Reinforced concrete beam

Abstract

To provide a beam structure that can suppress the occurrence of cracks in an area near a column-beam joint and prevent the occurrence of concrete peeling or collapse due to excessive external force.SOLUTION: A reinforced concrete beam 1 is joined between columns 3A and 3B and includes a plurality of main reinforcements 13, 15, 17, and 19. At least a part of the plurality of main reinforcements terminates at a predetermined position away from joint surfaces 10A and 10B of joints between the columns 3A, 3B and the concrete beam 1. A compressive force is applied in the beam depth direction in a range from the positions where a part of the main reinforcements terminate to the joint surfaces.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a beam structure, and more particularly to a reinforced concrete beam structure. [Background technology]

[0002] Traditionally, the beams in reinforced concrete structures (hereafter referred to as RC structures) can suffer cracks and other damage due to external forces such as earthquakes. When a beam is damaged, it is necessary to carry out repair work to ensure the continued use of the building. However, if the damage occurs along the entire length of the beam, this will result in prolonged repair work and increased costs, and ultimately the building itself will have to be rebuilt. Patent Document 1 discloses a configuration in which some of the main reinforcements extending along the entire length of a beam are cut off to achieve so-called hinge relocation toward the center of the beam, thereby preventing cracks from occurring near the bending yield hinge at the joint between the beam and the column. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-18420 Summary of the Invention [Problem to be solved by the invention]

[0004] However, although the above beam structure simplifies repair work by reducing the occurrence of cracks at the above joints, it is still difficult to suppress damage near the column-beam joints, which are outside the cut-off range (the range from the tip of the cut-off main reinforcement to the joint surface), and even if the damage is not severe enough to pose a problem to earthquake resistance, cracks and peeling of the concrete in the above range close to the columns will cause concern for the continued use of the building by residents and users.

[0005] The present invention has been made to solve the above-mentioned problems, and provides a beam structure that can reduce the occurrence of cracks in the area near the column-beam joint (beam end). [Means for solving the problem]

[0006] In order to solve the above problem, the present invention provides a reinforced concrete beam having multiple main reinforcements connected between columns, in which at least some of the multiple main reinforcements terminate at a predetermined position from the joint surface of the joint between the column and the concrete beam, and a compressive force is applied in the beam depth direction in the range from the position where some of the multiple main reinforcements terminate to the joint surface. With this configuration, compressive force is generated in the beam depth direction in the range from the position where some of the main reinforcement bars terminate to the joint with the column, thereby suppressing the occurrence of cracks at the end of the beam. Alternatively, the compressive force may be applied by a prestress plate and a PC steel rod. The planar dimensions of the prestress plate may also be configured to include the length and depth of the beam in the range up to the joint between the column and the beam. With this configuration, the entire area of ​​both end faces in the beam depth direction in the range from the tip of the main reinforcement, where cracks are likely to occur, to the joint between the column and the beam (beam end) is included in the range of the prestressing plate, making it possible to transmit compressive force uniformly and suppressing concrete peeling and falling off due to crushing. The prestress plate may also be configured to be bent in the depth direction of the reinforced concrete beam in the depth direction of the beam. In addition, the main reinforcements other than those terminating at predetermined positions may be configured to have an anchored portion attached to the concrete in the longitudinal direction of the beam, and a non-anchored portion from which the attachment to the concrete has been removed. This configuration can suppress cracks from occurring on the concrete surface in the non-anchored area. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a schematic diagram of a beam-column structure according to an embodiment of the present invention; [Figure 2] 2A-2C are cross-sectional views of the beam-column structure of FIG. 1, taken along lines A-A, B-B, and C-C. [Figure 3] FIG. 1 is a diagram showing a reinforcement diagram and specifications of a test specimen for a structural experiment. [Figure 4] FIG. [Figure 5] 1 is a graph showing a loading cycle. [Figure 6] FIG. 10 is a diagram showing the shear force-deformation angle relationship of each test specimen. [Figure 7] 10 is a graph showing a comparison of the positive load side envelope curves of each test specimen. [Figure 8] FIG. 1 is a diagram showing the initial stiffness of each test specimen, and the secant stiffness at each number of repetitions when R=1.0(%). [Figure 9] This is a diagram showing the cracking state of the test specimen when R=1.0(%) and the load was removed at the 10th cycle. [Figure 10] This is a diagram showing the cracking state of the test specimen when R=1.5(%) was removed in the first cycle. [Figure 11] FIG. 10 is a diagram showing the state of destruction at the end of the R=4.0(%) cycle. [Figure 12] FIG. 10 is a diagram showing the distribution of the residual crack area ratio on the side of the beam under normal loading. DETAILED DESCRIPTION OF THE INVENTION

[0008] [Overall structure] Below, a beam-column structure 1 having a reinforced concrete beam 10 will be described with reference to Figures 1 and 2. As shown in the figures, the beam-column structure 1 includes reinforced concrete columns 3A and 3B and a beam 10, also made of reinforced concrete, joined to the columns 3A and 3B and installed between the columns 3A and 3B. The beam 10 includes upper main reinforcement bars 13 and lower main reinforcement bars 15 extending between the columns 3A and 3B. Both ends of the upper main reinforcement bars 13 and lower main reinforcement bars 15 extend through the columns 3A and 3B, respectively, toward the other beam 12, indicated by the dashed lines. Depending on the position of the beam 10 throughout the entire structure, it may be bent and anchored within the columns 3A and 3B. Throughout this specification, each main reinforcement bar in the beam 10 is assumed to be a deformed steel bar with a rib formed around its periphery.

[0009] As shown in Fig. 2(a), the upper main reinforcement 13 is composed of a plurality of upper main reinforcement 13A to 13D arranged at the uppermost end face side of the beam 10. The lower main reinforcement 15 is composed of a plurality of lower main reinforcement 15A to 15D arranged at the lowermost end face side of the beam 10.

[0010] In addition to the upper end side main reinforcements 13 and the lower end side main reinforcements 15, the beam 10 also has upper end side main reinforcements 17 and lower end side main reinforcements 19 that extend toward the columns 3A and 3B, respectively. As shown in Fig. 2(b), the upper end side main reinforcements 17 are made up of upper end side main reinforcements 17A to 17D that are arranged directly below the positions of the upper end side main reinforcements 13A to 13D. In addition, the lower end side main reinforcements 19 are made up of lower end side main reinforcements 19A to 19D that are arranged directly above the positions of the lower end side main reinforcements 15A to 15D. Furthermore, one end of the upper end main reinforcement 17 and the lower end main reinforcement 19 on the column 3A; 3B side, like the upper end main reinforcement 13 and the lower end main reinforcement 15, either penetrates the column 3A; 3B and extends to the other beam 12 side shown by the chain line, or is bent and fixed within the column 3A; 3B.

[0011] The other ends of the upper end main reinforcements 17 and the lower end main reinforcements 19 on the beam 10 side extend toward the center of the beam 10 and terminate at a predetermined distance from the joint surfaces (joint surfaces) 10A and 10B between the columns 3A and 3B and the beam 10. In other words, the upper end main reinforcements 17 and the lower end main reinforcements 19 are cut off. Mechanical fasteners, such as screw-type or grout-injection type, are fastened to the other ends of the upper end main reinforcements 17 and the lower end main reinforcements 19 that terminate within the beam 10, thereby securing them to the beam 10. As shown in FIG. 2, the upper end main reinforcements 13 and the lower end main reinforcements 15, the upper end main reinforcements 17 and the lower end main reinforcements 19, arranged in the beam 10, are wrapped around stirrups (stilts S) (not shown in FIG. 1) that are arranged at predetermined intervals over the entire length of the beam 10.

[0012] The column-beam structure 1 having the above-described basic structure is a so-called hinge relocation structure in which the position where the yield hinge occurs (assumed hinge position) is located away from the joint faces 10A; 10B toward the center of the beam 10, mainly because the end upper main reinforcement 17 and the end lower main reinforcement 19 are cut off within the beam 10. This structure reduces the possibility that damage will occur at the joint between the columns 3A; 3B and the beam 10 due to external forces such as earthquakes, making repairs difficult.

[0013] [About fixed and non-fixed parts] Of the eight main reinforcements consisting of upper end side main reinforcements 13A to 13D and lower end side main reinforcements 15A to 15D extending over the entire length of the beam 10, the upper end side main reinforcements 13A; 13D and lower end side main reinforcements 15A; 15D that are closest to the corners (four corners in this example) of the beam 10, which has a vertically elongated rectangular cross section, are provided with anchoring portions P1; P2; P3 and non-anchoring portions Q1; Q2 along their extension direction. The anchoring portions P and non-anchoring portions Q will be described in detail below.

[0014] As shown in Figure 1, the fixed portion P1 is a central section (central fixed portion) that includes the center of the longitudinal direction of the beam 10 (between columns 3A and 3B) and extends in the column 3A; 3B direction with a predetermined dimension. The non-fixed portions Q1 and Q2 are sections that sandwich the fixed portion P1 and extend in the column 3A; 3B direction with a predetermined dimension from the end of the fixed portion P1. The fixed portions P2 and P3 are sections (column-side fixed portions) that are adjacent to the non-fixed portions Q1 and Q2, respectively, and extend in the column 3A; 3B direction.

[0015] As shown in Figures 2(a) and 2(b), the circumferential surfaces of the upper main reinforcement bars 13A; 13D and the lower main reinforcement bars 15A; 15D at the anchorage sections P1, P2, and P3 are in direct contact with the surrounding concrete, ensuring adhesion between the surfaces of the main reinforcement bars and the concrete. Meanwhile, as shown in Figure 2(c), the circumferential surfaces of the upper main reinforcement bars 13A; 13D and the lower main reinforcement bars 15A; 15D at the non-anchored sections Q1; Q2 adjacent to the anchorage section P are covered in a sheath tube 20 along their length as an adhesion removal device. The end of the sheath tube 20 on the column 3A; 3B side coincides with the assumed hinge position, and the non-anchored sections Q1; Q2 are sections that extend continuously from the end of the anchorage section P1 to the assumed hinge position. Since the sheath pipe 20 is attached to the circumferential surfaces of the upper end main reinforcement 13A; 13D and the lower end main reinforcement 15A; 15D, the sheath pipe 20 removes adhesion between the surface of each main reinforcement and the concrete in the non-anchored portions Q1; Q2.

[0016] That is, of the eight main reinforcements in this example, some of the main reinforcements located at the corners (upper end side main reinforcements 13A; 13D and lower end side main reinforcements 15A; 15D) have sections in their length direction where adhesion to the concrete is ensured (anchored sections) and sections in which adhesion has been removed (non-anchored sections).With this configuration, the beam 10 has anchored sections P1, P2, P3 in its length direction where the main reinforcements are anchored to the concrete (larger), and non-anchored sections Q1; Q2 where the anchored sections P are less anchored to the concrete (smaller).

[0017] [Means for applying compression force] As shown in Figures 1 and 2(b), prestressing steel bars 30 and steel plates 32 are disposed as compressive force applying means in the range of anchorage sections P2 and P3, i.e., the range from the tips of the cut-off upper end main reinforcement 17 and lower end main reinforcement 19 to the joint surfaces (joint surfaces) 10A and 10B (hereinafter referred to as the beam-end region). As shown in Figure 1, the prestressing steel bars 30 are disposed at equal intervals along the length of the beam-end region and extend in the depth direction at anchorage sections P2 and P3. Steel plates 32 are disposed on the concrete surface in the depth direction of the beam-end region (upper end surface 34A; lower end surface 34B). The ends of each prestressing steel bar 30 penetrating the steel plates 32 are mechanically fastened with nuts or the like to introduce tension into the prestressing steel bars 30, and a compressive force in the depth direction is generated in the beam-end region via the steel plates 32.

[0018] The steel plate 32 is large enough to cover almost the entire concrete surface in the beam-end region, applying uniform compressive force in the depth direction to the beam-end region. A rubber plate (not shown) is interposed between the steel plate 32 and the concrete surface to absorb unevenness in the concrete. The ends of the steel plate 32 may be bent in the depth direction. This configuration further suppresses spalling and falling of concrete when excessive external force is applied to the beam, preventing spalling and falling, which would prevent the transmission of compressive force from being interrupted. In other words, the steel plate 32 preferably has an area substantially corresponding to the beam-end region to prevent spalling and falling of concrete. It is more preferable to protect not only the upper end surface 34A and the lower end surface 34B, but also the side surfaces, including the corners, by bending.

[0019] [About the structural experiment] Next, we describe structural experiments on RC beams in which the bond between the main reinforcement bars was partially removed and prestressing was applied in the beam depth direction at the beam end, as described above. Figures 3(a) and (b) show the reinforcement diagram and specifications of the test specimens used in the experiments. Each test specimen was a full-scale RC beam specimen, modeled after a high-rise RC building. It was a cantilevered specimen cut with the inflection point at the midpoint of the beam span. The beam cross section was 550mm x 900mm, and the distance from the edge of the stub to the load point was 2500mm. Furthermore, the main reinforcement in the section from the edge of the stub to 750mm was 4+4-D38. Beyond that, the double-stage reinforcement was cut off and mechanical anchors were installed to make it 4-D38. The hinge formation position was intentionally shifted from the end of the beam to the center (cutoff position). In addition, the above design concept has the same strength as a beam (conventional beam) with main reinforcement of 4+2-D38 along its entire length, while also ensuring a strength margin. Here, the strength margin is the ratio of the strength Vk at the bending ultimate strength Mk at the second-stage reinforcement cutoff position to the strength Vu at the bending ultimate strength Mu at the end of the beam, and the bending ultimate strength was calculated using the approximate formula (Equation 1) given in the RC standards of the Architectural Institute of Japan. Equation 1 Mu,Mk=0.9a t σ y d where a t : Cross-sectional area of ​​tensile steel bar (mm 2 ), σ y : Yield strength of main reinforcement (N / mm 2 ), d: effective depth (mm).

[0020] Specimens 1, 2, and 3 have anchored and non-anchored sections as shown in Figures 1 and 2, and are specimens to which compressive force (prestress) is applied in the depth direction at the ends by the steel plate and six PC steel bars as the compressive force application means mentioned above. The PC steel bars are prestressed to a value of 3 N / mm for Specimen 1 so that the value obtained by dividing the tension of the six PC steel bars by the area of ​​the steel plate exceeds the average shear stress τu generated in the beam at the bending ultimate strength at the cut-off position. 2A tension of approximately 4.5 N / mm2 was applied to specimen 2, so that the average shear stress intensity τu was about 4.5 N / mm2. The average shear stress intensity τu was calculated using (Equation 2). Specimen 3 is a specimen that has undergone repair work on specimen 1. Specimen 4, which serves as a comparative example, is a conventional specimen from specimens 1 to 3 that does not have the compressive force application means, and specimen 5 is a specimen with normal adhesion properties that does not have the non-anchored portion described above. Specimen 6 is a specimen that has undergone repair work on specimen 5. Equation 2 τ u =V k / bD where Vk is the ultimate bending strength at the second-stage reinforcement cutoff position (N), b is the beam width (mm), and D is the beam depth (mm).

[0021] [Loading method] Figure 4 shows a schematic diagram of the loading device. As shown in the figure, the test specimen stub was fixed to the reaction floor, and the beam was loaded in the vertical direction using a hydraulic jack installed at the free end of the beam. A pantograph was attached to the free end of the beam to restrain the out-of-plane deformation of the test specimen.

[0022] Figure 5 is a graph showing the loading cycle. Loading was performed under displacement control using the deformation angle R, calculated by dividing the displacement position at the loading point by the shear span. For specimens 2 and 4, which were not repaired, R = 0.0625, 0.125, and 0.25 (%) was repeated twice each with positive and negative rotation, followed by R = 0.5 and 1.0 (%), repeated 10 times each with positive and negative rotation, and then R = 1.5, 2.0, 3.0, and 4.0 (%), repeated twice each. For specimens 1 and 5, which were to be repaired, the pre-repair loading was R = 0.0625, 0.125, 0.25 (%), repeated twice each with positive and negative loads, and R = 0.5, 1.0 (%), repeated ten times with positive and negative loads. After that, repairs were carried out using the epoxy resin injection method, and then the post-repair loading was R = 0.0625, 0.125, 0.25, 0.5, 1.0, 1.5, 2.0, 3.0, 4.0 (%), repeated twice each with positive and negative loads (the specimens loaded after repair were specimens 3 and 6). The number of repetitions at R = 0.5 and 1.0 (%) was set at 10 because previous research has reported that the width of residual cracks in components increases when they are subjected to repeated loading multiple times. In addition, for specimens 2, 3, and 6, the reduction in strength at the end of loading at R=4.0(%) was slight, so a single push load was applied to the positive side only at R=5.0(%).

[0023] [About the experimental results] Restoring force characteristics Figure 6 shows the shear force-deformation angle relationship for each specimen, along with the yielding condition of the main reinforcement, and Figure 7 shows a comparison of the normal loading envelope curves for each specimen. In the figure, the shear force vk at the ultimate bending strength at the assumed hinge position is shown by a dashed line, and the yielding condition of the main reinforcement is shown separately for the outer and inner main reinforcement.

[0024] The maximum strength of each specimen was roughly the same, and they followed a stable hysteresis loop until the end of loading. After the maximum strength of each specimen, the strength gradually decreased due to flexural compression failure of the concrete at the second-stage reinforcement cut-off position. Comparing the envelope curves of each specimen, no significant differences were observed in the shear force-deformation angle relationship up to R = 4.0 (%), and no influence could be confirmed due to the presence or absence of bond removal or the presence or absence of beam end prestress. On the other hand, at R = +5.0 (%), it can be confirmed that specimens 3 and 6 showed a greater decrease in strength than specimen 2.

[0025] Furthermore, when examining the yielding conditions of the main reinforcement bars of each specimen, it can be seen that in specimen 6, the outer and inner main reinforcement bars yielded at roughly the same deformation angle, whereas in specimens 1, 2, and 4, the inner main reinforcement bars, which had not undergone bond removal, reached yield strain first, followed by the outer main reinforcement bars, which had undergone bond removal.

[0026] Figure 8 shows the initial stiffness of each specimen, and the secant stiffness at each repetition when R = 1.0 (%). The initial stiffness is the slope of the line connecting the start of loading and the point when R = +0.03125 (%), and the slope of the line connecting the peak point of secant stiffness R = +1.0 (%) and the origin. No significant differences were observed in the initial stiffness of each specimen.

[0027] The ratio of the initial stiffness after repair to the initial stiffness before repair was 0.55 for specimen 3 and 0.57 for specimen 6, meaning that the initial stiffness after repair was significantly lower than before repair. This is thought to be due to the fact that the elastic modulus of the epoxy resin used for repair is smaller than that of concrete, and that fine cracks that could not be repaired remained.

[0028] On the other hand, with regard to the secant stiffness at each cycle when R=1.0(%), the value of the secant stiffness gradually decreased as the number of cycles increased for each specimen, and by the 10th cycle it had decreased by about 4% to 5% from the first cycle, whereas by the first cycle after repair the secant stiffness had recovered to the same level as the first cycle before repair. From this, it can be considered that by observing cracks and measuring crack widths at the first cycle of each deformation angle and carrying out repair, the damage state at the end of the R=0.5(%) cycle after repair had recovered to the same level as the damage state at the end of the R=0.5(%) cycle before repair.

[0029] Damage characteristics Crack observations and crack width measurements were performed on the side (front) and top of the beam at the first cycle for each deformation angle, as well as at the peak of the 10th cycle at R = 0.5 and 1.0 (%) and at the time of unloading. The width perpendicular to the crack was defined as the crack width, and the crack width was measured at the beam edge and at points crossing the grid lines drawn on the surface of the specimen using a crack scale (minimum division 0.03 mm).

[0030] Crack condition Figure 9 shows the cracking conditions of specimens 1, 2, 4, and 5 at R=1.0(%) and the 10th cycle after unloading. Figure 10 shows the cracking conditions of specimens 2, 3, 4, and 6 at R=1.5(%) and the 1st cycle after unloading. Figure 11 shows the fracture conditions of specimens 1, 2, 4, and 5 at R=4.0(%) and the end of the cycle. In Figures 9 and 10, cracks under normal loading extend downward from the top surface of the specimen, while cracks under normal loading extend upward from the bottom surface of the specimen. The cracks in the figures are indicated by different line thicknesses according to the measured crack width Wcr. Note that cracks that occurred during loading before repair and were repaired were considered to have no cracks at the start of loading after repair.

[0031] For each specimen, a bending crack appeared at the second-stage reinforcement cut-off position at R=0.0625(%) cycles. As the deformation angle increased, the damage area of ​​specimen 5 spread toward the free end of the beam and toward the end of the beam. On the other hand, for specimens 1, 2, and 4, in which the main reinforcement at the four corners had been removed, damage was suppressed in the section where the main reinforcement had been removed, and cracks were mainly concentrated at the second-stage reinforcement cut-off position. However, for specimen 4, after R=0.5(%) cycles, the bending crack that appeared at the second-stage reinforcement cut-off position transitioned to a diagonal crack, and the damage area gradually expanded toward the end of the beam.

[0032] On the other hand, in specimens 1 and 2 according to the embodiment, in which prestress was applied in the beam depth direction at the beam end, the extension of diagonal cracks was suppressed, and damage to the beam end was suppressed. This effect was particularly significant in specimen 2, in which the PC pressure bonding force was increased. Furthermore, when examining the state of failure at the end of the R=4.0(%) cycle, specimens 4 and 5, and specimen 6, which was repaired and reloaded after specimen 5, showed significant crushing and spalling of the cover concrete at the beam end, whereas specimens 2 and 3 according to the embodiment suppressed crushing at the beam end. In particular, specimen 2 was able to prevent further crushing, which is thought to be why the reduction in strength at R=5.0(%) was smaller than that of the other specimens.

[0033] Regarding the repaired specimens 3 and 6, the cracks of approximately 0.1 to 0.2 mm that were the target of repair in both specimens were poorly filled with epoxy resin, and cracks appeared in the repaired areas from the early stages of loading. On the other hand, the crack that appeared at the cutoff position of the second reinforcement was caused by the tensile strength of the epoxy resin being greater than that of the concrete, and a new crack appeared in the concrete part near the repaired crack. This suggests that the crack at the cutoff position of the second reinforcement was sufficiently filled with epoxy resin. Furthermore, for specimen 3, at the end of the R=1.5(%) cycle, the remaining crack width was generally less than 0.2 mm, except for the crack that appeared at the cutoff position of the second reinforcement, confirming the effect of reducing the damage area by removing the main reinforcement even after repair.

[0034] Crack area ratio distribution Figure 12 shows the distribution of the residual crack area ratio on the side of the beam when the test specimen was divided into four sections (sections A to D) and each section was subjected to normal loading. The crack area was calculated by replacing the continuously changing actual cracks with parallelogram cracks of (crack width at the measurement point x measurement grid spacing), and the residual crack area ratio was calculated by dividing the total area of ​​cracks remaining in each section when unloading at each deformation angle by the area of ​​each section.

[0035] For each specimen, the residual crack area ratio was large in section C, which includes the two-stage reinforcement cut-off position. Furthermore, when comparing specimen 5 with specimen 4, damage in specimen 4 was suppressed in the bond removal sections (sections A and B). However, in section D at the beam end, specimen 4 had a larger crack area ratio. On the other hand, in specimens 1 and 2, to which compressive force was applied, the crack area ratio was reduced not only in the bond removal section but also in the beam end section, confirming the significant effect of applying prestress in the beam depth direction at the beam end.

[0036] According to the above experimental results, in specimen 4, where only the main reinforcement was removed, the bending cracks that occurred at the two-stage cutoff position turned into diagonal cracks and progressed toward the beam end as the deformation angle increased, resulting in increased damage at the beam end.However, in specimens 1 and 2, where prestress was applied in the depth direction at the beam end, it became clear that the progression of diagonal cracks could be suppressed and damage at the beam end could be reduced.

[0037] Furthermore, in the beam of Specimen 2, in which the prestress in the depth direction was increased compared to Specimen 1, the crushing of the cover concrete at the beam end was suppressed, and the decrease in strength at a deformation angle of R = 5.0 (%) was significantly reduced compared to the other specimens, making it clear that high integrity is ensured in the event of an earthquake. Furthermore, in the case of prestressed beams, the extent of damage at the beam end is significantly suppressed, so the amount of sealing material and injection equipment required for repair can be significantly reduced, and therefore the repair costs can be significantly reduced. [Explanation of symbols]

[0038] 1 Column beam structure, 3A; 3B column, 10 beams, 13 upper main reinforcement, 15 lower main reinforcement, P1; P2; P3 anchored section, Q1; Q2 non-anchored section, 30 PC steel bar, 32 steel plate

Claims

1. A reinforced concrete beam connected between columns and having a plurality of main bars, At least a portion of the multiple main reinforcements terminate at a predetermined position from the joint surface of the joint between the column and the concrete beam, A reinforced concrete beam characterized in that a compressive force is applied in the beam depth direction in the range from the position where some of the main reinforcements terminate to the joint surface.

2. 2. A reinforced concrete beam according to claim 1, wherein the compressive force is applied by a prestressing plate and a PC steel rod.

3. A reinforced concrete beam according to claim 2, characterized in that the planar dimensions of the prestressing plate include the length and depth of the beam in the range up to the joint between the column and the beam.

4. 4. The reinforced concrete beam according to claim 3, wherein the prestressing plate is bent in the depth direction of the reinforced concrete beam in the depth direction of the beam.

5. A reinforced concrete beam as described in claims 1 to 4, characterized in that the main reinforcements other than the portion of the main reinforcement that terminates at the specified position have an anchored portion attached to the concrete in the longitudinal direction of the beam and a non-anchored portion from which the attachment to the concrete has been removed.

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