Design method for high-strength reinforced concrete beam-column joint capable of improving anti-seismic performance

Abstract

The invention belongs to the technical field of building structure design, and particularly relates to a design method of a high-strength reinforced concrete beam-column joint capable of improving anti-seismic property, which limits and adjusts the hooping rate of stirrups in a core area of the beam-column joint to be greater than 1.359% through matching use of ultra-high performance concrete, common concrete and high-strength steel bars; the change of a node failure mode from core area shear failure to beam end bending failure is realized, and the node ductility is obviously improved; the joint axial pressure ratio is smaller than or equal to 0.2, so that the displacement ductility and the energy dissipation capacity are prevented from being remarkably reduced due to the too high axial pressure ratio; meanwhile, the distance between one end, close to the column, of the unbonded section area of the unbonded area and the surface of the column is larger than or equal to 0.5 times of the beam height, the length is 1.0-1.5 times of the beam height, and the damage area is prevented from being located in the core area; a gradual change area is arranged to prevent stress sudden change; the connecting pipe is arranged, so that the ultra-high performance concrete and the common concrete work in a highly cooperative manner; and a shear bearing capacity calculation formula is innovated.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of building structure design, and particularly relates to a high-strength reinforced concrete beam-column joint design method for improving seismic performance. BACKGROUND

[0002] High-strength steel bars (500 Pa and above) have significant advantages in the promotion of green low-carbon buildings. The strength of high-strength steel bars far exceeds that of ordinary steel (such as 335 MPa grade), which can greatly reduce the amount of steel used per unit of building area. The use of 635 MPa grade steel bars instead of ordinary steel bars can save more than 20% of steel; in high-rise or large-span buildings, the saving rate can reach 30%. Steel production has high carbon emissions (2 kg of CO2 per kg of steel), and high-strength steel bars directly reduce carbon emissions by reducing the amount used. Promoting 500 MPa and above steel bars can reduce carbon emissions in the construction industry by more than 20%, and simultaneously reduce iron ore and coal consumption. In addition to saving materials and reducing carbon emissions, high-strength steel bars also have high plasticity, high yield ratio, and seismic resistance, improving the safety of building structures. At the same time, it reduces the workload of logistics transportation, on-site processing and connection, and saves civil construction costs by more than 10%. High-strength steel bars have become the core material of green buildings to replace traditional low-strength steel bars through material saving, carbon reduction, and efficiency improvement. Because the strength of the steel bar is relatively high, the yield strain of the steel bar is greater than that of the ordinary steel bar. Under the same load conditions, the yield displacement of the high-strength steel bar is greater than that of the ordinary steel bar, so the ductility of the component is lower, and therefore whether the application of high-strength steel bars meets the seismic requirements of the specification needs to be studied. When the strength of the steel bar is high, the bond stress of the concrete will be large when the steel bar yields, which will accelerate the bond degradation of the joint, thereby changing the force transfer mechanism of the joint from "truss mechanism" to "diagonal compression strut mechanism". At the same time, the concrete in the diagonal compression zone of the joint will crush earlier, leading to the premature failure of the joint. Therefore, the core problem of the application of high-strength steel bars in beam-column joints is the brittle shear failure of the core area of the joint, the reduction of displacement ductility, and the acceleration of stiffness degradation, which affects the overall seismic performance of the structure. SUMMARY

[0003] In order to solve the problem that when existing high-strength steel bars are used in beam-column joints, the core area of ​​the node is prone to brittle shear failure, reduced displacement ductility, accelerated stiffness degradation, and affects the overall seismic performance of the structure, the present invention provides a high-strength reinforced concrete beam-column node design method with improved seismic performance. Through the synergistic mechanism of core area parameters (steel strength, core area stirrup ratio, concrete material combination, axial compression ratio), a key technical solution for optimizing node structure and accurately calculating shear bearing capacity is proposed. By releasing stress in the unbonded section area, the damage is controlled in the non-core area of ​​the beam end. At the same time, ultra-high performance concrete and high-strength steel bars are used in the core area to work together to improve the seismic performance of the node. Factors such as axial compression ratio and core area stirrup ratio are taken into consideration, so that the seismic performance of the node is greatly improved compared with the use of high-strength steel bars alone, and at the same time, the national development strategy requirements of green, low-carbon, energy-saving and environmental protection are met.

[0004] In order to achieve the above object, the technical solution of the present invention is:

[0005] A method for designing high-strength reinforced concrete beam-column joints to improve seismic performance comprises the following steps:

[0006] Step 1: Select high-strength steel bars with a tensile strength standard value greater than or equal to 500 MPa as beam longitudinal reinforcement and stirrups in the core area of ​​the node and within 1.0 times the beam height near the core area of ​​the beam and column. Delineate an unbonded section on the beam longitudinal reinforcement, and the distance from the end of the unbonded section near the column to the column surface is greater than or equal to 0.5 times the beam height. The length of the unbonded section is 1.0-1.5 times the beam height.

[0007] Step 2: Adjust the stirrup ratio of the core area of ​​the beam-column joint to be greater than 1.359%, the stirrup diameter to be greater than or equal to 10mm, and the spacing to be less than or equal to 100mm. The core area is filled with ultra-high performance concrete with a tensile strength greater than or equal to 120MPa and a fiber content of 2%-3%. The axial compression ratio of the joint is less than or equal to 0.2.

[0008] Step 3: A corrugated tube is sheathed on the surface of the longitudinal reinforcement of the beam in the unbonded section area, and the ends of the tube are sealed with sealant. A gradient zone with a length of 0.5 times the beam height is set at both ends of the unbonded section area, and the surface of the steel bars in the gradient zone is coated with a slow-bonding material;

[0009] Step 4: Install a removable steel formwork in the core area of ​​the beam-column joint. Pre-attach a 3mm thick rubber pad to the inside of the formwork. Set a serrated partition with a tooth depth of 20mm or more at the end of the core area. Apply a micro-expansion interface agent with an expansion rate of 0.02% or more to the partition.

[0010] A connecting pipe is installed on the template at the end of the core area. The connecting pipe is set at 45 degrees, with its upper end passing through the upper side of the core area and the lower end being closed and extending into the lower end of the beam outside the core area;

[0011] Step five, pouring ordinary concrete outside the beam core area, and after the initial setting of ordinary concrete, the partition plate and connecting pipe are removed, and the core area is poured with ultra-high performance concrete;

[0012] Step six, the formula (I) is used to calculate the shear capacity of the joint:

[0013] In formula (I)

[0014] V j Shear capacity of high-strength steel reinforced beam-column joint / MPa;

[0015] F c Concrete compressive strength / MPa;

[0016] B c h c Section size of column end / mm;

[0017] H j Joint section height / mm;

[0018] F yv Tensile strength of stirrup / mm;

[0019] A sv Total cross-sectional area of stirrup arranged in the same section / mm2;

[0020] s is the spacing of stirrups / mm;

[0021] h0 is the effective height of the joint section / mm;

[0022] a' s Distance from the force point of longitudinal reinforcement to the edge of concrete / mm.

[0023] Preferably, the distance between the two ends of the core area and the column surface is 0.3-1.0 times the beam height.

[0024] Preferably, the stirrup ratio in step two is greater than or equal to 2.718%.

[0025] Preferably, the stirrup ratio is 2.718%.

[0026] Preferably, the axial compression ratio of the joint in step two is less than or equal to 0.1.

[0027] Preferably, the corrugated pipe in step three is a PE corrugated pipe.

[0028] Preferably, the PE corrugated pipe can be replaced with hot melt wax coated on the surface of the steel bar in the unbonded section area.

[0029] Preferably, the connecting pipe in step four is a PVC pipe with a diameter of 20-30 mm.

[0030] Preferably, the connecting pipe in step four is fixed by binding with the steel bars in the beam.

[0031] Preferably, the unbonded section in step one has a length of 1.0 times the height of the beam.

[0032] Through the above technical solutions, the beneficial effects of the present application are:

[0033] 1. By optimizing the stirrup ratio and the concrete material (such as using ultra-high performance concrete), the present application significantly improves the ultimate bearing capacity of the joint (about 40.1% higher than that of a joint with ordinary steel bars), effectively overcomes the low displacement ductility (reduced by 89.3%) and rapid stiffness degradation, and significantly improves the ductility (the ductility is increased by 72.8% by increasing the stirrup ratio), energy dissipation capacity and hysteresis performance of the joint.

[0034] 2. The present application provides a synergistic effect law of key parameters such as steel strength, core stirrup ratio, axial compression ratio and core concrete material, and a quantitative influence of the key parameters on the performance (failure mode, bearing capacity, ductility, energy dissipation and stiffness) of the joint, which provides scientific guidance for fine and performance-based design of the joint.

[0035] 3. The beam-column joint design scheme of the present application can significantly improve the seismic performance: unbonding design reduces cracks in the core area, increases the energy dissipation ratio at the beam end, and increases the ductility coefficient.

[0036] The failure mode of the joint is controllable (guided to the better ductility beam end bending failure);

[0037] The joint bearing capacity is increased by ≥10%, which makes the beam-column damage concentrated in the unbonded area, and the core area of the joint is basically free of cracks (ultra-high performance concrete supports crack resistance). BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 The figure is a schematic diagram of the loading system of the present application.

[0039] Figure 2 The figure is the final failure pattern of test specimen 1 after the seismic performance test of the present application.

[0040] Figure 3 The figure is the final failure pattern of test specimen 2 after the seismic performance test of the present application.

[0041] Figure 4 The figure is the final failure pattern of test specimen 3 after the seismic performance test of the present application.

[0042] Figure 5 The figure is the final failure pattern of test specimen 4 after the seismic performance test of the present application.

[0043] Figure 6 This is the hysteresis curve diagram of the seismic performance test of specimen 1 of the present invention.

[0044] Figure 7 This is the hysteresis curve diagram of the seismic performance test of specimen 2 of the present invention.

[0045] Figure 8 This is the hysteresis curve diagram of the seismic performance test of specimen 3 of the present invention.

[0046] Figure 9 This is the hysteresis curve diagram of the seismic performance test of specimen 4 of the present invention.

[0047] Figure 10 It is a comparison diagram of the energy consumption curves of test pieces 1-4 of the present invention.

[0048] Figure 11 This is a comparison chart of the shear bearing capacity test values ​​and calculated values ​​of specimens 1-4 of the present invention.

[0049] Figure 12 This is the stress-strain relationship curve of high-strength steel bars.

[0050] Figure 13 This is the compression failure curve of ultra-high performance concrete.

[0051] Figure 14 This is the compression hardening curve of ultra-high performance concrete.

[0052] Figure 15 This is the tensile softening curve of ultra-high performance concrete.

[0053] Figure 16 This is the tensile failure curve of ultra-high performance concrete.

[0054] Figure 17 Schematic diagram of damage distribution of specimen 9 of the present invention after simulation of seismic performance test.

[0055] Figure 18 Schematic diagram of damage distribution of the specimen 10 of the present invention after the simulation of the seismic performance test.

[0056] Figure 19 Schematic diagram of damage distribution of the specimen 11 of the present invention after the simulation of the seismic performance test.

[0057] Figure 20 Schematic diagram of damage distribution of the specimen 12 of the present invention after the simulation of the seismic performance test.

[0058] Figure 21 Schematic diagram of damage distribution of specimen 13 of the present invention after simulation of seismic performance test.

[0059] Figure 22 Schematic diagram of damage distribution of the specimen 14 of the present invention after the simulation of the seismic performance test.

[0060] Figure 23 This is a schematic diagram of the connection pipe arrangement structure of the present invention. DETAILED DESCRIPTION

[0061] The present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0062] A method for designing high-strength reinforced concrete beam-column joints to improve seismic performance comprises the following steps:

[0063] Step 1: Select high-strength steel bars with a tensile strength standard value greater than or equal to 500 MPa as beam longitudinal reinforcement and stirrups in the core area of ​​the node (beam-column junction area) and within 1 times the beam height of the beam and column near the core area. Delineate an unbonded section on the beam longitudinal reinforcement, and the distance from the end of the unbonded section near the column to the column surface is greater than or equal to 0.5 times the beam height. The length of the unbonded section is 1.0-1.5 times the beam height.

[0064] The length of the unbonded area in step 1 is 1.0 times the beam height.

[0065] The distance between the two ends of the core area and the column surface is 0.3-1.0 times the beam height. The core area refers to the beam-column node position and the area extending between 0.3-1.0 times the row height at both ends along the length direction of the beam.

[0066] By demarcating the unbonded section area, the distance between the unbonded section and the column surface is greater than or equal to 0.5 times the beam height, effectively avoiding the overlap of the plastic hinge area and the core area. The unbonded section area is used to release stress and control the damage of the beam to the non-core area at the beam end. After an earthquake, since the damage is concentrated in the unbonded section area, only the steel bars in the unbonded section need to be replaced, and repairs are quick.

[0067] Step 2: Adjust the stirrup ratio of the core area of ​​the beam-column node to be greater than 1.359%, the stirrup diameter is greater than or equal to 10mm, and the spacing is less than or equal to 100mm. The core area is filled with ultra-high performance concrete with a tensile strength greater than or equal to 120MPa and a fiber content of 2%-3%, and the node axial compression ratio is less than or equal to 0.2.

[0068] Furthermore, in the step 2, the stirrup ratio is greater than or equal to 2.718%. Preferably, the stirrup ratio is 2.718%. For beam-column nodes equipped with 500 MPa grade and above high-strength steel bars, the node failure mode is transformed from shear failure in the core area to bending failure at the beam end by controlling the stirrup ratio in the core area within a specific range, thereby significantly improving the node ductility.

[0069] Furthermore, in step 2, the node axial compression ratio is less than or equal to 0.1, and the axial compression ratio is reasonably controlled (should not exceed 0.2) to avoid a significant reduction in displacement ductility and energy dissipation capacity due to an excessively high axial compression ratio.

[0070] Step three: a corrugated tube is sheathed on the surface of the longitudinal reinforcement of the beam in the non-bonded section area, and the tube ends are sealed with sealant. A gradient zone with a length of 0.5 times the beam height is set at both ends of the non-bonded section area, and the surface of the steel bars in the gradient zone is coated with slow-bonding material.

[0071] The corrugated pipe in step three is a PE corrugated pipe, and the PE corrugated pipe can be replaced with hot melt wax coated on the surface of the steel bars in the non-bonded section area.

[0072] By setting up the corrugated pipe, the bonding between the concrete and the steel bars is eliminated, forming a plastic hinge area.

[0073] Step 4: Install a removable steel formwork in the core area of ​​the beam-column node, pre-attach a 3mm thick rubber pad on the inside of the formwork, and set a serrated partition with a tooth depth greater than or equal to 20mm at the end of the core area (the side of the partition away from the core area is serrated). The partition is coated with a micro-expansion interface agent with an expansion rate greater than or equal to 0.02%.

[0074] The partition is used to form the end of the non-core area concrete close to the core area into a zigzag shape. Then, when the ultra-high performance concrete of the core area is poured, it flows into the zigzag groove. After the pouring is completed, it is ensured that the core area and the non-core area (ultra-high performance concrete is poured in the core area, and ordinary concrete is poured in the non-core area) are tightly interlocked and embedded.

[0075] A connecting pipe is installed on the template at the end of the core area. The connecting pipe is set at 45 degrees, with its upper end passing through the upper side of the core area and the lower end closed and extending into the lower end of the beam outside the core area. Figure 23 As shown (the PVC pipe in the figure is the connecting pipe).

[0076] The connecting pipe described in step 4 is a PVC pipe with a diameter of 20-30 mm.

[0077] The connecting pipe described in step 4 is fixed by tying it to the steel bars in the beam. The connecting pipe is firmly tied to the steel bars nearby, and structural fixing steel bars can be set if necessary.

[0078] By setting the connecting pipe, an inclined inlet is left at the end of the concrete in the non-core area, so that the subsequently poured ultra-high performance concrete can flow into it.

[0079] Step 5: pour ordinary concrete outside the core area of ​​the beam, remove the partitions and connecting pipes after the ordinary concrete has initially set, and pour ultra-high performance concrete in the core area.

[0080] The super high performance concrete is poured by layer pouring core area (less than or equal to 500 mm per layer), fast insertion and slow pulling of the plug-in vibrator, and steam curing (constant temperature for 48 h at 60 DEG C) with the covering curing film.

[0081] The core area concrete and the non-core area concrete are engaged through the sawtooth structure by the partition plate, and the inlet left by the connecting pipe at the position of the non-core area concrete is used, one end of the connecting pipe is inserted into the longitudinal reinforcement at the bottom of the non-core area ordinary concrete beam and the end is closed to avoid the concrete entering the pipe, the other end is extended out of the end beam of the super high performance concrete, after pulling out the partition plate and the super high performance concrete poured after the connecting pipe, the super high performance concrete flows into the hole formed by the connecting pipe at the end of the ordinary concrete, forming the structure of the super high performance concrete embedded in the ordinary concrete, realizing the high cooperation of the super high performance concrete and the ordinary concrete.

[0082] Further, the super high performance concrete can be selected as the super high performance concrete with the tensile strength greater than or equal to 120 MPa and the fiber content of 2%-3%, the high toughness and crack resistance protection joint is used, and the super high performance concrete is bonded with the high strength steel bar, and the bending resistance is enhanced. The ordinary concrete can be selected as the C30-C40 concrete.

[0083] Step six, the formula (one) is used to calculate the joint shear capacity:

[0084] In the formula (one)

[0085] V j The shear capacity of the high strength steel bar beam column joint is / MPa.

[0086] F c The compressive strength of the concrete is / MPa.

[0087] B c , h c The section size of the column end is / mm.

[0088] H j The section height of the joint is / mm.

[0089] F yv The tensile strength of the stirrup is / mm.

[0090] A sv The full section area of the stirrup arranged in the same section is / mm 2 .

[0091] s is the spacing of the stirrup / mm.

[0092] h0 is the effective height of the joint section / mm.

[0093] a' sDistance from longitudinal reinforcement force point to concrete edge / mm.

[0094] The shear capacity of the concrete beam-column joint of the 500 MPa grade and above high-strength steel is checked by the above formula (one).

[0095] As an implementable manner, the beam longitudinal reinforcement adopts a "three-section reinforcement structure" along the full length of the beam, specifically a bonded reinforcement section + a non-bonded reinforcement section area + a bonded reinforcement section, and the stress is released through the non-bonded section area to control the damage in the non-core area of the beam end. Through the synergistic mechanism of the core parameters (reinforcement strength, core area stirrup ratio, axial compression ratio, core area concrete material), the four protection mechanisms of the core area stirrup ratio of the high-strength steel joint core area, the use of ultra-high performance concrete, the setting of the axial compression ratio, and the setting of the non-bonded area of the beam end are realized. The node zero damage and the controllable energy dissipation of the beam end are realized.

[0096] Through the synergistic work of the core area using ultra-high performance concrete and high-strength steel, the seismic performance of the joint is improved. And considering the axial compression ratio and the core area stirrup ratio, the seismic performance of the joint is greatly improved compared with the use of high-strength steel alone, and the effect of green low carbon, energy saving and environmental protection is also realized.

[0097] By using ultra-high performance concrete in the core area of the beam-column joint and ordinary concrete in the non-core area, the construction requirement of strong joint and weak component is achieved. The high-strength steel of 500 MPa and above works synergistically to take advantage of high-strength steel and greatly improve the seismic performance of the beam-column joint.

[0098] Under the action of earthquake, plastic deformation is concentrated in the non-bonded section, and energy is dissipated through steel yielding. The ultra-high performance concrete joint area avoids damage due to ultra-high strength, realizing "strong joint and weak component".

[0099] Example 1:

[0100] The size and reinforcement of the beam-column joint are taken as an example, with the beam section being 300*400mm and the length being 1700mm, the column section being 400*400mm and the length being 3000mm, the high-strength steel reinforcement in the joint being as shown in Table 1.1, the core area stirrup ratio being 2.718%, and the axial compression ratio being 0.2.

[0101] Table 1.1 Test specimen design parameters

[0102]

[0103] Note: In Table 1.1, D represents high-strength steel bars. For example, 6D20 refers to 6 high-strength steel bars with a diameter of 20 mm. 6D10+8D10 refers to 6 high-strength steel bars with a diameter of 10 mm plus 8 high-strength steel bars with a diameter of 10 mm. The yield strength of the high-strength steel bar with a diameter of 10 mm is 642.0 MPa and the ultimate strength is 830.0 MPa. The yield strength of the high-strength steel bar with a diameter of 20 mm is 645.5 MPa and the ultimate strength is 829.3 MPa.

[0104] The seismic performance test of high-strength reinforced concrete beam-column joints was carried out on the above scheme. The control group was equipped with high-strength steel bars, C50 concrete beam-column joints, and the core area stirrup ratio and axial compression ratio parameters were exactly the same.

[0105] The seismic test of beam-column joints adopts monotonic antisymmetric loading to simulate the stress state of the joints under earthquake. To ensure the accuracy of the test data and the normal operation of the equipment. Before the formal test, the pre-load repeated load test is carried out twice, and the pre-load value is 30% of the cracking load. After loading, the readings are measured to check whether the loading device, node specimens, and instruments and equipment are working normally, and then the formal test is carried out. First, the calculated axial pressure is applied to the upper end of the column, and load-displacement dual control is adopted during loading. The yielding of the main tensile reinforcement of the beam is used as the boundary. Load control is used before, and displacement control is used after. During load control, the load when the main tensile reinforcement of the beam yields is taken as Py, and the monotonic antisymmetric load control values ​​applied are 0.3Py, 0.6Py and 0.9Py. During displacement control, the yield displacement is taken as Δy, and the monotonic antisymmetric displacement control values ​​applied are 1Δy, 2Δy, 3Δy, etc., and each level is cycled 3 times until the specimen is destroyed. The schematic diagram of the loading system is as follows Figure 1 shown.

[0106] like Figures 2-5 As shown,

[0107] Final failure mode: The final failure modes of the four specimens are divided into two situations: specimens JD1, JD3 and JD4 suffered bending failure at the beam end, and specimen JD2 suffered shear failure in the core area. It can be seen that the reinforcement condition of the core area is an important factor affecting the failure mode of the node. When the stirrup ratio in the core area is low, the node specimen will suffer shear failure in the core area.

[0108] The failure modes and crack development of JD1 and JD3 are very similar, indicating that the change in axial compression ratio has little effect on the failure characteristics of high-strength reinforced concrete beam-column joints.

[0109] The final damage of the bending failure of the beam end is the formation of cracks running through the beam end, but the main damage area is the upper and lower ends of the beam root. The concrete in this area is crushed and falls off in large quantities. The concrete in the areas around the upper and lower cracks running through the beam end is relatively intact, and no large-scale concrete falling occurs.

[0110] The failure mode of JD2 is core shear failure. The core region of JD2 is subjected to shear, and the middle region is concrete bulging and shedding, forming X-shaped cross cracks through the sides of the column, and large pieces of concrete directly shedding at the end of the crack, with a large gap between the end cracks. It can be seen that increasing the volumetric stirrup ratio of the joint can effectively strengthen the core region of the joint and change the failure mode of the joint.

[0111] The core region of JD4 is super high performance concrete, which also forms cracks through the beam end, but the width range of the cracks and the surrounding concrete damage are smaller than those of other joint specimens. It can be seen that the use of super high performance concrete in the core region of the joint can effectively increase the seismic performance of the joint, and also conforms to the design principle of "strong joint, weak component".

[0112] Hysteretic performance: The hysteretic curve mainly expresses the relationship between beam end load and beam end displacement, and can better reflect the ductility and energy dissipation of the joint. The more full the hysteretic curve formed by the joint under cyclic loading is, the better the hysteretic performance of the joint is, as shown in Fig. 6. Figures 6-9

[0113] The hysteretic curve of high-strength steel bar specimen JD1 gradually presents "arch" pinch after yielding. The hysteretic curve of JD2 shows significant "Z" type folding characteristics after Δy, and the loop area decreases sharply after peak load, and the bearing capacity decreases suddenly when the reverse loading appears, indicating that the shear crack in the core region penetrates when the stirrup constraint is insufficient, which causes the shear crack to penetrate and the stiffness to change suddenly, and the hysteretic curve presents a brittle failure mode. The symmetry of the hysteretic loop bearing capacity of the specimen JD1 with axial compression ratio of 0.2 is better than that of the specimen JD3 with axial compression ratio of 0.1 in the positive loading segment. However, the difference in the hysteretic curve path of JD2 increases due to the weakening of the inhibitory effect of axial compression on the core region unloading expansion during reverse loading. It shows that moderately increasing the axial compression ratio can enhance the compression-shear composite bearing mechanism of the core region. The loop area of specimen JD4 with super high performance concrete in the core region is increased by 37.6% compared with JD1, and the loop shape remains approximately "spindle-shaped" before 3Δy. The high tensile toughness of super high performance concrete inhibits the expansion of crack width, so that the core region forms a distributed microcrack network rather than a discrete main crack, thereby effectively delaying the stiffness decay and improving the fullness of the hysteretic loop.

[0114] ​Ductility: In seismic analysis, ductility is a key parameter that reflects a structure's deformation capacity. The higher the ductility of a component, the greater its ability to dissipate energy under earthquake action. The ductility coefficient μ is the ratio of the displacement Δu at which a structure or component reaches ultimate failure to its yield displacement Δy, i.e., μ = Δu / Δy. The calculated ductility coefficients for the four specimens were 4.20, 2.43, 3.06, and 4.10, respectively. The ductility coefficient of JD1 was 72.8% higher than that of JD2. This indicates that using denser reinforcement in the core area can improve the ductility of the specimen. The ductility coefficient of JD1 was 37.3% higher than that of JD3, indicating that increasing the axial compression ratio can improve the ductility of the specimen. The ductility coefficient of JD1 was 2.4% higher than that of JD5. This indicates that the use of ultra-high performance concrete in the core area of ​​the joint has little effect on the ductility of the specimen.

[0115] Energy dissipation capacity: Energy dissipation capacity is another important indicator for evaluating the seismic performance of structures or components. This section uses cumulative energy dissipation to evaluate the energy dissipation capacity of specimens:

[0116]

[0117] Where i represents the loading level, j represents the number of cycles corresponding to each loading level, and E i,j represents the area corresponding to each hysteresis loop.

[0118] The energy consumption of the specimen can be evaluated by the cumulative energy consumption curve. Specifically, the cumulative energy consumption of the specimen at a certain point refers to the sum of the areas of all hysteresis loops from the start of the test to that point. By analyzing these curves, we can more intuitively understand the differences and characteristics of energy consumption of different specimens. The energy consumption curves of the four specimens (JD1-4) are shown in Figure 10 shown.

[0119] During the loading process, the cumulative energy dissipation curves for each specimen exhibited a significant nonlinear growth pattern. During the initial loading phase (0-Δy), the energy dissipation rates for all specimens varied slightly and showed a gentle growth trend, indicating that energy accumulation was primarily due to elastic deformation of the structure. After entering the yield phase, the energy dissipation rate exhibited a gradient differentiation. The total cumulative energy dissipation for specimen JD1 was 155 kN·mm. The high-strength rebar specimens exhibited a rapid initial energy dissipation rate, but the energy dissipation rate slowed significantly during the plastic phase. This "fast initial growth rate and low latent energy" characteristic suggests that the increased bearing capacity of the high-strength rebar, achieved through delayed yielding, failed to translate into sustained energy dissipation capacity. The shortening of the hardened phase and accelerated failure combined to degrade the overall energy dissipation capacity. The cumulative energy dissipation curve for specimen JD1 exhibited a step-like upward trend, with the total energy dissipation of 155 kN·mm throughout the entire process representing a 58.2% increase compared to the 98 kN·mm for the low-stirrup specimen JD2. When the displacement reaches 2Δy, the cumulative energy consumption of JD1 reaches 1.8 times that of JD2, and as the loading continues, this difference gradually expands to 2.3 times the peak displacement. The difference in energy consumption between the two groups of specimens is mainly concentrated in the post-peak stage. When the displacement reaches 2Δy, the energy consumption of JD2 has reached 85.4%, while the energy consumption of JD1 to 3Δy remains at 72.3%. Combined with the observation of cracks in the core area, it can be seen that the dense stirrups disperse the single main crack into multiple microcracks by constraining the lateral deformation of the concrete, thereby increasing the energy dissipation path for each loading cycle. The increase in the stirrup ratio changes the shear failure mode of the node from concentrated damage to distributed energy consumption, and by maintaining the stability of the shear stiffness of the core area, it prolongs the continuous growth time of the plastic energy dissipation section.

[0120] Compared to JD3, the total cumulative energy dissipation of specimens JD1 and JD3 decreased from 201 kN·mm to 155 kN·mm, a 22.9% reduction. Comparing the cumulative energy dissipation curves for specimens JD1 and JD3 reveals that the influence of the axial pressure ratio on energy dissipation capacity has a significant phased effect. While forward loading improves energy absorption efficiency by enhancing interfacial friction, long-term high pressure accumulation exacerbates damage in the core area, limiting the potential for later energy dissipation.

[0121] Specimen JD4, constructed with an ultra-high performance concrete core, experienced a similar cumulative energy consumption growth rate to that of specimen JD1, constructed with conventional concrete, during the initial plastic phase. However, after entering the failure phase, the incremental energy consumption slope increased by 37%, ultimately resulting in a 42% increase in total energy consumption compared to JD1. The combination of ultra-high performance concrete and a high stirrup ratio effectively suppressed the brittle nature of high-strength steel reinforcement nodes.

[0122] Shear capacity calculation:

[0123] The measured value is 1087.8 kN, the calculated value using the "Concrete Structure Design Standard" GB50010-2010 is 752.9 kN, and the calculated value using the formula of the present invention is 1087.5 kN. It can be seen that the solution provided by the present invention has higher prediction accuracy.

[0124] At the same time, the calculation formula provided by the present invention is used to calculate the shear bearing capacity of specimens 2 and specimens 5-8. The results are shown in Table 1.2 (Vt is the test value of the node shear bearing capacity; Vc is the calculated value of the formula in this paper) and Figure 11 The mean of the ratio of the calculated value to the measured value is 1.02, and the standard deviation and coefficient of variation are both 0.11.

[0125] Table 1.2 Comparison of shear bearing capacity test values ​​and calculated values ​​for specimens 2 and 5-8

[0126]

[0127] Referring to the data in Table 1.2, the design parameters of specimens 5-8 are derived from the following four documents, as follows:

[0128] JD5 (Specimen 5): Zhang Jianxin. Study on seismic performance test and design method of high-strength reinforced high-toughness concrete frame joints[D]. Tianjin: Hebei University of Technology, 2016;

[0129] JD6 (Specimen 6): Wang Qi. Research on seismic performance of new prefabricated high-strength reinforced concrete frame nodes[D]. Tianjin: Hebei University of Technology, 2020;

[0130] JD7 (Specimen 7): Ge Hongliang. Experimental study on seismic performance of middle-layer nodes in frames with HRB500 steel bars[D]. Chongqing: Chongqing University, 2007;

[0131] JD8 (Specimen 8): Han Fei. Research on seismic performance of 735Mpa grade high-strength reinforced concrete frame nodes[D]. Jinan: Shandong University, 2021.

[0132] Example 2:

[0133] Based on the results of Example 1, the dimensions and reinforcement of the beam-column joint in this example are identical to those of JD4 in Example 1. The core area stirrup ratio is 2.7, and the axial compression ratio is 0.2. Unlike Example 1, an unbonded section is included within the beam. This example focuses on testing the effect of the depth of ultra-high performance concrete (UHPC) embedded within the beam on its seismic performance and the location of the plastic hinge. The UHPC exhibits an elastic modulus of 49,000 MPa, a compressive strength of 114 MPa, and a tensile strength of 9 MPa. See Table 2 for specimen details.

[0134] Table 2 Specimen details

[0135]

[0136] Referring to the strain curve diagram as shown in Figures 12-16 The nonlinear analysis was performed by MIDAS / FEA NX, and the loading system was the same as that of Example 1. The concrete damage distribution of each test piece at the time of failure was calculated as shown in Figures 17-22 It can be seen that the reference test piece JD9 has serious damage in the range of 120 mm from the beam end to the column surface and in the core zone, the JD10 has no damage in the core zone and local damage in the concrete in the range of 120 mm from the beam end to the column surface, the JD11 has no damage in the core zone and the super high performance concrete extending into the beam end, and the concrete in the unbonded section has large area damage, the JD12-JD14 has no damage in the core zone and the super high performance concrete extending into the beam end, and the concrete in the unbonded section has local damage. The longer the super high performance concrete extends into the beam end, the fewer the number of local damage of the concrete in the unbonded section. It can be seen that the damage of the concrete in the unbonded section is less when the super high performance concrete extends into the beam end by 0.5h, and the damage range of the concrete in the unbonded section is the smallest when the super high performance concrete extends into the beam end by h.

[0137] The high-strength steel test piece with the core zone replaced by super high performance concrete has significant advantages over the ordinary steel test piece. The shear bearing capacity of the core zone is significantly improved, and the damage development of the plastic hinge zone at the beam end is controllable. Although high-strength steel has the inherent defect of insufficient ductility, the application of the present application can effectively compensate for the loss of ductility through the optimization of the stirrup ratio and the use of super high performance concrete, forming an ideal failure mode of "strong node, weak component". In summary, the present application performs excellently in terms of bearing capacity, core zone integrity and energy dissipation capacity, especially when combined with high-performance concrete, it becomes an optimal solution to meet the seismic requirements in high-intensity regions.

[0138] It should be noted that the adjustment of each parameter in the core zone of the beam-column joint is not isolated, but mutual influence and synergistic effect can achieve the best effect. For example, increasing the stirrup ratio alone can improve ductility, but the effect is better when combined with super high performance concrete. High axial compression ratio can weaken the gain effect of stirrup ratio and super high performance concrete.

[0139] The above-described embodiments are only preferred embodiments of the present application and do not limit the scope of the application. Any equivalent changes or modifications made in accordance with the structure, features and principles described in the patent scope of the present application shall be included in the patent scope of the present application.

Claims

1. A design method for high-strength reinforced concrete beam-column joints to improve seismic performance, characterized in that: The following steps are involved: Step 1: Select high-strength steel bars with a tensile strength standard value greater than or equal to 500 MPa as beam longitudinal reinforcement and stirrups in the core area of ​​the node and within 1.0 times the beam height near the core area of ​​the beam and column. Delineate an unbonded section on the beam longitudinal reinforcement, and the distance from the end of the unbonded section near the column to the column surface is greater than or equal to 0.5 times the beam height. The length of the unbonded section is 1.0-1.5 times the beam height. Step 2: Adjust the stirrup ratio of the core area of ​​the beam-column joint to be greater than 1.359%, the stirrup diameter to be greater than or equal to 10mm, and the spacing to be less than or equal to 100mm. The core area is filled with ultra-high performance concrete with a tensile strength greater than or equal to 120MPa and a fiber content of 2%-3%. The axial compression ratio of the joint is less than or equal to 0.

2. Step 3: A corrugated tube is sheathed on the surface of the longitudinal reinforcement of the beam in the unbonded section area, and the ends of the tube are sealed with sealant. A gradient zone with a length of 0.5 times the beam height is set at both ends of the unbonded section area, and the surface of the steel bars in the gradient zone is coated with a slow-bonding material; Step 4: Install a removable steel formwork in the core area of ​​the beam-column joint. Pre-attach a 3mm thick rubber pad to the inside of the formwork. Set a serrated partition with a tooth depth of 20mm or more at the end of the core area. Apply a micro-expansion interface agent with an expansion rate of 0.02% or more to the partition. A connecting pipe is installed on the template at the end of the core area. The connecting pipe is set at 45 degrees, with its upper end passing through the upper side of the core area and the lower end being closed and extending into the lower end of the beam outside the core area; Step 5: pouring ordinary concrete outside the core area of ​​the beam, removing the partitions and connecting pipes after the initial setting of the ordinary concrete, and pouring ultra-high performance concrete in the core area; Step 6: Calculate the shear bearing capacity of the node using formula (1): In formula (1) V j Shear bearing capacity of high-strength reinforced steel beam-column joints / MPa; F c is the compressive strength of concrete / MPa; B c 、h c is the cross-sectional size of the column end / mm; H j is the node section height / mm; F yv is the tensile strength of stirrups / mm; A sv The total cross-sectional area of ​​the stirrups arranged in the same section / mm2; s is the stirrup spacing / mm; h0 is the effective height of the node section / mm; a' s It is the distance from the resultant force point of the longitudinal reinforcement to the edge of the concrete / mm.

2. A high-strength reinforced concrete beam-column joint design method for improving seismic performance according to claim 1, characterized in that: The distance between the two ends of the core area and the column surface is 0.3-1.0 times the beam height.

3. The method for designing high-strength reinforced concrete beam-column joints for improving seismic performance according to claim 1, characterized in that: In the step 2, the stirrup ratio is greater than or equal to 2.718%.

4. A method for designing high-strength reinforced concrete beam-column joints for improving seismic performance according to claim 3, characterized in that: The stirrup ratio is 2.718%.

5. The method for designing high-strength reinforced concrete beam-column joints for improving seismic performance according to claim 1, characterized in that: In the second step, the node axial compression ratio is less than or equal to 0.

1.

6. A method for designing high-strength reinforced concrete beam-column joints for improving seismic performance according to claim 1, characterized in that: The corrugated pipe described in step 3 is a PE corrugated pipe.

7. A method for designing high-strength reinforced concrete beam-column joints for improving seismic performance according to claim 6, characterized in that: The PE corrugated pipe can be replaced with hot melt wax coated on the surface of the steel bars in the non-bonded section area.

8. The method for designing high-strength reinforced concrete beam-column joints for improving seismic performance according to claim 1, characterized in that: The connecting pipe described in step 4 is a PVC pipe with a diameter of 20-30 mm.

9. The method for designing high-strength reinforced concrete beam-column joints for improving seismic performance according to claim 1, characterized in that: The connecting pipe described in step 4 is fixed by tying it to the steel bars in the beam.

10. The method for designing high-strength reinforced concrete beam-column joints for improving seismic performance according to claim 1, characterized in that: The length of the unbonded area in step 1 is 1.0 times the beam height.

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