Sprayed concrete construction method for 3D printing of building structure

Abstract

The invention discloses a sprayed concrete construction method for 3D printing of a building structure, and relates to the technical field of building engineering, and the method comprises the following steps: S100, based on the operation cycle of a nozzle driving system, collecting pressure waveform data in a concrete spraying process, extracting a dominant frequency and amplitude change sequence, and generating a pressure disturbance feature vector with a time label; and S200, according to the pressure disturbance feature vector, the lowest-order inherent frequency and the response sensitive bandwidth of a current printing unit are dynamically modeled in combination with the printing track layer height, the concrete age data and the forming geometric parameters, and a structure dynamic response baseline is constructed. According to the method, identification and control of injection disturbance and structure inherent frequency resonance risks are achieved, a feedforward regulation and control mechanism and a closed loop feedback mechanism are fused, the instability problem caused by structure resonance is avoided, the injection parameter adjustment precision and the path execution stability are improved, and the forming precision, the structure safety and the construction continuity in the three-dimensional printing process are guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of construction engineering, and in particular to a shotcrete construction method for 3D printing of building structures. Background Art

[0002] Sprayed concrete construction for 3D printing of building structures refers to a new construction method that uses a spraying method to precisely deposit and shape special 3D printing concrete materials along the path of a digital model during the construction process, thereby directly constructing building structural components such as walls, beams, columns, and shells. This method usually relies on three-dimensional modeling and path planning technology to convert the design drawings of the building structure into an executable spray printing trajectory. The concrete is continuously sprayed through the nozzle at a set position, direction, and speed, so that the material is quickly stacked, bonded, and solidified after spraying, forming a building entity with structural strength and geometric accuracy. Compared with traditional formwork casting, this method can eliminate the formwork installation and disassembly process, reduce manual intervention, improve construction efficiency, and achieve precise shaping of complex surfaces, special-shaped structures, and layered partitions. It is suitable for scenarios such as customized building components, rapid construction, and optimized resource utilization.

[0003] The existing technology has the following shortcomings: During the shotcrete 3D printing process, the nozzle continuously sprays concrete slurry at high speed and in an intermittent pulsating manner under high pressure. The jet stream forms periodic pressure waves as it propels forward. These pressure waves exert a continuous dynamic impact on the printed structure, which has not yet fully solidified. When the pulsating frequency of the pressure waves approaches or equals the natural vibration frequency of the printed structure in its current state, it can easily trigger a resonance effect, significantly amplifying the local vibration amplitude of the structure in a short period of time. This can cause loosening, debonding, or microcracks to propagate at the interfaces between concrete layers still in the early stages of solidification, further inducing local structural instability or even overall deformation and collapse, which not only compromises the molding accuracy but can also cause construction interruptions and equipment damage.

[0004] The above information disclosed in this Background section is only for enhancement of understanding of the background of the present disclosure and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. Summary of the Invention

[0005] The purpose of the present invention is to provide a shotcrete construction method for 3D printing of building structures to solve the problems in the above-mentioned background technology.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for constructing sprayed concrete for 3D printing of building structures, comprising the following steps: S100, based on the operating cycle of the nozzle drive system, collects pressure waveform data during the shotcrete process, extracts the main frequency and amplitude change sequence, and generates a pressure disturbance feature vector with a time tag; S200, based on the pressure disturbance eigenvector, combined with the printing trajectory layer height, concrete age data and molding geometric parameters, dynamically models the lowest-order natural frequency and response sensitive bandwidth of the current printing unit to build a structural dynamic response baseline; S300 compares the structural dynamic response baseline with the pressure disturbance eigenvector in the frequency domain, constructs a resonance risk superposition index, identifies high-risk resonance frequency bands, and generates a frequency band avoidance mark sequence with spatial and temporal labels; S400, based on the frequency band avoidance mark sequence, executes the nozzle output rhythm control strategy, introduces a nonlinear pulse modulation mechanism at the nozzle control end, and weakens the energy coupling between the injection pressure and the structural natural frequency through phase and amplitude perturbations within the frequency range; S500, during the nozzle output rhythm control process, introduces a structural vibration attenuation self-feedback mechanism, fusing the structural micro-vibration response signal with the frequency band avoidance mark sequence to generate a scrambling feedback factor, which is used to continuously optimize the nozzle output rhythm and achieve dynamic decoupling of the excitation frequency and the structural response frequency; S600, based on the closed-loop operation of the nozzle output rhythm control and structural vibration attenuation self-feedback mechanism, constructs a frequency disturbance risk distribution map covering the printing path, superimposes it with the structural time-varying stability window for analysis, pre-adjusts the printing path and injection rhythm, and realizes closed-loop construction with controllable resonance risks throughout the entire process.

[0007] Preferably, step S100 includes: Multiple piezoelectric dynamic pressure sensors are fixedly installed near the nozzle outlet to synchronously collect pressure waveform data during the concrete spraying process at a sampling frequency of more than 5000 Hz; Perform low-pass filtering and noise reduction processing and zero-point offset reference correction on the collected pressure data; The main frequency and main amplitude of each injection are extracted and matched with the nozzle spatial trajectory in time sequence to generate a pressure disturbance feature vector containing injection time, spatial position, main frequency value, main amplitude and main frequency variation; The continuity of the feature vector is checked. When three consecutive groups of change values ​​exceed the threshold, they are marked as abnormal and the data is re-collected.

[0008] Preferably, step S200 includes: Extract the layer height parameters of the current printing layer and reconstruct the 3D geometric shape of the current printing building unit in combination with the spatial coordinate data of the printing path; The age of the build location is determined based on the difference between the printing time and the jetting completion time. The corresponding compressive strength, elastic modulus, and shear modulus values ​​are obtained based on the ratio scheme, and temperature and humidity are introduced for correction. Input the geometric shape and mechanical parameters into the structural response modeling process, set the boundary conditions, and calculate the lowest-order natural frequency and its response sensitive bandwidth; The lowest-order natural frequency and response-sensitive bandwidth are bound to the spatial coordinates of the injection point and the injection time to construct the structural dynamic response baseline.

[0009] Preferably, step S300 includes: Extract the nozzle jet frequency, jet amplitude, feedback factor, structural vibration response, path segment number, spatial coordinates and time tags from the historical printing data. Count the number of high feedback factor events, the number of over-threshold amplitude jet behaviors and the number of response peak violations for each path segment to determine the risk score for each path segment. Construct a frequency perturbation risk distribution map for the printing path, and establish a time-varying stability window based on the elastic modulus growth law corresponding to the age of the printed structure. Analyze the path number correspondence between the distribution map and the stability window to identify path segments with risk scores exceeding the tolerance threshold. Rearrange the printing order of identified path segments, placing low-risk path segments in the early construction phase and postponing the execution of high-risk path segments until the stability window is expanded; Adjust the nozzle jet frequency disturbance range of the high-risk path section to ±2.5 Hz, extend the jet interval to 1.2 seconds, load the adjustment parameters into the printing instructions, and verify the effectiveness of the control strategy through continuous monitoring of subsequent feedback factors.

[0010] Preferably, after generating the frequency band avoidance mark sequence, the frequency value, time label, three-dimensional spatial coordinate, printing path segment number and injection amplitude in each mark record are arranged in the order of the printing path to construct a frequency avoidance database for subsequent nozzle output rhythm regulation, and the high-risk frequency band data in the database is called in real time during the printing process to instruct the nozzle to avoid the resonant excitation frequency range at the corresponding time and spatial position.

[0011] Preferably, step S400 includes: At the nozzle control end, the printing path segment number and the corresponding jetting frequency of the jetting action to be regulated are determined based on the frequency band avoidance mark sequence; Calculate the nozzle transition time and determine the start time of frequency control based on the distance between the current nozzle position and the injection point in the high-risk frequency band; At the start of frequency control, the nozzle is controlled to perform frequency disturbance and amplitude disturbance operations, so that the nozzle injection frequency switches between multiple discontinuous frequencies, and the injection pressure fluctuates between multiple amplitudes according to a preset ratio; After the disturbance is completed, the frequency disturbance parameters and amplitude disturbance intensity are adjusted according to the real-time collected structural vibration response results to realize active avoidance control of frequency excitation in the printing process.

[0012] Preferably, step S500 includes: Three-axis acceleration sensors are placed in key areas of the printing structure build path to collect the micro-vibration response signal of the structure during the printing process, and output the acceleration peak value, vibration frequency component and duration; Compare and analyze the vibration response signal with the frequency band avoidance mark sequence to generate a scrambling feedback factor; Dynamically adjust the nozzle injection frequency and injection pressure amplitude based on the scrambling feedback factor to change the nozzle output rhythm; The adjustment behavior and structural response results are recorded in a closed loop, the nozzle injection control strategy is continuously optimized, and the dynamic decoupling of the nozzle excitation frequency and the structural response frequency is achieved.

[0013] Preferably, step S600 includes: Extract nozzle jet frequency, jet amplitude, feedback factor, structural vibration response, path segment number, spatial coordinates and time tags from historical printing data to evaluate the risk value of each path segment; Construct a frequency perturbation risk distribution map of the printing path and overlay the time-varying stability window of the printed structure to identify the path segments that need to be optimized; Rearrange the printing order of the path segments that need to be optimized, and adjust the nozzle jet frequency disturbance range and jet interval time; The rearranged and adjusted path segments are loaded into the printing instructions, and the control effect is verified through feedback factors.

[0014] In the above technical solution, the technical effects and advantages provided by the present invention are: This invention achieves full-process identification, avoidance, regulation, and feedback control of the resonance risk between the jet disturbance frequency and the natural frequency of the printed structure, effectively avoiding problems such as amplitude amplification, interlayer loosening, debonding, and local structural instability caused by nozzle excitation triggering structural resonance during the printing process. This method not only has real-time response capabilities but also integrates feedforward control and closed-loop feedback mechanisms, forming a synergistic mechanism in the dimensions of fine-tuning jet parameters, path optimization execution, and dynamic structural adaptation. This allows the entire printing process to maintain high molding accuracy and structural stability even in complex stress disturbance environments, significantly improving the continuity, safety, and quality control capabilities of printing tasks. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, a brief introduction to the drawings required for use in the embodiments will be given below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0016] Figure 1 This is a flow chart of the method for sprayed concrete construction for 3D printing of building structures according to the present invention. DETAILED DESCRIPTION

[0017] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these example embodiments are provided so that the description of this disclosure will be thorough and complete and will fully convey the concepts of the example embodiments to those skilled in the art.

[0018] The present invention provides Figure 1 The sprayed concrete construction method for 3D printing of building structures shown includes the following steps: S100, based on the operating cycle of the nozzle drive system, constructs a spray spectrum analysis process to collect complete pressure waveform data during the nozzle spraying process, extracts the corresponding main frequency and amplitude change sequence, and converts the main frequency and amplitude change sequence into a pressure disturbance feature vector containing a time series label; In order to achieve high-precision acquisition of the nozzle jet disturbance characteristics during the shotcrete 3D printing process, the following steps are implemented in detail: On the basis of the stable operation of the nozzle drive device, the injection cycle set by the printing task is used as the time reference to determine the start and end time of each complete injection process, and the pressure signal within the corresponding time period is selected as the analysis window. A number of high-sensitivity pressure sensors are fixedly installed near the nozzle outlet. The sensor type is preferably a piezoelectric dynamic pressure sensor with a response time of less than 0.1 milliseconds and a measuring range of 0 to 2 MPa, which can adapt to the rapid pressure fluctuations that occur during high-speed intermittent injection. All sensors synchronously collect pressure waveform data generated by concrete injection at a fixed sampling frequency of more than 5000 Hz. The data collection covers the startup phase, peak phase, continuous phase and attenuation phase of the injection process to ensure that no important pressure change details are missed. The collected raw pressure data is transmitted to the back-end processing unit through a wired signal transmission line and enters the subsequent feature extraction link.

[0019] The collected pressure data is preprocessed, including signal denoising and pressure baseline correction. During the signal denoising process, a physical low-pass filter is used to filter out environmental mechanical disturbance signals below 50 Hz to ensure that the retained pressure waveform fully reflects the real disturbance caused by the nozzle injection action. In the pressure baseline correction stage, by measuring the static value of the pressure during the injection interval, the zero offset compensation value is set, and the pressure values ​​in the entire data sequence are unified to eliminate the data offset caused by the measurement device error. Subsequently, a single waveform segment in each continuous injection behavior is extracted, and the peak recognition method is used to determine the highest pressure point of the waveform segment, and the rise time from the beginning to this point and the fall time from this point to the end are measured, thereby constructing a complete cycle record of each injection. In each cycle, the highest frequency position of the pressure fluctuation in the cycle is identified and recorded, and its corresponding pressure amplitude is measured. The frequency is used as the main frequency and the pressure value is used as the main amplitude to form the first batch of valid feature point data.

[0020] The dominant frequency and dominant amplitude data for all injection cycles are arranged in chronological order. Combined with the time points and spatial positions recorded in the nozzle ejection trajectory, each dominant frequency and dominant amplitude data point is assigned a clear time label and spatial coordinate label to construct a pressure perturbation feature vector. This feature vector is a data unit consisting of five parameters: the time of injection, the three-dimensional spatial position of the injection (including X, Y, and Z coordinates), the dominant frequency value of the injection (in Hertz), the corresponding dominant amplitude (in kilopascals), and the absolute difference in dominant frequency between the current and previous injections (in Hertz). This difference is used to reflect the degree of perturbation stability of the injection behavior. Through this combination of information, the perturbation characteristics of each injection point are fully digitally expressed and can be mapped one-to-one to the spatial construction state of the printed structure.

[0021] To ensure the stability and effectiveness of the acquired pressure disturbance characteristic vector, continuity analysis and fluctuation stability detection are performed after the characteristic vector is generated. The specific operation is: a ratio analysis is performed on the main frequency change value and the main amplitude change value between each group of adjacent injection points. When three consecutive groups of change values ​​exceed the set threshold at the same time, it is determined that a disturbance anomaly has occurred in this segment of data. At this time, the original data in the corresponding time period is marked as an invalid record, and the pressure data acquisition process is automatically re-triggered. The above steps are repeated until the data for this segment converges stably. In this way, short-term injection anomalies caused by uneven concrete density, pumping system fluctuations, or pipeline blockages can be effectively filtered out, ensuring that all formed pressure disturbance characteristic vectors have stable, continuous, traceable, and comparable characteristics, serving as the basis for high-quality input data for subsequent printing structure response analysis and nozzle rhythm control.

[0022] The core function of this step is to accurately extract and structure the dynamic pressure disturbance characteristics generated during the nozzle spraying process, providing fundamental data support for subsequent resonance response analysis of the printed structure and nozzle spraying strategy control. During the 3D printing process of sprayed concrete, the nozzle is driven by high pressure and ejects concrete paste in a high-speed, pulsating manner. This spraying process is inevitably accompanied by transient pressure fluctuations and periodic disturbances. These disturbances not only affect material deposition accuracy but can also, under certain conditions, excite the natural vibration response of the printed structure, creating a potential resonance risk. Therefore, it is necessary to acquire the pressure waveform in real time throughout the nozzle operation process, identify the dominant frequency (representing the rhythmic characteristics of the spraying disturbance) and dominant amplitude (representing the energy intensity of the spraying disturbance) corresponding to each spraying action, and assign clear timestamps to these frequency and amplitude information. This allows the construction of a set of pressure disturbance feature vectors with temporal, structural, and physical significance. This vector enables a dynamic correlation between nozzle behavior and the state of the printed structure, providing a quantitative basis for subsequent prediction of printed component response, identification of resonant segments, and nozzle spraying rhythm control. In short, this step is the key link in realizing digital perception of jet disturbances, frequency characteristic analysis and construction of control pre-input. It is the data entry and logical starting point of the entire dynamic control process.

[0023] S200, based on the pressure disturbance eigenvector, constructs a modeling process for describing the dynamic characteristics of the printed structure at the early age stage. By jointly calculating the layer height parameters of the printing trajectory, the age evolution data of the concrete material, and the real-time forming geometric parameters of the structure, the lowest-order natural frequency and response sensitive bandwidth of the current printed building unit are dynamically calculated to form a structural dynamic response baseline corresponding to the pressure disturbance eigenvector; In order to accurately construct a method for describing the dynamic response characteristics of a 3D printed structure at an early stage, ensure that the lowest-order natural frequency of the current printed building unit and its corresponding response sensitive bandwidth can be dynamically calculated, and ultimately form a structural dynamic response baseline that corresponds one-to-one with the ejection pressure disturbance eigenvector, the following steps are included: According to the progress of the nozzle printing path, the layer height parameter of the current printing layer is extracted. This parameter comes from the change of the Z-axis coordinate in the printing path, that is, the height difference between two adjacent layers. In three-dimensional building structures, the geometric characteristics of each layer usually have nonlinear changes, so it is necessary to combine the X and Y coordinate data in the printing path to obtain the boundary shape of the current construction contour in real time. With the current injection point as the center, the number of constructed layers is traced downward, and the three-dimensional geometric shape of the local construction unit corresponding to the position is reconstructed by combining the thickness value, wall width, curvature radius, inclination data, node position and other parameters of each layer. During the reconstruction process, based on the millimeter-level precision segmented contour, the layer-by-layer superposition method is used to complete the restoration of the construct shape to ensure that the formed geometric form can truly reflect the actual accumulated solid shape during the printing process.

[0024] Based on the concrete mix used for the printed structure, early-age mechanical property evolution data suitable for that mix is ​​selected. Based on this, the actual age of the current build location is determined based on the age-growth characteristics of the concrete material. This is done by calculating the difference between the current print time and the time when the initial injection was completed at that location to obtain the accurate age duration. Based on this age, the compressive strength (in MPa), static elastic modulus (in GPa), and shear modulus (in GPa) values ​​at the current age are obtained item by item from a pre-set material property comparison table in the laboratory as input parameters. When material properties are not available in tabular form, data interpolation can be performed based on experimentally fitted curves. Furthermore, to improve adaptability to actual construction environments, this step incorporates real-time on-site measurements of ambient temperature (in degrees Celsius) and humidity (in percentage) for correction, accounting for the impact of the external environment on the material hydration reaction rate and early stiffness growth. Ultimately, a set of mechanical property parameters specific to the current print unit at a specific time and location is obtained.

[0025] The resulting 3D geometry and corresponding mechanical property parameters are input into the structural response modeling process. A 3D solid model encompassing the critical structural regions of the printed structure is constructed, centered at the current printing position, with clear boundary conditions assigned to all elements. The bottom is set as a fixed support to simulate the structural constraints imposed by the solidified underlying layer on the current printed layer. The top and sides are set as free boundaries to reflect the actual stress conditions in the areas undergoing molding or not yet printed. The elastic modulus, shear modulus, and density values ​​obtained in the second step are assigned to each corresponding component of the model. Based on this, the natural frequencies of the printed structure are calculated, prioritizing the lowest-order natural frequencies (i.e., those with the lowest frequency and the largest response amplitude) and calibrating them in Hertz (Hz). Furthermore, the frequency range within the frequency response curve where the response amplitude is at least half the maximum is recorded to define the frequency bandwidth sensitive to external perturbations for the current printed element. All frequency response parameters should be derived from a linear response model established in structural mechanics based on physical properties and boundary conditions, without relying on artificial assumptions or empirical estimates, to ensure the modeling process has a theoretical basis and is technically reproducible.

[0026] The lowest-order natural frequency value and response-sensitive bandwidth calculated in the third step are bound to the three-dimensional spatial coordinates (X, Y, Z) of the current injection point and the injection time (in seconds) to construct a complete structural dynamic response baseline. This baseline forms a one-to-one correspondence in time and space with the aforementioned injection pressure perturbation eigenvector, providing core reference data for subsequent frequency domain comparisons and resonance risk identification. To ensure timely updates of the dynamic response baseline, the modeling process is refreshed once per completed print layer during the printing process. Whenever the nozzle rhythm or path changes, the structural response model of the corresponding area is immediately rebuilt to reflect the actual dynamic behavior in the current state.

[0027] This step aims to establish a dynamic response baseline for the structure by modeling its dynamic mechanical properties in real time at an early age, corresponding to the nozzle jet pressure perturbation characteristics. This provides a precise basis for identifying resonance risks and implementing jet control strategies. During the jet-type 3D printing process, printed components exhibit rapidly changing mechanical properties before they are fully cured. Their natural frequencies depend not only on the physical properties of the printing material but also on the coupled influence of multiple factors, including the height, geometry, boundary conditions, and stiffness evolution corresponding to the current printing layer. Therefore, simplified estimates cannot be made using static modeling or fixed parameters. Instead, the lowest-order natural frequency and response sensitivity bandwidth must be comprehensively calculated by combining the print trajectory layer height information acquired in real time during the printing process, the concrete age growth curve, and the 3D geometric state of the current printing segment. The core value of this dynamic modeling lies in identifying the structure's response to specific frequency perturbations at a given time and spatial location. This is particularly true during the early, incompletely cured stage of the printed structure, when its natural frequency is extremely low and susceptible to resonance excitation by the nozzle's high-frequency pressure waves. The structural dynamic response baseline formed in this step can be used as a reference standard for frequency comparison and regulation, accurately determining whether the nozzle injection frequency intersects or overlaps with the structural response frequency, and providing scientific quantitative support for subsequent nozzle rhythm adjustment and disturbance avoidance strategies. It is the core computational support link in the entire dynamic resonance suppression mechanism.

[0028] S300 compares the structural dynamic response baseline with the pressure disturbance eigenvector in the frequency domain, constructs a resonance risk superposition index, identifies the corresponding high-risk resonance frequency bands, and converts the high-risk frequency bands into frequency band avoidance mark sequences with spatial location information and time series labels; To identify the structural resonance risk that may be caused by the overlap of the nozzle excitation frequency and the natural frequency of the printed structure during shotcrete 3D printing, and thus implement frequency avoidance control, this step compares the dynamic response baseline of the printed structure with the nozzle disturbance characteristics in the frequency domain. By constructing a resonance risk superposition index, high-risk frequency segments are identified and then converted into a frequency band avoidance marker sequence with clear spatiotemporal labels. The specific implementation steps are as follows: Two key data sets are acquired during the printing process: the first is the dynamic response baseline of the printed structure, including the lowest-order natural frequency value (in Hertz) of the current building unit and its upward and downward extended response sensitive bandwidth; the second is the nozzle pressure perturbation characteristic vector, including the dominant frequency value (in Hertz) of each jet action, the corresponding dominant amplitude (in kilopascals), the coordinates of the nozzle jet position in three-dimensional space (expressed in X, Y, and Z), and the timestamp of the jet occurrence (in seconds). These data are uniformly quantized by frequency range, and a comparative data list is created on the same frequency axis, with the jet frequencies arranged in sequence and the structural natural frequencies and their response bandwidths constructed as intervals for subsequent comparison.

[0029] The overlapping relationship between the nozzle jet frequency and the structural response range is compared and analyzed one by one. For each nozzle jet action, determine whether its main frequency falls within the frequency range formed by the natural frequency ± response bandwidth of the printed structure. For example, when the lowest-order natural frequency of the structure is 45Hz and the response bandwidth is ±2.5Hz, the identification range is 42.5Hz to 47.5Hz. If the nozzle jet frequency is 46.2Hz, it is considered to fall into the risk range. If the jet frequency of a certain printing construction unit falls into this range for more than three consecutive times, and the corresponding main amplitude exceeds the construction set threshold (such as greater than 0.6 kPa), then the frequency segment is recorded as a potential excitation area where the structure may produce a significant response. The frequency, amplitude, spatial coordinates and timestamp of all jet actions that fall into the risk range are recorded to form a preliminary set of possible resonance points.

[0030] Based on the set of possible resonance points, a resonance risk superposition index is constructed. This index comprehensively considers two factors by assigning weight coefficients: the proximity between the nozzle injection frequency and the structural natural frequency; the smaller the difference, the higher the risk weight; and the absolute value of the injection disturbance amplitude. The higher the pressure amplitude, the greater the excitation energy to the structure and the higher the risk level. For example, if the injection frequency is less than 0.5 Hz from the structural natural frequency and the pressure disturbance amplitude exceeds 1.0 kPa, the risk index for that point can be assigned 1.0; if the frequency distance is 1.5 Hz and the amplitude is 0.5 kPa, the risk index is assigned 0.3. The total resonance risk value for that spatiotemporal segment is calculated by taking the weighted average of the risk indices of all injection actions within a given time window. If this value exceeds a preset threshold (e.g., a risk index greater than 0.7), the frequency segment is marked as high-risk.

[0031] All identified high-risk frequency segments are converted into a frequency band avoidance mark sequence. Specifically, for each jetting action whose risk index exceeds the threshold, the dominant frequency value, the specific time of jetting (accurate to the second level), the three-dimensional coordinate position (accurate to the millimeter level), and the print path index position are extracted. This information is then organized into a standard record unit. Each record unit includes five data items: frequency value (Hz), time tag (s), spatial coordinates (X, Y, Z, in mm), print path segment number, and jet amplitude (kPa). This frequency band avoidance mark sequence serves as a direct basis for subsequent nozzle jetting rhythm control, enabling accurate identification and spatial positioning of resonant high-risk jetting actions.

[0032] This step identifies key frequency bands with potential resonance risks by comparing the dynamic response characteristics of the printed structure with the pressure disturbance characteristics generated during the nozzle injection process in the frequency domain. These high-risk frequency bands are then clearly localized to specific printing time and space coordinates, providing a precise basis for the avoidance control of the nozzle injection strategy. During the early, not-yet-fully-cured stage of shotcrete 3D printing, the printed structure exhibits significant low stiffness and high response. Its lowest-order natural frequency is typically in the low-frequency range of tens of hertz, making it susceptible to excitation by the periodic pressure waves generated by the high-speed, intermittent, pulsating spraying of concrete by the nozzle. When the dominant frequency of the injection disturbance approaches or even coincides with the structure's current natural frequency, it triggers an amplitude amplification effect in the localized build area, known as structural resonance. This can cause microcrack propagation, loosening, and debonding at the interlayer interface, and even localized instability of the entire build unit. Therefore, this step precisely locates which injection frequencies fall within the structure's high-response range by frequency-domain cross-comparing the structure's natural frequency and its response-sensitive bandwidth with the dominant frequency data corresponding to each nozzle injection. On this basis, a resonance risk superposition index is constructed to quantify the potential threat of resonance, combining the nozzle jet amplitude and the proximity of the jet frequency to the natural frequency. This index is then used to screen the most risky excitation frequency bands. Ultimately, the frequency values ​​of these high-risk frequency bands, their corresponding jet timings, the nozzle spatial positions, and the print path segment numbers are combined into standardized data units to form a frequency band avoidance marker sequence. This sequence directly serves as the execution input for nozzle output control, implementing a jet control strategy that actively avoids the natural frequency of the structure. This is the key link in ensuring that the resonance risk of the entire printing process is controllable.

[0033] S400, based on the frequency band avoidance mark sequence, implements the output rhythm control strategy of the nozzle injection parameters. A nonlinear pulsation modulation mechanism is introduced at the nozzle control end. By applying phase and amplitude perturbations in the frequency range that intersects with the natural frequency of the structure, the energy coupling effect between the periodic pressure excitation and the natural frequency of the structure is weakened. To prevent the nozzle from exciting the natural frequency of the printed structure at an early stage during the concrete spraying process, which could lead to structural resonance, local debonding, or interlayer cracking, an active control strategy based on a frequency band avoidance mark sequence is adopted. By precisely adjusting the nozzle's output rhythm and implementing a nonlinear pulsation modulation mechanism at the nozzle control end, the energy coupling path between the excitation frequency and the structural natural frequency is destroyed, effectively suppressing the resonance risk. The implementation of this strategy includes the following steps: Obtain all high-risk jet frequency points identified in the frequency band avoidance mark sequence. This sequence is a structured data set arranged in the order of the printing path, where each data unit contains the high-risk frequency value (in Hertz), the corresponding nozzle jet time (in seconds), the three-dimensional spatial position coordinates (expressed in X, Y, Z, in millimeters), and the printing path segment number. After the printing control system receives the sequence, it extracts all high-risk jet points that are in the printing process and have not yet been executed in chronological order. For each jet point, the system compares its frequency value with the lowest-order natural frequency of the current structural response baseline and its response sensitive bandwidth. If the jet frequency falls within the structural response frequency band, it is marked as "jet action that needs to be regulated" and placed in the regulation queue.

[0034] The print path segment numbers of the jetting actions that need to be regulated are read one by one in the control queue, and the nozzle movement transition duration is calculated based on the distance between the actual position of the current nozzle and the corresponding high-risk point. This calculation is derived based on the spatial coordinate difference of each point in the path planning data and the current nozzle movement speed (in mm / s). Further combined with the minimum response time of the nozzle jet frequency adjustment in the printing task (determined by the response speed of the nozzle controller, usually less than 1 second), the control start time of each high-risk point is determined. After determining the control time, the nozzle jet frequency adjustment value and the jet pressure amplitude adjustment parameters corresponding to that moment are set in advance, expressed in frequency offset (in Hertz) and amplitude reduction ratio (for example, three fixed gears of 10%, 15%, and 20%). The above parameters will be written into the print instruction queue as nozzle control commands.

[0035] The nozzle control device automatically executes a pre-set nonlinear pulsation modulation operation within the control time window. This modulation operation involves two dimensions of perturbation control: frequency perturbation and amplitude perturbation. Regarding frequency perturbation, the controller adjusts the pulsation period of the drive pump to vary the fixed injection frequency (for example, 45 Hz) by small, periodic variations within the control range. For example, by setting the 45 Hz frequency upward and downward by 0.8 Hz, 1.2 Hz, and 0.5 Hz, this creates a discontinuous injection frequency sequence, preventing the nozzle from continuously residing within the structure's natural response frequency band. Regarding amplitude perturbation, the opening of the pump pressure control valve is adjusted to produce periodic fluctuations in the pressure output for each injection. For example, over five consecutive injections, the injection pressure is set to 100%, 85%, 70%, 90%, and 80% (based on the rated maximum pressure). This nonlinear fluctuation effectively disrupts the periodicity of the pressure wave excitation, reducing the structure's effective response to the excitation energy and thus interrupting the accumulation of excitation energy.

[0036] After the nonlinear pulsation modulation is completed, the nozzle continues to perform the jetting task along the print path toward the next build segment. The control system records the results of this control action and the corresponding jetting point information, and monitors the structural micro-vibration response data of this jetting segment in real time. The sensor used is a high-sensitivity accelerometer mounted on the peripheral components of the nozzle, with a data sampling frequency of no less than 500 Hz. If the monitoring data shows that the peak structural vibration after the jetting point is controlled is lower than a preset safety threshold (e.g., 0.1g), the control effect is considered effective and the frequency band is marked as "successfully avoided." If a trend of continuous vibration amplification or control failure is observed, instructions are added to the print path to extend the perturbation duration or increase the amplitude perturbation intensity. This closed-loop adjustment mechanism can be updated in real time through print control instructions, ensuring that the nozzle output rhythm is always dynamically aligned with the structural state, ultimately achieving active interruption and controllable avoidance of resonant energy coupling throughout the printing process.

[0037] This step, after identifying high-frequency bands with resonance risks during the printing process, dynamically adjusts the nozzle's jet parameters to achieve substantial suppression of structural resonance and energy intervention control, thereby ensuring the mechanical stability and print quality of the building structure's 3D printing process. In shotcrete 3D printing, because the nozzle sprays slurry in a high-speed, periodic, pulsating manner, it is very easy to create excitation conditions within a specific frequency range that coincide with the natural frequency of the printed structure, leading to localized resonant responses in the structure. This resonance amplifies the vibration response in the early stages of the structure, before it has fully solidified, causing micro-cracks between layers, material debonding, and even localized instability in the component. In severe cases, it can interrupt the entire printing process. To this end, this step reads the high-risk frequency points identified in the frequency band avoidance marker sequence and performs real-time control of the nozzle's jet parameters. Specifically, a nonlinear pulsation modulation mechanism is introduced at the nozzle control end to slightly perturb the jet frequency and jet pressure, allowing the jet's main frequency to avoid the response bandwidth of the structure's natural frequency. The control method includes two dimensions: frequency perturbation and amplitude perturbation. In terms of frequency, by applying perturbations to the nozzle drive cycle, the frequency is shifted up and down around the original set value, interrupting the continuous residence of the jet frequency in the resonance section. In terms of amplitude, by adjusting the order of strength of the pump pressure output, the constant state of the jet amplitude is broken, and the linear response accumulation of the structure to periodic excitation is disturbed. This nonlinear perturbation mechanism does not rely on shutting down or stopping the jet action, but achieves "soft cutting" of the excitation path without interrupting the normal printing rhythm, reducing the energy coupling efficiency between the periodic pressure wave and the natural frequency of the structure from the source. The ultimate goal is to weaken the effect of external excitation on the resonant amplification of the structure, improve the stability of the structure during the forming process, reduce the risk of structural defects caused by resonance, and provide a dynamic vibration avoidance control strategy for the 3D printing system that is both real-time and safe.

[0038] S500: During the execution of the nozzle output rhythm control strategy, a structural vibration attenuation self-feedback mechanism is introduced. The real-time collected micro-vibration response signal of the printed structure is integrated with the frequency band avoidance mark sequence to generate a scrambling feedback factor. Based on the scrambling feedback factor, the nozzle output rhythm is continuously adjusted to achieve dynamic decoupling and continuous optimization of the nozzle excitation frequency and the structural response frequency. To achieve dynamic adaptability during nozzle output rhythm control, a structural vibration attenuation self-feedback mechanism is introduced during the operation of the control strategy. This mechanism aims to continuously modify the nozzle excitation behavior based on the real-time response state of the printed structure, ensuring that it stays away from the natural frequency range of the structure and reducing the risk of resonance excitation. This implementation process consists of the following steps: Miniature triaxial accelerometers are installed at key locations along the print structure's build path to capture real-time microvibration response signals generated during the printing process. The sensors have a range of at least ±2g, a minimum resolution better than 0.005g, and a sampling frequency of at least 1000 Hz. The sensors are mechanically fixed or secured with high-strength adhesives to locations prone to structural response, such as overhanging joints, corners, and free edges. During the printing process, the system records the peak acceleration, duration, and primary frequency components of surface microvibration, using the moment the nozzle completes each material deposition as the time reference. This data is then chronologically output to the control and computation unit, generating a microvibration response data sequence. Each data entry includes the acquisition time, peak acceleration (in m / s²), frequency component (in Hz), and duration (in ms). The data is then linked to the nozzle's position coordinates at that moment and the jetting frequency parameters, enabling spatiotemporal matching of jet excitation and structural response.

[0039] The high-risk frequency interval identified in the current printing segment is extracted from the frequency band avoidance mark sequence and compared with the current jetting frequency executed by the nozzle. The system determines whether there is a frequency coupling risk based on the difference between the jetting frequency of each nozzle and the natural frequency of the corresponding printing unit. At the same time, the structural vibration response data obtained in the previous step is read. If the current jetting action causes the structural acceleration to exceed 0.15m / s², or the vibration duration exceeds 200 milliseconds, and the difference between the response frequency and the natural frequency of the structure is less than 1.5 Hz, it is determined that the jetting behavior produces potential resonant excitation. The system generates a frequency interference feedback factor based on three indicators: vibration response intensity, frequency proximity and duration. The feedback factor is expressed as a value between 0 and 1. The closer the feedback factor is to 1, the higher the degree of coupling between the jetting frequency and the structural response.

[0040] The control strategy for dynamically adjusting the nozzle injection frequency and injection amplitude is based on the value of the perturbation feedback factor. The specific operation is as follows: when the perturbation feedback factor is higher than 0.7, the control unit immediately adjusts the nozzle injection frequency out of the structural response range, and the frequency adjustment range is ±2.0 Hz. The nozzle drive pump cycle is linearly weighted and adjusted according to the feedback factor, and the frequency perturbation frequency is increased from once per second to twice per second. At the same time, the injection pressure amplitude is perturbation-adjusted, and the original injection pressure value is reduced by 10%, 20%, 15%, 10%, and 5% in sequence, forming an asymmetric pulsation mode, thereby destroying the original frequency coupling path. If the perturbation feedback factor is between 0.4 and 0.7, the current control parameters are maintained unchanged, and the re-verification mechanism within the monitoring cycle is activated; when the feedback factor is lower than 0.4, it is considered that the nozzle excitation frequency and the structural response frequency are sufficiently decoupled, and the control strategy maintains the current state without adjustment.

[0041] The nozzle output parameter adjustment behavior and the changing trend of the printed structure response are recorded in a closed loop. The control unit re-collects the micro-vibration response data after each injection behavior and updates the frequency interference feedback factor. If the feedback factor is less than 0.4 for three consecutive injection cycles, the injection strategy is recorded as "effective decoupling" and the current parameter configuration is solidified for the reference strategy of subsequent similar printing segments; if the feedback factor continues to increase and exceeds 0.8, the system determines that the current control intensity is insufficient, and automatically expands the frequency perturbation range to ±3.0 Hz, and increases the injection amplitude reduction to a maximum of 25%. In addition, the system records the high-risk sections, feedback factor change curves and control execution results as a control result log for reference in subsequent printing path planning optimization. Through this structural vibration attenuation self-feedback mechanism, a closed-loop matching of the nozzle output rhythm control and the dynamic state of the printed structure is achieved, so that the printing process has self-regulation ability and robustness in the early stages, improving structural stability and printing continuity from the source.

[0042] This step aims to achieve a closed-loop coupling between the nozzle's excitation behavior and the actual response of the printed structure by introducing a self-feedback mechanism for structural vibration attenuation during the nozzle's execution of the output cadence control strategy. This allows for dynamic adaptability and continuous optimization of the nozzle's output cadence, ensuring that resonance risk remains within a controllable range throughout the 3D printing process. Specifically, during 3D printing, the printed structure is in its early stages, with low natural frequencies and incompletely established structural stiffness. It is highly susceptible to the periodic jetting disturbances of the nozzle, leading to vibration amplification, interface loosening, or localized microcracking. Traditional nozzle cadence control strategies rely solely on predictive avoidance, making them difficult to adapt to structural frequency fluctuations caused by material property changes, environmental disturbances, or path morphology changes during real-time construction. Therefore, this step deploys a highly sensitive micro-vibration sensor during the printing process to collect real-time acceleration response data of the printed structure under each jetting action. This data is then integrated with the high-risk frequency intervals in the frequency band avoidance marker sequence for analysis to construct a frequency perturbation feedback factor. This feedback factor quantifies whether the current jetting frequency is effectively coupled with the structural response range and adjusts the nozzle's jetting frequency perturbation range and jetting amplitude perturbation cadence accordingly. When the feedback factor increases, indicating an enhanced structural response, the nozzle output frequency will move further away from the structural natural frequency, and the density of nonlinear perturbation frequencies will increase. When the feedback factor decreases, indicating a stable structural vibration response, the nozzle rhythm can maintain its current state or moderately adjust back to the energy-saving range. Through the above mechanism, the nozzle output behavior is upgraded from the original "preset one-way control" to "real-time perception-driven adaptive regulation," establishing a self-learning, self-adjusting closed-loop system between printing excitation and structural response, significantly improving molding stability, structural safety, and construction continuity during the printing process.

[0043] S600, based on the closed-loop operation of the nozzle output rhythm control and structural vibration attenuation self-feedback mechanism, constructs a frequency perturbation risk distribution map covering the entire 3D printing path. This frequency perturbation risk distribution map is superimposed and analyzed with the time-varying stability window of the printed structure. The jetting path of subsequent printing tasks is pre-arranged and the jetting rhythm is adjusted, achieving dynamic closed-loop control of the entire build process while keeping the resonance risk under control. To ensure that each path segment in the 3D printing process is always in a state of controlled resonance risk when constructing different structural units, and to further improve the stability and safety of the printing system, after the nozzle output rhythm control strategy and the structural vibration attenuation self-feedback mechanism form a closed-loop operation, based on the collected historical printing process data, a frequency disturbance risk distribution map covering the entire printing path is constructed. This is then superimposed and analyzed with the time-varying stability window of each stage of the printed structure. Based on this, the injection path of subsequent printing tasks is pre-arranged and the injection rhythm is dynamically adjusted. This process includes the following steps: After each printing phase, the print records are extracted and organized, including nozzle jet frequency, jet amplitude, feedback factor, structural micro-vibration response data, print path segment number, spatial coordinates, and time tags. Nozzle jet frequency is recorded in Hertz, jet amplitude is in kilopascals, and feedback factor is a dimensionless value between 0 and 1. Micro-vibration response data includes maximum acceleration (in m / s²) and vibration duration (in milliseconds). Print path segments are numbered sequentially starting at 0, with spatial coordinate accuracy at the millimeter level and time tag accuracy at 0.1 second. During data organization, nozzle jetting behaviors are paired with corresponding structural vibration responses. A risk assessment is performed for each path segment based on the cumulative number of high feedback factor events, high amplitude jetting behaviors, and response peak over-threshold events within each path segment.

[0044] The above path segment risk data is plotted as a frequency perturbation risk distribution map. The entire printing path is divided into several fixed-length segments, each set to 50 mm in length, and the numbers correspond to the printing order. For each path segment, the number of high-feedback-factor jetting behaviors that occur during the corresponding printing process (a feedback factor value greater than 0.7 is considered a high-risk jetting), the number of structural vibration peaks greater than 0.2 m / s², and the number of times the jetting frequency falls within the range of ±2.5 Hz of the lowest-order natural frequency of the structure are counted. These three data items are converted into a risk score using a weighted average. The risk score is expressed as a percentage, with a maximum score of 100% and a minimum score of 0%. The different risk levels are represented by color shades, gradually transitioning from green (low risk, score 0%-20%) to red (high risk, score above 80%). The map has spatial coordinate labels and path number labels, visually reflecting areas of dense frequency perturbation distribution on the printing path.

[0045] By combining the material property changes of the printed structure over time, a time-varying stability window is constructed. This window is based on the growth curve between concrete age and elastic modulus, calculated from the printing time and age. Using an elastic modulus that increases by 10% per hour as a reference, when the printed structure is less than 30 minutes old, the maximum tolerable excitation frequency deviation range is set to ±1.5 Hz, and the upper limit of the tolerable peak acceleration is 0.12 m / s². For ages between 30 minutes and 1 hour, the tolerable frequency deviation range increases to ±2.5 Hz, and the upper limit of the peak acceleration is raised to 0.2 m / s². After more than 1 hour, the corresponding tolerance is further increased. This window is overlaid and compared with the frequency perturbation risk map by path number. When the risk score of a path segment exceeds the stability tolerance threshold for that age, it is marked as a "path segment requiring optimization."

[0046] For path segments marked as "needing optimization," the jet path is rearranged and the jet rhythm is adjusted. During the rearrangement operation, low-risk path segments are prioritized for the initial printing phase or at the beginning of the printing order, while high-risk path segments are postponed until the structure is fully solidified and the stability window is wider. Regarding rhythm adjustment, for high-risk path segments, the nozzle jet frequency perturbation range is increased from ±1.0 Hz to ±2.5 Hz, and the jet interval is extended from the original 0.8 seconds to 1.2 seconds to reduce the instantaneous excitation density of the structure and the possibility of exciting resonance. The results of this path rearrangement and rhythm adjustment are reloaded into the print control instruction set, and their effectiveness is verified in real time during the actual printing process. If the feedback factor value of the corresponding path segment continues to be below 0.4 in subsequent executions, it indicates that the control strategy is effective and the path segment is marked as "stable pass"; if the feedback factor value increases again, the perturbation intensity is further increased and the printing order is reevaluated.

[0047] This step, building on the closed-loop control of nozzle output rhythm and structural vibration response self-feedback mechanisms, further systematizes, visualizes, and proactively analyzes risk data from the entire 3D printing process. This allows for global dynamic optimization of the printing path and jetting rhythm, ensuring that the entire building component remains within a controllable resonance risk during construction. Specifically, during the 3D printing process, as the structure accumulates layer by layer, its dynamic mechanical properties, such as natural frequency and stiffness, continuously change with factors such as printing time, build thickness, and material age, forming a "time-varying stability window" with a significant time dependency. The nozzle jetting behavior itself continuously generates periodic perturbation pressure waves. Once these perturbations coincide with the natural frequency of a particular stage of the structure, they can excite local resonances, leading to amplified vibration amplitudes, interlayer debonding, component instability, and even interruption of the overall build process. Therefore, relying solely on real-time, local feedback control cannot fully cover potentially high-risk sections along the printing path; centralized analysis of data from the entire process is essential. By constructing a frequency perturbation risk distribution map, the high feedback factor events, high vibration response amplitudes, and frequency overlaps that actually occurred on all path segments can be centrally displayed, forming a "risk heat map" with time labels and spatial coordinates. This map can intuitively identify key sections in the path that are prone to excitation resonance. Furthermore, by superimposing and comparing this map with the stability tolerance of the structure at different time periods, it can be clearly indicated which printing path segments will be within the time window of low structural stability in the original plan, thereby triggering the path rearrangement mechanism, adjusting the high-risk segments to a more mature and rigid stage of the structure, or optimizing their injection frequency and injection interval parameters. This mechanism is not only forward-looking and global, but also truly realizes the "construction of a risk-minimizing path plan", thereby upgrading the injection excitation control strategy from local response to full-process coordinated control, greatly improving the operability, stability, and molding quality safety margins of 3D printed structures in complex construction tasks.

[0048] The above-mentioned sprayed concrete construction method for 3D printing of building structures achieves full-process identification, avoidance, regulation, and feedback control of the resonance risk between the spray disturbance frequency and the natural frequency of the printed structure, effectively avoiding problems such as amplitude amplification, interlayer loosening, debonding damage, and local structural instability caused by nozzle excitation triggering structural resonance during the printing process. This method not only has real-time response capabilities but also integrates feedforward control and closed-loop feedback mechanisms, forming a synergistic mechanism in dimensions such as fine-tuning of spray parameters, path optimization execution, and dynamic structural adaptation. This allows the entire printing process to maintain a high level of molding accuracy and structural stability even in complex stress disturbance environments, significantly improving the continuity, safety, and quality control capabilities of the printing task.

[0049] The above description is merely illustrative of certain exemplary embodiments of the present invention. It goes without saying that those skilled in the art will be able to modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and description are illustrative in nature and should not be construed as limiting the scope of protection of the claims.

Claims

1. A method for spraying concrete for 3D printing of building structures, characterized in that: The following steps are involved: S100, based on the operating cycle of the nozzle drive system, collects pressure waveform data during the shotcrete process, extracts the main frequency and amplitude change sequence, and generates a pressure disturbance feature vector with a time tag; S200, based on the pressure disturbance eigenvector, combined with the printing trajectory layer height, concrete age data and molding geometric parameters, dynamically models the lowest-order natural frequency and response sensitive bandwidth of the current printing unit to build a structural dynamic response baseline; S300 compares the structural dynamic response baseline with the pressure disturbance eigenvector in the frequency domain, constructs a resonance risk superposition index, identifies high-risk resonance frequency bands, and generates a frequency band avoidance mark sequence with spatial and temporal labels; S400, based on the frequency band avoidance mark sequence, executes the nozzle output rhythm control strategy, introduces a nonlinear pulse modulation mechanism at the nozzle control end, and weakens the energy coupling between the injection pressure and the structural natural frequency through phase and amplitude perturbations within the frequency range; S500, during the nozzle output rhythm control process, introduces a structural vibration attenuation self-feedback mechanism, fusing the structural micro-vibration response signal with the frequency band avoidance mark sequence to generate a scrambling feedback factor, which is used to continuously optimize the nozzle output rhythm and achieve dynamic decoupling of the excitation frequency and the structural response frequency; S600, based on the closed-loop operation of the nozzle output rhythm control and structural vibration attenuation self-feedback mechanism, constructs a frequency disturbance risk distribution map covering the printing path, superimposes it with the structural time-varying stability window for analysis, pre-adjusts the printing path and injection rhythm, and realizes closed-loop construction with controllable resonance risks throughout the entire process.

2. The method for constructing shotcrete for 3D printing of building structures according to claim 1, characterized in that: Step S100 includes: Multiple piezoelectric dynamic pressure sensors are fixedly installed near the nozzle outlet to synchronously collect pressure waveform data during the concrete spraying process at a sampling frequency of more than 5000 Hz; Perform low-pass filtering and noise reduction processing and zero-point offset reference correction on the collected pressure data; The main frequency and main amplitude of each injection are extracted and matched with the nozzle spatial trajectory in time sequence to generate a pressure disturbance feature vector containing injection time, spatial position, main frequency value, main amplitude and main frequency variation; The continuity of the feature vector is checked. When three consecutive groups of change values ​​exceed the threshold, they are marked as abnormal and the data is re-collected.

3. The method for constructing shotcrete for 3D printing of building structures according to claim 1, characterized in that: Step S200 includes: Extract the layer height parameters of the current printing layer and reconstruct the 3D geometric shape of the current printing building unit in combination with the spatial coordinate data of the printing path; The age of the build location is determined based on the difference between the printing time and the jetting completion time. The corresponding compressive strength, elastic modulus, and shear modulus values ​​are obtained based on the ratio scheme, and temperature and humidity are introduced for correction. Input the geometric shape and mechanical parameters into the structural response modeling process, set the boundary conditions, and calculate the lowest-order natural frequency and its response sensitive bandwidth; The lowest-order natural frequency and response-sensitive bandwidth are bound to the spatial coordinates of the injection point and the injection time to construct the structural dynamic response baseline.

4. The method for constructing shotcrete for 3D printing of building structures according to claim 1, characterized in that: Step S300 includes: Extract the nozzle jet frequency, jet amplitude, feedback factor, structural vibration response, path segment number, spatial coordinates and time tags from the historical printing data. Count the number of high feedback factor events, the number of over-threshold amplitude jet behaviors and the number of response peak violations for each path segment to determine the risk score for each path segment. Construct a frequency perturbation risk distribution map for the printing path, and establish a time-varying stability window based on the elastic modulus growth law corresponding to the age of the printed structure. Analyze the path number correspondence between the distribution map and the stability window to identify path segments with risk scores exceeding the tolerance threshold. Rearrange the printing order of identified path segments, placing low-risk path segments in the early construction phase and postponing the execution of high-risk path segments until the stability window is expanded; Adjust the nozzle jet frequency disturbance range of the high-risk path section to ±2.5 Hz, extend the jet interval to 1.2 seconds, load the adjustment parameters into the printing instructions, and verify the effectiveness of the control strategy through continuous monitoring of subsequent feedback factors.

5. The method for constructing shotcrete for 3D printing of building structures according to claim 4, characterized in that: After generating the frequency band avoidance mark sequence, the frequency value, time label, three-dimensional spatial coordinates, printing path segment number and injection amplitude in each mark record are arranged in the order of the printing path to construct a frequency avoidance database for subsequent nozzle output rhythm regulation. During the printing process, the high-risk frequency band data in the database is called in real time to instruct the nozzle to avoid the resonant excitation frequency range at the corresponding time and spatial position.

6. The method for constructing shotcrete for 3D printing of building structures according to claim 1, characterized in that: Step S400 includes: At the nozzle control end, the printing path segment number and the corresponding jetting frequency of the jetting action to be regulated are determined based on the frequency band avoidance mark sequence; Calculate the nozzle transition time and determine the start time of frequency control based on the distance between the current nozzle position and the injection point in the high-risk frequency band; At the start of frequency control, the nozzle is controlled to perform frequency disturbance and amplitude disturbance operations, so that the nozzle injection frequency switches between multiple discontinuous frequencies, and the injection pressure fluctuates between multiple amplitudes according to a preset ratio; After the disturbance is completed, the frequency disturbance parameters and amplitude disturbance intensity are adjusted according to the real-time collected structural vibration response results to realize active avoidance control of frequency excitation in the printing process.

7. The method for constructing shotcrete for 3D printing of building structures according to claim 1, characterized in that: Step S500 includes: Three-axis acceleration sensors are placed in key areas of the printing structure build path to collect the micro-vibration response signal of the structure during the printing process, and output the acceleration peak value, vibration frequency component and duration; Compare and analyze the vibration response signal with the frequency band avoidance mark sequence to generate a scrambling feedback factor; Dynamically adjust the nozzle injection frequency and injection pressure amplitude based on the scrambling feedback factor to change the nozzle output rhythm; The adjustment behavior and structural response results are recorded in a closed loop, the nozzle injection control strategy is continuously optimized, and the dynamic decoupling of the nozzle excitation frequency and the structural response frequency is achieved.

8. The method for constructing shotcrete for 3D printing of building structures according to claim 1, characterized in that: Step S600 includes: Extract nozzle jet frequency, jet amplitude, feedback factor, structural vibration response, path segment number, spatial coordinates and time tags from historical printing data to evaluate the risk value of each path segment; Construct a frequency perturbation risk distribution map of the printing path and overlay the time-varying stability window of the printed structure to identify the path segments that need to be optimized; Rearrange the printing order of the path segments that need to be optimized, and adjust the nozzle jet frequency disturbance range and jet interval time; The rearranged and adjusted path segments are loaded into the printing instructions, and the control effect is verified through feedback factors.

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