JP6021497B2 - Composite structural beam - Google Patents

Description

  The present invention relates to a composite structural beam that is installed between columns and joined to the column as a structural member that forms the frame of the structure. Specifically, the present invention relates to a beam in which at least one of the left and right ends is made of reinforced concrete and the other part or the center is made of steel frame, and one member has different structural types.

  There are various types of structures such as reinforced concrete structures, steel structures, steel reinforced concrete structures, and steel pipe concrete structures, but there are characteristics such as the size and use of the structures and the required performance. Accordingly, it was common for a single construction type to be used for one construct.

In recent years, reinforced concrete structures with excellent economic efficiency and durability have been applied to a wide range of buildings, from low-rise buildings to high-rise buildings, in conjunction with the development of high-performance water-reducing agents. On the other hand, steel structures have the advantage of being easy to assemble on-site and can be constructed quickly, and are widely used as structures suitable for large span frames and high-rise buildings.
However, the cost of steel frames is often increased due to the high price of steel, and the rigidity is lower than that of reinforced concrete, so that there is a drawback that deformation during an earthquake tends to increase.

  On the other hand, in reinforced concrete construction, it is difficult to secure a large space by expanding the span because the concrete is weak against tensile force. In order to secure a span of 10 m or more in reinforced concrete construction, use a tension material in the beam. It was necessary to increase the bending strength of the end and center of the beam by introducing prestress. Recently, however, composite beams have been developed that combine the advantages of steel and reinforced concrete.

  For example, Patent Document 1 was developed for the purpose of expanding the span of a reinforced concrete structure, and is a composite structural beam composed of a reinforced concrete structure at both ends joined to a column, and a steel structure using H-shaped steel between them. Is disclosed. In such a beam, there is a problem in that stress concentration is likely to occur because the material strength, rigidity, shape, and size of each of the embedded portions where different kinds of structural members are joined are different.

In order to solve this problem, in Patent Document 1, two axial bars (fixing bars) arranged in the direction of the material axis of the reinforced concrete part on the steel flange are moved up and down for the purpose of smoothly transferring the stress between the steel frame and the reinforced concrete part. Flared welded to the flange of the steel, the steel frame end is securely fixed to the reinforced concrete part.
Reinforced concrete at both ends of the beam increases the rigidity of the entire beam, and the central part where the moment is large is a steel frame to ensure bending strength, and a rational structure that realizes light weight, such as offices, factories, warehouses, etc. Applicable to buildings for use.

    However, since it is difficult to manage the welded portion of the fixing bar and inspection is necessary, the welding operation must be performed in the factory in advance. In addition, if the shaft flange such as the beam main bar and anchor bar is welded to the steel flange in advance, the beam length that must be taken into consideration during transportation becomes longer. There was also a problem in carrying in to the site, such as a limit on the number of bottles.

  Therefore, in Patent Document 2, a joint structure beam in which a joint portion such as a long nut or a coupler is welded to a flange at the end of a steel frame in advance, and the rebar (main bar) is screwed and mechanically joined after being brought into the field. Has been proposed.

Japanese Patent Publication No. 07-65381 JP 2007-291636 A

However, in the composite structural beam described in Patent Document 2, the outer diameter of the long nut or coupler to be welded to the steel flange is larger than the diameter of the main bar. A level difference occurs between the main reinforcing bars and the main reinforcing bars (fixing bars) fixed to the steel frame cannot be directly bound to the shear reinforcing bars.
For this reason, there exists a possibility that it may become disadvantageous on the fixing performance of the fixing muscle which plays the role which mainly transmits the tensile force of a steel-frame flange to concrete. In addition, due to the arrangement of the reinforcing bars, the beam crosses the orthogonal beam main bars within the column beam joint, so that it is necessary to get in the way when the beam is installed or to change the position (level) of the beam main bars.

  In addition, when it is desired to make the slab thicker or when a tension material is provided on the upper end of the beam to form a prestressed concrete structure, the unreinforced region above the upper flange may become large in the cross section of the reinforced concrete portion. In order to reinforce this non-barbed area, it is necessary to arrange reinforcing bars called additional striking bars in both the vertical and horizontal directions separately from the bar and floor bar arrangements.

  Further, since the position (level) of the fixing bar is determined by the cross-sectional dimension of the steel frame, the cross-sectional area of the reinforced concrete portion is limited. When it is desired to increase the rigidity of the reinforced concrete cross section and increase the rigidity and bending strength, it is necessary to provide a fixing bar separately from the main bar as in the conventional example shown in FIG. 4 without using both the main bar and the fixing bar. .

  The present invention is intended to solve the above-mentioned problems, and provides a composite structural beam that can be reliably and easily constructed without previously joining a main reinforcing bar to a steel frame embedded in a reinforced concrete part to be joined to a column. With the goal.

In order to solve the above-described problems, the present invention provides a reinforced concrete portion in which at least one of the left and right ends is made of reinforced concrete, and the other portion is made of a steel frame portion, and the cross section of the reinforced concrete portion is caused by the steel frame portion. A larger composite structural beam, comprising an anchor bar that is embedded in and fixed to the reinforced concrete part, and has a role of transmitting the tensile force of the flange to the concrete, the level of the anchor bar However, it is possible to adjust between the upper and lower flange surfaces to the beam main bar position, and the extra length portions of the plurality of fixing bars which are bent at least at one end are formed in the steel frame portion embedded in the reinforced concrete portion. It is locked.
The axial reinforcement referred to here is a reinforcing bar arranged along the material axis direction of the beam in the reinforced concrete portion, and includes both the main reinforcement and the fixing reinforcement. The term “locking” means not only a state in which the shaft bar is securely fixed to the steel frame, but also a state in which the bent curved portion and the surplus portion at the end thereof are fixed to the steel frame with a binding wire or the like.

As shown in Patent Documents 1 and 2, a conventional general composite structural beam has a symmetrical shape in which both ends of a steel frame are embedded and fixed to a pair of reinforced concrete portions located at the ends of the material. However, the present invention is not limited to this, and includes a composite structural beam in which one end is reinforced concrete and the other is steel.
For example, a beam with an asymmetrical structure is constructed with a reinforced concrete core part that bears the seismic force acting on the building, and other parts such as a frame surrounding it and a frame facing the outside are made of steel frames. It is suitable for the case. If the span is not so large, there may be a semi-rigid joint in which the steel side is not rigidly joined but is joined to the steel column only by the web.

According to such a composite structural beam, there is no need to weld or mechanically fix the anchor bar to the steel frame, and only the bent bar is locked to the steel frame during normal bar arrangement work. It is easy to adjust the height and length of the muscles and can be constructed relatively easily.
Further, since the shaft bars are not attached at the factory, the length of the entire beam does not become long at the time of carrying in, so that the cost for transportation can be suppressed.

  An opening is provided in the flange of the steel frame, or a steel plate provided with an opening is fixed to the flange, and an extra length portion of the bent shaft reinforcement (main reinforcement, fixing reinforcement) is inserted into the opening. After inserting the upper and lower axis bars into the opening, the surplus length portion may be substantially parallel to the surface of the steel web, and the surplus length portions may be overlapped and bound.

  When opening an opening in a steel flange, in order to avoid the effects of cross-sectional defects, the position as close as possible to the end of the steel frame or the stress transmission area of the buried part (usually about 1.5 to 2 times the steel frame) should be removed. It is better to provide in the position. When a steel plate having an opening is fixed to the steel flange, the position (surface) may be either the upper or lower surface or the side surface of the flange as long as the strength higher than the force transmitted to the main bar can be ensured, and the fixing means is not limited.

  A screw rebar may be used for the bent shaft bars (main bars and anchor bars) and fixed to the flange of the steel frame or the steel plate with a nut. As a result, the extra length portion of the shaft is fixed to the steel flange, so that the force borne by the steel can be more smoothly transmitted to the reinforced concrete portion.

  The surplus length means the straight line portion beyond the end point of bending when the reinforcing bar is bent. However, when the diameter of the axis reinforcement (main reinforcement, anchoring reinforcement) is large or the slab is thin, it is assumed that the curved portion between the bending start point and the bending end point is locked to the steel frame. It is defined as the extra length part including the part.

  You may weld the said steel plate to the flange of the span center side (opposite end part) of the said steel frame part embed | buried. The anchor reinforcement does not stop at the end of the steel frame, but the reinforced concrete part becomes stronger by extending to the span side. Thereby, not only can the degree of fixation of the embedded portion be further increased, but also the effect of reinforcing the bearing pressure of the fixing portion is expected when a prestress is introduced by arranging a tension material on the upper end of the beam.

  According to the present invention, stress transmission between the steel frame portion and the reinforced concrete portion can be reliably performed, construction can be easily performed, and transportation restrictions can be reduced. In addition, because the cross section of reinforced concrete can be determined regardless of the steel frame, it is possible to increase the stress center distance j (main bar interval) to reduce the amount of beam main bars, reduce the diameter, or conversely the same main bars. Even in the amount, it is possible to increase the bending strength of the beam end.

It is an elevation sectional view showing the composite structure beam concerning Embodiment 1 of the present invention. It is AA 'sectional drawing of the composite structure beam shown in FIG. It is an elevation sectional view showing the composite structure beam concerning Embodiment 2 of the present invention. It is a figure which shows the conventional composite structure beam.

  The composite structural beam 7 according to the first embodiment of the present invention is a composite structural beam that is joined to a reinforced concrete column 6 standing up by a predetermined span and constitutes a building frame together with the plurality of columns 6. Specifically, both ends are composed of a reinforced concrete portion 2 made of reinforced concrete, and the central portion is made of a steel frame portion 1 made of steel frame, and designed for vertical loads that always act and horizontal loads during earthquakes. .

The steel part 1 having an H-shaped cross-section is embedded in the reinforced concrete part 2 for a predetermined length, but the position of the embedded part 3 (joint part) is generally 1/4 of the span in which bending stress during long-term loading is reduced. A place away from the pillar is about 1/5.
The length of embedding the steel frame portion 1 may be determined in consideration of the stress transmitted to the reinforced concrete portion 2, fixing means such as fixing bars and studs fixed to the steel frame portion 1, and the shear reinforcement method of the embedded portion 3. According to the results of experiments by the inventors, sufficient performance can often be exhibited at about 1.5 to 2 times the steel frame.

  Although FIG. 1 shows the end of the composite structural beam 7, the reinforced concrete portions 2 at both ends are rigidly joined to the reinforced concrete columns 6 standing on the floor slab, and together with the columns, an earthquake resistant frame is configured. The slab is formed in the upper part of the upper flange 11 of the steel frame, but is omitted in the drawing together with the reinforcement of the slab and the stud placed on the steel frame.

In the present embodiment, as shown in the cross-sectional view of FIG. 2, the beam main reinforcing bars 5 as axial bars are arranged in eight rows in the top and bottom, and two of the four upper bars and the lower bars are fixed anchors. 4 is also arranged. These axis bars are fixed at one end in the beam-column joint as in the normal beam main bar. However, if you want to bend and yield the beam end at an early stage in the event of an earthquake, the anchor bar 4 is placed inside the beam-column joint. In some cases, the reinforced concrete portion 2 is not fixed.
The other end of the fixing bar 4 which is an axial bar is engaged with the extra length part 41 of the fixing bar through the openings provided in the upper and lower flanges 11 and 12 at the end of the steel part 1 embedded in the reinforced concrete part 2. It has been stopped.

The size of the opening is slightly larger than the maximum diameter of the fixing muscle 4, but its position is farther than the assumed stress transmission region 31 (for example, 1.7 times the steel frame) in consideration of the effect of the cross-sectional defect. It is provided on the part side. At the time of bar arrangement, it is only necessary to overlap the extra length 41 of the upper and lower bars and bind them with a binding line. Therefore, the position (level) of the fixing muscle 4 can be easily adjusted, and it is easy to cope with a sudden design change. .
Even when the slab is thick, the fixing bar 4 can also serve as the beam main bar 5 and does not need to be provided separately. If the beam main reinforcing bars 5 are arranged at a position close to the upper end of the cross section, it is not necessary to separately provide additional reinforcing bars (not shown) as in the prior art.

  Further, if screw reinforcing bars are used for the fixing bars 4, the extra length portion 41 of the inserted fixing bars 4 can be reliably fixed to the steel frame 1 by sandwiching and locking the upper and lower surfaces of the flanges with nuts. In this case, as shown in FIG. 1, it is not necessary to provide a margin for overlapping the surplus length portions 41 of the upper and lower fixing muscles 4, and the surplus length portion 41 has the flange 11, the length necessary for screwing the nut. It suffices to protrude from the lower surface or the upper surface of 12.

  Since the bending strength of the reinforced concrete portion 2 depends on the size of the distance j (distance between stress centers) between the upper and lower main bars, it is easier to secure the bending strength than fixing the fixing bar 4 to the flange. . As a result, not only can the bending strength of the beam end be increased, but the diameter of the main bar 5 can be reduced, or the amount of main bar can be reduced to reduce the cost.

Next, as a second embodiment of the present invention, a method for locking the fixing muscle 4 without opening an opening in the flange will be described. For example, as shown in FIG. 3, it is also conceivable to weld and fix a steel material 42 ′ that hooks a bent portion of the fixing steel 4 and a steel plate 42 having an opening to the flanges 11 and 12.
In this case, you may provide in the stress transmission area 31, and it is not limited to the edge part of the embedded steel frame. Rather, it is conceivable that the installation near the span side (opposite side of the column) effectively restrains the steel frame at the boundary between the steel frame part 1 and the reinforced concrete part 2 and works in terms of stress transmission.
Further, the welding of the steel plate 42 and the steel material 42 ′ may be performed on either the side surface or the upper surface of the flange as long as it can bear the force transmitted from the steel frame to the fixing muscle.

In order to secure a larger span, a large bending strength is required at both ends of the beam, so it is assumed that prestress is introduced by placing a tension material in the direction of the material axis on the upper end side of the reinforced concrete part 2. The
If the detail is normal, the tendon is arranged in the vicinity of the flange. Therefore, if the fixing muscle 4 is in a position close to the span side, it also functions as reinforcement of the prestress fixing portion. Further, since the prestress is transmitted to the steel frame through the bent portion of the fixing muscle 4, it is considered that the degree of fixation of the steel frame portion 1 and the strength of the embedded portion 3 are also increased.

  As shown in FIGS. 1 to 3, shear reinforcement bars 21 are arranged around the beam main bars 5 at a predetermined interval, and the fixing bars 4 are also bound to the shear reinforcement bars 21. Although there are cases where the shear reinforcement bars 21 are densely or intensively arranged at both end positions of the embedded portion 3 in order to assist stress transmission and increase the degree of fixation of the steel frame, they are not shown here.

  In the first and second embodiments, the span side of the beam main bar 5 is bent in the same manner as the fixing bar 4, but the fixing method is not limited to this, and a plate or a hump is attached to the tip. It may be fixed in a straight state, or may be fixed on the concrete surface at the end of the embedded portion 3 by extending the main bar to the outside of the embedded portion 3.

  Similarly, the means for fixing the beam main reinforcement 5 to the reinforced concrete column 6 is not limited. In the beam-column joint, the beam reinforcement and the shear reinforcement from two orthogonal directions intersect inside the column reinforcement, and the bar arrangement is often complicated. However, if one direction is a composite structural beam 7 with a large span and the normal direction is composed of a reinforced concrete beam with a normal span, the beam will be different (the level of the main reinforcement) and the fit will be better, making it easier to place the bar. Become.

  As described above, the embodiment of the composite structural beam according to the present invention has been described in the case where both ends are made of reinforced concrete and the center is made of steel. However, the present invention is not limited to this embodiment, and it may be an asymmetric composite beam having one end portion made of reinforced concrete and the other end made of steel. Each element constituting the present invention can be appropriately changed without departing from the spirit of the invention.

  For example, in the above-described embodiment, eight main bars constituting the axial bars are used, and four of the main bars are fixed bars, and the extra length portions are inserted into the steel flange and locked. As long as sufficient force can be transmitted between them and the necessary structural performance can be exhibited, the number can be reduced. There is no need to make the diameter of the fixing muscle equal to the diameter of the other main muscle, and the diameter and strength (yield point) may be determined according to the magnitude of the transmitted force.

  Further, the upper and lower fixing bars are not necessarily separate reinforcing bars, and one reinforcing bar may be bent into a U shape and locked to the steel frame. In this case, it is difficult to pass through the opening provided in the steel flange or plate, so a steel plate or steel bar is welded to provide a locking part that protrudes to the side of the flange, and the fixing bar bending part is hung there. They may be bound and fixed.

  Also about a steel frame, regardless of whether it is a rolled shape steel or a welded assembly, the cross-sectional shape is not limited to the H shape. In addition, when the stress of the steel frame is large or when it is desired to shorten the embedding length, a stud may be placed on the steel frame as necessary. The stud is generally used as a shear transmission bar due to the dowel action. For example, if a stud with a head with a predetermined length is placed on the end face of the steel flange in a direction parallel to the beam main bar, It is also possible to transmit the tensile force of the flange, or part of it, to the concrete.

  When the span is long, a joint may be provided on the steel frame and divided into both end portions and a central portion. When dividing a steel frame, it is also possible to precast the steel frame in a state where a part of the steel frame is embedded in the reinforced concrete part. For example, if the slab part is left behind and used as a half-precast member, it is emulated by laying the concrete in the remaining part together with the beam-column joint and other parts after slab reinforcement and slab reinforcement. An integrated frame is formed in the same manner as the conventional precast method.

  Or you may build a reinforced concrete part after carrying in a steel frame like the conventional construction method. After laying the steel frame in place, install the formwork after placing the axial reinforcement such as the main reinforcement and anchoring reinforcement and the shear reinforcement, and cast the concrete together with other parts such as columns and slabs. By doing so, the entire frame may be integrated.

  In addition, it is reasonable in terms of construction to arrange the fixing bars together with the reinforcing bar arrangement of the reinforced concrete part. However, the timing is not particularly limited as long as it is before placing concrete. A convenient time can be determined according to the construction method to be used and conditions such as transportation or lifting.

DESCRIPTION OF SYMBOLS 1 Steel part 11 Upper flange 12 Lower flange 2 Reinforced concrete part 21 Shear reinforcement 3 Embedding part 31 Stress transmission area 4 Anchorage (axial)
41 Extra length 42 Steel plate 5 Beam main reinforcement j Distance between main reinforcements 6 Reinforced concrete columns 7 Composite structural beams

Claims (3)

At least one of the left and right ends is a reinforced concrete part made of reinforced concrete, the other part is made of a steel part, and the cross section of the reinforced concrete part is a composite structural beam larger than the steel part ,
With an end portion of the steel part is embedded and fixed to the reinforced concrete section, the tensile force of the flange becomes a fixing muscle responsible for transmitting to the concrete,
In order that the level of the anchoring bars can be adjusted between the upper and lower flange surfaces and the beam main bar position,
A composite structural beam characterized in that at least one end of each of the plurality of fixing bars bent at one end is locked to the steel part embedded in the reinforced concrete part. An opening is provided in the flange of the steel frame portion, or a steel plate provided with an opening is fixed to the flange, and an extra length portion of the bent fixing bar is inserted into the opening. Item 2. The composite structural beam according to Item 1. The composite structural beam according to claim 1 or 2, wherein the bent fixing bar is a screw reinforcing bar, and is fixed to a flange of the steel frame portion or a steel plate fixed to the flange with a nut.

Images