KR20020004747A - CFT(Concrete-Filled steel Tube) structure arranging spiral hoop - Google Patents

Abstract

PURPOSE: CFT(Concrete-Filled steel Tube) structure using a spiral hoop is provided to increase confined effect of a steel tube and concrete by arranging spiral hoops inside the steel tube. CONSTITUTION: CFT structure consists of steel tubes(11,12), spiral hoops(15) arranged in the steel tubes, and concrete(17) filled in the steel tubes. The steel tubes are carbon steel tubes, particularly used with an angular steel tube(11) or a circular steel tube(12). The spiral hoops have structure of arranging axial hoops of a pillar spirally or annularly. The spiral hoops are arranged inside the steel tubes to work the same like in general steel concrete structure. The concrete is filled in the steel tubes to prevent the inner force of the steel tubes from lowering by inhibiting the partial buckling distortion of the steel tubes. The concrete has high strength without coming off by cracking of a steel concrete pillar for the concrete is kept by the steel tubes. The stronger the concrete, the higher the confined effect of the steel tubes. If the confine effect reaches the maximum inner force, the inner pressure lowers rapidly by shear fracture of concrete. Thereby, the strength of the concrete is decided by considering the sharing rate of inner force of the pillar.

Description

Concrete-filled steel tube (CFT) structure arranging spiral hoop}

The present invention relates to a concrete filled steel pipe (CFT) structure using a spiral rebar. More specifically, the present invention relates to a CFT structure using spiral reinforcing bars that can maximize the axial compression cross-sectional force by enhancing the lateral restraint effect between the concrete and the steel pipe by reinforcing the spiral reinforcing bars inside the steel pipe in the CFT structure filling the steel pipe with concrete. .

CFT stands for Concrete-Filled Steel Tube and refers to a concrete filled steel pipe filled with concrete in a steel pipe. CFT is adopted as a pillar member among the main structural members of the frame to resist high axial force. The CFT structure exhibits excellent performance in various aspects, such as fire resistance and construction, as well as structural aspects such as rigidity, strength, and deformation, because steel pipes constrain concrete.

The advantages of the CFT structure are as follows.

First, the CFT column prevents the decrease in the strength of the steel pipe due to the buckling of the filled concrete by confining the local buckling to the steel pipe.In this case, the concrete is bound by the steel pipe, so it can be seen in the reinforced concrete column or the steel reinforced concrete column. Likewise, there is no peeling due to cracking and high strength. In addition, the CFT column exhibits high yield strength and large deformation capacity by the confined effect, which is the interaction between the concrete and the steel pipe.

Second, since the concrete filled inside the CFT structure has a large heat capacity, it is possible to suppress the temperature rise of the steel pipe due to the fire, so that the CFT column does not have to keep the thickness of the fireproof coating thin or under the certain conditions.

Third, in the conventional reinforced concrete structure or steel reinforced concrete structure, concrete placing works are performed after construction work such as reinforcement work and formwork, whereas steel pipes have the function of reinforcement and formwork in the CFT structure, so separate construction work is performed. The construction period can be shortened because it can be omitted.

Fourth, CFT structure can be applied to buildings such as office building, high-rise complex, sales facility, etc. by using steel pipe and concrete in the existing steel reinforcement concrete structure to form a beautiful appearance and smooth structural cross section. have. In addition, it is widely applicable to high-rise buildings, long spans, and industrialized buildings with space efficiency due to urbanization.

On the other hand, the CFT structure is not only the above advantages.

If the combination of strength of steel pipe and concrete is appropriate, the CFT column exhibits axial compressive cross-sectional force greater than the sum of the yield strengths of the steel pipes by the confined effect on the internal concrete of the steel pipe. If it exceeds a certain limit, the confined effect does not appear, and the axial compression force is smaller than the sum of yield strength of steel pipe and concrete. However, the CFT structure can not specify the upper limit of the strength of concrete, the limit of the width ratio (diameter / thickness) of the steel pipe such that the restraining effect is eliminated, and is limited or applied in spite of the various advantages of the aforementioned CFT structure. I have a problem with

Another object of the present invention is to provide a concrete filled steel pipe (CFT) structure using a spiral reinforcement to enhance the confined effect of the steel pipe and concrete by reinforcing the spiral reinforcement inside the steel pipe in the CFT structure.

Another object of the present invention is to provide a concrete filled steel pipe (CFT) structure using a spiral reinforcement, which enables simple work in construction by using a pre-assembled spiral reinforcing bar.

Figure 1a is a plan view of an embodiment using a square steel pipe in the present invention.

Figure 1b is a plan view of an embodiment using a round steel pipe in the present invention.

2 is a cross-sectional view of a concrete filled steel pipe structure using the spiral reinforcement of the present invention.

<Description of Major Codes in Drawings>

1: Concrete Filled Steel Tube (CFT) Column 11: Square Steel Pipe

12: round steel pipe 15: spiral rebar

17: concrete

The present invention will be described with reference to the drawings.

1a and 1b is a plan view of an embodiment of the concrete filled steel pipe structure using the spiral reinforcement of the present invention, the present invention is a steel reinforcing bar (11, 12), the spiral reinforcement (15) is placed inside the steel pipe (11, 12) And concrete 17 filled in the steel pipe.

The steel pipes 11 and 12 are carbon steel pipes for general building structures, and FIGS. 1A and 1B show a case in which a square steel pipe 11 or a circular steel pipe 12 is used as a steel pipe as an embodiment of the present invention. The steel pipes 11 and 12 may use any of seamless steel pipes produced by cold or hot rolling or welded steel pipes made by welding steel materials. The width-thickness ratio (diameter / thickness) of the steel pipes 11 and 12 in the CFT structure has a great influence on the strength of the CFT column, and is determined by considering the column bearing capacity of the steel pipe.

Spiral reinforcement (spiral hoop) is a reinforcing bar arranged in a spiral or annular surrounding the axial reinforcement of the column in a general reinforced concrete structure, and serves to bear the shear force for the buckling and horizontal force of the main bar. In the present invention, the spiral hoop 15 is reinforced inside the steel pipes 11 and 12 and acts the same as in a general reinforced concrete structure. If the spiral reinforcement 15 is used in a state of prefabricated in a spiral shape while maintaining a polygon in a factory or a field, it is possible to facilitate construction since it only needs to be inserted into a steel pipe.

The concrete 17 is filled in the steel pipes 11 and 12 to constrain the local buckling deformation of the steel pipe and prevent the strength reduction of the steel pipe due to buckling. Since the concrete 17 is constrained by the steel pipe, there is no dropout phenomenon due to the cracks appearing in the reinforced concrete pillars or the steel reinforced concrete pillars, so that the concrete 17 has a high strength. At this time, the concrete 17 must be filled without voids in the steel pipes (11, 12) to ensure the required strength, so that the mixing plan is made excellent flowability and less settling.

As the strength of concrete increases, the confined effect on the steel pipe of the filled concrete is enhanced, but after reaching the maximum strength, the concrete shows brittle behavior in which the strength decreases rapidly due to shear failure of the concrete. The strength is determined by considering the column bearing capacity.

Referring to the method of implementing a concrete filled steel pipe (CFT) structure using a spiral reinforcement of the present invention.

First, the steel pipes 11 and 12 are installed at the column positions, and the spiral reinforcing bars 15 are placed in the steel pipes 11 and 12 and then filled with concrete 17, thereby completing the installation of the CFT columns. In this case, when the circular steel pipe 12 is used as the steel pipe, the confined effect between the concrete and the steel pipe is more exhibited than when the square steel pipe 11 is used. If used, it is easy to install inside the steel pipe (11, 12). In addition, the filling operation of the concrete (17) does not affect the process allows for an overall reduction in air.

As a method of filling concrete in a steel pipe, there are a bottom-up pumping method, a centrifugal forming method, and an injection molding method from above, and the press-in method is mainly applied.

Press-fit method is a method of filling high flow concrete from the plinth at once. In the indentation method, an appropriate indentation height is determined at the time of construction planning so that the steel pipe is not deformed by the indentation pressure acting during the concrete indentation construction. In addition, the installation should be managed so as not to exceed the standard value after installing a simple pressure gauge near the indentation pressure port. In this case, the reference value is calculated from the width, thickness and yield strength of the steel pipe. For example, when the steel pipe width is 600 mm, the steel pipe thickness is 28 mm, and the yield strength is 3,300 kgf / cm 2, the reference value is 15.8 kgf / cm 2.

The present invention improves the lateral restraint effect of the steel pipe and concrete by reinforcing the spiral reinforcement inside the steel pipe in the CFT structure to solve the local stress and to maximize the axial compression cross-sectional force, and also pre-assembled with the spiral reinforcement The work in construction is simplified by using

Claims (2)

Steel pipes 11 and 12; A spiral hoop 15 arranged inside the steel pipe; And, Concrete 17 is filled in the steel pipe; Concrete filled steel pipe (CFT) structure using a spiral reinforcement comprising a. The method of claim 1, wherein the concrete filled steel pipe (CFT) structure using a spiral reinforcement, characterized in that using the pre-assembled state of the spiral reinforcement (15)