JP2008057323A - Exposed steel frame plinth structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exposed steel frame plinth structure capable of realizing reduction in material costs by reasonably miniaturizing component members and capable of avoiding abrupt collapse of a building and being applied to a wide variety of buildings, by well balancing loads distributed to plinths and columns as a whole at the time of an earthquake and effectively using the bearing force of the component members to prepare for the collapse of the building. <P>SOLUTION: In the exposed steel frame plinth structure, a column member 1 is designed to have a height ratio of point of contraflexure of 0.3-0.6 via the steel frame plinth structure of an exposed type, a plasticizing member 8 which yields to a bending moment acting on the column member 1 before an anchor bolt 5 and is plasticized is interposed between a base plate 4 and the bottom end of the column member 1, and the height from the top face of the base plate 4 up to the joint section 9 of the plasticizing member 8 and the column member 1 is set to 1.5 times the diameter or the length of a side of the column member 1 or more. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  In the present invention, in the event of a large earthquake, before the yielding of the anchor bolt, plasticization starts reliably at the lower part than the joint part of the column base metal with the column material, and the seismic energy is efficiently absorbed. The present invention relates to a steel structure exposed column base structure.

  In the seismic design of a building structure, a structural design is performed to prevent collapse of a building against a rare large earthquake by absorbing seismic energy by plastic deformation of any structural member. When an exposed column base structure is used as the column base structure of a building structure, the structural members that can be selected as the structural member that first plasticizes and absorbs the seismic energy during an earthquake are anchor bolts, column base hardware, or column materials. One of them.

By the way, by forming a cross-sectional defect at the rising part formed at the upper part of the base plate and making the proof strength of the cross-sectional defect equal to the design proof strength of the column, the base plate that constitutes the column base metal is made plastic during an earthquake, etc. There is known a technique that reliably guides between a cylinder and a pillar material (see Patent Document 1). In this prior art, a case where a groove portion having a width of 8 mm and a depth of 4 mm is formed as a cross-sectional defect portion formed in the rising portion of the column base metal is illustrated. However, in order to absorb seismic energy, the plasticization caused by the bending moment acting on the column base is generally also in a fairly wide range. Although the initiation of plasticization can be guided to the groove, the plasticization region is small, so depending on the magnitude of the earthquake, it cannot absorb the seismic energy, but returns from the cross-sectional defect due to stress concentration. There was also a risk of occurrence. In addition, the height of the rising portion of the column base metal in the prior art is at most about half the width of the column material, and the welding position with the column material is also low. It was also easy to receive, and the possibility of fracture from the welded joint due to excessive stress concentration was also a problem. Incidentally, column base hardware is generally manufactured by forging or casting, but in the case of forging, it is technically difficult to manufacture a column base metal having a rising portion protruding above the base plate, Even if it can be manufactured, there is a technical problem in that the cost increases because the formation of the cross-sectional defect portion formed of a groove or a hole must be relied upon for machining. In addition, in the case of casting, it is necessary to have a gradient for extracting the column base metal as a casting from the mold, and similarly, the formation of a cross-sectional defect portion consisting of grooves and holes must be relied on machining, There was also a technical problem that the cost would increase.
Utility Model Registration No. 2567435

As another conventional technique, when a member having a lower cross-sectional performance than the column material is arranged between the bottom end of the column material and the base plate, and a bending moment exceeding a certain value acts, it precedes the column material, anchor bolt and base plate. A technique is known in which the low-section member yields and a plastic hinge is formed (see Patent Document 2). However, the column base structure adopted in this prior art is merely an improvement of the problem as a pin column base, and since the fixing degree of the column base is low, the bending moment acting on the column base is small. However, since the bending moment acting on the column head was large, the proof strength of the split column material had to be increased, which was expensive. Moreover, even if it is a pin column structure, a bending moment acts on the column base part in reality, which may cause one of the causes of building collapse in the event of a large earthquake. Therefore, the prior art can be applied to a large-span building having a wide span between columns to which the design method of the pin column base structure in which the bending moment acting on the column base does not become a big problem, and the like. The scope of application was very limited.
Japanese Patent Laid-Open No. 10-183759

  The present invention was invented in view of the conventional technical situation as described above, and distributes the load shared by the column base and column in a comprehensive manner in a well-balanced manner, effectively increasing the strength of each component. By making use of it to prepare for the collapse of buildings, it is possible to reduce the cost of materials by rationally reducing each component, and in addition to various buildings that can avoid sudden collapse of buildings An object of the present invention is to provide an exposed steel column base structure that can be widely applied.

  In the present invention, in order to solve the above-described problem, in a steel structure exposed-type column base structure in which a column member is erected by fixing a lower portion of a column member to a base plate fixed by anchor bolts fixed in foundation concrete. The column material is set so that the inflection point height ratio of the column material is 0.3 to 0.6 via the column base structure, and between the base plate and the lower end portion of the column material, With respect to the acting bending moment, a plasticizing member that yields and plasticizes before the anchor bolt is interposed, and the height from the upper surface of the base plate to the connecting portion between the plasticizing member and the column member is The technical means of setting at least 1.5 times the diameter of the column material or the length of one side was adopted. According to the present invention, a semi-fixed column base structure in which the inflection point height ratio of the column material is 0.3 to 0.6 is adopted as a basic structure, so that compared to a pin column base structure or a fixed column base structure In addition, the bending moment generated by the seismic action is distributed in a well-balanced manner between the column part and the column base part, and further, a plasticizing member that yields and plasticizes before the anchor bolt is interposed in the lower part of the column material. The base plate that constitutes the column and column base is constructed by shifting the part to the spindle type hysteresis characteristics, so that the ability to absorb seismic energy is greatly improved, and sudden collapse of the building due to seismic action can be avoided. In addition, it is possible to provide a column base structure that is capable of reducing the size of each component member such as the anchor bolt and the like, and having excellent seismic performance. Furthermore, in the present invention, the height from the upper surface of the base plate to the connecting portion between the plasticizing member and the column member is set to at least 1.5 times the diameter of the column member or the length of one side. A large absorption region can be secured, and it is avoided that an excessive force acts on the connecting portion between the plasticizing member and the column member and breaks from the connecting portion.

According to the present invention, the following effects can be obtained.
(1) In the present invention, a semi-fixed column base structure in which the inflection point height ratio of the column material is 0.3 to 0.6 is adopted as the basic structure of the column base part. Compared with the column base structure, the bending moment generated by the seismic action is distributed in a balanced manner between the column part and the column base part, and further, a plasticizing member that yields and plasticizes before the anchor bolt is interposed at the lower part of the column material. The column base is made to shift to the spindle-type hysteresis characteristics, so that the seismic energy absorption capacity is greatly improved and the sudden collapse of the building due to the seismic action can be avoided. Compared to the conventional fixed column base structure that realizes the spindle type by deformation, the structural components such as the base plate and anchor bolts can be reduced overall, and the seismic performance is excellent. Provide a column base structure It is possible.
(2) Moreover, the height from the upper surface of the base plate to the connecting portion between the plasticizing member and the column material is set to at least 1.5 times the diameter of the column material or the length of one side, and a wide plasticization region is formed between them. Since it is formed, a plasticized region having a large energy absorption capability is formed at the base portion of the column member to which a large bending moment acts during an earthquake, so that the seismic performance can be greatly improved.
(3) Further, the height from the upper surface of the base plate to the connecting portion between the plasticizing member and the column member is set to at least 1.5 times the diameter of the column member or the length of one side, and the connecting portion is set to the upper surface of the base plate. Because it is configured to be separated from the base part of the column material where the maximum bending moment acts at the time of an earthquake, the load acting on the connection part between the plasticizing member and the column material is reduced according to the bending moment gradient applied to the column base. Therefore, it is possible to reliably avoid the breakage from the connecting portion. By reducing the load acting on the connecting portion between the plasticizing member and the column member, it is possible to reduce the cost by reducing the size of the fixing means for the connecting portion.

  INDUSTRIAL APPLICABILITY The present invention is widely applied to a steel-frame-exposed-type column base in which the column material is erected by fixing the lower end portion of the column material to a base plate fixed by anchor bolts embedded in the foundation concrete. be able to. The column material can be applied to a circular or square shape. Moreover, it is not limited to the form of the anchor bolt itself or the fixing method. As the plasticizing member, it can be plasticized by yielding before the anchor bolt with respect to the bending moment acting on the column material, and any member having a predetermined strength may be used. It may be the one used or a different material. For example, it is formed into a circular or square pipe shape by hot working using the same material as the column material, or it is formed by cold working using the same material as the column material and then processed by heat treatment What removed the hardening etc. is possible. Moreover, what was formed in the predetermined shape by the casting which does not produce work hardening may be used. In the case of this casting, it may be formed integrally with the base plate. Incidentally, if the plasticizing member is made of a material having a large deformation such as a hot rolled material and having a yielding shelf, the ability to absorb seismic energy can be made higher.

  FIG. 4 is an explanatory diagram showing the relationship between the fixed state of the column base and the bending moment applied to each part. (A), (B), (C) in a figure is a schematic diagram according to the fixing state of a column base part. As shown in the figure, in a state where the lower part of the column 1 is fixed to the foundation concrete 2 via the column base structure corresponding to the fixed state and the upper part is fixed to the beam 3, for example, a horizontal force is applied to the beam 3 for the experiment. In consideration, when the height H from the lower part of the column 1 is taken on the vertical axis and the bending moment M is taken on the horizontal axis, a bending moment diagram like the bold line shown in the figure is obtained. Point C in the figure is an inflection point. At this height position, the bending moment is zero, and the sign of the curvature of the column bending curve changes. It has been found that the bending moment diagram takes various forms as in (A) to (C) depending on the fixed state of the lower part of the column, that is, the column base structure.

  Next, three forms of the column base structure will be described. Generally, the column base structure of a building structure is roughly classified into a fixed column base structure and a pin column base structure. In the fixed column base structure, an embedded column base or a rooted column base is generally adopted, and the fixing degree of the column base is high. As shown in FIG. The inflection point height ratio at the inflection point C, that is, the height Hc of the inflection point C / the height Hs of the column 1 is 0.6 or more. By the way, the exposed column base can also be configured as a fixed column base structure by setting the thickness and size of the base plate that makes up the column base, the diameter of the anchor bolts and the number of installation bolts to be sufficient. However, it may lead to an increase in the size of the column base and the construction cost may be high. On the other hand, the pin column base structure is easier to construct than the fixed column base structure and has the merit that the foundation can be made smaller. In this pin column base structure, the column base is regarded as a pin by design, but there are almost no actual column bases having a complete pin base structure. As this pin column structure, for example, as shown in FIG. 5A, anchor bolts 5 for fixing the base plate 4 to the foundation concrete 2 are arranged in the vicinity of the surface position of the column member 1 or slightly inward. However, it is a form adopted when the degree of fixation is low. In the column member 1 using this pin column structure, the bending moment at the time of earthquake is distributed to the state shown in FIG. 4C, and the inflection point height ratio Hc / Hs in this case is about 0. 0. The bending moment acting on the column base is small and can be applied to a large span building structure with a wide column interval.

  In addition to the above, there is a semi-fixed column base structure as an intermediate column base structure between the fixed column base and the pin base. As this semi-fixed column base structure, for example, as shown in FIG. 5 (B), there is a form in which a relatively small number of anchor bolts 5 are arranged on the base plate 4 outside the column member 1. The inflection point height ratio Hc / Hs is about 0.3 to 0.35. In addition, as shown in FIG. 5C, there is a form in which the number of anchor bolts 5 is increased to increase the degree of fixation, and reinforcing ribs 6 are provided on the base plate 4. In this case, the inflection point height ratio Hc / Hs is about 0.4 to 0.5. The bending moment in these semi-fixed column base structures is almost distributed to the state shown in FIG.

  From the above, in the semi-fixed column base structure where the inflection point height ratio Hc / Hs is 0.3 to 0.6, the bending moment borne by the column base is smaller than that of the column head, and accordingly, The proof stress of the anchor bolt 5 which comprises a column base part can be set small compared with a fixed column base structure. That is, it is possible to reduce the diameter of the anchor bolt 5 or to reduce the number of installations to reduce the size of the column base or to reduce the construction cost. However, if the anchor bolt 5 having a lower proof strength than the column material 1 is used, the hysteresis characteristic with respect to the bending moment acting on the column base when an excessive horizontal force is applied due to a large earthquake or the like becomes a slip type. Energy absorption is poor and the anchor bolt 5 may be broken, which may cause a sudden collapse of the building. Therefore, in the present invention, the hysteresis characteristic of the column base is obtained by interposing a plasticizing member that tends to yield and plasticize before the anchor bolt 5 against the bending moment acting on the column base at the bottom of the column 1. Is precisely shifted to the spindle type, thereby avoiding a sudden collapse of the building due to the breakage of the anchor bolt 5, which is characterized in that respect. In other words, a semi-fixed column base structure having an inflection point height ratio Hc / Hs of 0.3 to 0.6 is adopted to reduce the load on the anchor bolt 5 constituting the column base portion and to reduce the size of the member. In addition, it is characterized in that the history characteristic of the column base portion is accurately shifted to a spindle type by applying a plasticizing member to avoid sudden collapse of the building due to an excessive load caused by an earthquake.

  FIG. 6 is an explanatory diagram illustrating the behavior at the time of an earthquake related to the spindle-type exposed column base structure, and FIG. 7 is an explanatory diagram schematically showing the hysteresis characteristics of the column base portion. In FIG. 7, the relationship between the bending moment M on the vertical axis and the rotation angle θ on the horizontal axis is as shown in the conceptual diagram of FIG. Therefore, in the case of the exposed column base structure related to the spindle type, when the bending moment Ma acts on the base portion, that is, in the vicinity of the coupling portion between the column member 1 and the base plate 4 via the column member 1 in the event of an earthquake, 6, the base portion of the pillar material 1 is greatly deformed as in the state B from the state A and the base portion of the pillar material 1 is plasticized before the anchor bolt 5 is plasticized. That is, when the base portion of the column member 1 starts to be deformed by the action of the bending moment Ma, first, it is elastically deformed in the first half, and when it exceeds the elastic region, it is plasticized to reach the state B. Next, when a reverse bending moment Mb is applied, the column 1 is deformed in the opposite direction to reach the state C. The deformation process from the state B to the state C will be described with reference to FIG. 7. In the first half, the elastic deformation is first restored from the deformation state shown in the state B, and subsequently the elastic deformation due to the bending moment Mb is made. . Then, when the elastic region is exceeded in the latter half, it becomes plastic, and it reaches a state C inclined past the vertical state of state A while being plastically deformed. As described above, the hysteresis characteristic in the exposed column base structure according to the present invention is a spindle type, so that the fastening nut 7 of the anchor bolt 5 is lifted from the upper surface of the base plate 4 in the middle like a slip type. The process in which the seismic energy is not absorbed without the load being transmitted is not involved. Therefore, in the case of the exposed-type column base structure according to the present invention, the seismic energy absorption is very good, and the earthquake resistance of the structure that prevents the building from being suddenly collapsed against a large earthquake by absorbing the seismic energy. It is very effective from the viewpoint of performance. Further, it is possible to avoid a situation in which the fastening nut 7 of the anchor bolt 5 is lifted from the upper surface of the base plate 4 and the fixing force with respect to the pillar material 1 is lost.

By the way, as the column material 1, various materials, such as a cold-rolled material, a welding assembly material, and a shaped steel, are used. In general, cold-rolled materials that are often used have variations due to work hardening. Therefore, the actual proof stress is 10 kgf than the design standard strength (so-called standard strength “F value”) of the column 1 used in the design. / Mm ² sometimes exceeded, and the following problems were caused by the difference in mechanical properties of the individual components. In other words, if the column material 1 is designed to be plasticized first if the actual proof stress of the column material 1 is too high as expected, the deformation of the column material 1 actually remains within the elastic range, and there is a margin. Excessive load is transmitted as it is to the column base without any part, and the hysteresis characteristics of the column base shift to the slip type. In the worst case, the anchor bolt 5 breaks or the foundation concrete 2 breaks down. There was a problem that could cause a sudden collapse of the building. Therefore, in the prior art, in order to surely realize the so-called spindle type hysteresis characteristic shown in FIG. 7, it is necessary to make the plastic proof strength of the column base part sufficiently large. There was a tendency to become oversized. On the other hand, in the case of the exposed column base structure according to the present invention, the plasticizing member that yields prior to the anchor bolt 5 with respect to the bending moment acting on the column member 1 is used as described above. Since it is interposed in the lower part, not only can the spindle-type hysteresis characteristics be realized more accurately, but also the plastic proof strength of the column base can be improved compared to the conventional fixed column base structure in which the column 1 itself is plastically deformed. It is also possible to set a smaller value.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration explanatory view showing an embodiment of the present invention, and FIG. 2 is an enlarged longitudinal sectional view showing a part of the column base metal. As shown in the figure, in this embodiment, a plasticizing member 8 is integrally formed on the upper surface of a base plate 4 constituting a column base metal by welding or the like, and an end portion of the column member 1 is connected to an end portion of the plasticizing member 8. And a column base structure in which the column material 1 is erected with respect to the basic concrete 2 through the base plate 4 is adopted. At the site, after anchor bolts 5 are embedded and fixed at predetermined positions of the foundation concrete 2, the bolt holes of the base plate 4 are aligned with the upper ends of the anchor bolts 5, and the base plate 4 is temporarily attached by the tightening nuts 7. By tightening and fixing to the upper surface of the foundation concrete 2, the pillar material 1 is erected at a predetermined position. Thereafter, the level of the base plate 4 is further adjusted so that the pillar material 1 is vertically erected, and the grout material 10 is filled between the foundation concrete 2 and the base plate 4. After the grout material 10 is solidified, the base plate 4 is finally tightened by the tightening nut 7, so that the column material 1 is reliably erected at a predetermined position.

  As shown in FIG. 2, in the present embodiment, the height Hp of the plasticizing member 8 is set to a dimension that is 1.5 times the diameter of the column member 1, that is, the plasticizing member 8 itself, or the length D of one side, The case where it connects to the lower end part of the column 1 by welding is shown. Incidentally, in the present invention, as described above, the height Hp to the connecting portion 9 between the columnar member 1 and the plasticizing member 8 is set to at least 1. of the diameter of the columnar member 1, that is, the plasticizing member 8, or the length D of one side. It is characterized by being set to 5 times. The grounds for deriving the height of the plasticizing member 8 are obtained from the results of experiments and their analysis. If the diameter or length of one side of the column 1 is D, the height range of the plasticizing member 8 from the upper surface of the base plate 4 to approximately 0.3D to 0.5D is constrained by integration with the base plate 4. In actuality, the region above the constrained region functions as a plasticizing region, and plastic deformation occurs. On the other hand, needless to say, if a large bending moment acts on the welded portion, the possibility of fracture from the welded portion increases. In the present embodiment, by combining them, the height Hp of the connection portion 9 between the welded portion, that is, the column member 1 and the plasticizing member 8, is set to a height of at least 1.5D from the upper surface of the base plate 4. While avoiding the fracture | rupture from a welding part avoiding the root part to which a big bending moment acts, it comprised so that a sufficient plasticization area | region could be ensured in the lower part of the column material 1. FIG. That is, below the connecting portion 9 between the plasticizing member 8 and the column 1, a remarkably large plasticized region of 1.5 times the diameter of the column 1 or the length D of one side is formed. Therefore, it is possible to sufficiently absorb seismic energy during a large earthquake. By the way, when the results of the experiment are combined, plasticization starts from 0.8 times the length of the column 1 or the length D of one side or equivalent, and the plasticization expands vertically. As the vertical width for expanding the plasticization, if the plasticization region of the diameter of the column 1 or the length D of one side is secured in the vertical direction, it can sufficiently cope with the absorption of earthquake energy of a considerably large earthquake. I can confirm that I can do it. Therefore, according to the present embodiment, the connecting portion 9 between the plasticizing member 8 and the column 1 is 1.5D apart from the upper surface of the base plate 4 including 1D as the vertical width for expanding plasticization. Therefore, the seismic energy can be sufficiently absorbed, and the bending moment acting on the connecting portion 9 is reduced, so that the breakage from the connecting portion 9 can be avoided.

  FIG. 3 is an explanatory diagram for explaining a process in which plastic deformation occurs in the plasticizing member 8 constituting the rising portion of the column base metal by the horizontal force acting on the column member 1. This figure shows the bending moment M on the horizontal axis and the height H on the vertical axis, and the straight line m represents the added state of the bending moment when a horizontal force is applied to the column 1. The straight line a is the ultimate strength of the column base, that is, the ultimate strength of the anchor bolt 5, the straight line b is the total plastic bending strength of the plasticizing member 8 constituting the rising portion of the column base metal, and the straight line c is the total plastic bending strength of the column 1. It represents. Here, according to one design example, those straight lines m and straight lines a to c are shown. A straight line m representing a bending moment when a horizontal force is applied to the column member 1 is shown as a straight line composed of a moment gradient α with the bending point zero as a reference point and a horizontal moment acting on the column member 1. As the force increases, the bending moment also increases, and the moment gradient α increases with the inflection point C as a reference point. As shown in the figure, when the straight line m intersects the straight line b, the plasticizing member 8 starts to be plasticized by a bending moment as shown by hatching. However, in the plasticizing member 8, the height range from the upper surface of the base plate 4 to about 0.3D to 0.5D is actually plasticized by the restraint due to the reinforcing action based on the integrity with the base plate 4. Although not likely to occur, this point is omitted in this explanatory diagram. When the horizontal force acting on the column material 1 further increases, the moment gradient α with respect to the inflection point C as a reference point further increases, and when the straight line m eventually intersects the straight line a, the load is applied to the column base part. The ultimate proof strength, that is, the ultimate proof strength of the anchor bolt 5 is reached and the anchor bolt is destroyed. However, the amount of energy absorbed by the plasticizing of the plasticizing member 8 is large so far, and the building is resistant to a considerably large earthquake. It becomes an effective means that can avoid sudden collapse of the.

  Incidentally, as the material of the steel material used in the above embodiment, a cold roll forming square steel pipe (BCR295) for a building structure is used for the column material 1, and a cold press forming square steel pipe for a building structure is used for the plasticizing member 8 ( BCP235) can be employed. In this case, when the yield values of the two are compared, the plasticized member / column material = 235/295 = 0.8, and the yield ratio is 1 or less. Since both strengths are equal, the maximum yield strength will not decrease. As the steel material to be selected, those having the same tensile strength and different yield values are suitable, but are not limited. It is also effective to use a hot-formed square steel pipe (SHC400) as the plasticizing member 8. This is because a cold-formed material retains residual stress during plastic processing during manufacture, and thus yield ratio is high and elongation is reduced, resulting in a decrease in plastic deformation ability. On the other hand, the hot-formed material has almost the same plastic deformation ability as that of the raw material because the effect of plastic strain due to the initial cold working is almost eliminated by hot rolling. It can be said that it is suitable for absorption.

It is schematic structure explanatory drawing which showed the Example of this invention. It is the longitudinal cross-sectional view which expanded and showed the part of the column base metal object of the Example. It is explanatory drawing for demonstrating the process in which plastic deformation arises in the plasticizing member which comprises the rising part of a column base metal object by the horizontal force which acts on a column material. It is explanatory drawing which showed the relationship between the fixed state of a column base part, and the bending moment added to each part. It is explanatory drawing which illustrated the method of fixing a base plate. It is explanatory drawing which illustrated the behavior at the time of the earthquake regarding a spindle-shaped exposed type column base structure. It is explanatory drawing which showed roughly the log | history characteristic of the same column base structure. It is the conceptual diagram which showed the relationship between the bending moment M and rotation angle (theta) in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Column material, 2 ... Foundation concrete, 3 ... Beam, 4 ... Base plate, 5 ... Anchor bolt, 6 ... Reinforcement rib, 7 ... Clamping nut, 8 ... Plasticizing member, 9 ... Connection part, 10 ... Grout material

Claims (1)

  In a steel exposed type column base structure in which a column material is erected by fixing the lower part of the column material to a base plate fixed by anchor bolts fixed in the foundation concrete, the column material via the column base structure The inflection point height ratio of 0.3 to 0.6 is set between 0.3 and 0.6, and between the base plate and the lower end of the column member, the anchor bolt causes a bending moment acting on the column member. A plasticizing member that yields and plasticizes first is interposed, and the height from the upper surface of the base plate to the connecting portion between the plasticizing member and the column member is at least the diameter of the column member or the length of one side. Steel structure exposed column base structure characterized by being set to 1.5 times.

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