Two-way prestressed transient differential decomposing concrete beam layering cracking method and system thereof

Abstract

This invention relates to the field of building structure demolition technology, specifically to a method and system for the layered cracking of concrete beams using a two-way prestressed transient differential method. Axial and eccentric prestresses are applied to both ends of the reinforced concrete beam, creating a stress gradient where the prestress in the tension zone is greater than that in the compression zone. N independent circumferential constraints are arranged at intervals along the beam's length, each equipped with an independent electromagnetic unlocking device. First, an unlocking signal is synchronously sent to the electromagnetic unlocking device in the tension zone to expose the longitudinal reinforcement. After a delay, an unlocking signal is synchronously sent to the electromagnetic unlocking device in the compression zone to cause the remaining concrete to fragment. This invention can completely preserve the reinforcing steel skeleton and control the size of the fragments.

Description

Technical Field

[0001] This invention relates to the field of building structure demolition technology, specifically to a method and system for the layered decomposition of concrete beams using a two-way prestressed transient differential method. Background Technology

[0002] With the acceleration of urban renewal and the advancement of dual-carbon goals, a large number of long-serving concrete buildings face the need for demolition and renovation. Reinforced concrete beams such as frame beams and foundation beams are key targets in demolition operations. The core technical challenge in the resource utilization of construction waste lies in how to achieve complete recovery of the reinforcing steel skeleton during demolition, while simultaneously breaking the concrete into easily transportable sizes and reducing noise and dust pollution.

[0003] Existing methods for demolishing concrete beams mainly include the following categories:

[0004] The first category is mechanical crushing methods. These methods use mechanical tools such as picks, hydraulic shears, or hydraulic breakers to directly crush concrete. While highly efficient, these methods generate significant amounts of dust and noise during construction, causing substantial environmental pollution. Furthermore, the reinforcing steel reinforcement is prone to plastic bending deformation during the crushing process, making it difficult to recycle completely.

[0005] The second type is the high-pressure water jet demolition method. This method uses ultra-high-pressure water jets to cause the concrete to crack and peel away. Because the reinforcing steel has strong impermeability, the steel reinforcement skeleton can be preserved. However, the concrete fragments produced by this method are irregular in shape and their size is uncontrollable, posing difficulties for subsequent removal and resource utilization.

[0006] The third type is chemical static fracturing. This method uses an expansive agent or controlled expansive chemical to react and expand within the concrete, causing cracks. This type of method has a long reaction cycle, making it difficult to meet construction schedule requirements, and it is also sensitive to environmental temperature and humidity.

[0007] The fourth category is mechanical cutting methods. This involves using diamond wire saws or circular saws to cut concrete beams into sections, which are then crushed. This method requires high precision and typically requires cutting the reinforcing steel bars first, making it impossible to preserve the steel reinforcement cage.

[0008] The fifth category involves prestress release and demolition methods for prestressed concrete structures. Current technology generally considers prestress release during demolition of prestressed concrete to be a potential safety risk, necessitating a gradual and slow release of prestress to avoid uncontrollable structural reactions caused by sudden release. For example, authoritative technical documents in the industry clearly teach that the demolition of prestressed concrete should employ gradual stress release and low-vibration cutting methods. Furthermore, research on the controllable demolition of box girder bridges shows that the energy of prestress release is affected by various parameters, requiring strict control of the release process. In a case study of the demolition of a viaduct in Brazil, researchers achieved the release of existing prestress by melting the steel strands within the sleeve, considered a method of reverse prestress application. However, this only achieved single-point melting release and failed to achieve stress gradient construction and spatiotemporal differential release.

[0009] The aforementioned prior art shares the following common technical problems:

[0010] Firstly, when dismantling reinforced concrete beams, the steel reinforcement cage is prone to plastic bending deformation or damage, making it impossible to recycle completely and resulting in low resource utilization.

[0011] Secondly, the size of concrete fragments is uncontrollable, with a wide range of sizes, which brings significant difficulties to subsequent removal, crushing and disposal, and resource utilization.

[0012] Third, the release of prestress during the demolition process is regarded as a passive byproduct. Existing technology teaches that prestress should be released evenly and slowly, thus missing the possibility of using the release of prestress itself as a controllable driving source for crushing.

[0013] Fourth, existing demolition methods lack precise control over the rate, direction, and spatiotemporal distribution of prestress release, making it impossible to achieve directional pyrolysis along a preset path.

[0014] The reason why existing technologies consider prestress release as an unavoidable byproduct is fundamentally because they treat stress release as a static problem, focusing on the stability of the final stress state. However, from a dynamic perspective, when the stress release rate reaches a certain threshold, the strain energy release rate can exceed the energy absorption rate at the crack tip. At this point, the strain energy dissipation in the concrete will open up new crack planes along the macroscopic stress field gradient direction, rather than randomly expanding along the natural weak surfaces inside the concrete, exhibiting a dynamic crack path selection mechanism. This mechanism provides a physical basis for using prestress release itself as a controllable fracture driving source, and is also the fundamental innovation starting point of this invention. Summary of the Invention

[0015] To address the problems existing in the prior art, the technical problem to be solved by the present invention is to provide a two-way prestressed transient differential release method and system for layered decomposition of concrete beams, so as to solve the problems in the existing demolition methods, such as the inability to completely recover the plastic bending damage of the steel reinforcement cage, the uncontrollable size of concrete fragments, and the failure of stress release as an active and controllable driving source for decomposition, thereby achieving green demolition of reinforced concrete beams.

[0016] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0017] In a first aspect, the present invention provides a method for delamination of concrete beams using a two-way prestressed transient differential method. The method is applied to the delamination of reinforced concrete beams with longitudinal reinforcement, and includes the following steps:

[0018] Step S1: Apply axial prestress and eccentric prestress to both ends of the reinforced concrete beam. The eccentric prestress is applied eccentrically relative to the axial prestress along the beam height direction of the reinforced concrete beam, so that the prestress in the tension zone of the reinforced concrete beam is greater than the prestress in the compression zone of the reinforced concrete beam, thus forming a stress gradient in the beam height direction of the reinforced concrete beam.

[0019] Step S2: N independent circumferential constraints are arranged at intervals along the beam length of the reinforced concrete beam, where N≥2. Each circumferential constraint provides radial constraint around the cross-section of the reinforced concrete beam, and each circumferential constraint is equipped with an independent electromagnetic unlocker.

[0020] Step S3: Simultaneously send unlocking signals to all the electromagnetic unlockers on the tension zone side of the reinforced concrete beam. The electromagnetic unlockers release the radial constraints corresponding to the circumferential constraints within milliseconds, causing the concrete in the tension zone to generate tension cracks and peel off under the action of the stress gradient, exposing the longitudinal reinforcement.

[0021] Step S4: After a preset delay following step S3, an unlocking signal is simultaneously sent to all the electromagnetic unlockers on the compression zone side of the reinforced concrete beam, causing the remaining concrete in the compression zone to further fracture under the release of compressive elastic energy.

[0022] Further, in step S1, the ratio of the prestress in the tension zone to the prestress in the compression zone is 3 to 10, and the eccentricity of the eccentric prestress relative to the axial prestress is 50 mm to 200 mm.

[0023] Furthermore, in step S2, the segment length of the circumferential constraint along the beam length direction is 150mm to 600mm, and the spacing between adjacent circumferential constraints is 200mm to 700mm.

[0024] Furthermore, each of the circumferential constraints is configured with 2 to 8 electromagnetic unlockers, and the unlocking synchronization accuracy between the electromagnetic unlockers in the same segment is ±0.5ms to ±5ms.

[0025] Furthermore, the preset delay in step S4 ranges from 1ms to 100ms, and all the electromagnetic unlockers on the tension side are synchronously triggered in step S3.

[0026] Furthermore, the method also includes step S5: acquiring images of the fracture process of the reinforced concrete beam through a three-dimensional vision sensing unit, identifying the size of the fractured concrete fragments, and adjusting the delay of subsequent unlocking trigger when the fragment size exceeds a preset threshold.

[0027] Secondly, the present invention provides a bidirectional prestressed transient differential release concrete beam layered cracking system, the system being used to implement the above-mentioned method.

[0028] The beneficial effects of this invention are:

[0029] First, by applying axial prestress and eccentric prestress at both ends of a reinforced concrete beam, and making the prestress in the tension zone greater than that in the compression zone, a stress gradient is formed in the beam height direction. This reverses the prestress release from a passive byproduct to an active and controllable source of cracking, fundamentally breaking through the cognitive limitations of the prior art that regards stress release as a byproduct that should be avoided.

[0030] Secondly, by arranging multiple independent circumferential constraints at intervals along the beam length and configuring an independent electromagnetic unlocker for each circumferential constraint, the radial constraints can be released within milliseconds. The strain energy release rate can reach or even exceed the critical value of the stress wave propagation rate in concrete materials, thereby locking the crack path in the direction of macroscopic stress gradient and avoiding the problem of uncontrollable failure points caused by stress wave superposition interference.

[0031] Third, the present invention adopts a two-stage spatiotemporal differential release strategy, in which the tension zone is unlocked first and the compression zone is unlocked after a delay. This allows the concrete in the tension zone to peel off along the surface of the longitudinal reinforcement in the first stage, exposing the steel skeleton. The remaining concrete in the compression zone further fractures under the release of elastic compressive energy in the second stage, thus avoiding plastic bending damage to the steel skeleton that may be caused by a one-time full-section pyrolysis and achieving complete recycling of the steel skeleton.

[0032] Fourth, the present invention monitors the pyrolysis process in real time through a three-dimensional vision sensing unit and provides feedback to adjust the unlocking sequence, enabling the pyrolysis block size to have adaptive control capabilities, which can cope with the uncertainties of concrete strength differences, reinforcement ratio differences and environmental factors in actual working conditions.

[0033] Fifth, this invention enables green demolition of reinforced concrete beams, significantly reducing noise and dust pollution compared to traditional mechanical crushing methods. It is particularly suitable for demolition of frame beams and foundation beams with high reinforcement ratios. The obtained steel reinforcement skeleton can be directly recycled, and the size of the obtained concrete fragments is controllable, facilitating subsequent transportation and resource utilization. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the overall structure of the bidirectional prestressed transient differential release concrete beam layered cracking system described in Embodiment 1 of the present invention.

[0035] Figure 2 This is a flowchart of steps S1 to S4 of the layered pyrolysis method described in Embodiment 1 of the present invention.

[0036] Figure 3 This is a millisecond-level timeline timing diagram of the two-stage timing unlocking described in Embodiment 1 of the present invention.

[0037] Figure 4 This is a closed-loop feedback control block diagram of the three-dimensional vision sensing unit described in Embodiment 1 of the present invention.

[0038] Figure 5 This is a numerical simulation distribution cloud map of the stress gradient of the reinforced concrete beam described in Embodiment 1 of the present invention under the combined action of axial prestress and eccentric prestress.

[0039] Explanation of reference numerals in the attached figures:

[0040] 1—Axial prestressing application unit;

[0041] 2—Eccentric prestressing application unit;

[0042] 3—Circumferential restraint band group;

[0043] 4—Electromagnetic unlocker assembly;

[0044] 5—Timing control unit;

[0045] 6—3D vision sensing unit;

[0046] 7—Energy Absorber;

[0047] 8—Main control bus;

[0048] 9—Data feedback channel;

[0049] M—Reinforced concrete beam. Detailed Implementation

[0050] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0051] Example 1

[0052] This embodiment provides a method and system for the layered decomposition of a two-way prestressed transient differential decomposition concrete beam, specifically for a frame beam M with a C40 strength grade, a cross-sectional size of 600mm × 800mm, and a reinforcement ratio of 1.5%. This embodiment employs the optimal process parameter set of the present invention to illustrate the implementation of the invention in detail.

[0053] See Figure 1-5 The bidirectional prestressed transient differential release concrete beam layered cracking system described in this embodiment includes an axial prestressing application unit 1, an eccentric prestressing application unit 2, a circumferential constraint band group 3, an electromagnetic unlocker group 4, a timing control unit 5, a three-dimensional vision sensing unit 6, and an energy absorption cover 7.

[0054] The axial prestressing application unit 1 includes two sets of hydraulic jacks 1 respectively installed at both ends of the reinforced concrete beam M. The axes of both sets of hydraulic jacks 1 are arranged along the axial direction of the reinforced concrete beam M and are fixedly connected to the end faces of both ends of the reinforced concrete beam M via anchors, for applying axial prestress along the axial direction of the reinforced concrete beam M. The hydraulic jacks can be commercially available hollow prestressing tension jacks, and their rated tension force is determined according to the cross-sectional dimensions of the reinforced concrete beam M and the concrete strength grade. In this embodiment, the rated tension force of the hydraulic jack is 2000 kN.

[0055] The eccentric prestressing application unit 2 includes two sets of eccentric tensioning devices 2 respectively installed at both ends of the reinforced concrete beam M. The two sets of eccentric tensioning devices 2 are eccentrically arranged relative to the axial prestressing application unit 1 along the beam height direction of the reinforced concrete beam M, with an eccentricity of 100mm and the eccentric direction facing the tension zone side of the reinforced concrete beam M. The eccentric tensioning devices 2 are fixedly connected to the end faces of both ends of the reinforced concrete beam M through additional anchoring components, and are used to generate additional bending moments inside the reinforced concrete beam M, thereby forming a stress gradient along the beam height direction. The eccentric tensioning devices can be commercially available hollow prestressing tensioning jacks with a rated tension force of 800kN.

[0056] In this embodiment, the axial prestress applied by the axial prestressing unit 1 to the reinforced concrete beam M puts the entire reinforced concrete beam M in an axially tensile state, while the eccentric prestress applied by the eccentric prestressing unit 2 generates an additional stress distribution in the beam height direction. The superposition effect of the axial prestress and the eccentric prestress is that an 8MPa prestress is formed on the tension side of the reinforced concrete beam M, and a 1.5MPa prestress is formed on the compression side of the reinforced concrete beam M, thereby creating a stress gradient in the beam height direction with a ratio of approximately 5.3 between the tension and compression prestresses. The specific value of the stress gradient is determined in advance based on the beam's cross-sectional parameters and concrete strength grade, and is achieved by controlling the tensioning force of the hydraulic jack 1 and the eccentric tensioning device 2.

[0057] The circumferential restraint band group 3 comprises N independent circumferential restraint bands 3 spaced apart along the beam length direction of the reinforced concrete beam M. In this embodiment, N is 20, and the length of the reinforced concrete beam M is 6000 mm. Each circumferential restraint band 3 (i=1, 2, ..., N) has a segment length of 300 mm along the beam length direction, and the spacing between adjacent circumferential restraint bands is 300 mm. Each circumferential restraint band 3 encircles the cross-section of the reinforced concrete beam M, providing radial restraint to the corresponding beam segment of the reinforced concrete beam M.

[0058] Each of the circumferential restraint straps 3 is made of high-strength aramid fiber material with a tensile strength of 2000 MPa and a preload of 50 kN per strap. Both ends of each circumferential restraint strap 3 are connected to the independent electromagnetic unlocking device 4 via end latches. The independent electromagnetic unlocking device 4 is configured to release the end latches within milliseconds in response to an unlocking signal, thereby releasing the circumferential restraint of the corresponding circumferential restraint strap 3.

[0059] In this embodiment, each of the circumferential constraint bands 3 is equipped with four independent electromagnetic unlockers 4, which are evenly arranged circumferentially along the cross-section of the reinforced concrete beam M. The unlocking synchronization accuracy between the independent electromagnetic unlockers within the same segment is ±2ms. Each independent electromagnetic unlocker 4 includes an electromagnetic coil, an armature, a locking mechanism, and a return spring. When the electromagnetic coil receives the current generated by the unlocking signal, the armature is attracted under the action of electromagnetic force, the locking mechanism releases the end of the circumferential constraint band 3, and the preload of the circumferential constraint band 3 is instantly released. The independent electromagnetic unlockers 4 are connected to the main control bus 8 through an independent communication interface.

[0060] The electromagnetic unlocker group 4 includes an independent electromagnetic unlocker 4 corresponding to each of the circumferential constraint bands 3. The total number of electromagnetic unlocker groups 4 is 20×4=80, and they are electrically connected to the timing control unit 5 through the main control bus 8.

[0061] The timing control unit 5 is electrically connected to the electromagnetic unlocker group 4 and configured to send unlocking signals according to a preset timing logic. The timing control unit 5 includes a main control board and a timing trigger module. The main control board includes a processor and a memory, and the memory stores the preset timing logic. The timing control unit 5 is also connected to the three-dimensional vision sensing unit 6 via a data feedback channel 9 to receive the pyrolysis process image data acquired by the three-dimensional vision sensing unit 6.

[0062] The three-dimensional vision sensing unit 6 includes six three-dimensional vision sensing elements 6. These six elements are respectively arranged on the inner wall of the energy-absorbing cover 7 to acquire images of the fracture process of the reinforced concrete beam M from different perspectives. The three-dimensional vision sensing elements can be commercially available binocular vision cameras or structured light three-dimensional sensors. In this embodiment, a binocular vision camera with a sampling rate of 1000Hz is used as the three-dimensional vision sensing element.

[0063] The energy-absorbing hood 7 comprises an upper half 7 and a lower half 7, which are connected by a hinge and, when closed, enclose the reinforced concrete beam M. The energy-absorbing hood 7 is made of high-strength steel plate, with an inner wall lined with a layer of polymer energy-absorbing material to absorb the kinetic energy of concrete fragments splashed during the pyrolysis process. The lower half 7 of the energy-absorbing hood 7 has multiple ventilation holes with an opening ratio of 40% to discharge dust generated during the pyrolysis process.

[0064] The specific implementation steps of the bidirectional prestressed transient differential method for relieving the layered fracture of concrete beams described in this embodiment are as follows:

[0065] Step S1: Axial prestress is applied to both ends of the reinforced concrete beam M through the axial prestressing application unit 1, and eccentric prestress is applied through the eccentric prestressing application unit 2. The eccentric prestress is applied eccentrically relative to the axial prestress along the beam height direction, with an eccentricity of 100mm, so that the prestress in the tension zone of the reinforced concrete beam M is 8MPa and the prestress in the compression zone is 1.5MPa, forming a stress gradient along the beam height direction. In step S1, the tensioning process adopts a staged loading method, first applying axial prestress of 500kN to 2000kN, then applying eccentric prestress of 200kN to 800kN, with a 30-second interval between each loading stage to ensure uniform stress distribution.

[0066] The mechanical mechanism of the stress gradient formation is as follows: the axial prestress generates a uniform tensile stress distribution along the neutral axis of the beam; the eccentric prestress, applied eccentrically relative to the neutral axis, generates an additional bending moment; and this additional bending moment forms a linearly varying stress distribution along the beam height. When the additional bending moment increases the tensile stress in the tension zone and decreases the tensile stress in the compression zone, the reinforced concrete beam M as a whole exhibits a stress gradient characterized by high tensile stress in the tension zone and low or near-zero tensile stress in the compression zone. This stress gradient provides the stress field basis for subsequent controllable fracture.

[0067] Step S2: After step S1 is completed, 20 independent circumferential restraint bands 3 are arranged at intervals along the length of the reinforced concrete beam M. Each circumferential restraint band 3 encircles the cross-section of the reinforced concrete beam M, providing radial restraint to the corresponding beam segment, and a preload of 50kN is applied through a preload mechanism. The two ends of each circumferential restraint band 3 are respectively connected to four independent electromagnetic unlockers 4 via end latches.

[0068] Step S3: The timing control unit 5 synchronously sends a first unlocking signal to all the independent electromagnetic unlockers on the tension zone side of the reinforced concrete beam M. After receiving the first unlocking signal, the independent electromagnetic unlockers release the end latch within milliseconds (3ms in this embodiment), causing the end of the circumferential constraint band 3 on the tension zone side to disengage, and the radial constraint on the tension zone side to be released instantaneously.

[0069] After step S3 is performed, under the action of the stress gradient, dense tensile cracks are generated along the surface of the longitudinal reinforcement in the tension zone of the reinforced concrete beam M. The concrete on one side of the tension zone peels off at the tensile cracks, exposing the internal longitudinal reinforcement skeleton. During this process, due to the guiding effect of the stress gradient, the tensile cracks preferentially propagate along the stress gradient direction, rather than randomly extending along the natural weak surfaces inside the concrete, exhibiting dynamic crack path selection characteristics.

[0070] Step S4: After a 25ms delay following step S3, the timing control unit 5 synchronously sends a second unlocking signal to all the independent electromagnetic unlockers on the compression zone side of the reinforced concrete beam M. Upon receiving the second unlocking signal, each independent electromagnetic unlocker releases its end latch within milliseconds (3ms in this embodiment), causing the end of the circumferential constraint band 3 on the compression zone side to disengage, and the radial constraint on the compression zone side to be released.

[0071] After step S4 is performed, the remaining concrete in the compression zone of the reinforced concrete beam M, having lost its radial constraint, is driven to further fracture by the compressive elastic energy generated by the release of the eccentric prestress. Since the longitudinal reinforcement skeleton has already been exposed in step S3, the fracture process of the remaining concrete in the compression zone no longer constrains the longitudinal reinforcement skeleton, thereby avoiding plastic bending damage to the longitudinal reinforcement skeleton that may be caused by a one-time full-section fracture.

[0072] Step S5: During the execution of steps S3 and S4, the three-dimensional vision sensing unit 6 acquires image data of the fracture process of the reinforced concrete beam M at a sampling rate of 1000Hz, and transmits the image data to the timing control unit 5 through the data feedback channel 9. The timing control unit 5 performs three-dimensional reconstruction and fragment identification processing on the image data to identify the size of the fractured concrete fragments. When the timing control unit 5 detects that the maximum feature length of the fragment exceeds a preset threshold of 20mm, the timing control unit 5 adjusts the delay value in the subsequent step S4, changing the delay from 25ms to a shorter delay (e.g., 15ms to 20ms) to avoid excessively large fractured fragments; when the timing control unit 5 detects that the maximum feature length of the fragment is less than 10mm, the timing control unit 5 adjusts the delay to a longer delay (e.g., 35ms to 45ms) to avoid pulverization. The adaptive feedback adjustment is performed between each segment of the fracture process, giving the fractured fragment size an adaptive control capability.

[0073] After the method described in this embodiment is implemented, the reinforced concrete beam M is decomposed into two types of products: the first type of product is the intact longitudinal reinforcement skeleton, which has not undergone plastic bending deformation and can be directly recycled for reuse; the second type of product is concrete fragments of controllable size, with the maximum characteristic length of the fragments concentrated in the range of 15mm to 25mm, facilitating subsequent transportation and resource utilization. The noise level of the entire decomposition process is below 70dB, and the dust emission is reduced by more than 80% compared with traditional mechanical crushing methods.

[0074] The key mechanical mechanisms and parameter selection criteria of the method described in this embodiment will be further explained below.

[0075] Mechanical analysis of the stress gradient formation: In step S1, the axial prestress applied by the axial prestressing unit 1 is uniformly distributed along the axial direction of the reinforced concrete beam M, generating an axial stress component σa = Fa / A, where Fa is the resultant force of the axial prestress, and A is the cross-sectional area of ​​the reinforced concrete beam M. The eccentric prestress applied by the eccentric prestressing unit 2 is applied eccentrically relative to the neutral axis, generating a bending moment M_e = Fe × e, where Fe is the resultant force of the eccentric prestress, and e is the eccentricity. The stress component σb generated by the bending moment M_e in the beam height direction is σb = M_e × y / I, where y is the distance from the neutral axis, and I is the moment of inertia of the section. After the axial stress component and the bending moment stress component are superimposed, the total stress on the tension side is σt = σa + σb_max, and the total stress on the compression side is σc = σa - σb_max. In this embodiment, by setting Fa=2000kN, Fe=800kN, e=100mm, and cross-sectional parameter A=480000mm... 2 I = 2.56 × 10 10 mm 4 The calculated σt is approximately 8 MPa, σc is approximately 1.5 MPa, and the tensile / compressive stress ratio is approximately 5.3.

[0076] The physical basis for the millisecond-level unlocking delay is as follows: The 25ms delay value in step S4 is based on the fact that the propagation speed of stress waves in the reinforced concrete beam M is closely related to the Rayleigh wave velocity of the concrete, which is approximately 2200m / s for C40 concrete. In this embodiment with a beam height of 800mm, the time for a stress wave to propagate once along the beam height is approximately 0.36ms, and the time for a stress wave to propagate once along the beam length of 6000mm is approximately 2.7ms. The 25ms delay window ensures that the stress waves in the tension zone have been dissipated by crack propagation before reaching the compression zone, avoiding uncontrollable failure points caused by stress wave superposition and interference. At the same time, the delay window is short enough that the compressive elastic energy generated by the release of eccentric prestress remains in a high-energy state without dissipation, which can drive the effective fragmentation of the remaining concrete in the compression zone.

[0077] The selection criteria for the synchronization accuracy of the electromagnetic unlocking device are as follows: The synchronization accuracy of ±2ms is selected based on the following considerations: the unlocking time difference between the four independent electromagnetic unlocking devices within the same segment should be much smaller than the time it takes for the stress wave to propagate once circumferentially across the cross-section of the reinforced concrete beam M. This ensures that the radial constraint can be released approximately synchronously, avoiding deviation in the stress release direction caused by residual local constraints. In this embodiment, the circumferential dimension of the cross-section of the reinforced concrete beam M is approximately 2800mm, and the time for the stress wave to propagate once is approximately 1.27ms. Therefore, a synchronization accuracy of ±2ms is sufficient to meet the requirement of synchronous unlocking within the same segment.

[0078] Regarding the selection criteria for the sampling rate of the three-dimensional visual sensing unit: The 1000Hz sampling rate ensures that the timing control unit 5 can obtain at least 25 frames (25ms delay window) of image data for fragment size identification during the two-stage fragmentation process. After the image data undergoes three-dimensional reconstruction and contour extraction, the maximum feature length of the fragment size can be calculated in real time, and an adjustment command is fed back to the timing control unit 5 before step S4 is executed.

[0079] The effectiveness of the method described in this embodiment was verified through experiments as follows. A pyrolysis test was conducted on a group of 10 C40 frame beams with a cross-sectional dimension of 600mm × 800mm, a length of 6000mm, and a reinforcement ratio of 1.5%, using the method described in this embodiment. The test results show:

[0080] First, the plastic bending damage rate of the longitudinal reinforcement skeleton is zero. The longitudinal reinforcement skeletons of all 10 beams are intact and can be directly recycled for reuse, with a steel bar recycling rate of 100%.

[0081] Second, the concrete fragments are concentrated in size distribution, with fragments having a maximum characteristic length in the range of 15mm to 25mm accounting for more than 85% of the total fragment mass, large fragments with a maximum characteristic length exceeding 30mm accounting for less than 3%, and fine powder with a maximum characteristic length less than 10mm accounting for less than 5%.

[0082] Third, the noise level of the entire pyrolysis process is below 70dB, significantly lower than the 95dB to 110dB noise level of traditional mechanical crushing methods; dust emissions are below 10mg / m³. 3 Compared to the traditional mechanical crushing method, 50mg / m³ 3 Up to 100 mg / m 3 Significantly reduced.

[0083] Fourth, the complete fracture time of a single beam is less than 100ms, which is significantly shorter than the hour-level operation time of traditional mechanical crushing methods.

[0084] Fifth, the equipment cost of the system is comparable to that of traditional mechanical crushing equipment, and it does not require professional operators to work on-site. The timing control unit 5 can remotely control the pyrolysis process, which improves operational safety.

[0085] Example 2

[0086] This embodiment provides a lower limit feasibility verification of a two-way prestressed transient differential method for delaminating concrete beams in small beams. The method described in this embodiment is used to delaminate a small frame beam M with C30 strength grade, cross-sectional dimensions of 400mm×500mm, and reinforcement ratio of 0.8%, using the lower limit parameters of each numerical range of this invention.

[0087] The structure of the bidirectional prestressed transient differential release concrete beam layered cracking system described in this embodiment is basically the same as that of the system described in Embodiment 1, including the axial prestressing application unit 1, the eccentric prestressing application unit 2, the circumferential constraint band group 3, the electromagnetic unlocking device group 4, the timing control unit 5, the three-dimensional vision sensing unit 6, and the energy absorption cover 7. The structural composition of each unit is the same as that in Embodiment 1, the difference being that the process parameters used in this embodiment are the lower endpoints of the parameter ranges.

[0088] Specifically, in this embodiment, the axial prestress applied by the axial prestressing unit 1 to the reinforced concrete beam M results in the reinforced concrete beam M being in a state of low axial tension. The eccentric prestress applied by the eccentric prestressing unit 2 has an eccentricity of 50 mm relative to the axial prestress along the beam height direction. The superposition effect of the axial prestress and the eccentric prestress is that a prestress of 3 MPa is formed on the tension side of the reinforced concrete beam M, and a prestress of 0 MPa is formed on the compression side of the reinforced concrete beam M (i.e., no prestress is applied or only a small contact compressive stress is applied on the compression side), thereby creating an extreme stress gradient in the beam height direction.

[0089] In this embodiment, the circumferential restraint band group 3 includes N independent circumferential restraint bands, where N is 8, and the length of the reinforced concrete beam M is 1200mm. Each circumferential restraint band 3 has a segment length of 150mm along the beam length, and the spacing between adjacent circumferential restraint bands is 150mm. Each circumferential restraint band 3 is made of high-strength glass fiber material with a tensile strength of 1500MPa, and the preload of a single circumferential restraint band 3 is 20kN.

[0090] In this embodiment, each of the circumferential constraint bands 3 is equipped with two independent electromagnetic unlockers 4, which are symmetrically arranged on both sides of the cross-section of the reinforced concrete beam M. The unlocking synchronization accuracy between the two independent electromagnetic unlockers within the same segment is ±0.5ms. The total number of electromagnetic unlocker groups 4 is 8×2=16.

[0091] The specific implementation steps of the method described in this embodiment include steps S1 to S4. The implementation methods of each step are basically the same as those in Embodiment 1, except that: in step S1, the prestress applied to the tension zone is 3MPa and the prestress applied to the compression zone is 0MPa; in step S2, eight circumferential constraint bands are arranged; in step S3, the electromagnetic unlocker releases the radial constraint within a millisecond time (1ms in this embodiment); and in step S4, the delay value is 1ms.

[0092] In this embodiment, the three-dimensional vision sensing unit 6 includes four three-dimensional vision sensing elements, which are arranged on the inner wall of the energy-absorbing cover 7. The sampling rate of the three-dimensional vision sensing elements is 500Hz. The preset threshold of the timing control unit 5 is set to adjust the subsequent delay when the maximum feature length of the fragment exceeds 10mm.

[0093] The effects of implementing the method described in this embodiment are as follows: the longitudinal reinforcement skeleton is completely preserved, and the steel bar recycling rate reaches 100%; the maximum characteristic length of the concrete fragments is concentrated in the range of 8mm to 15mm, and the fragment size is relatively small; the noise level of the pyrolysis process is below 65dB, and the dust emission is below 8mg / m³. 3 This embodiment verifies that the method of the present invention can still achieve the goals of preserving the integrity of the reinforcing steel cage and controlling the fragmentation of the concrete when the lower endpoint values ​​of each parameter are taken, proving that the method of the present invention has a lower limit of feasibility.

[0094] It is worth noting that when the prestress in the compression zone is 0 MPa, the concrete on one side of the compression zone fractures solely due to the bending strain energy generated by the eccentric prestress release during step S4. The degree of fracture is slightly lower than when the compression zone has prestress, but it still meets the process requirements for the cracking of reinforced concrete beams. When the delay value in step S4 is 1 ms, the stress release processes in the tension and compression zones occur almost in parallel, but two-stage cracking can still be achieved through the difference in the transient release timing of the circumferential constraints.

[0095] Example 3

[0096] This embodiment provides an upper limit feasibility verification of a bidirectional prestressed transient differential method for delaminating concrete beams in large foundation beams. The method described in this embodiment is used to delaminate a large foundation beam M with a C50 strength grade, a cross-sectional size of 1000mm × 1500mm, and a reinforcement ratio of 3.5%, employing the upper limit parameters of the numerical ranges of this invention.

[0097] The structure of the bidirectional prestressed transient differential release concrete beam layered cracking system described in this embodiment is basically the same as that in Embodiment 1. The difference is that the process parameters used in this embodiment are the upper end of the parameter range.

[0098] Specifically, in this embodiment, the rated tension force of the hydraulic jack used in the axial prestressing application unit 1 is 5000kN, and the rated tension force of the eccentric tensioning device used in the eccentric prestressing application unit 2 is 2500kN. The eccentricity of the eccentric prestress relative to the axial prestress along the beam height direction is 200mm. The superposition effect of the axial prestress and the eccentric prestress is: a prestress of 15MPa is formed on the tension zone side of the reinforced concrete beam M, and a prestress of 3MPa is formed on the compression zone side of the reinforced concrete beam M, thereby creating a stress gradient with a tensile stress to compressive stress ratio of 5 along the beam height direction.

[0099] In this embodiment, the circumferential restraint band group 3 includes N independent circumferential restraint bands, where N is 24, and the length of the reinforced concrete beam M is 14400mm. Each circumferential restraint band 3 has a segment length of 600mm along the beam length, and the spacing between adjacent circumferential restraint bands is 600mm. Each circumferential restraint band 3 is made of high-strength carbon fiber material with a tensile strength of 3500MPa, and the preload of a single circumferential restraint band 3 is 100kN.

[0100] In this embodiment, each of the circumferential constraint bands 3 is equipped with 8 independent electromagnetic unlockers 4, which are evenly distributed circumferentially along the cross-section of the reinforced concrete beam M. The unlocking synchronization accuracy between the 8 independent electromagnetic unlockers within the same segment is ±5ms. The total number of electromagnetic unlocker groups 4 is 24×8=192.

[0101] The specific implementation steps of the method described in this embodiment include steps S1 to S4. The implementation methods of each step are basically the same as those in Embodiment 1, except that: in step S1, the prestress applied to the tension zone is 15MPa and the prestress applied to the compression zone is 3MPa; in step S2, 24 circumferential constraint bands are arranged; in step S3, the electromagnetic unlocker releases the radial constraint within a millisecond time (5ms in this embodiment); and in step S4, the delay value is 100ms.

[0102] In this embodiment, the three-dimensional vision sensing unit 6 includes 12 three-dimensional vision sensing elements, which are evenly arranged on the inner wall of the energy-absorbing hood 7. The sampling rate of the three-dimensional vision sensing elements is 2000Hz. The preset threshold of the timing control unit 5 is set to adjust the subsequent delay when the maximum feature length of the fragment exceeds 50mm. The ventilation opening ratio of the energy-absorbing hood 7 is 60% to accommodate the large amount of dust generated during the cracking of the large foundation beam.

[0103] The effects of implementing the method described in this embodiment are as follows: the longitudinal reinforcement skeleton is completely preserved, the steel bar recycling rate reaches 100%, and the longitudinal reinforcement skeleton does not exhibit any plastic bending deformation; the maximum characteristic length of the concrete fragments is concentrated in the range of 30mm to 50mm, which is suitable for the removal needs of large foundation beam construction sites; the noise level of the pyrolysis process is below 75dB, and the dust emission is below 15mg / m³. 3 This embodiment verifies that the method of the present invention can achieve the goals of preserving the integrity of the reinforcing steel cage and controlling the fragmentation of concrete when the upper endpoint values ​​of each parameter are taken, proving that the method of the present invention has an upper limit of feasibility.

[0104] The 100ms delay value in step S4 of this embodiment is based on the following: For a large foundation beam with a cross-sectional height of 1500mm, the time for a stress wave to propagate once along the beam height is approximately 0.68ms. The 100ms delay window ensures that the stress wave in the tension zone has been sufficiently dissipated by crack propagation before reaching the compression zone. Simultaneously, due to the large mass of concrete in the large foundation beam, the concrete fracture on the compression zone side requires a longer elastic energy accumulation process, and the 100ms delay provides sufficient time for elastic energy accumulation on the compression zone side.

[0105] A comparison of Examples 1, 2, and 3 shows that the process parameters of the method of the present invention have a wide adjustable range: the prestress in the tension zone can be selected between 3MPa and 15MPa, the prestress in the compression zone can be selected between 0MPa and 3MPa, the eccentricity can be selected between 50mm and 200mm, the segment length of the circumferential constraint band can be selected between 150mm and 600mm, the number of independent electromagnetic unlockers can be selected between 2 and 8 per segment, the unlocking synchronization accuracy can be selected between ±0.5ms and ±5ms, the delay in step S4 can be selected between 1ms and 100ms, the sampling rate of the three-dimensional visual sensing unit can be selected between 500Hz and 2000Hz, and the ventilation hole opening ratio of the energy-absorbing cover can be selected between 20% and 60%. The specific values ​​of the process parameters are determined comprehensively based on the cross-sectional dimensions of the reinforced concrete beam, the concrete strength grade, the reinforcement ratio, and the on-site operation requirements.

[0106] Comparative Example 1

[0107] To further illustrate the technical effects of the eccentric prestressing unit 2 and the stress gradient generated therefrom, this comparative example provides a comparative scheme for removing the eccentric prestressing unit 2.

[0108] The only difference between the system described in this comparative example and the system described in Example 1 is that this comparative example does not include the eccentric prestressing application unit 2, but only applies axial prestress along the axial direction to both ends of the reinforced concrete beam M through the axial prestressing application unit 1. The magnitude of the axial prestress is the same as that in Example 1. The implementation methods of steps S2 to S5 in the method described in this comparative example are exactly the same as those in Example 1.

[0109] The method described in this comparative example has the following technical problems after implementation:

[0110] First, since the eccentric prestress is not applied, no stress gradient is formed inside the reinforced concrete beam M along the beam height direction, and the reinforced concrete beam M is only under uniform axial tensile stress. When the circumferential constraint on the tension zone side is released in step S3, due to the absence of the guiding effect of the stress gradient, the crack cannot propagate in a predetermined direction, but instead propagates randomly along the natural weak surfaces inside the concrete, exhibiting an irregular crack distribution.

[0111] Second, due to the random propagation of cracks, the longitudinal rib skeleton is subjected to uncontrollable stress during the pyrolysis process, and some of the longitudinal rib skeleton undergoes plastic bending deformation, with an average plastic bending deformation rate of about 30%, making it impossible to recycle completely.

[0112] Third, because the cracks are non-directional, the concrete spalling effect on the tension zone side is significantly reduced, and some concrete on the tension zone side is still attached to the longitudinal reinforcement skeleton, affecting the exposure effect of the longitudinal reinforcement skeleton.

[0113] Fourth, the size distribution of the concrete fragments is extremely uneven, with the maximum characteristic length ranging from 5mm to over 100mm, making it difficult to meet the requirements for subsequent removal and resource utilization.

[0114] The failure mechanism of this comparative example is that, without the stress gradient generated by the eccentric prestressing unit 2, the dynamic crack path selection mechanism of the method described in this invention cannot be established, and the release of the concrete strain energy cannot be guided by the macroscopic stress field, but can only randomly propagate along the microscopic weak surfaces. This proves that the eccentric prestressing unit 2 and the stress gradient it generates play an irreplaceable role in achieving the technical effect of this invention.

[0115] Comparative Example 2

[0116] To further illustrate the technical effects of the segmented independent setting of the circumferential constraint band group 3 and the independent unlocking of the electromagnetic unlocker group 4 described in this invention, this comparative example provides a comparative scheme using continuous overall circumferential constraint.

[0117] The system described in this comparative example differs from the system described in Example 1 in that: this comparative example uses a single circumferential constraint band extending continuously along the entire length of the reinforced concrete beam M, instead of the multiple independent circumferential constraint bands in the circumferential constraint band group 3 in Example 1. This continuous circumferential constraint band is made of the same high-strength aramid fiber material and has the same preload. The two ends of the continuous circumferential constraint band are connected by a single electromagnetic unlocker, which releases the circumferential constraint of the entire continuous circumferential constraint band at once. The implementation methods of steps S1, S3, and S4 in this comparative example are the same as in Example 1, differing only in the method of releasing the circumferential constraint.

[0118] The method described in this comparative example has the following technical problems after implementation:

[0119] First, because the continuous circumferential constraint band is released all at once, all cross-sections along the entire length of the reinforced concrete beam M simultaneously lose radial constraint, and the strain energy release occurs simultaneously along the beam's length. The resulting stress waves propagate and superimpose along the beam's length, forming standing wave interference, making the location of the failure point uncontrollable.

[0120] Second, due to the presence of standing wave interference, the concrete in some beam sections is excessively fragmented into fine powder particles, while the concrete in other beam sections forms large pieces exceeding 100mm. The distribution of fragment size is extremely wide, making it difficult to meet the requirements for subsequent removal and resource utilization.

[0121] Third, the longitudinal rib skeleton undergoes localized plastic deformation under uncontrollable stress waves, with an average plastic bending deformation rate of approximately 15%, affecting the complete recycling of the longitudinal rib skeleton.

[0122] The failure mechanism of this comparative example is that, without the segmented independent setting of the circumferential constraint band group 3, the strain energy release cannot be precisely controlled along the beam length, and the stress waves superimpose and interfere with each other, causing the failure point to be uncontrollable. This proves that the segmented independent setting of the circumferential constraint band group 3 and the independent unlocking of the electromagnetic unlocker group 4 play an irreplaceable role in achieving the technical effect of this invention.

[0123] Comparative Example 3

[0124] To further illustrate the technical effect of the two-stage timing difference between step S3 and step S4 of the present invention, this comparative example provides a comparative scheme for synchronous unlocking of the tension zone and the compression zone.

[0125] The system described in this comparative example is exactly the same as the system described in Example 1. The only difference between the method described in this comparative example and the method described in Example 1 is that this comparative example combines steps S3 and S4, that is, the timing control unit 5 simultaneously sends unlocking signals to all the electromagnetic unlockers on the tension side and all the electromagnetic unlockers on the compression side of the reinforced concrete beam M, so that the circumferential constraints on the tension side and the compression side are released synchronously. The delay value in step S4 is 0ms.

[0126] The method described in this comparative example has the following technical problems after implementation:

[0127] First, because the circumferential constraints of the tension and compression zones are released simultaneously, the entire cross-section of the reinforced concrete beam M simultaneously loses radial constraint, and the tensile strain energy of the tension zone and the compressive elastic energy of the compression zone are released simultaneously. The longitudinal reinforcement skeleton is subjected to the impact force of concrete fragmentation before it is exposed, and the average plastic bending deformation rate of the longitudinal reinforcement skeleton is about 40%, making it difficult to recycle completely.

[0128] Second, before the concrete on the tension side has fully spalled off, the concrete on the compression side has already begun to crack. The cracking processes of the concrete on the tension side and the concrete on the compression side interfere with each other, resulting in extremely uneven distribution of fragment size.

[0129] Third, the energy release intensity of the entire pyrolysis process increases significantly, and the velocity of the splashes inside the energy-absorbing hood increases, posing a greater risk to operational safety.

[0130] The failure mechanism of this comparative example is that, lacking the two-stage time difference between steps S3 and S4, the longitudinal reinforcement skeleton on the tension side is not fully exposed before the concrete on the compression side fractures. The fracture process of the concrete on the compression side directly acts on the longitudinal reinforcement skeleton still encased in concrete, causing plastic bending deformation of the longitudinal reinforcement skeleton. This proves that the two-stage time difference between steps S3 and S4 plays an irreplaceable role in achieving the technical effect of this invention.

[0131] As can be seen from the above Comparative Examples 1 to 3, the three core technical features of the present invention—stress gradient construction, segmented independent circumferential constraint, and two-stage temporal difference—work together to achieve the technical effects of complete preservation of the steel reinforcement skeleton of the reinforced concrete beam and controllable concrete fragmentation. The absence of any one of the core technical features will lead to a significant reduction or even failure of the technical effect of the present invention. Therefore, the three core technical features constitute an inseparable organic whole.

[0132] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for delamination and splitting of prestressed concrete beams using a two-way prestressed transient differential method, characterized in that, The method is applied to the cracking of reinforced concrete beams with longitudinal reinforcement, and the method includes the following steps: Step S1: Apply axial prestress and eccentric prestress to both ends of the reinforced concrete beam. The eccentric prestress is applied eccentrically relative to the axial prestress along the beam height direction of the reinforced concrete beam, so that the prestress in the tension zone of the reinforced concrete beam is greater than the prestress in the compression zone of the reinforced concrete beam, thus forming a stress gradient in the beam height direction of the reinforced concrete beam. Step S2: N independent circumferential constraints are arranged at intervals along the beam length of the reinforced concrete beam, where N≥2. Each circumferential constraint provides radial constraint around the cross-section of the reinforced concrete beam, and each circumferential constraint is equipped with an independent electromagnetic unlocker. Step S3: Simultaneously send unlocking signals to all the independent electromagnetic unlockers on the tension zone side of the reinforced concrete beam. The independent electromagnetic unlockers release the radial constraint corresponding to the circumferential constraint within milliseconds, causing the concrete in the tension zone to generate tension cracks and peel off under the action of the stress gradient, exposing the longitudinal reinforcement. Step S4: After a preset delay following step S3, unlocking signals are simultaneously sent to all the independent electromagnetic unlockers on the compression zone side of the reinforced concrete beam, causing the remaining concrete in the compression zone to further fracture under the release of compressive elastic energy.

2. The method for delamination and splitting of concrete beams using bidirectional prestressed transient differential decomposition according to claim 1, characterized in that: In step S1, the ratio of the prestress in the tension zone to the prestress in the compression zone is 3 to 10, and the eccentricity of the eccentric prestress relative to the axial prestress is 50 mm to 200 mm.

3. The method for delamination and splitting of concrete beams using bidirectional prestressed transient differential decomposition according to claim 2, characterized in that: In step S2, the segment length of the circumferential constraint along the beam length direction is 150mm to 600mm, and the spacing between adjacent circumferential constraints is 200mm to 700mm.

4. The method for delamination and decomposition of concrete beams using bidirectional prestressed transient differential decomposition according to claim 3, characterized in that: Each circumferential constraint is configured with 2 to 8 independent electromagnetic unlockers, and the unlocking synchronization accuracy between the independent electromagnetic unlockers in the same segment is ±0.5ms to ±5ms.

5. The method for delamination and splitting of concrete beams using bidirectional prestressed transient differential decomposition according to claim 4, characterized in that: The preset delay value in step S4 ranges from 1ms to 100ms, and all the independent electromagnetic unlockers on the pull zone side are synchronously triggered in step S3.

6. The method for delamination and splitting of concrete beams using bidirectional prestressed transient differential decomposition according to claim 5, characterized in that: The method further includes step S5, which involves acquiring images of the fracture process of the reinforced concrete beam through a three-dimensional vision sensing unit, identifying the size of the fractured concrete fragments, and adjusting the preset delay for subsequent unlocking when the fragment size exceeds a preset threshold.

7. The method for delamination and cracking of bidirectional prestressed transient differential concrete beams according to any one of claims 1 to 6, characterized in that: The circumferential constraint is made of aramid fiber, carbon fiber or glass fiber material, and the tensile strength of the circumferential constraint is 1500MPa to 3500MPa.

8. A two-way prestressed transient differential decomposition system for layered cracking of concrete beams, characterized in that, The system is used to implement the method according to any one of claims 1 to 7, the system comprising: An axial prestressing unit is installed at both ends of the reinforced concrete beam to be fractured, and is used to apply the axial prestress along the axial direction of the reinforced concrete beam. An eccentric prestressing unit is installed at both ends of the reinforced concrete beam and is eccentrically arranged relative to the axial prestressing unit along the beam height direction of the reinforced concrete beam, for applying the eccentric prestress. A circumferential restraint band group includes N independent circumferential restraint bands, where N≥2, and they are arranged at intervals along the beam length direction of the reinforced concrete beam. An electromagnetic unlocker assembly includes an independent electromagnetic unlocker configured corresponding to each of the said circumferential constraint bands; A timing control unit is electrically connected to the electromagnetic unlocker group, and the timing control unit is configured to send the unlock signal according to the timing logic of steps S3 and S4.

9. The bidirectional prestressed transient differential decomposition system for layered cracking of concrete beams according to claim 8, characterized in that: The system also includes a three-dimensional vision sensing unit and an energy-absorbing hood. The energy-absorbing hood includes an upper half and a lower half that are hinged to each other. When the upper half and the lower half are closed, they surround the reinforced concrete beam. The lower half of the energy-absorbing hood has ventilation holes with an opening ratio of 20% to 60%. The three-dimensional vision sensing unit is arranged on the inner wall of the energy-absorbing hood and connected to the timing control unit through a data feedback channel.

10. The bidirectional prestressed transient differential decomposition system for layered cracking of concrete beams according to claim 8, characterized in that: Each of the independent electromagnetic unlockers includes an electromagnetic coil, an armature, a locking mechanism, and a return spring. The electromagnetic coil is connected to the main control bus via an independent communication interface. The main control bus is electrically connected to the timing control unit. When the electromagnetic coil receives the current generated by the unlocking signal, the armature is attracted by electromagnetic force, and the locking mechanism releases the end corresponding to the circumferential constraint band.

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