KR101883114B1 - Double Composite Steel Box Girder Bridge and Method for Fabricating thereof - Google Patents

Abstract

The present invention relates to a double composite steel box girder bridge, to compositely form both of upper and lower flanges of a steel box girder, which is installed in a negative moment section of a continuous point part in a composite steel box girder continuous bridge, with concrete, and a construction method thereof and, more specifically, to a double composite steel box girder bridge, which improves a structure and a rebar arrangement method of a steel box related to lower concrete compositely formed with the lower flange of a steel box girder to remarkably reduce construction costs of the lower concrete and improve structural performance thereof, and a control method thereof. According to the present invention, the double composite steel box girder bridge comprises: the steel box; lower concrete of a rebar concrete material deposited inside the steel box; and horizontal and vertical ribs installed in the lower flange of the steel box. A method to construct the double composite steel box girder bridge comprises: a rebar arrangement step of arranging a rebar for the lower concrete, wherein the horizontal rib is formed with a plate-shaped member with one long direction and the vertical rib is discontinuously installed with respect to the horizontal rib in order to induce a horizontal crack in the lower concrete; a releasing agent coating stop of coating a releasing agent on the horizontal rib; a concrete depositing/curing step of depositing/curing concrete for the lower concrete; and a crack repairing step of repairing the crack generated in the lower concrete in a method, which injects a lower viscosity epoxy resin before depositing concrete for the bottom plate constructed on the upper part of the steel box.

Description

Technical Field [0001] The present invention relates to a double composite steel box girder bridge,

The present invention relates to a double synthetic steel box girder bridges and a construction method thereof for synthesizing both an upper flange and a lower flange of a steel box girder installed on a consecutive point portion of a continuous bridge portion of a steel box composite girder bridge with concrete, A double composite steel box girder bridges capable of drastically reducing the construction cost of the lower concrete and improving the structural performance by improving the construction method including the structure of the steel box and the arrangement method related to the lower concrete to be combined with the lower flange of the box girder, And a construction method.

Steel box girders have excellent resistance to bending and torsion and have good workability on the field and have been widely applied to long bridge or curved bridge. Concrete has much less rigidity and strength than steel, but it has excellent structural efficiency per unit price only in terms of compressive strength. In recent years, the use of steel box girder bridges has been gradually decreasing due to the development of various concrete girder bridges having excellent economic efficiency by utilizing the advantages of such concrete. In order to overcome this situation, a variety of economical steel box girder bridge methods have been continuously developed. One of the typical methods of improving the economical efficiency of a steel box composite girder bridge is a double composite steel box girder bridge. As shown in Fig. 1 (a), the double composite steel box girder bridge is composed of a composite structure of a bottom plate concrete and a steel box girder. The composite girder bridge girder bridges are formed by combining concrete on the lower flange of a steel box girder This is a method that reduces the thickness of steel material and minimizes or eliminates a number of stiffeners required to prevent local buckling of the lower flange under compression stress, thereby improving the economic efficiency. FIG. 1 (b) is a cross-sectional perspective view of a steel box girder, showing that studs (shear connectors) are installed in the lower flange for synthesis with the lower concrete. Various types of shear connectors can be used, but studs are most widely used because they are easy to install and economical. As shown in FIG. 1 (b), the cross-sectional shape of the steel box is often a rectangular cross-section (not shown) of an opening form in which the upper part of the box is opened or a closed end face in which the upper part is closed.

One of the most difficult processes of double composite steel box girder bridges is the construction of lower concrete. Generally, the construction of the lower concrete is performed after the steel box girder is installed on the lower structure. Therefore, the installation work of the lower concrete reinforcement and the concrete pouring work are performed in the air after the steel box is constructed. Although the lower concrete can be constructed from the ground, the steel box girder is constructed by assembling three or five steel box segments manufactured by the factory in the ground and assembling it into a small block unit of an appropriate weight. In many cases, it is impossible to install the lower concrete on the ground because it is mostly divided into small blocks in the section where the lower concrete is laid. In addition, when the lower concrete is constructed on the ground, the weight of the steel box is increased and the weight of the steel box is increased. However, since the weight of the lower concrete is added thereto, If the weight of the temporary block increases, the capacity of the crane increases and the operation speed decreases. As a result, the cost of the installation increases.

Another problem of double composite steel box girder bridges is the shrinkage problem of the lower concrete. The shrinkage of concrete is divided into autogenous shrinkage and drying shrinkage. Autogenous shrinkage occurs mainly in the short term and drying shrinkage occurs in relatively long term. The low strength concrete has a large amount of drying shrinkage instead of the small amount of self-shrinkage, and the high strength concrete has a large amount of self-shrinkage but low drying shrinkage. Generally, the shrinkage amount is higher in high strength concrete. When concrete is synthesized by casting in a very rigid structure such as a steel box girder, the shrinkage of the concrete is strongly restrained by the steel girder, so that a large tensile stress is generated in the concrete. Such a tensile stress exceeds the allowable tensile stress So cracks inevitably occur. Especially, high-strength concrete has a large amount of self-shrinkage occurring in the short-term, causing many cracks at the beginning of concrete curing. So far, only concrete with a compressive strength of 40 MPa or less has been used in the under-cast concrete. In the steel box synthetic girder using the precast concrete used for continuous bridges and the method of manufacturing the same, precast concrete is used in the lower concrete to generate sufficient shrinkage before the synthesis (in particular, magnetic shrinkage) However, considering the reality of the double synthetic steel box girder bridges in Korea, which is often applied in the form of curved bridge or cross section, precast underconcrete can be manufactured by using the method of reducing the shrinkage of concrete Of course, there are many difficulties in installing it, so there are many restrictions on the application and the problem is not economical at all.

FIG. 2 is a graph showing a load-under-concrete strain curve according to the number of repetitive loads simulating working loads as a result of cyclic loading test of a double synthetic steel box girder. The compressive strain is a positive sign. The static test of the solid line is the initial load-strain curve and the remainder is the load-strain curve after a certain number of cyclic loads. Finally, it is the result of 5,600,000 repetitive loads. As can be seen in FIG. 2, it can be seen that the change in the load-strain curve varies considerably depending on the number of repeated loads. The initial characteristics of the cyclic load are that the compressive strain is almost zero until a constant load is reached. This means that the cracks are closed until the tensile stress caused by the concrete shrinkage is canceled and the compressive stress is not applied to the lower concrete at the measured position It means. If the strain gauge is immediately adjacent to the crack generated by the shrinkage, compressive stress may be applied to the lower concrete and the compressive strain at the location immediately adjacent to the crack may be zero before the crack is closed. However, as the number of repeated loads increases, it tends to be constant. This is because the occurrence pattern of the initial cracks is very irregular, so that the difference in the measured strain values may be considerable depending on the measurement position. However, if the number of repeated loads increases, fine cracks are uniformly distributed over the entire region, Because. In the final test results, the load-strain curve consists of two straight lines with different slopes and a transition curve therebetween. At first, the slope is small and the slope increases later. This means that the average stiffness of the lower concrete is reduced due to the effect of the lower concrete cracks caused by the shrinkage and cyclic loading in the small load region (only the concrete stiffness exists between cracks and cracks) Are gradually closing, and it is understood that after all the cracks are closed by the increase of the load, the concrete returns to the original stiffness of the lower concrete. It can be seen that the tensile stress caused by the shrinkage of the lower concrete degrades the performance of the lower concrete by canceling a considerable part of the compressive stress to be shared by the lower concrete against the action bending moment. As the lower concrete has a higher compressive force acting on the lower part of the steel box, the steel material thickness of the lower flange can be made thinner, so that the economical efficiency of the double synthetic steel box girder bridge is improved, so that the influence of shrinkage of the lower concrete needs to be minimized. Also, as the compressive strength of concrete increases, the stiffness increases. Therefore, when high strength concrete is used in the lower concrete, the compressive force acting on the lower part of the steel box can be further divided and the thickness of the lower concrete can be reduced. Therefore, the structural efficiency of double composite steel box girders can be improved considerably if high strength concrete can be used.

In order to control the cracks generated in the concrete by the shrinkage of the concrete, the reinforcing bars are arranged not to fundamentally suppress the cracks but to distribute the generated crack evenly and to limit the crack width. The lower concrete reinforcing bars are installed vertically and horizontally in the upper and lower stages, respectively, as in the bottom plate slab. Even though the structure is simple, reinforcing works in the steel box installed on the lower structure is very difficult. As can be seen in the photograph of FIG. 3, a large number of studs are closely installed on the lower flange of the double synthetic section for the synthesis with concrete. Although not shown in the photograph, the upper part of the steel box is partially closed or closed, or truss type horizontal bracing is installed It is difficult to input the material, and the work space inside the box is also narrowed and the working efficiency is considerably reduced.

Since the lower flange of the double synthetic steel box girder is thin, when the concrete is placed on the lower flange, the deflection of the lower flange becomes too large due to the concrete load, so that the bending stress of the plate may be excessive. FIG. 4 is a photograph showing a state in which a temporary stiffener is installed in the lower part of the lower flange in a transverse direction, and the concrete is fastened with bolts so as to be removed when the concrete reaches a predetermined strength. These temporary stiffeners are relatively closely arranged at regular intervals. The biggest problem of using these temporary stiffeners is the cost of demolition. Removal of the temporary stiffener is done after the steel box girder is installed in the substructure, so it is also a problem in the air demolition, but repainting of the bolt site is cumbersome and costly. FIG. 5 is a photograph of a double composite steel box small block prior to installation. In order not to use the temporary reinforcement shown in FIG. 4, a T-shaped lateral rib and a straight type vertical rib, which are generally used for local buckling reinforcement of a lower flange, This is an example in which the bottom flange frame is installed to prevent excessive sagging of the lower flange when the lower concrete is poured. Of course, these transverse ribs and vertical ribs also help to prevent local buckling of the lower flange due to the weight of the steel box girder and the unstressed lower concrete load. However, the problem is that if lateral ribs are used in the lower concrete section, it is necessary to penetrate the through ribs through the horizontal ribs and to install them in order to arrange continuous longitudinal (throttling) rebars across the entire lower concrete section. Long longitudinal reinforcing bars are used to minimize joints of longitudinal reinforcing bars. Therefore, it is economically and structurally efficient that long reinforcing bars are used. Therefore, if possible, long reinforcing bars should be used. In a narrow space, Passing while working is very inefficient. According to one report, in case of FIG. 5, the cost of working the reinforcing bars of the lower concrete is about three times the cost of the ordinary slab working. The holes at the lower end of the transverse ribs in FIG. 5 are the holes through which the longitudinal reinforcing bars at the lower end of the lower concrete pass, the upper longitudinal reinforcing bars passing over the transverse ribs, have. In FIG. 5, the upper part of the steel box is closed in the lower concrete pouring section, and the upper part of the steel box is open in the other section, but it is reinforced by the horizontal stiffener. It can also be seen that the surface that comes into contact with the lower concrete is not painted.

The method of placing the reinforcing bars of the lower concrete of the conventional double composite steel box girder bridges is based on the design standard slab reinforcing steel laying method as the design standard of the highway bridges. Since the double composite steel box girder bridges are not general bridging methods, there is no separate regulation on the method of laying down the lower concrete in the design standard, so the traditional slab laying method is applied. This is because the bottom plate slab and the lower concrete of the moment section of the double composite continuous girder bridge are slab type and the flexural compressive stress of the composite girder acts on the common load. However, the bottom slab is exposed to the outside and the load is directly contacted, but the lower concrete is protected inside the steel box and the load is not directly contacted. The bottom plate slab limits the crack width of the concrete because the prevention of corrosion of the reinforcing bar due to moisture (especially chloride) penetrated through the crack is very important. In the case of reinforced concrete, crack widths of 0.3 mm or less are generally acceptable and need not be repaired. If the crack width is 0.3 mm or more, epoxy resin with low viscosity should be injected to repair cracks. As a current technology, there is no structurally reliable repair method other than surface treatment for cracks with a crack width of 0.3 mm or less. In the design standard, the crack width is limited to 0.3 mm or less along with the predetermined concrete covering thickness at the time of designing in order to avoid troublesome crack repair work. When the stress acting on the concrete exceeds the tensile stress, cracks occur in any form and the total crack width in the tensile stress direction of the generated cracks is proportional to the tensile stress acting. Therefore, in order to reduce the size of the crack width and to avoid crack repair, it is necessary to arrange the reinforcing bars appropriately in the direction of tensile stress so that the cracks with a small crack width can be uniformly distributed at regular intervals. As shown in FIG. 6, the cracks in the lower concrete of the conventional double synthetic steel box girder bridges arranged in such a manner are uniformly distributed over the entire length at intervals of 1 to 2 m in the direction perpendicular to the throat, As expected, the crack width is less than 0.3 mm and the width of the lower concrete is small, so longitudinal cracks do not occur in the lower concrete but longitudinal cracks occur at the interface between the steel box girder abutment and the lower concrete.

The lower concrete is protected in the closed box and is unlikely to be exposed to water containing chloride. Therefore, it is practically not necessary to repair cracks to prevent moisture penetration. Therefore, the concept of the limitation of the crack width applied to the bottom plate concrete is practically meaningless in the lower concrete. Therefore, applying the method of laying the bottom plate slab to the lower concrete results from considering only the fact that the bottom plate slab and the lower concrete are both slab form, without considering the original reason for placing the reinforcing bars. Therefore, in order to maintain the continuity of the longitudinal reinforcing bars as in the case of the bottom plate slab, it is necessary to rethink the method of arranging the reinforcing bars so as to make it difficult to penetrate the lateral ribs and the vertical reinforcing materials as shown in Fig.

The present invention has been made in order to solve the problems of the background art described above, and it is an object of the present invention to improve the method of laying down a conventional lower concrete, which induces fine cracks requiring no maintenance by using the same laying method as in a bottom plate slab concrete, The present invention also provides an economical and structurally efficient method of constructing a double composite steel box girder bridge which can dramatically increase the efficiency of the operation and improve the structural efficiency of the lower concrete.

As a means for solving the above-mentioned problems,
A method of constructing a double composite steel box girder bridge including a steel box, a lower concrete of reinforced concrete material laid inside the steel box, and a vertical rib and a lateral rib provided on a lower flange of the steel box,
Wherein the transverse ribs are made of a long plate-shaped member in one direction to induce transverse cracks in the lower concrete, and the longitudinal reinforcing bars are discontinuously installed on the basis of the transverse ribs, ;
Applying a release agent to the lateral ribs;
A concrete casting / curing step for casting / curing the concrete for the lower concrete; And
And a crack repairing step of repairing the cracks occurring in the lower concrete by injecting a low viscosity epoxy resin into the upper part of the steel box before the bottom plate is installed. .
It is preferable to form a long notch in one direction on the upper side of the lateral ribs in the surface of the concrete in the concrete pouring / curing step.
It is further preferable that the method further comprises a delayed hardening agent application step of applying a delayed hardening agent to the surface of the steel box which is in contact with the lower concrete.
The present invention also provides a double composite steel box girder bridge constructed according to the above-described construction method of the double composite steel box girder bridge.

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According to the present invention, the longitudinal reinforcing bars of the lower concrete are discontinued at the lateral rib positions, and the notch, the releasing agent and the retarding hardening agent are suitably used to induce concrete shrinkage cracks having a crack width capable of repairing the longitudinal reinforcing bars discontinuity, It is possible to provide a double synthetic steel box girder bridge and a construction method which are economical and structurally improved in efficiency by improving the workability of reinforcing bars while minimizing deterioration of compression stress sharing performance of the lower concrete by repairing cracks.

1 (a) is a side view of a conventional three span duplex composite steel girder bridge.
1 (b) is a cross-sectional perspective view of a conventional open-form double composite steel box girder.
FIG. 2 is a load-strain diagram of a lower concrete according to a cyclic load test of a double composite steel box girder bridge. FIG.
FIG. 3 shows a state where a lower concrete reinforcing bar is disposed inside a conventional double synthetic steel box (when there is no lateral rib).
FIG. 4 is a cross-sectional view of a conventional double composite steel box girder, in which a transverse reinforcing member is installed outside the lower flange of a steel box to control the deflection of the lower flange in accordance with the placement of the lower concrete.
Fig. 5 is an internal view of a double composite steel box girder prior to placement of a lower concrete reinforcing bar to control the deflection of a lower flange when a lower concrete is laid using a conventional lateral rib and a vertical rib.
6 is a view for explaining a crack pattern occurring in a lower concrete of a conventional double composite steel box girder bridge.
7 is a side cross-sectional view showing a method of disposing a longitudinal reinforcement to induce transverse cracking along the transverse lateral ribs of the present invention and a notch installed;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method of constructing a steel box composite girder bridge according to a preferred embodiment of the present invention will be described with reference to the drawings.

FIG. 7 is a side cross-sectional view showing a method of arranging longitudinal bars and a notch provided to induce transverse cracking along the transverse lateral ribs of the present invention.

A method of constructing a steel box composite girder bridge according to the present invention is a method of constructing a composite box girder bridge comprising a steel box, a reinforced concrete bottom concrete placed in the steel box, a steel box composite girder bridge including a vertical rib and a lateral rib, This method is effective in improving the structural efficiency of the lower concrete by concentrating and repairing the cracks induced in the lower concrete to one place. With respect to the construction of the steel box composite girder bridge, the construction not described in the present invention such as the manufacture of a steel box, the mounting of a steel box composite girder, the construction of a bottom plate, It is not related to the technical features, so that the description thereof will be omitted and only the characteristic configuration of the present invention will be described.

The method of constructing the steel box composite girder bridge according to the present embodiment includes a step of laying, a step of applying a stripping agent, a step of applying a delayed hardening agent, a concrete casting / curing step, and a crack repairing step.

7, the vertical reinforcing bars 10 are disposed on the transverse ribs 1, as shown in the cross-sectional view of FIG. 7, in order to induce the lateral cracks to concentrate on the lower concrete, ) In a non-continuous manner. The arrangement of the transverse reinforcing bars (not shown) in addition to the longitudinal reinforcing bars can be arranged in the same manner as in the conventional technique.

As described in the background art, reinforcement is intended to induce uniform heat generation of a group of cracks having a small crack width. When the heat is discontinuously arranged on the basis of the lateral ribs, cracks are concentrated on the upper side of the transverse ribs . In general, the lateral ribs divide the lower concrete into uniform longitudinal lengths and are suitable as a position for inducing cracks because they form a kind of partition. In the present embodiment, the transverse ribs use a long plate-like member in one direction, and it is possible to induce cracks to occur along the transverse ribs by not providing the transverse rib studs as shown in Fig.

On the other hand, when the reinforcing bar arrangement method of the present invention for discontinuing the longitudinal reinforcing bars 10 is used, the length of the longitudinal reinforcing bars is shortened, and the reinforcing bars are not installed as they are passed through the through holes of the lateral ribs, It becomes easy. In other words, since the interval between the lateral ribs is about 5 m and the width of the lower flange is about 2 m, the maximum length of the lower concrete reinforcing bars of the present invention is about 5 m. Therefore, the conventional reinforcing bars The lower concrete reinforcing work of the present invention is relatively easier.

In the step of applying the release agent, the release agent (20) is applied to the lateral rib (1) before the concrete pouring / curing step to induce cracks to occur along the lateral ribs. Applying a release agent to the lateral ribs can help prevent cracks from concentrating along the lateral ribs by preventing adhesion between the lateral ribs and the concrete.

The retarding curing agent applying step is a step of applying a retarding curing agent 30 to a portion of the lower flange 2, abdomen or the like which is in contact with the lower concrete among the steel boxes, and weakens the adhesion force between the steel and concrete at the beginning of curing, So that the width of cracks in the reinforcing discontinuity portion (the upper portion of the lateral rib) is increased. The reason for using delayed hardening agent is that the delayed hardening agent does not generate an adhesive force at the initial stage of curing but the adhesive force develops after a lapse of time. On the other hand, if high-strength concrete is used for the lower concrete, the shrinkage is too large to cause undesirable transverse cracks between the transverse ribs and transverse ribs in addition to the transverse cracks induced in the transverse ribs. Thereby reducing the adhesive force between the lower concrete and the steel box so that the intended large cracks can be concentrated on the lateral ribs.

The concrete pouring / curing step is a step of pouring and curing the concrete 40 for the lower concrete. At this time, a long notch 41 is formed in one direction on the upper side of the lateral rib 1 in the surface of the concrete 40. The notch 41 serves as a groove as shown in FIG. 7 to guide the notch 41 to concentrate the lateral cracks and to extend the depth of the notch just above the lateral ribs have.

The notch 41 can be formed in such a manner that a thin plate with a release agent is inserted into the top of the concrete and the concrete is removed after it is hardened.

The crack repairing step is a step of repairing the cracks generated in the lower concrete by injecting a low viscosity epoxy resin (not shown) into the cracks before the bottom plate is installed on the upper part of the steel box.

Although the shrinkage strain of concrete increases with time, the crack width of the lower concrete is the largest before the bottom plate concrete is put into the concrete, so that the compressive strain due to the bottom plate concrete load and the secondary high static load such as packing and barrier are much larger. It is most effective to repair the crack immediately before it. The cracks of the lower concrete according to the present invention are repaired by a low viscosity epoxy resin injection method. Since crack length is short and the number of the cracks is small, the epoxy resin is injected from the top to the bottom so that the work is easy and the maintenance cost is very low . On the other hand, it is possible to measure the width of the crack before the repair of the crack, so that the increase of compressive stress sharing ability of the lower concrete can be evaluated.

As described in the background, the longitudinal tensile stress due to the constraint of the shrinkage of the lower concrete by the steel box girder substantially compensates the compressive stress sharing ability of the lower concrete which dominates the structural efficiency of the double composite girder. Conventionally, the width of the crack generated in the lower concrete by the tensile stress due to the shrinkage is controlled to a crack width that does not require crack repairing, which is specified in the design standard, so as to avoid crack repair work. In the present invention, By allowing the lower concrete to receive more compressive stress as much as the stress corresponding to the deformation of the crack width, by injecting cracks with a crack width of 0.3 mm or more so as to be able to repair cracks and to repair cracks with low viscosity epoxy resin, And the effect of increasing the structural efficiency of the concrete can be expected.

Since the crack repair is performed just before the bottom plate concrete placement, the initial shrinkage ratio of the lower concrete as well as the crack occurrence interval is an important factor, and the size of the crack can be predicted to some extent by calculation. However, since cracks in concrete are difficult to control originally due to the nature of the material, it is necessary to secure a large width of cracks at a desired position by adding safety means. To this end, a release agent 20 is applied to the lateral ribs 1 The notch 41 is formed, and the delayed curing agent 30 is also used.

According to the present invention, it is possible to use any high-strength cast-in-place concrete in a lower concrete which can only use concrete having a compressive strength of 40 MPa or less due to excessive shrinkage strain. The use of high strength concrete in the lower concrete increases the rigidity of the lower concrete, so that the lower concrete can have more load sharing, which increases the structural efficiency and economic efficiency of the double composite steel box girder.
Hereinafter, one embodiment of the double composite steel box girder bridge according to the second aspect of the present invention will be described.

Since the double composite steel box girder bridge according to the present embodiment is a double composite steel box girder bridge constructed by the above-described construction method of the double composite steel box girder bridge, the construction method has already been described. Therefore, It is possible to carry out the engineer, so that further explanation will be omitted.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, The present invention can be embodied as a method of constructing various types of steel box composite girder bridges within the scope of the technical idea of the present invention.

1: transverse rib 2: lower flange
10: longitudinal reinforcement 20: exfoliating agent
30: retarding hardener 40: concrete

Claims (4)

A method of constructing a double composite steel box girder bridge including a steel box, a lower concrete of reinforced concrete material laid inside the steel box, and a vertical rib and a lateral rib provided on a lower flange of the steel box,
Wherein the transverse ribs are made of a long plate-shaped member in one direction to induce transverse cracks in the lower concrete, and the longitudinal reinforcing bars are discontinuously installed on the basis of the transverse ribs, ;
Applying a release agent to the lateral ribs;
A concrete casting / curing step for casting / curing the concrete for the lower concrete; And
And a crack repairing step of repairing the cracks occurring in the lower concrete by injecting a low viscosity epoxy resin into the upper part of the steel box before the bottom plate is installed. .
The method according to claim 1,
Wherein a long notch is formed in one direction on the upper side of the lateral ribs of the surface of the concrete in the concrete pouring / curing step.
3. The method of claim 2,
Further comprising the step of applying a retarder to the surface of the steel box which is in contact with the lower concrete.
A steel box girder bridge constructed by a method of constructing a double composite steel box girder bridge according to any one of claims 1 to 3.



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