Reinforced Concrete Beam

Abstract

To provide a beam structure that can suppress and control damage caused by external forces while ensuring structural performance of a beam.SOLUTION: There is provided a reinforced concrete beam 10 having a plurality of main bars joined between columns 3A; 3B, in which at least a part of the plurality of main bars has a central anchorage portion P1 where the main bars and concrete are adhered in a predetermined range from the center of the beam 10 in a longitudinal direction to a direction of the columns 3A; 3B, and non-fixed portions Q1; Q2 where the adhesion between the main bars and concrete in a predetermined range other than the central anchorage portion P1 is removed through adhesion removal means.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 be damaged, such as by cracks, by 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, but 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, in order to suppress and control damage to the joint between a column and a beam (hereinafter referred to as the column-beam joint), which is difficult to repair, a first main bar is arranged near the center of the beam and a second main bar that is larger in diameter or stronger than the first main bar is arranged near the end of the beam, and the first and second main bars are connected to each other with a reinforcing bar joint, thereby achieving so-called hinge relocation toward the center of the beam, thereby preventing cracks near the bending yield hinge from reaching the column-beam joint. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-143566 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, as is clear from the drawings in the above patent documents, although the above beam structure can suppress damage at the beam-column joint, the damage caused by cracks extends to almost the entire beam, and although the possibility of continued use is improved, repair work after damage remains difficult. In addition, since cracks in beams are generally caused by the stress transmission of the reinforcing bars arranged in the beam to the concrete, measures can be considered to reduce the range of cracks or control the occurrence range by, for example, weakening the anchorage of part of the reinforcing bars by not adhering them to the concrete, but there is a concern that the structural performance against external forces such as earthquakes will be reduced compared to general beams because the hysteresis characteristics approach the so-called slip type, which has poor energy absorption, due to the reduction in anchorage.

[0005] The present invention has been made to solve the above-mentioned problems, and provides a beam structure that can suppress and control damage caused by external forces while ensuring the structural performance generally required of beams. [Means for solving the problem]

[0006] In order to solve the above problems, the present invention provides a reinforced concrete beam having a plurality of main reinforcements that are joined between columns, wherein at least a portion of the plurality of main reinforcements have a central fixing portion where the main reinforcements and the concrete are attached in a predetermined range from the center of the beam in the longitudinal direction toward the column direction, and a non-fixed portion where the attachment between the main reinforcements and the concrete in a predetermined range other than the central fixing portion has been removed by an attachment removal means; A fixing plate is provided at the boundary between the central fixing portion and the non-fixing portion. , the The anchor plate is a plate-like body having openings through which at least two main reinforcements can be inserted, one above the other in the longitudinal cross section of the beam. The composition was as follows. According to this configuration, the structural performance of the beam can be ensured while the non-anchored portions can suppress and control the occurrence of cracks. Also, The fixing properties can be improved by the bearing resistance of the fixing plate. Also, The anchor plate is a plate-like body having openings through which all main reinforcement bars having non-anchored portions can be inserted. It may be. In addition, the main reinforcement having a central fixing portion and a non-fixing portion may be configured to be located at least at a corner portion when viewed in vertical cross section of the beam. According to this configuration, cracks occurring on the concrete surface can be more effectively suppressed and controlled. In addition, a position a predetermined distance away from the joint between the pillar and the beam toward the center of the beam may be set as an assumed hinge, and the pillar side end of the non-fixed portion may be set as the position of the assumed hinge. With this configuration, damage to the joints between the columns and beams can be suppressed. The adhesion removal means may also be a sheath tube attached to the outer periphery of the main reinforcement. [Brief description of the drawings]

[0007] [Figure 1] 1 is a schematic cross-sectional view of a beam-column structure according to one embodiment of the present invention; [Diagram 2] 2A-2C cross-sectional views of the beam-column structure in FIG. 1, FIG. 2B cross-sectional views of the beam-column structure in FIG. 1, and FIG. [Diagram 3] FIG. 2 is a partially enlarged view of a reinforced concrete beam. [Figure 4] FIG. 2 is a cross-sectional view showing an outline of the fixing steel plate. [Diagram 5] FIG. 2 is a diagram showing details of an analysis target and an analysis model. [Figure 6] FIG. 2 is a diagram showing specifications of a model to be analyzed and analysis parameters. [Figure 7] This is a schematic diagram showing the boundary and loading conditions. [Figure 8] This is a graph showing the shear force-member angle relationship up to zero displacement after unloading at R=±1 / 67 rad. [Figure 9] FIG. 13 is a diagram showing the analytical value of maximum strength and the calculated value of shear force at ultimate bending strength. [Figure 10] FIG. 1 is a schematic diagram showing the cracking state of each model. [Figure 11] FIG. 1 is a diagram showing material properties of concrete and reinforcing steel. [Figure 12] FIG. 1 is a schematic diagram showing a structural testing setup. [Figure 13] FIG. 13 is a diagram showing the shear force-member angle relationship. [Figure 14] FIG. 1 is a diagram for explaining division into regions for observation. [Figure 15] FIG. 1 is a diagram for explaining a method for measuring cracks. [Figure 16] FIG. 1 is a diagram illustrating modeling of a crack. [Figure 17] FIG. 1 is a schematic diagram showing a crack state. [Figure 18] FIG. 13 is a diagram showing the change in the number of cracks. [Figure 19] FIG. 13 is a diagram showing the transition of maximum crack width. [Figure 20] FIG. 13 is a diagram showing the distribution of residual crack area ratio. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] [Overall structure] Hereinafter, a column-beam structure 1 having a reinforced concrete beam 10 will be described with reference to Figs. 1 and 2. As shown in Fig. 1, the column-beam structure 1 includes columns 3A and 3B of reinforced concrete, and a beam 10 of reinforced concrete joined to the columns 3A and 3B and erected between the columns 3A and 3B. The beam 10 includes upper end main reinforcement 13 and lower end main reinforcement 15 extending between the columns 3A and 3B. Both ends of the upper end main reinforcement 13 and the lower end main reinforcement 15 extend through the columns 3A and 3B, respectively, to the other beam 12 side shown by the chain line. Depending on the position of the entire structure of the beam 10, it may be bent and fixed in the columns 3A and 3B. Throughout this specification, each main reinforcement arranged in the beam 10 is assumed to be a deformed reinforcing bar with a rib formed around it.

[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 on the uppermost end surface side of the beam 10. The lower main reinforcement 15 is composed of a plurality of lower main reinforcement 15A to 15D arranged on the lowermost end surface side of the beam 10.

[0010] The beam 10 is provided with the upper end side main reinforcement 13 and the lower end side main reinforcement 15, as well as the end upper end side main reinforcement 17 and the end lower end side main reinforcement 19 which extend toward the columns 3A and 3B, respectively. As shown in Fig. 2(b), the end upper end side main reinforcement 17 is composed of the end upper end side main reinforcement 17A to 17D arranged directly below the positions of the upper end side main reinforcement 13A to 13D. The end lower end side main reinforcement 19 is composed of the end lower end side main reinforcement 19A to 19D arranged directly above the positions of the lower end side main reinforcement 15A to 15D. In addition, one end portion of the upper end side main reinforcement 17 and the lower end side main reinforcement 19 on the column 3A; 3B side, like the upper end side main reinforcement 13 and the lower end side main reinforcement 15, either penetrates the column 3A; 3B and extends to the other beam 12 side shown by the dashed line, or is bent and fixed within the column 3A; 3B.

[0011] The other ends of the upper end side main reinforcement 17 and the lower end side main reinforcement 19 on the beam 10 side extend toward the center of the beam 10 and terminate at a position a predetermined distance away from the joint surface (joint surface 10A; 10B) between the columns 3A; 3B and the beam 10. The other ends of the upper end side main reinforcement 17 and the lower end side main reinforcement 19 terminating within the beam 10 are fastened with mechanical fasteners, for example, of a screw type or grout injection type, to fix them to the beam 10 side. As shown in FIG. 2, the upper end side main reinforcement 13 and the lower end side main reinforcement 15, the upper end side main reinforcement 17 and the lower end side main reinforcement 19 arranged in the beam 10 are wrapped around ribs (stilts S) not shown in FIG. 1 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 location where the yield hinge occurs (assumed hinge location) is located toward the center of the beam 10 from the joint faces 10A; 10B mainly by cutting off the main reinforcement bars 17 on the upper end side and the main reinforcement bars 19 on the lower end side. This structure reduces the possibility that damage will occur to the joints between the columns 3A; 3B and the beam 10 due to external forces such as earthquakes, making repairs difficult.

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

[0014] As shown in Fig. 1, the fixing portion P1 is a central section (central fixing 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-fixing portions Q1 and Q2 are sections that extend in the column 3A;3B direction with a predetermined dimension from the end of the fixing portion P1, sandwiching the fixing portion P1. The fixing portions P2 and P3 are sections (column-side fixing portions) that are adjacent to the non-fixing portions Q1 and Q2, respectively, and extend in the column 3A;3B direction.

[0015] As shown in Fig. 2(a) and (b), the peripheral surfaces of the upper end side main reinforcement 13A;D and the lower end side main reinforcement 15A;15D at the anchoring parts P1, P2, P3 are in direct contact with the surrounding concrete, and the adhesion between the surface of each main reinforcement and the concrete is ensured. On the other hand, as shown in Fig. 2(c), the peripheral surfaces of the upper end side main reinforcement 13A;D and the lower end side main reinforcement 15A;15D at the non-anchoring parts Q1;Q2 adjacent to the anchoring part P are covered with a sheath tube 20 as an adhesion removal means in the length direction. In addition, the end of the sheath tube 20 on the column 3;3B side coincides with the above-mentioned assumed hinge position, and the non-anchoring parts Q1;Q2 are sections that extend continuously from the end of the anchoring part P1 to the assumed hinge position. Since the sheath pipe 20 is attached to the peripheral surfaces of the upper end main reinforcement 13A;D 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-fixed portions Q1;Q2.

[0016] That is, among the eight main bars in this example, some of the main bars located at the corners (upper end side main bars 13A; 13D and lower end side main bars 15A; 15D) have a section in their length direction where adhesion to the concrete is secured (anchored section) and a section in their length direction where adhesion is removed (non-anchored section). With this configuration, the beam 10 has anchored sections P1, P2, P3 in their length direction where the main bars are anchored to the concrete (larger), and non-anchored sections Q1; Q2 in their length direction where the main bars are not anchored to the concrete (smaller) than these anchored sections P.

[0017] [About other formats] Next, another embodiment of the beam 10 having a fixed portion and a non-fixed portion will be described with reference to Figures 3 and 4. In the figures, the same components as those in the above embodiment are designated by the same reference numerals, and the description thereof will be omitted.

[0018] FIG. 3 is an enlarged cross-sectional view showing the boundary between the fixed portion P1 and the non-fixed portions Q1 and Q2 of the beam 10. As shown in FIG. As shown in the figure, an anchoring steel plate 25 is provided at each of the boundaries. As shown in Fig. 4, the anchoring steel plate 25 is a vertically long rectangular shape (strip-like) extending in the vertical direction of the cross section of the beam 10, and is composed of a steel plate 25A having circular holes through which the upper end side main reinforcement 13A and the lower end side main reinforcement 15A corresponding to the top and bottom can be inserted, and a steel plate 25B also having a strip-like shape and having circular holes through which the upper end side main reinforcement 13D and the lower end side main reinforcement 15D corresponding to the top and bottom can be inserted, respectively. As shown in FIG. 3, each steel plate 25A; 25B ​​is positioned at the boundary between the fixed portion P1 and the non-fixed portion Q1; Q2 with the main reinforcements inserted therethrough, and is firmly fixed between the upper main reinforcement 13A and the lower main reinforcement 15A, and between the upper main reinforcement 13D and the lower main reinforcement 15D by means of an anchoring nut 26 screwed in from the fixed portion P1 side and an anchoring nut 27 screwed in from the non-fixed portion Q1; Q2 side.

[0019] In other words, in comparison with the above-mentioned embodiment, the anchoring steel plate 25 is an anchoring member arranged to correspond to the upper end side main reinforcements 13A; 13D and the lower end side main reinforcements 15A; 15D which have sections where adhesion to the concrete has been removed, and the anchoring steel plate 25 ensures adhesion to the concrete. In other words, the anchoring portion P1 in this example is the section from one anchoring steel plate 25 to the other anchoring steel plate 25, and due to the main reinforcement between the anchoring steel plates 25;25 and the anchoring of both anchoring steel plates 25;25 to the concrete, the anchoring portion P1 has a greater anchorage to the concrete than the beam 10 in the previously described embodiment.

[0020] Next, the analysis results showing the usefulness of the beam 10 according to each of the above embodiments will be described. The analysis is a nonlinear three-dimensional finite element analysis, and Figures 5(a) and 5(b) show the details of the analysis target and the analysis model, and Figures 6(a) and 6(b) show the specifications of the model to be analyzed and the analysis parameters.

[0021] As shown in Figure 5, this analysis model is a super high-rise RC structure, and is assumed to be half-scale of the actual size. It consists of one span of RC beam members and stubs with an internal span of 3050 mm. As shown in Figure 6(a), the beam cross section is 275 mm wide and 450 mm deep. The assumed hinge position is 450 mm from the beam edge (joint surface), and the main reinforcement up to that position is 4+4-D19. In addition, the second-stage reinforcement (corresponding to the end upper end main reinforcement 17 and end lower end main reinforcement 19 in Figure 1) is cut off at the assumed hinge position and mechanically fixed. The hinge position is intentionally moved to the center of the beam by setting the central part of the beam to 4-D19. The above design concept is intended to achieve the same strength as a beam with 4+2-D19 main reinforcement over the entire length. In addition, two sets of ribs are placed at the cut-off position of the second-stage reinforcement. The slab is 350mm wide on each side and is attached on both sides.

[0022] As shown in Fig. 6(b), a total of eight models were analyzed using the analysis parameters of the rebars to be removed ("none", "four corners", "all"), the anchorage type ("straight line", "steel plate") at the center of the span (corresponding to anchorage part P1 in Fig. 1), and the presence or absence of a slab. The rebars to be removed were classified into three parameters: B model with normal bond properties in which the bond was not removed, DBC model in which the bond was removed from the main bars at the four corners on the side with the smaller moment than the assumed hinge position, and DBA model in which the bond was removed from all main bars in the same section as the DBC model. The anchorage type in the center of the span had two parameters: the SA model, which has bond characteristics as a straight anchorage (main reinforcement only), and the PA model, which has straight anchorage and also has an anchoring steel plate (main reinforcement + steel plate). Here, the required anchorage length was calculated with reference to the RC Standards of the Architectural Institute of Japan13), and the section where the bond is not removed (anchored section) in the SA model was set to 300 mm on both sides (600 mm in total) from the beam inflection point position. In the PA model, the section where the bond is not removed (anchored section) was set to 200 mm (400 mm in total), and an anchoring steel plate (PL12) was inserted at both ends to anchor the main reinforcement near the inflection point. Regarding the presence or absence of a slab, the model name was given an N if the slab was not attached, and an S if it was attached.

[0023] For each of the above models, an analysis was performed under the boundary and loading conditions shown in Figure 7. As shown in the figure, one side of the beam was the force-applying stub, and the other side was the vertical displacement restrained stub. In the force-applying stub, rotation was restrained to generate antisymmetric bending in the beam, and a forced displacement δ was applied to the node on the axis in the central depth direction shown by the imaginary line. In addition, in the vertical displacement restrained stub, vertical displacement was restrained while horizontal displacement was allowed. In addition, the force was applied with displacement control based on the member angle R calculated from the beam's inside span (3050 mm), and was repeated with positive and negative alternation. In detail, two cycles of forced displacements of R = ±1 / 1600, 1 / 800, 1 / 400, 1 / 200, and 1 / 100 rad were performed, and one cycle of forced displacement of R = ±1 / 67 rad was performed.

[0024] Figure 8 shows the shear force-member angle relationship up to zero displacement after unloading at R=+1 / 67rad, which was possible to analyze in common for all models, and Figure 9 shows the analytical value of maximum strength and the calculated value of shear force at ultimate bending strength. The dashed line in Figure 8 is the calculated value of shear force at ultimate bending strength, Qu_cal. The ultimate bending strength Mu was calculated using the simplified formula (Equation (1)) shown in the RC Standards of the Architectural Institute of Japan13). Also, in the model with a slab, when the slab is on the tension side at the top end, the cross-sectional area a of the tensile reinforcement is t The calculation was done by taking into account the reinforcing bars of the slab. For the model without slab, Qu_cal = 190kN, and for the model with slab, Qu_cal = 205kN. Equation (1) Mu = 0.9a t σ y d a t : Cross-sectional area of ​​tensile steel bar [mm 2 ], σ y : Yield strength of tensile steel bar [N / mm 2 ], d: Effective depth [mm].

[0025] In all models, the hysteresis curve did not become slip-type up to R=1 / 100rad cycles, but drew a stable spindle-shaped loop. Also, as shown in Fig. 8, at R=1 / 67rad cycles, the DBC-SA-N model (Fig. 8(b)), which has bond removal sections for the main reinforcement bars at the four corners and has a straight line anchor at the center, was unable to exert an anchoring effect and showed a slight decrease in both stiffness and strength. However, the DBC-PA-N (Fig. 8(c)), which has a steel plate anchor at the center, and The maximum strength of the DBC-PA-S model (same as (g)) significantly exceeded the calculated value.

[0026] In addition, when comparing the maximum positive strength of the N model without a slab, the DBA-SA-N model (d) which has bond removal sections for all main bars and has a straight-line fixed center, showed a decrease of approximately 28% at 158kN compared to 218kN for the BN model with normal bond properties, and the DBC-SA-N model (b) which has bond removal sections for the main bars at the four corners and has a straight-line fixed center, showed a decrease of approximately 11% at 193kN.

[0027] The difference in the rate of strength reduction between DBA, which has bond removal sections in all main bars, and DBC, which has bond removal sections in the main bars at the four corners, is thought to be because the tensile strength of all tensile bars in DBA is smaller than that of BN, while in DBC, the tensile bars of the inner main bars other than those at the corners, which have bond, yield and bear the tensile force, just like the BN model.

[0028] Compared to the BN model, the DBA-PA-N model (e) in which all main reinforcements had bond-removal sections and the center was fixed with steel plates showed a drop of 204kN, a drop of about 6%, while the DBC-PA-N model (c) in which the main reinforcements at the four corners had bond-removal sections and the center was fixed with steel plates showed a drop of 209kN, a drop of about 4%, and the drop in strength was significantly suppressed. This is thought to be because the steel plates increased the fixing effect at the center of the span, ensuring the switching of the tensile and compressive loads of the main reinforcements. In addition, when comparing the S model with a slab, almost no effect of bond removal was observed, and both models had almost the same strength. This is thought to be because the compressive force borne by the upper end reinforcements was reduced by the attachment of the slab.

[0029] Next, the crack range in each model will be described with reference to Figure 10. This figure shows the cracking conditions of each model at R = +1 / 100rad. As shown in this figure, in all models with hinge relocation structure, large cracks have occurred in the section from the column edge to the assumed hinge position. In addition, in comparison with the B model (BN, BS) with normal bond properties, in each model with the bond removal section, there are fewer cracks in the range on the side where the moment is smaller than the assumed hinge position (towards the center of the span), and it can be seen that the damage range is effectively suppressed. In addition, in comparison with the DBC model and the DBA model, that is, depending on whether the main reinforcement with the bond removal section is the four corners or all of them, it can be seen that the influence on the damage range of the cracks is small. In other words, the concrete cover thickness of the main reinforcement bars located at the corners of the beam cross section is smaller than that of the main reinforcement bars on the inside, and considering that cracks in the concrete are caused by stress transmission from the main reinforcement bars, it is thought that providing adhesion removal sections in the main reinforcement bars at the four corners close to the concrete surface is extremely effective in reducing damage to the beam.

[0030] In addition, when we look at the anchorage type in the center, the SA model with linear anchorage has no cracks in the center of the span, but the PA model with steel plate anchorage has small cracks on the surface roughly corresponding to the position of the steel plate. Also, no significant difference was observed with or without a slab, and the effect of suppressing the damage range was also observed on the top surface of the slab.

[0031] Taking the above analysis results into consideration, it was confirmed that the DBC-SA-N model, in which bond removal sections are provided in the main reinforcement bars at the four corners and the center is linearly fixed, and the DBC-PA-N model, in which steel plate fixings are provided in addition to linear fixings, have excellent balance in terms of structural performance and as a beam structure that can suppress and control damage, although there are differences in strength.

[0032] Next, the results of structural experiments on the beam member of the present invention are shown. The specimen for this structural test is composed of a one-span RC beam member with an inside span of 3050 mm and a stub, as shown in Figure 5. As shown in Figure 6(a), the cross section of the beam is 275 mm wide and 450 mm high. The assumed hinge position is 450 mm from the beam edge (joint surface), and the main reinforcement up to that position is 4+4-D19. In addition, the two-stage reinforcement (corresponding to the end upper end side main reinforcement 17 and the end lower end side main reinforcement 19 in Figure 1) is cut off at the assumed hinge position and mechanically fixed. The hinge position is intentionally moved to the center of the beam by setting the central part of the beam to 4-D19. The above design concept is intended to achieve the same strength as a beam with main reinforcement of 4+2-D19 over the entire length. In addition, two sets of ribs are placed at the cut-off position of the two-stage reinforcement. The slab is 350 mm wide on each side and is attached on both sides (corresponding to the DBC-PA-S model in the analysis parameters).

[0033] The material properties of the concrete used in the test specimens are shown in Figure 11(a). The concrete had a nominal strength of Fc50, a compressive strength of 58.6 (N / mm2), a splitting strength of 2.8 (N / mm2), and a Young's modulus of 32,800 (N / mm2). The material properties of the reinforcing bars are shown in Figure 11(b).

[0034] Figure 12 shows the setup for the structural test. The vertical displacement restraint (right) stub of the test specimen was fixed to the reaction floor via a jig. The actuator and the force application (left) stub were connected via a force beam. Out-of-plane restraint was achieved by connecting the force beam to the pantograph. A counterweight was used to offset the weight of the parallel crank connected to the force beam, the force application jig, and the test specimen itself. The actuator was used to apply alternating positive and negative incremental loads in the vertical direction.

[0035] The alternating positive and negative incremental loading was displacement controlled by the member angle R calculated from the beam's internal span and the vertical displacement of the load-applied (left) side stub, and the load cycle consisted of two cycles at deformation angles of R = ±1 / 800, 1 / 400, 1 / 200, 1 / 100, 1 / 67, and 1 / 50 rad, and one cycle at a deformation angle of R = +1 / 33 rad.

[0036] Figure 13 shows the relationship between shear force and member angle obtained from structural testing. No reduction in strength was observed up to R=1 / 33rad, and the hysteresis curve formed a stable spindle-shaped loop. The maximum load was 250KN on the positive side and 210KN on the negative side, and although the negative side was slightly lower, the results were equivalent to the calculated shear force at ultimate strength. From the above, it was found that the structure had sufficient structural performance.

[0037] Next, the evaluation of the damage state of the test specimen will be explained with reference to Figures 14 to 20. For the evaluation, the crack occurrence state of the test specimen during the structural experiment was visually observed, and the maximum width of each crack was measured. Based on the results of the observation and measurement, the damage state was evaluated with a focus on the crack occurrence position, the number of cracks related to the repair effort, the maximum crack width indicating the degree of damage, and the crack area related to the repair cost.

[0038] As shown in Figure 14, in order to confirm the effects of adhesion removal and central anchorage when observing the test specimens, the beam members were divided into eight regions A through H (hereafter referred to as observation regions) by determining a prescribed dimension from one end of the beam. Observations were made on two surfaces, the side of the beam and the top surface of the slab, and the characteristics of the cracks and their width. Observations were made at the first peak of each deformation angle cycle and when the load was removed, and continued until the cycle in which the cover concrete peeled off and it became impossible to evaluate the cracks.

[0039] Figure 15 shows the method for measuring crack width. In the case of beams, cracks were checked for cracks crossing the beam edge, the beam main reinforcement, and a position 85 mm from the beam main reinforcement (see Figure 15(a)), and in the case of the slab top surface, cracks crossing the slab edge, the slab main reinforcement, the beam end, and the beam main reinforcement were checked. In addition, the crack width was measured in the direction perpendicular to the crack using a crack scale (minimum scale 0.03 mm) (see Figure 15(b)).

[0040] The crack area was calculated by replacing and modeling the actual crack shown in Fig. 16(a) with a parallelogram crack model as shown in Fig. 16(b), and the continuously changing crack was calculated as a parallelogram crack of "crack width at measurement point x measurement interval". In addition, the crack area was totaled for each of the eight areas A to H, and the total value was divided by the area of ​​each area to calculate the crack area ratio γAcr.

[0041] Figure 17 shows the cracking condition at R=1 / 100rad. For the side of the beam, bending cracks occurred at the expected hinge position (the boundary between AB and GH in the observation area) during the R=1 / 800rad cycle, and then, as the deformation increased, the cracking range expanded from the expected hinge position toward the column edge. The crack width of the cracks that occurred at the expected hinge position was large, and the cracks that occurred in other areas were fine. At the R=1 / 50rad cycle, it was observed that the cover concrete around the expected hinge position was gradually destroyed, peeling occurred, and the range expanded. For the top surface of the slab, bending cracks occurred at the expected hinge position during the 1 / 800rad cycle, and then, as the deformation increased, the cracking range expanded from the expected hinge position toward the column edge. The majority of cracks penetrated in a straight line. Even during large deformation, cracks were concentrated at the expected hinge locations, with almost no cracks occurring in the adhesion-removed sections. Most of the cracks that occurred in areas other than the expected hinge locations were very small and less than 0.1 mm in size.

[0042] Figure 18 shows the number of cracks that occurred on the side of the beam and the slab. The vertical axis shows the cumulative number of cracks that occurred in each cycle, and the horizontal axis shows each cycle. On the side of the beam, there were 41 cracks when R=-1 / 100rad, 46 when R=-1 / 67rad, and 47 when R=-1 / 50rad. On the top of the slab, after 17 cracks occurred by R=-1 / 100rad, the number of cracks did not increase until 1 / 50rad. On both the side of the beam and the top of the slab, the number of cracks gradually increased until the cycles at which the beam main bars and slab main bars respectively yielded, but after yielding, only the cracks that occurred at the expected hinge positions became larger, and almost no new cracks occurred in other areas.

[0043] Figure 19 shows the transition of maximum crack width of beams and slabs at the peak and upon unloading of each loading cycle. The residual maximum crack width of the beams upon unloading was 0.35 mm when R = -1 / 200 rad and 0.35 mm when R = -1 / 100 rad, while the residual maximum crack width of the top surface of the slab upon unloading was 0.2 mm when R = -1 / 200 rad and 0.6 mm when R = -1 / 100 rad. Furthermore, the Architectural Institute of Japan's seismic performance evaluation guidelines indicate Damage Level II: Repair Limit I (crack width in components of 0.2 to 1.0 mm or less in a full-scale building) as an index of the level of damage that can be repaired with small-scale repairs, and taking into account the dimensions of the test specimen, the crack width index is about half the value, or 0.5 mm. Regarding the maximum remaining crack width of the beam when unloaded, when the general design criteria for level 2 earthquake motion, R=1 / 100rad, is taken into consideration and the size effect of the test specimen is evaluated based on the above guidelines, the crack width of the member in a full-scale building is 0.2 to 1.0 mm, which corresponds to damage level II: repair limit I (minor repairs required). Therefore, it was found that if the beam member of the present invention is adopted in an actual building, the building can be used continuously with minor repairs even after an earthquake.

[0044] Figure 20 shows the residual crack area ratio γAcr for each observation area on the side of the beam and the top of the slab when the positive load is removed. The vertical axis shows the residual crack area ratio for each observation area, and the horizontal axis shows the area shown at the top of the figure. The areas (B and G) including the assumed hinge positions on both the side of the beam and the top of the slab have a significantly larger residual crack area ratio compared to other areas, but the residual crack area ratio on the column side is small, and there is almost no residual crack area ratio in the area where the adhesion has been removed. Therefore, with the beam member according to the present invention, it is possible to limit the areas that need to be repaired for earthquake damage to the assumed hinge positions, thereby reducing repair costs.

[0045] Although the present invention has been described above through the embodiments, the technical scope of the present invention is not limited to the above embodiments. It is clear to those skilled in the art that various modifications and improvements can be made to the above embodiments, and it is clear from the claims that such modifications and improvements can also be included in the technical scope of the present invention.

[0046] In the above embodiment, the cross-sectional shape of the beam 10 is rectangular, and the reinforcing bars located at the corners (four corners) are provided with adhesion removal sections to form non-anchored sections, but a different angular shape is also acceptable, and in such a shape, damage can be suppressed and controlled by providing adhesion removal sections to the main bars closest to the angular corners to form non-anchored sections. Also, in the above embodiment, the anchoring steel plates 25 are configured as strips to be hung over the main bars on the top and bottom in cross section, but the anchoring steel plates 25 may be individually provided to correspond to each main bar, or may be hung over the main bars on the left and right in cross section, or may be provided as a square-shaped anchoring steel plate having holes through which all the main bars having adhesion removal sections can be inserted.

[0047] In addition, it is believed that the length of the anchoring section relative to the overall length of the beam 10 in the above embodiment can be set based on the required anchoring length of tensile reinforcement using deformed reinforcement in the RC structural calculation standards. Where: the bond splitting strength : Stress of reinforcing bar at joint surface :Nominal diameter of deformed bar : 1.0 if fixed in the core : Correction coefficient for required fixing length (0.7 for mechanical fixing devices) However, the above formula is for fastening to a joint, and although its applicability to fastening inside the beam 10 is uncertain, it is assumed that it may be similar.

[0048] In the above embodiment, the length of the adhesion removal section relative to the overall length of the beam 10 may be appropriately determined based on the bending crack strength and the bending moment distribution of the beam when a plastic hinge occurs. The bending crack occurrence moment is given by the following formula. Where: Compressive strength of concrete : Section modulus taking into account reinforcing bars N: Axial force D: Material thickness

[0049] It is considered desirable to compare the bending crack strength calculated by the above formula with the bending moment distribution of the beam when plastic hinges occur, and to remove the adhesion of the main reinforcement in the places where the bending moment exceeds the bending crack strength. Also, the adhesion removal section does not have to be a continuous section as shown in Figure 1, and the adhesion removal section and the fixed section may be formed, for example, alternately in shorter sections. Taking the above into consideration, it is necessary to properly evaluate the required anchorage length in the center of the beam 10 and the location where bending cracks will occur, and set the lengths of the adhesion removal section and anchorage section. [Explanation of symbols]

[0050] 1 Column beam structure, 3A; 3B column, 10 beams, 13 upper main reinforcement, 15 lower main reinforcement, P1; P2; P3 fixed part, Q1; Q2 non-fixed part, 25 fixed steel plate

Claims

1. A reinforced concrete beam having a plurality of main bars and connected between columns, At least a portion of the plurality of main reinforcements, A central anchorage portion to which the main reinforcement and concrete are attached in a predetermined range from the center of the longitudinal direction of the beam toward the column direction; a non-anchored portion in which the adhesion between the main reinforcement and the concrete in a predetermined range other than the central anchored portion is removed by an adhesion removing means; having A fixing plate is provided at the boundary between the central fixing portion and the non-fixing portion, A reinforced concrete beam characterized in that the anchor plate is a plate-like body having openings through which at least two main reinforcements can be inserted, above and below when viewed in longitudinal section of the beam.

2. A reinforced concrete beam as described in Claim 1, characterized in that the anchoring plate is a plate-like body having openings through which all of the main reinforcement bars having the non-anchored portions can be inserted.

3. A reinforced concrete beam as described in claim 1 or 2, characterized in that the main reinforcement having the central fixing portion and the non-fixing portion is located at least at the corner portion when viewed in longitudinal cross section of the beam.

4. A position spaced a predetermined distance from the joint between the column and the beam toward the center of the beam is set as an assumed hinge; A reinforced concrete beam as claimed in any one of claims 1 to 3, characterized in that the column side end of the non-fixed portion is set as the position of the assumed hinge.

5. 5. A reinforced concrete beam according to claim 1, wherein the adhesion removal means is a sheath pipe attached to the outer periphery of the main reinforcement.

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