KR100704849B1 - Reinforced concrete fireproof structure through partial coating - Google Patents

Abstract

The present invention confirms that the deterioration of the fire resistance of the reinforced concrete member is due to the rapid temperature rise of the reinforcement of the longitudinal edge of the reinforced concrete member, and through partial partial coating that economically and efficiently enhances the fire resistance through the partial fireproof coating of the corner of the reinforced concrete member only. The present invention relates to a reinforced concrete fireproof structure.

 The present invention provides a reinforced concrete fireproof structure through a partial coating in which the refractory material is partially coated only around the corners of the square in the reinforced concrete member designed to be square. When the reinforced concrete member is designed to be mixed with high-strength concrete having a compressive strength of 40 MPa or more, the high-strength concrete is preferably designed to mix with the organic fiber, and the refractory material is heated to test the reinforced concrete member from the corners of the square. Afterwards, cover to the point where longitudinal cracking occurs. Particularly, the present invention proposes a reinforced concrete fireproof structure in which a fireproof material is coated with a width of 100 mm or more from four corners of a square pillar when the reinforced concrete member is designed with a reinforced concrete square pillar having a thickness of 40 mm. At this time, it is sufficient that the fireproof material is coated with a thickness of 2 mm or more and 5 mm or less.

Reinforced Concrete, Longitudinal Reinforcing Bar, Temperature, Fireproof, Partially Coated, Edge

Description

Fire resisting structure by the partial covering of reinforced concrete}

1A and 1B are a cross-sectional view 1a and a lateral rectus detail 1b of a column test specimen used in a heating test.

2 is a comparison graph between the standard fire curve and the actual heating curve applied to the test body.

Figure 3 is a picture of the inside of the furnace after the heating test for 3 hours.

4A to 4C are graphs of temperature history according to the thickness of the refractory material and are graphs of temperature history of the surface portion 4a, the edge longitudinal bars 4b, and the intermediate longitudinal bars 4c.

5 is a graph of the correlation between the heat transfer rate by the outside air and the edge longitudinal reinforcing bar after 3 hours of heating.

Figure 6a is a photograph of the appearance of the longitudinal crack after 3 hours of heating of the cross section size 500x500mm pillar.

Figure 6b is a photograph of the appearance of longitudinal cracking after 3 hours of heating the cross section size 305x305mm column.

7 is a cross-sectional view of a reinforced concrete column partially coated with a refractory material in one embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

C: concrete F: fireproof material

R: Cast bar S: Band bar

D: fireproof coating width

The present invention relates to a reinforced concrete fireproof structure through partial coating, and more particularly, it is confirmed that the degradation of the fire resistance of the reinforced concrete member is due to the rapid temperature rise of the longitudinal longitudinal reinforcement, and partially fired only the reinforced concrete member edge The present invention relates to a reinforced concrete fireproof structure through partial coating, which has improved fire resistance performance economically and efficiently through coating.

When concrete and rebar are exposed to high temperatures, the strength and modulus of elasticity decrease. The modulus of elasticity continues to decrease with increasing temperature. As a result, the strength of the reinforced concrete member is reduced when exposed to high temperatures due to fire. In the reinforced concrete member, most of the rebar is located relatively close to the surface in the cross section of the member, so that the temperature of the rebar is very high when exposed to a fire for a long time. This may lead to the destruction of the reinforced concrete member due to the decrease in the strength of the reinforcing bar, although there are many concrete parts having a relatively low strength loss inside the reinforced concrete member. Thus, the temperature of the rebar in the reinforced concrete member is one of the very important factors.

When the reinforced concrete member is exposed to a high temperature, its strength decreases. At this time, the time at which the strength remains above a certain standard is called fire resistance. In general, fire resistance is divided into 1 hour, 2 hours, and 3 hours. In particular, reinforced concrete columns are designed to have fire resistance of 3 hours, although they are different depending on their location because they are the main members of a building structure. There are two ways to evaluate the fire resistance of reinforced concrete columns.

The first method is to evaluate the contraction degree of the column by applying a constant load to the column and conducting a heating test as shown in KS F 2257-1. Fire resistance is defined as the time measured and within the reference value.

The second method is briefly mentioned in KS F 2257-7, but it is a non-heating heating test that is widely used in Japan. It is a method of defining the fire resistance performance until the temperature of the longitudinal rebar in the reinforced concrete column does not exceed 500 ℃. .

In the first method, since the temperature of the used longitudinal bar is not a criterion for determination and the test method is cumbersome, in Japan, the second test method based on the temperature standard of the longitudinal rebar is made of a fire resistance evaluation method. There is a situation.

According to the results of the evaluation of fire resistance, the method of improving the fire resistance of reinforced concrete members is as follows: 1) to improve the concrete cover; 2) to add a fireproof plate resistant to high temperatures to the surface of the column; and 3) to fire resistance with excellent fire resistance. It can be divided into a method of applying the material to the entire surface.

The first method has the disadvantage that the cross section of the pillar is too large and the available space is reduced. For example, the concrete covering thickness of the reinforced concrete column developed by Kajima Construction in Japan is 72 mm, which is 32 mm higher than the general coating thickness of 40 mm. Increased. In this case, the width of the column is 64mm (32 + 32), which increases, so that not only concrete use is increased but also the distance between the pillars is shortened, thus reducing the available area and increasing the weight of the building. The second and third methods have a disadvantage in that economic efficiency is reduced because the front of the pillar is coated with a fireproof material.

The present invention has been made to improve the above-mentioned conventional problems, it is confirmed that the degradation of the fire resistance performance of the reinforced concrete member due to the rapid temperature rise of the reinforcement of the reinforcement concrete member through the test in the reinforced concrete member designed in a square The purpose of the present invention is to provide a reinforced concrete fireproof structure through partial coating, which is economically and efficiently improving fire resistance by partially fireproof coating only around the edges of concrete members.

In order to achieve the above object, the present invention provides a reinforced concrete fireproof structure through a partial coating in which the refractory material is only partially coated around the corners of the square in the reinforced concrete member designed in a square. When the reinforced concrete member is designed to be mixed with high-strength concrete having a compressive strength of 40 MPa or more, the high-strength concrete is preferably designed to mix with the organic fiber, and the refractory material is heated to test the reinforced concrete member from the corners of the square. Afterwards, cover to the point where longitudinal cracking occurs.

Particularly, the present invention proposes a reinforced concrete fireproof structure in which a fireproof material is coated with a width of 100 mm or more from four corners of a square pillar when the reinforced concrete member is designed with a reinforced concrete square pillar having a thickness of 40 mm. At this time, it is sufficient that the fireproof material is coated with a thickness of 2 mm or more and 5 mm or less.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings and preferred embodiments.

The present invention is economical by confirming that the temperature of the longitudinal reinforcing bars located at the corners of the rectangular reinforcement concrete member suddenly rises in the event of fire and does not satisfy the fire resistance and partially covers the refractory material only at the corners to suppress the rise. There are technical features to make it possible to efficiently improve the fire resistance. In other words, even when heated for 3 hours with a standard fire heating curve, the temperature of all the longitudinal cast iron in the reinforced concrete member does not exceed 500 ℃ to achieve the most efficient three-hour fire resistance performance. Here, the longitudinal direction is the direction in which the reinforcing steel reinforcement in the reinforced concrete member, in the case of the reinforced concrete column will be in the longitudinal direction. As the refractory material used in the present invention, it is generally possible to use a conventional refractory material used for protection of steel frame in case of fire.

On the other hand, concrete becomes water vapor when there is a sudden temperature rise inside the concrete and escapes into the gaps in the concrete. When the steam generation rate is faster than the exiting speed, steam pressure is generated. Spalling is caused by the premature dropping of concrete cladding, which causes the longitudinal rebar to be exposed to high temperatures, causing the reinforced concrete member to collapse quickly. Therefore, when the reinforced concrete member is designed to be mixed with high strength concrete having a concrete compressive strength of 40 MPa or more, it is preferable to mix the organic fiber in the high strength concrete and mix the designed design. This is because the thermal explosion usually does not occur in normal strength concrete, because the thermal phenomenon easily occurs in high strength concrete.

In other words, high-strength concrete is manufactured by adding water, fine aggregates, coarse aggregates, and high performance water reducing agents to improve fluidity to powder materials composed of cement and fly ash, slag, or silica fume. When the level of compressive strength used is over 40MPa, it is defined as high-strength concrete.The higher the concrete strength, the less porosity in the interior, which effectively prevents the discharge of voids (mainly water vapor pressure). This happens easily. Therefore, in high-strength concrete, organic fibers are incorporated into concrete to prevent such thermal expansion. Since the organic fibers are melted before the thermal explosion occurs, the passage in which the glass fibers are melted becomes a passage through which the void pressure (mainly water vapor pressure) is effectively discharged, thereby preventing the thermal explosion phenomenon.

The present invention was completed as a result of determining the appropriate fireproof thickness and coating location based on this after grasping the effect of the refractory material on the rise of temperature in the concrete in the reinforced concrete member.

EXAMPLE

1. Preparation of test body

The concrete specimens were designed to have a relatively large cross section of 500 mm x 500 mm x 800 mm, as shown in Figures 1a and 1b. Longitudinal reinforcement bars were reinforced to 8D25 and band reinforcements to D10. The net cover was 40mm and the value used in the field was generally used. This is according to the conventional reinforced concrete column design. A total of five sensors were installed to measure the temperature at each location in the cross section, two of which drilled a 2 mm diameter hole in the longitudinal bars, so that the temperature sensing part was located at the center of the longitudinal bars. The temperature sensor diameter is 1.6mm and the temperature sensing part is 4mm from the sensor end.

Concrete mixing ratio is as shown in Table 1, in order to prevent thermal expansion phenomenon PP (polypropylene) fiber (length 6mm, diameter 46㎛) 0.2vol.% Was mixed.

[Table 1] Concrete mixing ratio

Water Binder Ratio W / B (%) Fine Aggregate S / a (%) unit weight (kg / m ³ ) High Performance Reducer SP (%) Water (W) Cement (C) Silica fume (SF) Fly Ash (FA) Fine Aggregate (S) Coarse aggregate (G) 25 42 165 515 46 99 629 878 2.0

The concrete members were air cured after the concrete was poured and coated with the refractory material to be sprayed after 18 days of age in order to grasp the temperature change of the longitudinal rebar according to the refractory thickness. As the experimental variable, the thickness of the fireproof material was selected as 0, 10, 20, 30mm, and the fireproof material was applied only to the side of the pillar, but not on the upper and lower surfaces. In addition, the heating test was carried out at 35 days of age, and the compressive strength at this time was 80.8 MPa, indicating a very high compressive strength, which corresponds to high strength concrete.

During the heating test, 50mm of rock wool sheets were laid on the lower surface of the concrete member, and two sheets were covered on the upper surface to allow the heat into the side coated with the refractory material capable of heat in the heating furnace. The heating temperature in the furnace was fitted to the standard time-heating temperature curve of the ISO-KS standard, and the actual heating temperature curve for 3 hours is shown in FIG. 2. The ISO-KS standard time-heat temperature curve is a reference value used to evaluate the fire resistance performance of various materials and members. 3 is a picture of the inside of the furnace immediately after the heating test for 3 hours.

2. Temperature history after heating test

Figures 4a, 4b and 4c shows the temperature hysteresis curve for each point according to the thickness of the refractory material. As can be seen from each figure, even if the fire-resistant coating of 10mm on the concrete surface, the temperature of the concrete surface and the longitudinal reinforcing bar was found to decrease rapidly.

On the other hand, when fireproof coating is not performed, the longitudinal longitudinal reinforcing bars between the two edges after 3 hours do not exceed 500 ° C, while the longitudinal reinforcing bars located at the corners exceed 500 ° C from about 140 minutes later. The temperature was found to increase to 600 ° C. The reason why the temperature of the longitudinal longitudinal rebars is high seems to be caused by heat from both sides of the edge.

After heating for 3 hours the temperature of the edge longitudinal reinforcement according to the thickness of the refractory material is summarized in Table 2. As can be seen from Table 2, the edge longitudinal reinforcing bar is increased to about 600 ℃ after 3 hours heating does not satisfy the 3 hours fire resistance performance. Therefore, it was found that a fireproof material of appropriate thickness should be installed.

[Table 2] Edge longitudinal rebar temperature according to fireproof thickness

Fireproof Coating Thickness (mm) Edge longitudinal rebar temperature (° C) after 3 hours 0 598 10 317 20 238 30 166

On the basis of the above test results, a variable called air convection coefficient at the concrete surface by the outside air was introduced in order to calculate the optimum fire-resistant coating thickness at which the edge longitudinal rebar temperature satisfies 500 ° C after 3 hours of heating. This is because the temperature of the reinforcing bars in the concrete is a function of the heat transfer rate that occurs on the concrete surface. At this time, the heat transfer rate of concrete considering fireproof material is defined as shown in equation (1).

Here, d _i represents the thickness of the refractory material, and λ _i represents the thermal conductivity of the refractory material. In the present invention, a thermal conductivity of 0.04 kcal / (m 2 ° C hr) of the refractory material was used. After heating for 3 hours, the relationship between the temperature of the edge longitudinal reinforcement and the heat transfer rate calculated by Equation (1) is shown in FIG. 5, and the optimal regression equation is shown in Equation (2) below.

Where h _a is the heat transfer rate. Based on Equation (2), the thickness of the fire resistant material corresponding to the temperature of the longitudinal edge of the reinforcing bar is about 5 mm, and the thickness corresponding to 400 ° C. is about 5 mm in consideration of the safety factor.

From the above test results, (1) the middle longitudinal rebars between the edges do not exceed 500 ℃ even after 3 hours of heating, even if there is no fireproof material, and only the central longitudinal bars located at the corners exceed 500 ℃, (2) heating for 3 hours The test confirms that the thickness of the refractory material, such that the longitudinal rebar temperature does not exceed 500 ° C, is very thin, several mm. After all, the refractory material is effective only by applying a partial coating at the corners, and the thickness also leads to the conclusion that the thickness of 30 to 40 mm used in general steel is not necessary.

3. Reinforced concrete member after heating test

6A and 6B show the state of the column after 3 hours of heating. As can be seen in Figures 6a and 6b it was found that the cracks in the longitudinal direction during the heating test. FIG. 6A corresponds to a column of thickness 500 mm (concrete coating 40 mm) and FIG. 6B corresponds to a column of thickness 305 mm (concrete coating 40 mm), in which longitudinal cracking is 1/5 of the thickness, in the case of a 500 mm thickness column. In the case of a 305 mm column, it occurred at one third of the thickness. It can be seen that longitudinal cracking occurs about 100 mm from the edge regardless of the column thickness.

Longitudinal cracks are caused by temperature differences because the temperature near the edge of the column is relatively higher than elsewhere, and the location of the crack corresponds to the boundary between the very high and low temperatures. In other words, the area where the temperature is high from the edge of the column to the crack is generated, and the remaining sections (near the center) are classified into relatively low temperatures. As described above, the temperature of the longitudinal reinforcing bars located at the relatively low central temperature did not exceed 500 ° C. even when heated for 3 hours. Therefore, if the fireproofing material is covered to the place where the crack occurs at the edges, even if heat is applied at both edges, the temperature of the edge portion does not increase significantly, and the temperature of the longitudinal reinforcement of the edge portion may be reduced.

According to the above test results, as shown in FIG. 7, the longitudinal reinforcing bars (R) and the band reinforcing bars (S) are reinforced and partially coated with the refractory material (F) on the corners of the concrete (C) -coated rectangular reinforced concrete column. I can finish it in a structure. That is, the fireproof material (F) is coated at four corners from the edge of the reinforced concrete column to 100 mm (fireproof coating width, D).

Various methods can be considered as a coating method of a fireproof material. First, a method of thinly applying a fireproof paint, and a second method of adding a plate or sheet having excellent fire resistance without applying a fireproof material are predicted.

According to the present invention as described above, it is possible to improve the fire resistance performance of the entire member only by partially refractory coating only around the corners of the reinforced concrete member bar, the reinforced concrete structure is completed in a fire resistant structure having advantages in terms of economic efficiency and efficiency You can do it.

Claims (5)

In the reinforced concrete member designed in square shape, Reinforced concrete fire-resistant structure through partial coating, characterized in that the refractory material is only partially coated around the corners of the square. In claim 1, Reinforced concrete fire-resistant structure through the partial coating, characterized in that the organic concrete is mixed in the high-strength concrete when the reinforced concrete member is designed to be mixed with high-strength concrete having a compressive strength of 40MPa or more of concrete. The method of claim 1 or 2, The refractory material is a reinforced concrete refractory structure through the partial coating, characterized in that the coating of the reinforcement from the corner of the square to the point where the longitudinal crack of the member after the heating test of the reinforced concrete member. In claim 3, When the reinforced concrete member is designed with a reinforced concrete square pillar, the thickness of the reinforcing steel is 40 mm, the fire resistant concrete is reinforced by partial coating, characterized in that the fire resistant material is coated with a width of 100 mm or more from each of the four corners of the square pillar. rescue. In claim 4, Reinforced concrete fire-resistant structure through the partial coating, characterized in that the fire-resistant material is coated with a thickness of 2mm or more and 5mm or less.

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