled with concrete or CFT in the form of boxes or steel tubes. Therefore, the price of profile and pipe does not affect the final costs of the project.

CFT consists of two parts: steel and concrete:

The steel sections used in the section are steel boxes or pipes.
Plain concrete or self-compacting concrete (SCC) box be used in cross-sectional concrete cores. The steel structure surrounding the concrete core forms a composite section.

A very Important point about this type of structure is that various types of roof systems and types of beams are used in combination with these columns.

Advantages of CFT Structure

CFT columns have many great features that make them more useful than ever.

Some of these benefits include:

High tensile and compressive strength
Very good flexibility
High energy absorption capacity
Reduce construction time
Resistant to side loads

It should be noted that one of the main advantages of CFT columns or steel sections filled with concrete is the reduction of financial costs in the construction of structures. The use of CFT columns reduces the use of steel in the construction of structures, and finally you get a durable and quality structure at a low cost.

In this case, the price of the rebar will be saved and you can spend your budget on the rest of the parts.

Other very important and special advantages of CFT columns are local buckling adjustment of the steel section, increase in service life and concrete resistance due to adhesion. Concrete is always considered one of the best options in the construction of structures, but one of its most important disadvantages is the high construction time.

In addition, the use of CFT columns makes less space available in the structure. In most cases, the large size of columns prevents designers from using lateral load-bearing systems with flexural frames. So CFT columns eliminate this problem.

These columns create a useful interior space that can be used in the basement and multi-level parking.

Disadvantages of the CFT structure

Despite all the advantages of using CFT structures, we cannot ignore some of their minor disadvantages. The first limitation of these structures is that the area of the steel section must be at least one percent of the total area of the composite section. Another thing is that the ratio of width to thickness in steel cross-section components must be specified in advance. These two cases can be considered as the main limitations of CFT structures.

The importance of choosing a CFT structure

The choice of CFT structures in the design and construction of civil and industrial structures can be very important. This importance is due to the advantages and unique characteristics of these types of structures.

For example, CFT structures have a very high resistance to earthquake forces due to their composite structure. The concrete sections filled inside the steel tubes act as a resistance core and effectively control the earthquake forces until the earthquake forces can be managed.

Also, increasing the load bearing capacity, reducing the weight and dimensions of the structures, reducing the construction cost, long useful life of the structure, the multi-purpose of CFT structures, etc. are among the reasons for the importance of choosing CFT structures, especially in areas with high earthquake activity and the need for earthquake-resistant structures.

How to implement the CFT structure

As mentioned, CFT columns are made of boxes filled with concrete. According to the designer’s opinion, I-shaped profiles can be used inside the concrete, but this issue completely depends on the design of the structural engineer.

In order to know the behavior of CFT columns, we must know the parameters that affect their performance. So that in case of not acquiring this knowledge, it is actually not possible to use these sections economically and reliably in different structures.

The most important factors affecting the behavior of these sections are:

Corresponding column slenderness and steel wall compression
Confinement of concrete
Type of concrete and steel
Creep and slump of concrete
Type of structure connection and adhesion between materials
The degree of resistance of these sections against fire

The CFT structure is such that the steel shell acts as a longitudinal and transverse reinforcement. Also, the steel shell strengthens the concrete core. It can prevent the buckling of the steel pipe and increase the stability and tensile strength of the steel column.

Structural connection of CFT

Simple beam connections with CFT columns may not be significantly different from the usual cases in steel structures. Rigid connections in special and medium bending frames include stiffening plates and are located in front of the compression and tension wings of the beam.

These connections are applied in CFT columns in the form of diaphragms, which are more rigid and flexible than internal holes. In addition, the elimination of welding inside the column also allows for more monitoring of the welding quality.

Comparison of implementation of concrete structure and CFT structure

The comparison of concrete structure design and and CFT structure design and implementation is based on various factors. When we intend to compare these two, we must examine them from all aspects. In the following, we will compare the implementation of concrete structure and CFT structure.

Implementation of CFT constructs is usually faster. As an important advantage, the time required to construct CFT structures is reduced to about 60% compared to traditional concrete structures. This reduction in construction time means a reduction in costs and a shorter downtime of buildings.
CFT structures have smaller cross-sections, which is considered as an important advantage. These smaller dimensions lead to a reduction in the dimensions of the columns by nearly 40%. This increases the space inside the building and can provide the possibility of creating more spaces such as parking lots.
The smaller dimensions of CFT structures increase the number of parking spaces by about 10%. This is especially useful and important in construction projects with limited space.
Due to the high strength of the concrete core in CFT structures due to confinement, the thickness of the roof can be reduced. This helps to improve the construction options and the beauty of the design of the structures.
Encased concrete in CFT structures offers more resistance to bending and tensile forces due to its encasement in steel sections. This leads to an increase in stability and the ability to withstand bending and tensile forces in structures.
Due to the reduction of construction time, increase in the number of parking spaces, and reduction in the thickness of the roof, the costs of construction and maintenance of CFT structures are significantly reduced.
In CFT structures, there is no need to use formwork for concreting, which reduces time and cost and helps large and complex buildings.

Comparison of types of building structures

The numerous advantages of CFT structures make the total cost of CFT structures cheaper than steel structures by about 20%.

Another important advantage is that the construction and installation time of the CFT structure is reduced by 30% compared to the steel structure.

Conclusion

As you have read, CFT structures offer many advantages to designers and engineers due to their special characteristics. This structure is a mixture of steel and concrete and has high strength. Above, the most important advantages and disadvantages of CFT structures and their comparison with other types of structures were discussed.

For more detailed information about the implementation conditions and price of CFT structure and types of steel sections, you can contact the experts of Rooyesh Metal Industry Company.