KR101324408B1 - roof construction methods of LNG storage tank - Google Patents

Abstract

The present invention relates to a loop construction method of a LNG storage tank, and after the first pouring on the entire upper surface of the roof, the second division is divided into a plurality of sections in the radial direction in the radial direction, and stepwise upward pouring from the lower section to the upper section. Is carried out. In addition, the wire mesh 3 is installed in the upper apex section and the lower edge section of the loop.
Therefore, the settling crack is reduced without sagging in the concrete to be poured, and the settling crack is reduced, and the shrinkage crack and the dry shrink crack are reduced because the rigidity against tensile stress at the time of concrete shrinkage is reinforced by the laid wire mesh.
Therefore, the safety of the storage tank is improved, and the maintenance work of the loop is reduced.

Description

Roof construction methods of LNG storage tank

The present invention relates to a loop construction method of a liquefied natural gas storage tank, and more particularly to a loop construction method of a liquefied natural gas storage tank that can reduce the occurrence of surface cracks of the storage tank.

Natural gas (NG) produced overseas is brought into the country via a carrier in the form of liquefied natural gas (LNG) in order to reduce its volume and easily transport it.

The imported LNG is stored in a large-capacity storage tank built nearby by the dock unloading facility, and then supplied to the user through regasification.

The storage tank is a cylindrical reinforced concrete structure, the upper roof (roof) is made of a dome (dome) shape.

The bottom of the roof (that is, the part forming the inner upper surface of the storage tank) is a steel loop fixed by air support upward from the inside of the cylindrical body after construction, and reinforced concrete is constructed on the top of the steel loop to complete the loop. do.

However, the loop is a large-scale concrete structure (about 90m in diameter), and after the construction of concrete, a large amount of cracks are generated on the surface, and the surface cracks not only grow gradually but also cause corrosion of the internal reinforcing bar through the storage tank. It causes a serious problem in safety.

Therefore, after the construction of the roof concrete, a large number of personnel should be put in to perform the surface crack repair work for a long time.

Japanese Patent Laid-Open Publication No. 1994-185200 describes a technique for connecting a coil wire to a reinforcing bar and placing concrete to prevent cracking due to expansion or contraction due to drying shrinkage or temperature change of the concrete, and Korean Patent Laid-Open Publication No. 2005-0049458 The arc describes a technique for attaching supersheets to prevent the occurrence and growth of cracks.

The present invention has been invented to solve the above problems, it is possible to greatly reduce the occurrence of surface cracks of the LNG storage tank loop liquefaction to improve the safety of the LNG storage tank, and also to reduce the amount of maintenance work after construction It is an object of the present invention to provide a loop construction method of a natural gas storage tank.

According to an aspect of the present invention,

Reinforcing bar reinforcement step for reinforcing the reinforcing bar on the upper surface of the steel loop forming the inner surface of the LNG storage tank loop;

A wire mesh laying step of laying a wire mesh on an upper portion of the reinforcement bar;

A primary concrete placing step of placing concrete over the entire loop on the rebar and the wire mesh;

A secondary concrete placing step of placing concrete secondly on the upper surface of the concrete poured in the primary concrete placing step, and upwardly placing the secondary concrete from the lower edge portion of the loop toward the upper apex;

.

In addition, the secondary concrete placing step is characterized by dividing the entire section of the loop into a plurality of sections in the radial direction, step by step from the lower section to the upper section.

Further, in the wire mesh laying step, the wire mesh is installed in an upper section including an upper vertex of a loop in which plastic shrinkage cracking occurs in the entire section of the loop, and in a lower section around an edge where dry shrinkage cracking occurs. It is done.

In addition, it characterized in that it further comprises a vibration compacting step of vibration compacting the concrete poured in the secondary concrete pouring step with a vibration compacting device.

In addition, the first surface of the concrete poured in the secondary concrete placing step, first scraping and evenly grappling, trimming the surface scraped by the hook with a wooden trowel, and further comprising a first surface cleansing step to smooth the iron trowel. It is done.

In addition, after performing the first surface cleaning step, before the hardening of the pouring surface begins to cast the adjacent upper section, and during the casting of the upper section for the line-pouring section, the splattered concrete is blotted off and removed with a iron trowel. Characterized in that the second surface cleaning step to perform the finishing surface cleanup.

The method may further include a curing cloth laying step of covering the curing cloth on the upper surface of the concrete poured in the second concrete placing step.

In addition, it characterized in that it further comprises a watering step of sprinkling the water on the curing cloth.

According to the present invention as described above, by placing the concrete of the storage tank roof upward from the lower edge portion toward the upper apex, the concrete to be poured is supported on the pre-poured concrete and sag does not occur and is sufficiently This can be done to reduce the occurrence of settlement cracks.

In addition, by installing wire mesh in the upper section and the lower section of the loop, the stiffness corresponding to the internal tensile stress that causes the shrinkage crack in concrete shrinkage is improved, so that the occurrence of plastic shrinkage crack and dry shrinkage crack in the lower section is improved. Is reduced.

As described above, the cracks on the surface of the roof concrete are reduced so that the growth of the surface cracks and the corrosion of the internal reinforcing bars are not generated, thereby improving the safety of the storage tank.

In addition, as described above, the occurrence of cracks on the surface of the roof is reduced, so that the amount of post-crack repair work is reduced, thereby reducing manpower, time, and cost.

1 is a state in which the reinforcement is placed on the steel roof upper portion of the storage tank,
Figure 2 is a state in which a wire mesh is installed on the upper portion of the reinforcing bar in the state of FIG.
3 is a state in which concrete is primarily poured into the entire loop to the top of the reinforcing bars and wire mesh in the state of FIG.
4 is a state in which part of the concrete is poured in the lower edge of the loop in the state of FIG.
5 is a state diagram in which the concrete of the next step is poured upward of the loop adjacent to the concrete which was pre-poured in the state of FIG.
6 is a block diagram showing the construction steps of the present invention.

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

As shown in Figure 1 to 6, the present invention is the reinforcement step (S10) for reinforcing the reinforcing bar 2 on the upper surface of the steel loop (1) forming the inner surface of the LNG storage tank loop, the reinforcement Wire mesh installation step (S20) for laying a wire mesh (wire-mesh (welded wire mesh); 3) on the upper portion of the (2), and the concrete over the entire loop on the rebar (2) and the wire mesh (3) Primary concrete placing step (S30) to pour (4), and the second concrete is placed in the upper surface of the concrete poured in the first concrete pour step (S30), but the up-pouring from the lower edge of the loop toward the upper vertex To include the secondary concrete pouring step (S40).

In the reinforcing bar reinforcement step (S10), the main reinforcing bar is arranged vertically and horizontally at regular intervals on the entire upper surface of the steel loop 1, and the secondary reinforcing bars having a relatively small diameter are also arranged vertically and horizontally between the main reinforcing bars. .

In the wire mesh laying step (S20), the wire mesh 3 is installed in an upper section in which plastic shrinkage cracks are mainly generated, and a lower section in which dry shrinkage cracks are mainly generated in the entire section of the roof upper surface.

The wire mesh 3 is welded in a state in which a plurality of steel wires cross each other at right angles or obliquely.

The upper section in which the wire mesh 3 is installed is a section including an upper apex of the loop and is a section about 15.0 m downward from the loop center, and the lower section is a portion around the edge of the loop, that is, a ring beam part ( 11) It is a section about 11.6m radius upward.

The primary and secondary concrete placing steps (S30, S40) is made by dropping the concrete produced by mixing cement, aggregate and water from the ground using CPB (Concrete Placing Boom) to drop in a loop.

In the first concrete pouring step (S30), the concrete (4) is poured over the entire area of the loop, and the casting is performed with a thickness that covers the reinforcing bar 2 and the wire mesh 3 slightly. At this time, the concrete 4 may be poured upwards toward the upper apex at the lower edge portion of the loop.

The secondary concrete pouring step (S40) is to start the pouring in the lower edge portion of the loop, characterized in that to proceed with the pouring toward the upper apex. In other words, concrete pouring proceeds upward from the bottom of the roof to the top.

In addition, the secondary concrete pouring step (S40) divides the entire section of the loop at regular intervals along the radial direction, and performs the pouring of each section step by step (section placing step (S41)).

As shown in FIG. 4, the secondary concrete 5a is poured from the lower edge portion of the loop adjacent to the ring beam portion 11, which is the upper end of the LNG storage tank 10 body.

As described above, after the secondary concrete 5a is poured into the lowermost section of the loop, vibration compaction is performed using a vibration compactor. (Vibration compaction step S42).

Since the surface is inclined along the dome shape of the steel roof 1, the concrete pour surface uses concrete having a small slump (dough) as possible to suppress the flow of concrete along the inclined surface. Therefore, it is necessary to faithfully perform vibration compaction on the poured concrete to improve the compaction state.

After the vibration compacting step (S42), the first surface cleanup step (S43) is performed.

In the first surface clean-up step (S43), first, scrape excessively pour over the portion or fill the insufficient portion, and then after the first surface rougher scratched on the hook roughened by the pusher or wooden trowel Use a trowel to clean up smoothly.

After the first surface cleansing step (S43), before the curing begins to be poured on the pour surface, the second plaster is injected to perform the second surface cleansing step (S44).

Before the second surface cleaning step S44, concrete 5b is placed in an adjacent upper section of the pre-poured section. That is, the section placing step (S41) is repeatedly performed in a manner of placing concrete in the upper section adjacent to the section when the concrete placing, vibration compaction and the first surface cleanup of the corresponding section is made.

That is, as shown in FIG. 5, the operation of pouring concrete 5b again to the upper portion of the concrete 5a that is first placed on the lower side (meaning the upper portion of the loop inclination direction) is repeated.

At this time, the concrete of the first cast section can withstand without being sag by the load of concrete that is then poured in the adjacent upper part.

On the other hand, in the second surface cleanup step (S44) while the plasterers go up from the bottom (to wear a plate on the bottom of the shoe so that the footprint does not remain) sweeping the concrete splatters when pouring the upper section with a broom to remove, iron Use a trowel to clean the final finish.

After the second surface cleanup step (S44) is carried out to prevent the evaporation of water to cure the curing step (S45) covering the curing cloth 6 on the upper surface of the pour concrete (5a).

Then, the sprinkling step (S46) for spraying water on the laid curing (6).

Subsequently, the secondary concrete casting is completed in all sections of the loop by repeating the steps of section casting, vibration compaction, surface cleaning, curing cloth laying and spraying in the same manner as described above.

After completing the secondary concrete pouring of the entire loop section as described above, of course, to undergo the full curing period to express the strength of the roof concrete (cure step (S50)).

Now, the operational effects of the present invention will be described.

Conventionally, in the case of roof concrete pouring of LNG storage tank, the pouring was performed from the top of the roof downward. Therefore, since the concrete supporting the concrete being poured does not exist below the slope of the portion where the pouring is in progress, the pouring concrete was easy to slide down along the slope.

Therefore, despite the use of concrete with a small slump, because the settlement occurs due to the vibration generated during the compaction operation, sufficient compaction could not be performed.

On the contrary, the present invention performs a bottom-up casting process in which the pouring proceeds upwards from the bottom of the roof, so that the concrete in the pouring section can be supported by the concrete in the lower section in which the pouring section is placed, thereby overcoming the difficulty that the pouring surface is inclined. Of course, the vibration compaction can be sufficiently performed to prevent the settlement of the pour surface, thereby preventing the surface cracking caused by the settlement as much as possible.

In addition, for the same reason as above, it is necessary to install the deflection prevention pipe in order to prevent the concrete deflection along the inclined surface of the roof when placing concrete, and to perform the operation of removing the deflection prevention pipe again after the end of the section pouring. It is gone. Therefore, concrete pouring work can be carried out more easily.

In addition, the wire mesh 3 is fired on the concrete surface by improving the structural rigidity in response to the tensile stress generated when the poured concrete (constrained in the shrinking direction by the reinforcing bar 2) contracts Prevents shrink cracks and dry shrink cracks from occurring. In particular, there is an effect of reducing the plastic shrinkage crack and the dry shrinkage crack of the lower section.

In addition, in the past, when the water is sprayed to prevent drying, after the completion of the section pouring, the sprinkled water flows downward, so that the water flows along the surface to be poured afterwards. As the slide slipped, the settlement increased.

However, according to the present invention, the water sprayed on the upper part of the currently poured concrete flows along the upper surface of the concrete first poured on the lower side thereof and is discharged to the outside of the storage tank 10 so that the sprinkled water of the concrete of the section where the pouring is in progress. It does not affect the deflection, and compaction is improved, so that no settlement of concrete occurs. Therefore, it is possible to proceed with concrete pouring work more easily, it is possible to reduce the occurrence of settlement cracks.

In addition, the present invention covers the cured cloth on the upper surface of the poured concrete, and sprinkled with water on it, the rapid water evaporation phenomenon immediately after concrete pouring (LNG base is mainly dried in the coastal area, so the sea breeze is severe, the water evaporation phenomenon occurs badly. This prevents the occurrence of plastic shrinkage cracks as the surface curing of pour concrete is normal.

In addition, by uniformly drying the surface portion and the interior of the concrete for the same reason, it is possible to prevent the dry shrinkage cracking caused by the different dry shrinkage state of the surface portion and the interior of the concrete. As described above, the dry shrink crack can be prevented by reinforcing the tensile coping force by the wire mesh.

Table 1 below shows the crack reduction effect of the roof concrete according to the application of the present invention, Comparative Example 1 is the case of the downward casting, Comparative Example 2 is the case of upward casting, Comparative Example 3 is the upward casting And wire mesh laying.

division
Number of cracks
Crack total length (m)
Application method Crack Reduction Rate (%) for Comparative Example 1
Comparative Example 1
184
460.5
Downpouring
-
Comparative Example 2
138
343.6
Upward casting
About 25
Comparative Example 3
44
72.3 Upward pour and
Wire Mesh Laying
Approximately 84

As shown in Table 1, when down-pouring was performed according to the conventional method, 184 cracks were generated and the total length thereof was 460.5 m.

However, in the case of Comparative Example 2 to which the upward pour was applied according to the present invention, the number of cracks generated was 138 and the total length of the cracks was 343.6 m, which was reduced by about 25% when compared with the total length of the cracks of Comparative Example 1. .

In addition, according to the present invention, in the case of Comparative Example 3 to which both the up-pouring and the wire mesh laying were applied, the number of generated cracks was 44 and the total crack length was 72.3 m, which is about 84% reduction compared to Comparative Example 1.

As described above, the present invention has the effect of greatly reducing the cracks on the roof surface after construction by applying both wire mesh laying and up-pouring during roof concrete pouring.

10: LNG storage tank 1: steel loop
2: rebar 3: wire mesh
4: Concrete (primary casting) 5 (5a, 5b): Concrete (secondary casting)
6: cure gun

Claims (8)

Reinforcing bar reinforcement step for reinforcing the reinforcing bar on the upper surface of the steel loop forming the inner surface of the LNG storage tank loop;
A wire mesh laying step of laying a wire mesh on an upper portion of the reinforcement bar;
A primary concrete placing step of placing concrete over the entire loop on the rebar and the wire mesh;
A secondary concrete placing step of placing concrete secondly on the upper surface of the concrete poured in the primary concrete placing step, and upwardly placing the secondary concrete from the lower edge portion of the loop toward the upper apex;
Loop construction method of liquefied natural gas storage tank comprising a. The method according to claim 1,
In the secondary concrete pouring step, the entire section of the loop is divided into a plurality of sections in the radial direction, and the roof construction method of the liquefied natural gas storage tank, characterized in that the step of placing each step in stages. The method according to claim 1,
In the wire mesh laying step, the wire mesh is disposed in an upper section including an upper vertex of a loop in which plastic shrinkage cracks occur in an entire section of the loop, and in a lower section around an edge where dry shrinkage cracks occur. Loop construction method of LNG storage tank. The method according to claim 1,
Loop construction method of the liquefied natural gas storage tank, characterized in that further comprising a vibration compacting step of vibrating compacting the concrete poured in the secondary concrete pouring step with a vibration compacting device. The method according to claim 1,
In the secondary concrete placing step, the first surface of the concrete poured in the first step of scraping and evenly grading, the surface scraped by the hook, and trimmed with a wooden trowel, and further comprising a first surface trimming step of smoothing with iron trowel. Loop construction method of LNG storage tank. The method according to claim 5,
After the first surface cleanup step, before the hardening of the pour surface begins, pour the adjacent upper section, and remove the splattered concrete with a broom to remove the upper section with the iron trowel. Loop construction method of a LNG storage tank, characterized in that for performing the second surface cleaning step to clean up. The method according to claim 1,
Loop construction method of a liquefied natural gas storage tank, characterized in that it further comprises a curing cloth laying step of covering the curing cloth on the upper surface of the concrete poured in the secondary concrete placing step. The method of claim 7,
Loop construction method of a liquefied natural gas storage tank characterized in that it further comprises a watering step of spraying water over the curing cloth.

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