JP3104679U - Braceless reinforced concrete construction - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a feeling of openness of windows and the like and to make the appearance of a building clear even when a steel frame is externally reinforced and externally reinforced, and that a large horizontal load is repeatedly applied due to an earthquake or the like. Even in this case, the state where the existing RC structure and the steel frame are integrated can be maintained as long as possible.
SOLUTION: An H-shaped steel frame 3 is attached to an existing RC column 5 and an existing RC beam 8 located on the outer wall surface. However, the framework is not provided with braces. The H-shaped steel column 4 attached to the existing RC column 5 is selected to have a bending rigidity substantially equal to that of the existing RC column 5.
As a result, when a horizontal load is applied from the existing RC beam 8 or the H-shaped steel beam 6 due to an earthquake or the like, the existing RC column 5 and the H-shaped steel column 4 are deformed to the same extent, and additionally generated at a joint portion between the two. Stress as small as possible.
[Selection diagram] Fig. 1

Description

  The present invention relates to a braceless reinforced concrete reinforced concrete structure. More specifically, a steel frame is attached to a reinforced concrete structure having an opening such as a window by integrating a steel frame to strengthen a RC building with poor seismic performance. It is related to a seismic retrofit building.

  When reinforcing RC buildings with poor seismic performance, a method of increasing the column size is often adopted. This is performed in such a manner that an existing RC column 50 shown in FIG. 12A is surrounded by reinforced concrete 51 as shown in FIG. 12B or an iron plate 52 is wound as shown in FIG. 12C. However, this is limited to cases where the construction can be performed on all sides, such as a pier.

  As another reinforcing method, a method using a braid is used. This reinforcing method can be applied to a case where a school building, an apartment house, an office building, or the like having columns that cannot be encircled on all sides is reinforced from the outer wall surface. That is, a lattice structure composed of columns and columns and beams connected to the right and left between the columns is intended to be strengthened by braces.

  However, in the existing RC structure, it is impossible to directly bridge the brace between the RC column and the RC beam, so a frame structure is introduced. FIG. 13A shows an internal type using a steel frame 54 having a brace 53 attached thereto, and FIG. 13B shows an external type in which a steel frame 55 is mounted on the outside of a wall surface. Such steel frame braces are currently mainstream due to the short construction period and little increase in weight. Among them, the external construction method without removing the windows, waist walls, and sagging walls of the existing building has been remarkably increasing due to the fact that the construction period can be significantly shortened.

  Japanese Unexamined Patent Publication No. Hei 11-193639 discloses an external construction method of this kind, and describes that the construction is facilitated. In such a reinforcement structure, the stability of the steel frame is obtained by arranging the braces. That is, the steel frame is applied to the existing RC columns and the existing RC beams by applying them from the outside, and the braces are attached to the steel frames, so that the reinforcing effect of the braces extends to the RC structure.

  According to this, there is an advantage that construction can be performed while living. Also, in old apartment buildings where the outer surface is often monotonous, an H-shaped steel frame appears on the outer wall to give a sharp impression, or to give a moderate accent to the color, and to modify the design. May also contribute. Further, if a double-pipe steel pipe brace having an extremely small outer diameter (for example, refer to Japanese Patent Application Laid-Open No. 11-193570) is adopted, a light feeling can be exhibited in the building from its smart appearance.

  The reason that the braces are inserted into the steel frame is that the steel frame is softer (easy to deform) than the existing RC columns and the like. Therefore, it is recognized that the framework without the braces has an extremely weak effect as the reinforcement of the RC structure. It does not come off because there is. That is, in the building industry at present, there is a widespread idea that braces are absolutely indispensable for reinforcing RC structures.

  By the way, if a brace is used, the steel frame forming the frame does not need to be strong, and therefore a small cross section may be used. On the other hand, it is important to improve the performance of the brace to be incorporated, and it can be said that the present situation is that efforts are being made to devise and develop this point.

  As can be seen, the framework is a foothold for the attachment of the brace and, at best, only functions as an aid for the attachment of the brace. The steel frame is softer than the RC frame, and it is not possible to reinforce the RC structure with the steel frame. As described above, it is indispensable to interpose a brace for reinforcement. It is common sense.

  By the way, in the case of the brace structure, the stress of the brace is transferred to the steel column or beam to which the brace is attached. However, the brace structure has extremely high horizontal rigidity, for example, 50 to 100 times as compared with the rigid frame type structure. . By the way, in a building, since a floor slab usually restrains a beam in a building, deformation of the RC structure 56 subjected to a horizontal load mainly occurs at the RC column 57 as shown in FIG.

  However, as shown in FIG. 13B, when the steel frame 55 is attached to the RC frame 56, the steel frame frame has higher rigidity than the RC frame, so that it bears more horizontal force than the RC frame. become. By the way, as can be seen from FIG. 15, the horizontal force is intensively transmitted to the RC beam 60 at a portion other than the column / beam intersection, for example, at the gusset plate 59 a fixed only to the steel beam 58. In this case, the stress transmission from the steel frame 55 to the RC beam 60 has a distribution as indicated by the arrow B starting from the gusset plate 59a, and it is understood that the load on the stud dowel or the like described below locally increases.

  The steel frame 55 and the RC columns 57 and the RC beams 60 are integrated by placing a mortar or concrete after the chemical anchors and the stud dowels are arranged in the joint spaces facing each other. If the difference in the horizontal force borne by the difference in the horizontal rigidity between the steel frame column 61 of the steel frame frame 55 reinforced by the brace 53 and the RC column 57 of the RC structure 56 is large, an unreasonable force is applied to concrete or the like filling the joint space. That is, the exchange of force by the chemical anchor or the like becomes large, and the joint site is damaged. If the joint site is damaged, the reinforcing function of the framework is diminished.

  The brace itself, when used to reinforce a multi-family housing, is of course industrially refined, but if it is just outside the window, it will be annoying and hinder the sense of openness. No. It is inevitable that unfairness will occur between the doors of a single building and a section where a brace cannot be attached, and it is also in this respect that seismic retrofitting of apartment buildings is mostly untouched. Has been done.

Incidentally, when the brace is incorporated into the steel frame, the use of the gusset plate 59 is inevitable. At this time, the vicinity of the attachment portion of the gusset plate 59a to the steel beam 58 must be reinforced more strongly by using more steel than the gusset plate 59b at the intersection. Older buildings that require seismic reinforcement are often short-span, so the framework is often smaller. In that case, it cannot be denied that there is an uneconomical aspect in that the secondary usage rate of the steel material such as the gusset plate and the reinforcing plate is increased in the division of the amount of steel frame used.
JP-A-11-193639

  The present invention has been made in view of the above-mentioned problems, and its purpose is to avoid the installation of braces, to prevent the opening feeling of windows and the like, and to make the appearance of the building clear even when externally reinforced by a steel frame. Even if a large horizontal load is repeatedly applied due to an earthquake or the like, the existing RC structure and the steel frame are maintained as integrated as long as possible, thereby reinforcing the steel frame until it collapses. Brace that doubles the horizontal strength, avoids early collapse in the event of a large earthquake, minimizes the use of secondary steel materials, and promotes simplification and cost reduction of seismic reinforcement work. The purpose is to provide a reinforced concrete structure without seismic reinforcement.

  The present invention is applied to a reinforced concrete structure which is subsequently reinforced by a steel frame integrated with an outer surface having an opening such as a window. The feature of this is that, with reference to FIG. 1, the steel frame is an H-shaped steel frame 3 attached to existing RC columns 5 and existing RC beams 8 located on the outer wall surface without braces. The H-shaped steel frame had a flexural rigidity that was only 30% to 300% of the size of the existing RC column 5, that is, a flexural rigidity that was much smaller than that of an equivalent-sized steel frame having braces. An H-shaped steel column 4 is provided. When a horizontal load is applied from the existing RC beam 8 or the H-shaped steel beam 6 due to an earthquake or the like, the existing RC column 5 and the H-shaped steel column 4 are deformed to the same extent, and at the joint 9 between the two (see FIG. 2). In addition to suppressing the additional stress as much as possible, while suppressing the subsequent deformation even if the existing RC column 5 yields, the pseudoelastic deformation region of the existing RC column / H-shaped steel column composite 10 is H-shaped. The steel column 4 is secured to a level comparable to that of the steel column 4 and its horizontal strength is increased.

  As shown in FIG. 2A, it is preferable that the H-shaped steel column 4 be a welded H-shaped material whose web 4w is moved to the existing RC column side. Further, as shown in (b), the H-shaped steel column 4 attached to the existing RC column 5 is welded with a hoop reinforcement 22 on the outer surface side of the web 4w, and a mortar or concrete 24 is cast with the main reinforcement 23 assembled. By doing so, the bending rigidity is enhanced.

  The low yield point steel is adopted for the H-shaped steel column 4, and only the yield strength is reduced without lowering the bending rigidity of the reinforcing column, and the yield starts by about 2 to 4 times of the existing RC column 5. In addition, it is necessary to reduce the response stress by promoting plasticization during a large earthquake.

  As shown in FIG. 9, on the outer surface side of the web 4 w of the H-shaped steel column 4, an indoor RC beam 26 </ b> A connected to the existing RC column 5 to which the H-shaped steel column 4 is attached and extending in the front-rear direction perpendicular to the outer wall surface. Alternatively, the ends of the legs 25a of the T-shaped steel member 25 having a T-shape when viewed in a plan view are connected so as to be continuous above and below all floors at a position where they are aligned with the earthquake-resistant wall 26B, and three-dimensional reinforcement of the building is performed.

  The overhang amount of the T-shaped steel material 25A is set to the same length as the width of the veranda 27 of each house.

  As shown in FIG. 11C, the width of the indoor RC beam 26A or the RC beam on the existing earthquake-resistant wall is increased by embedding the unbonded PC steel bar 31 in the high-strength fluidized concrete 30 or mortar on the side surface. The expanded beam 32 is provided, and a post-tension is applied to the unbonded PC steel bar to secure a desired beam end bending moment, thereby enhancing horizontal strength.

  According to the present invention, since an H-shaped steel column to be attached to the existing RC column is selected to have a bending rigidity substantially equal to that of the existing RC column, both can be horizontally deformed to the same extent. . In the joint space between the existing RC column and the H-shaped steel column, the generation of additional stress due to the difference in mutual deformation is suppressed as much as possible, and the force exchanged via chemical anchors etc. is minimized. .

  As a result, the state where the existing RC structure and the steel frame are integrated is maintained as long as possible, and the horizontal strength is doubled by the reinforcing action by the steel frame until the building collapses. Can be avoided. In addition, the deformation range of the H-shaped steel columns exhibiting elastic behavior is larger than that of the existing RC columns, and the progress of damage to the existing RC columns that should have already yielded is suppressed until the H-beams yield. . In this manner, if the seismic energy absorption while the concrete side is broken can be delayed, the damage to the RC structure can be reduced, and the degree of repair can be reduced.

  The use of braces can be avoided so that no obtrusive objects appear in the windows, and the appearance of the building can be kept clean by placing H-shaped steel frames within the existing widths of the columns and beams. The feeling of unfairness due to the presence or absence of the frame is removed, and it becomes easier to obtain approval for seismic retrofitting of apartment buildings and tenant buildings, and the construction can be started earlier.

  If the brace is pinned to the gusset plate, the gusset plate may require a significant thickness, but such a gusset plate is not required because the brace is eliminated. If the gusset plate is not provided, it is not necessary to reinforce the web of the H-shaped steel beam to which the gusset plate is attached. Older buildings with shorter spans will eliminate this kind of secondary steel, which has been used in high proportions, which will help to reduce the cost of seismic reinforcement.

  If the web of the H-shaped steel column is arranged close to the existing RC column, it becomes easier to match the bending rigidity of the existing RC column. As a result, if the joint space becomes narrower, it is easy to align the H-shaped steel beam with the web of the H-shaped steel beam whose cross section is smaller than that of the H-shaped steel column, and the horizontal force acting on the H-shaped steel frame is transmitted. It also has an excellent structure.

  As the facing distance of the joint space becomes smaller, the distance of the exchange of the force at the joint part becomes shorter, and it becomes difficult for an excessive force to act on the structural material at the joint part. If the burden of power is reduced, the use of secondary materials such as anchors for joining can also be reduced. In addition, the amount of extremely expensive high-strength non-shrink mortar to be cast is greatly reduced, and simplification of the structure in this area and reduction of input materials are required, and rationalization and cost reduction, which are indispensable for work execution, are achieved.

  If hoop reinforcement is welded to the outer surface of the web of the H-shaped steel column and mortar or concrete is cast with the main reinforcement, even if the bending rigidity seems to be insufficient due to the web being moved to the existing RC column, Can be added to the existing RC columns.

  If a low yield point steel is adopted for the H-shaped steel column, only the yield strength is reduced without lowering the bending stiffness of the H-shaped steel column, and the yield starts at about 2 to 4 times that of the existing RC column. Can be. As a result, plasticization during a large earthquake can be promoted to reduce the response stress.

  If the leg end of T-shaped steel is welded to the center of the outer surface of the web of the H-shaped steel column, and it is provided so as to be connected vertically on all floors, seismic reinforcement in the front-rear direction and reinforcement in the vertical direction are also made. Combined with the horizontal reinforcement along the outer wall surface, reinforcement in the x, y, z triaxial directions can be achieved at once.

  If the leg length of the T-shaped steel material is adjusted to the amount of overhang of a veranda that is continuous for each floor of an apartment house or the like, more powerful seismic reinforcement can be applied in the front-back direction of the building using the space of the veranda.

  A high-strength fluidized concrete or mortar is cast on both sides of the existing RC beam connected to the earthquake-resistant wall to form a wide beam and post tension is applied with an unbonded PC steel bar to secure the desired beam end bending moment. Thus, the horizontal strength in the front-rear direction of the building can be doubled.

  Hereinafter, the braceless reinforced concrete structure according to the present invention will be described in detail based on its embodiments. In this method, a steel frame is attached to an outer wall surface of a reinforced concrete structure having an opening such as a window and integrated, thereby strengthening the RC structure later. It is needless to say that the construction can be carried out while using such a reinforcing form, but it should be particularly noted in the present invention that the H-shaped steel column of the H-shaped steel frame has a size substantially equal to that of the existing RC column made of concrete. A material having a high bending rigidity is selected.

  That is, the bending rigidity within the range of 30% to 300% of the existing RC column is provided, and it is not necessary to employ an extremely large brace structure whose bending rigidity is 50 to 100 times that of the existing RC column. That is. Therefore, the H-shaped steel column attached to the existing RC column has only a bending rigidity that can be regarded as substantially the same size as the existing RC column as compared with the bending rigidity of the brace structure.

  FIG. 1 shows a state in which an H-shaped steel frame 3 is attached to an outer wall surface of a section where a window 2 is present at a certain floor in the middle of RC structure 1. It has no braces as described above. Of the H-shaped steel frame 3, a steel frame 4 forming a column is attached to an existing RC column 5 located on an outer wall surface, and a steel frame 6 forming a beam extends in the left-right direction of the existing RC column 5 and extends vertically from an outer wall 7 or the like. It is only attached to the existing RC beam 8 that supports it including the load.

  The H-shaped steel frame 3 composed of the H-shaped steel columns 4 and the H-shaped steel beams 6 is a rigid steel frame having the same strength as that reinforced by the braces just because it does not have the braces. It is not what you are trying to do. The special consideration is taken that the H-shaped steel column 4 attached to the existing RC column 5 is selected to have a bending rigidity of substantially the same size as the existing RC column. It should be noted that the steel column (which is much softer than the braced frame) that is deformed to the same degree as that of the RC frame is trying to reinforce the RC structure.

  In summary, when a horizontal load is applied from the existing RC beam 8 or the H-shaped steel beam 6 due to an earthquake or the like, the existing RC column 5 and the H-shaped steel column 4 are deformed to the same extent. The difference between the resulting bending deformation and the bending deformation generated in the H-shaped steel column 4 is reduced, and the stress additionally generated at the joint portion 9 shown in FIG. 2A is suppressed as small as possible. I can do it.

Not only that, even if the RC column 5 yields at the horizontal displacement of δ _RC shown in FIG. 3A, the deformation after that is suppressed and the elastic horizontal deformation δ _H of the H-shaped steel column 4 becomes comparable. A large pseudoelastic deformation region S which is a polygonal line of the existing RC column / H-shaped steel column composite 10 but can be regarded as a substantially straight line is secured. In addition, the horizontal proof stress is drastically increased as described later.

  That is, in the existing RC columns 5 and the steel columns 4 having the same bending rigidity, the yield strength bending stress of the steel frame is considerably larger, so that the seismic performance after reinforcement can be increased at least three to four times. In normal reinforcement, it is better if the horizontal strength of the existing RC column is nearly doubled, but in the present invention, it far exceeds that and the brace is omitted to secure the opening as before. The H-section steel frame is housed within the width of existing concrete columns and beams, and there is almost nothing else.

  Referring to FIG. 2A, the H-section steel frame 3 is integrated with the existing RC columns 5 and existing RC beams 8 by using chemical anchors 11, stud dowels 12, spiral hoops 13 and high-strength non-shrink mortar 14. Is done. By the way, in a normal building, since a floor slab restrains a beam, deformation when a horizontal load is applied mainly occurs on a column as described in FIG.

  If the H-shaped steel beam 6 is integrated with the existing RC beam 8 and the bending stiffness of the H-shaped steel column 4 is matched to or close to that of the existing RC column 5 as described above, it is shown in FIG. As described above, the H-shaped steel column 4 is also deformed in the same manner as the existing RC column 5, and the difference between the two deformation amounts can be minimized. If this is the case, the stress exchanged via the chemical anchor and the stud dowel at the joint 9 (see FIG. 2) is kept to a minimum.

  That is, even if a horizontal load is applied due to an earthquake or the like, a large additional stress is prevented from being generated at this joint, and a horizontal load acting on one side between the steel frame and the RC frame is applied to the other and vice versa. Will be transmitted without difficulty. With such a ramen steel frame, unlike the brace structure described in the related art, the shear force can be exchanged over the entire length of the beam, so that the load on the stud dowel or the like is evened out.

  If this is shown in the figure, the steel frame 3 which is considered to be soft will undergo almost the same deformation as the RC frame 1 as shown in FIG. The joining structure can be simplified, and it becomes easy to rationalize the entire construction from design to construction. In addition, if the H-shaped steel column 4 attached to the existing RC column 5 has a size within 30% to 300% of the existing RC column 5, preferably 40% to 250%, the above rigidity can be obtained. It was confirmed in the study of the inventor that almost the same deformation was given as described above.

  The idea that braces are indispensable is now pervasive in the construction industry, as soft structures like steel cannot reinforce concrete structures. However, the present invention aims to eliminate the brace. Although the brace can be finished smartly by adopting a double steel tube shape, it is still an obstacle. In that sense, the elimination of braces will make it easier for the world to accept seismic retrofitting, and will promote seismic retrofitting in untouched buildings.

  If the brace is gone, you don't need a gusset plate to attach it. Smart brace appearances often use a pinned configuration, but the gusset plate used in the pin-supported configuration is thicker. Further, the web on the side of the H-shaped steel to which such a gusset plate is attached must be reinforced even in the form of a backing plate. Without braces, no such reinforcement is needed.

  In particular, an old building, particularly an old-type apartment house 15 shown in a plan view in FIG. 4A, generally has a short span and a small steel frame for earthquake resistance. When the brace structure is applied to the seismic reinforcement, the use ratio of the above-mentioned reinforcing material to the H-shaped steel as the main reinforcing material becomes so high that it cannot be ignored.

  In other words, secondary hand marks will appear everywhere. However, in the case of a braceless structure, the use ratio of such a reinforcing material is extremely close to 0 without limit, and the structure is simple and looks good. improves. In some cases, the appearance can be summarized so that it is difficult to determine whether or not it is reinforced.

  The present invention realizes the integral deformation and integral behavior of the existing RC structure / steel frame composite, preventing unnecessary force from acting on the joint, and consequently suppressing the deformation of the existing RC column while increasing the elastic deformation area. Secure large. In addition, the horizontal strength of the reinforcing structure is dramatically increased by a steel frame having a large strength by nature. There is no point in having a brace interposed in such a steel frame any longer, and the braceless reinforcement of RC structures is achieved only after this knowledge is obtained.

Here, one calculation example based on the model 16 in FIG. 5 will be described based on the model 16 in FIG. 5 to support the realization of the H-shaped steel column having the bending rigidity equal to that of the existing RC column described above and to enhance the strength. Assuming that the cross section of the existing RC column 5 is 60 cm × 60 cm, the second moment of area I is as follows.
^{I = 60 × 60 3/12} = 1,080,000cm 4

It is known that, in the design at the time of an earthquake, a small crack can generate a secondary moment of area of about 70% of I even at an allowable proof stress (elastic limit). Therefore, its _IRC is:
I _RC = 1,080,000 cm ⁴ × 0.7 = 756,000 cm ⁴

Based on this, the yield strength (yield moment) of the existing RC column is obtained as follows. Reinforcing bars are used, the total cross-sectional area a _t is 17.02Cm ^2, allowable stress f _t is a 2.4t / cm ^2. Stress center distance j and bending yield strength _RC M _y in this case is as follows.
j = 7d / 8 = 7/8. (60-5.0) = 48.1 cm
_{∴ RC M y = a t ·} f t · j
= 17.02 x 2.4 x 48.1 = 19.65 tm

Next, the H-shaped steel columns 4 will be determined. Its aspect is 40 cm × 40 cm, the flange thickness t _f = 2.5 cm, when the web thickness tw = 1.6 cm, the second moment I _S is as follows.
^{_{I S = 20 2 × 2.5 ×}} 40 × 2 + 1.6 × 40 3/12
= 88,533cm ⁴
When steel and concrete Young's modulus ratio and 10, equivalent moment of inertia of _eq I _S concrete is as follows.
_eq I _S = 88,533 × 10 = 885,330 cm ⁴
This is approximately equal to I _RC = 756,000 cm ⁴ determined above.

From this, the yield strength of the H-shaped steel column 4 is determined. _S M _y / _RC M _y section modulus Z _s and bending yield strength _S M _y further becomes as follows.
Z _S = 88,533 / 20 = 4,427 cm ³
_{S M y = 4,427 × 2.4 =} 106.2t · m
_{S M y / RC M y =} 106.2 / 19.65 = 5.4
Therefore, if sufficient stud dowels and chemical anchors are installed to transmit the strength of this H-shaped steel column, the horizontal strength of the column will be increased to 6.4 times that of the existing RC column by adding the above 5.4 to 5.4. Can be raised theoretically.

  Since the Young's modulus of iron is about ten times that of concrete, there is no particular problem in obtaining a column having the same flexural rigidity as concrete, as can be seen from the calculation examples. Although concrete and H-beams have very different qualities, their behavior in the elastic range is the same. When the bending stiffness is the same, the H-shaped steel has a higher yield strength in bending than RC, and thus basically has almost elastic strength.

As can be seen from FIG. 3A, if the horizontal strength of the existing RC column 5 is 1, the H-shaped steel column 4 of the reinforcing frame is about 5.6 as ordinary steel. At least it is elastic. It will be iron borne to the horizontal displacement amount [delta] _H corresponding thereto, damage to the concrete remains in that range. If the yield strength is low, concrete has to share the force, so the displacement is large and the RC column is severely damaged. In the present invention, the steel frame suppresses the damage of the concrete so that it does not easily progress even after yielding of the concrete.

  Conversely, since the H-section steel has an elastic behavior, there is a great merit that the concrete is less likely to break down due to this. In the conventional structure, the seismic energy was absorbed while being damaged, including the concrete. However, in the present invention, the damage of the concrete is suppressed as much as possible, and the subsequent repair is also easy.

  As described above, the bending rigidity of the H-shaped steel column attached to the existing RC column may be set to 30% to 300% of the existing RC column. In particular, it is better that the bending stiffness of the existing RC column is larger, but 250% is sufficient if suppression of steel consumption is considered. If the degree is set to such an extent on the large side, the effect of suppressing the occurrence of cracks in concrete even after exceeding the elastic limit of the RC column 5 is exhibited.

  On the other hand, if it approaches the smaller side, that is, 0%, it means that there is no reinforcement, so it is necessary to keep it at 30% at most. This is because even the reinforcement by the steel frame having only about 30% of the bending rigidity of the existing RC column may be sufficient when the RC structure is lightly aged. In any case, since the bending strength of the steel frame is significantly larger than that of concrete, it greatly contributes to reinforcement of RC columns. As a result, it is possible to reduce the damage to the concrete and guide the load to the foundation, thereby suppressing early instability of the building.

By the way, if a low yield point steel (σ _y = 1.5 t / cm ² ) is used for the H-section steel column 4, the yield strength is not reduced as shown in FIG. Only the bending strength can be reduced to about 1/2. The yield moment according to the above calculation example can be reduced from about 5.4 times to about 2.7 times the RC column 5.

  In that case, the yield can be started about two to four times the existing RC column, plasticization at the time of a large earthquake is promoted, and the response stress to the earthquake can be reduced. That is, the seismic energy is absorbed by a large plastic deformation with respect to an excessive force, and the proof strength is not suddenly reduced at that time, so that collapse at a stretch can be reduced as much as possible.

  This is because, if the yield strength of H-shaped steel columns is excessively high, there is no problem with the strength-type reinforcement applied to many low-rise buildings, but there is no problem with the toughness reinforcement for high-rise buildings. Often becomes. In order to clear the problem in the latter case, it is significant to reduce the yield strength as described above.

  FIG. 3 shows the load-displacement relationship in the horizontal direction when the RC column and the reinforced H-column have the same bending stiffness. As can be seen from the above description, the ordinary steel H-shaped column 4 has As shown in (a), the range in which the elastic behavior is exhibited is extremely large, and a large displacement is required before plasticizing after receiving a large earthquake.

  On the other hand, in FIG. 3B, yielding starts about three times as much as the existing RC columns, and plasticization can be promoted relatively early in the case of a large earthquake. It is known that the response to an earthquake can be significantly reduced by appropriately plasticizing, and the low response stress makes it easy to design the building foundation and other structural parts, and promotes highly economical design. Is a big positive factor.

  As mentioned above, making the bending stiffness equivalent is the basis of the present invention, but this also promotes the rationalization of the joining portion. FIG. 6 shows the relationship between the load and displacement in the horizontal direction corresponding to FIG. 3 when the bending rigidity of the H-shaped steel column 4 is extremely different from that of the RC column 5. Is largely compressed. In this case, the existing RC column / H-section steel column composite is not formed, which indicates that each of them is displaced and deformed independently. Therefore, there is no way to obtain a two-dot chain line N drawn by applying the load-displacement of the H-shaped steel column to the load-displacement of the RC column in a manner similar to the broken line in FIG.

  Next, the idea of the present invention is further extended. As shown in FIG. 7, the chemical anchor 11 is driven into the RC column 5, and the H-shaped steel column 4 is attached to the chemical anchor. The portion where the RC column 5 is exposed may be covered with an H-shaped steel column as shown in (a), or the H-shaped steel column 4 may face the surface as shown in (b). The protrusion of the H-shaped steel column is minimized, and only the narrow facing space 9A is filled with the high-strength non-shrink mortar.

  As described above, when the H-shaped steel column 4 approaches the existing RC column 5, the stud dowel is not required. In some cases, the bending rigidity can be made equivalent even with a reinforcement structure having a small amount of overhang, in which case a large amount of material is consumed for the rigid frame structure, but the consumption of secondary materials is significantly reduced. Moreover, the construction cost is reduced by half since the steel frame structure is simplified, and extremely low-cost construction is realized.

Incidentally, the connection axis of member direction of H-section steel column 4, the bending moment M ₅ of RC Columns 5 shown in FIG. 8 may be carried out at 0 and a position (inflection point position). That is, the bending moment at the intermediate position between the upper beam 6u and the lower beam 6d is M ₄ = 0 for the H-shaped steel column 4 like the RC column 5. The plate 17 welded to the lower end of the H-shaped steel column 4 faces the plate 17 attached to the upper end of the other H-shaped steel column, and both plates are fastened with high tension bolts 18.

  Returning to FIG. 7, when the H-shaped steel column 4 is to be fixed to the chemical anchor 11 fixed to the RC column 5, for example, as shown in (c), a stupid hole 19 is formed in the web 4 w of the H-shaped steel column 4. Can be opened. This is to ensure a gap 19a capable of absorbing a relative displacement of the chemical anchor with respect to the H-shaped steel column. After positioning the H-shaped steel column 4 with respect to the RC column and tightening it with the nut 20, the outer washer 21 can be welded to the web 4w to prevent the H-shaped steel column 4 from shifting.

  In the structure described so far, even if the H-shaped steel frame 3 is a roll-formed H-shaped steel having a web 4W drawn by a two-dot chain line in FIG. Any of the welded assembly materials can be used. However, in the latter case, since the position and length of the web 4w can be freely selected, the shape of a non-standard rolled H-section steel can be easily obtained.

  Therefore, even if standard products of rolled H-beams mass-produced for H-beams are adopted, if the flexibility of web selection is increased by using welded H-beams for the H-beams, the mounting target is It becomes easy to obtain an H-shaped steel column having a bending rigidity equivalent to that of the RC column 5. As shown in FIG. 2A, if the web 4w is moved toward the RC column, the facing space 9A becomes narrower, and the consumption of the expensive high-strength non-shrink mortar 14 can be suppressed.

  As the facing distance between the RC column 5 and the H-shaped steel column 4 decreases, the strength and bending stiffness of the joining portion are increased, which is extremely convenient. In addition, the H-shaped steel beam 6 can be centered with the web 6w, and the horizontal force can be transmitted to other H-shaped steel beams without unnecessary shearing force or moment. However, if there is a possibility that the bending rigidity becomes insufficient, as shown in FIG. 2B, the hoop reinforcement 22 is welded to the outer surface side of the web 4w, and the mortar or concrete 24 is cast with the main reinforcement 23 assembled. Thereby, room for enhancing the bending rigidity can be secured.

  The above reinforcement is applied to the case where the horizontal force acts from the x direction of the building as shown in FIG. However, in an old building to be reinforced, the interior is separated by a wall extending in the y direction, and the area as a living space is often insufficient. In many cases, the y-direction, that is, the front-back direction of the building, is designed so as to oppose the horizontal force by an indoor RC beam or a shear wall, so that it is often impossible to remove the wall to enlarge the room.

  Front-to-back reinforcement is usually done by adding shear walls or thickening existing walls, which makes the room even smaller. Therefore, in the present invention, as shown in FIG. 9, on the outer surface side of the web 4w of the H-shaped steel column 4, a steel material 25 having a T-shape as viewed in a plan view is provided so as to be continuous on all floors. The T-shaped steel member is welded to the H-shaped steel column 4 at a position where the leg 25a is continuous with the existing RC column 5 and is aligned with the indoor RC beam 26A or the earthquake-resistant wall 26B orthogonal to the outer wall surface.

  When the T-shaped steel member 25 is provided, the H-shaped formed by the web 4w of the H-shaped steel column 4 and the T-shaped steel member 25 functions as a seismic reinforcing column in the front-rear direction (y direction in FIG. 4A). I will do it. Since the H-shaped steel column 4 itself functions as a seismic strengthening column in the left-right direction (x direction), and the T-shaped steel material 25 is passed from the ground to the top floor although it has a reinforced structure, the x , Y, z are achieved in three dimensions. In addition, as shown in FIG. 4B, the T-shaped steel member 25 is attached to not only the front outer wall but also the rear outer wall of the building.

  In a case where a continuous veranda is provided on each floor of an apartment house or the like, reinforcement in the front-rear direction can be performed by using the space width of the veranda in a partition portion of each door or the like. That is, as shown in FIG. 4 (b), the legs 25a of the T-shaped steel material 25A are set to the same length as the width of the veranda 27, and the T-shaped steel material 25A is placed on a handrail 27a (FIG. See also).

  In this case, it is often not enough to simply attach the H-shaped steel column 4 to the outer surface of the RC column 5, and it is desirable to reinforce the indoor RC beam 26A and the earthquake-resistant wall 26B. FIG. 10 shows that T-shaped steel members 25 are attached to the front (left side in the figure) and the rear (right side in the figure) of the living space 28 on one floor, respectively. In such a case, as shown in FIG. 11C, reinforcement is applied to the indoor RC beam 26A that supports the floor slab 29 as necessary.

  11A corresponds to a cross section taken along line AA in FIG. 11C, and FIG. 11B corresponds to a cross section taken along line BB in FIG. As shown in (c), the high-strength fluidized concrete 30 or mortar is additionally struck on the side surface of the indoor RC beam 26A to form the widened beam 32. If post-tension is applied to the indoor RC beam 26A by tightening with the unbonded PC steel bar 31 after curing, a desired beam end bending moment is secured, and as a result, a necessary horizontal strength is obtained. If even one of the earthquake-resistant walls can be removed by such reinforcement, the internal space can be expanded.

The completion drawing which applied the steel frame of the H-shaped steel frame which applied the braceless seismic reinforcement reinforced concrete construction concerning this invention to the outer wall of a building. The mounting structure of an H-shaped steel frame is shown, (a) is a sectional view in which a welded H-shaped steel is used as a steel column, and (b) is a cross-sectional view when the bending rigidity of the steel column is increased. The horizontal deformation of the column is expressed with respect to the horizontal load. (A) is a load-displacement diagram when ordinary steel is used as the H-shaped steel column, and (b) is a low yield point steel for the H-shaped steel column. Load-displacement diagram when used. FIG. 2 is a plan view of an existing apartment house having a number of rooms partitioned by earthquake-resistant walls, where (a) is an example of a braceless seismic retrofitting structure for RC construction adapted to horizontal loads in the left and right direction, and (b) is T This is an example of a brace-less seismic retrofitting structure for RC construction that uses a shaped steel material to cope with horizontal loads in the longitudinal direction. A strength calculation model based on a braceless RC structure for RC construction. The load-displacement diagram in the horizontal direction when H-shaped steel columns with different bending stiffness are attached to existing RC columns. This is an integrated structure when the H-shaped steel column and the existing RC column are approached. (A) is a structural diagram when the H-shaped steel column is covered on the RC column. (B) is an H-shaped steel column. And (c) is a view showing how to fix an H-shaped steel column to a chemical anchor. Explanatory drawing of arrangement | positioning of the connection part of an H-shaped steel column at a reflex point. Sectional drawing of the mounting structure in which a T-shaped steel material is provided on the outer surface of the web of an H-shaped steel column. The seismic wall reinforcement structure figure which surrounds the living space when a T-shaped steel material is attached. (A) is a cross-sectional view taken along line AA in (c), (b) is a cross-sectional view taken along line BB in (c), and (c) is a cross-sectional view taken along line BB in (c). Is a sectional view of an interior RC beam supporting a floor slab. 4A and 4B are cross-sectional views of a RC column, FIG. 4B is a cross-sectional view of the RC column in which the periphery thereof is reinforced with reinforced concrete, and FIG. (A) is an installation drawing when a steel frame is internally attached, and (b) is an installation drawing when it is externally attached. The deformation due to the horizontal load of the existing RC structure and the steel frame attached to it is shown, (a) is an explanatory diagram of the behavior of the RC column and the RC beam in the RC structure, and (b) is the same deformation of the existing RC column and the steel column. FIG. The behavior diagram showing the stress transmission when the steel frame with the brace is externally attached to the RC structure.

Explanation of reference numerals

  DESCRIPTION OF SYMBOLS 1 ... RC construction (RC frame), 2 ... Window, 3 ... H-shaped steel frame (steel frame frame), 4 ... Steel frame (H-shaped steel column) to form a column, 4W, 4w ... Web, 5 ... Existing RC column , 6 ... steel frame (H-shaped steel beam) forming beam, 7 ... outer wall, 8 ... existing RC beam, 9 ... joining site, 10 ... existing RC column / H-shaped steel column composite, 22 ... hoop bar, 23 ... Main bar, 24 ... concrete, 25, 25A: T-shaped steel, 25a: leg, 26A: indoor RC beam, 26B: earthquake-resistant wall, 27: veranda, 30: high-strength fluidized concrete, 31: unbonded PC steel rod, 32 ... Widening beam.

Claims (7)

In a reinforced concrete structure reinforced afterwards by a steel framework integrated into the outer surface having an opening such as a window,
The steel frame is an H-shaped steel frame attached to existing RC columns and existing RC beams located on the outer wall surface without brace,
The H-shaped steel frame has a flexural rigidity that is only 30% to 300% of the existing RC column, that is, an H-shaped steel frame having a much smaller flexural rigidity than that of an equivalent-sized steel frame having braces. With shaped steel columns,
When a horizontal load is applied from an existing RC beam or H-shaped steel beam due to an earthquake or the like, the existing RC column and the H-shaped steel column are deformed to the same extent, and the additional stress generated at the joint between them is minimized. In addition to suppressing the deformation, even if the existing RC column yields, the subsequent deformation is suppressed, and the pseudoelastic deformation area of the existing RC column / H-shaped steel column composite is secured until it is comparable to that of the H-shaped steel column. Braceless seismic reinforced concrete structure with increased strength.   The braceless seismic reinforced concrete structure according to claim 1, wherein the H-shaped steel column is a welded H-shaped material whose web is brought to the existing RC column side.   The H-shaped steel column attached to the existing RC column is welded with a hoop reinforcement on the outer surface side of the web, and the bending rigidity is enhanced by driving mortar or concrete with the main reinforcement assembled. The braceless seismic retrofit reinforced concrete structure according to claim 1 or 2.   The H-shaped steel column is a low yield point steel, and only the yield strength is reduced without lowering the bending stiffness of the reinforcing column, and the yield starts when the bending strength is about 2 to 4 times that of the existing RC column. The braceless seismic reinforced concrete structure according to any one of claims 1 to 3, wherein plasticity during an earthquake is promoted, and response stress at that time is reduced.   On the outer surface side of the web of the H-shaped steel column, at a position where the H-shaped steel column is aligned with an interior RC beam or an earthquake-resistant wall that is connected to an existing RC column and extends in the front-rear direction orthogonal to the outer wall surface, The T-shaped steel member having a T-shape in a plan view is connected so as to be continuous above and below all floors, and the building is three-dimensionally reinforced. Braceless seismic reinforced concrete reinforced concrete construction described in section.   The reinforced concrete structure according to claim 5, wherein the overhang amount of the T-shaped steel material is the same as the width of a veranda or the like of each house.   The indoor RC beam or the RC beam on the existing earthquake-resistant wall is a widened beam whose width is increased by embedding an unbonded PC steel rod in high-strength fluidized concrete or mortar on the side surface, and posts the post on the unbonded PC steel rod. 7. The braceless seismic reinforced concrete structure according to claim 6, wherein the horizontal strength is enhanced by providing a desired beam end bending moment by applying tension.