Existing line protection cover design and construction method based on BIM + three-dimensional laser scanning

Abstract

The invention provides an existing line protection cover design and construction method based on BIM + three-dimensional laser scanning, belongs to the technical field of design and construction, and aims to solve the problems of insufficient precision, risk prevention and control lagging, cost waste and the like of a traditional design and construction method in an existing line protection cover project. High-precision digital duplicating of an existing line structure is achieved through three-dimensional laser scanning, precise adaptive design, hoisting simulation and construction management and control of a protection cover are completed in combination with the BIM technology, and a whole-process technical system of data acquisition, modeling design, hoisting simulation and field implementation is formed. According to the method, the core technical problems of existing line structure deviation adaptation, construction space conflict, high-altitude falling object protection and the like are effectively solved, the precision and efficiency of protection cover design construction are remarkably improved, interference of construction on existing line operation is reduced, and the method is suitable for safety protection engineering of existing lines close to operation metros, railways and the like.

Description

Technical Field

[0001] This invention belongs to the field of design and construction technology, specifically relating to a design and construction method for existing railway line protective covers based on "BIM + 3D laser scanning", which is applicable to the construction safety protection of buildings around operating lines such as subways and railways. Background Technology

[0002] With the acceleration of urbanization, construction projects near existing lines (such as subways and railways) are increasing. These projects need to address safety risks such as falling objects from heights and structural interference during construction while ensuring the normal operation of the existing lines. Therefore, special protective covers are required. However, traditional protective cover design and construction methods have the following significant drawbacks:

[0003] Insufficient measurement accuracy: Traditional two-dimensional measurement or total station single-point measurement methods have sparse measurement points, and errors are easy to accumulate. They are difficult to accurately reflect the true alignment and spatial position of existing line structures (such as box girders and bridge piers), resulting in a mismatch between the protective cover design and the actual structure on site.

[0004] Model disconnected from site: Traditional BIM models are based on ideal design drawings and do not take into account the actual situation such as construction deviations of existing structures and beam deflection. This can easily cause the protective cover to collide with the existing structure or have too large a gap, affecting the protective effect and installation efficiency.

[0005] Lagging risk identification: The lack of effective spatial conflict detection and hoisting simulation methods means that risks such as structural interference and hoisting collisions during construction can only be discovered during the on-site installation stage, resulting in high rework rates, project delays, and increased costs.

[0006] Drilling and anchoring rebar carries high risks: Traditional methods cannot accurately detect the distribution of rebar inside existing box girders, and the rebar is easily bumped during drilling, affecting the safety of the existing structure and reducing the reliability of rebar anchoring.

[0007] Low construction efficiency: The protective cover adopts a uniform specification design without modular adaptation to the differences in existing line span, clearance, etc., resulting in a large amount of on-site installation and adjustment work and a long time of interference with the operation of existing lines. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a design and construction method for protective covers of existing railway lines based on "BIM + 3D laser scanning". This method enables high-precision digital replication of existing railway line structures, precise adaptation design of protective covers, early prevention and control of construction risks, and refined management of on-site construction. It solves the problems of insufficient accuracy, delayed risk assessment, and cost waste in traditional methods, ensuring the safe operation of existing railway lines and the smooth progress of construction.

[0009] The present invention employs the following technical solution.

[0010] A design and construction method for existing power line protective covers based on "BIM + 3D laser scanning" includes:

[0011] Step 1: Perform 3D laser scanning data acquisition on the existing line structure;

[0012] Step 2: Perform point cloud data processing and construct a refined model of existing lines;

[0013] Step 3: Perform precise design of the protective cover based on BIM;

[0014] Step 4: Perform BIM4D hoisting simulation and scheme optimization;

[0015] Step 5: Conduct meticulous on-site construction and quality control.

[0016] Preferably, step 1 specifically includes:

[0017] A 3D laser scanner was used to perform a full-coverage scan of the existing railway line's piers, cap beams, box girders, and track structures to obtain point cloud data.

[0018] Preferably, step 2 specifically includes:

[0019] Point cloud data is preprocessed, stitched together, denoised, and geometrically fitted to establish a refined model of the existing line that is consistent with the actual situation on site.

[0020] Preferably, in step 2, the point cloud data preprocessing method includes:

[0021] The raw point cloud data acquired by the Leica P50 scanner is imported into Cyclone REGISTER 360, which automatically identifies the spatial coordinates and RGB texture information of the point cloud; for non-standard format data, CloudCompare is used to convert it into a unified .las format to ensure data compatibility.

[0022] Using the existing railway line's operational coordinate system as a reference, three or more uniformly distributed and highly stable existing structural feature points are selected as control points, and their coordinates are obtained through total station measurements.

[0023] Input the measured coordinates of the control points in Cyclone REGISTER 360, and use the coordinate registration function of the software to perform coordinate transformation on the point cloud data of each station using the least squares method, so that all point clouds are unified under the same coordinate system;

[0024] Based on the existing line structure type and construction segmentation, the overall point cloud is divided into independent processing units;

[0025] Manually crop irrelevant areas outside the scanning range, retaining the point cloud data of the existing line structure and the necessary surrounding space.

[0026] Preferably, in step 2, the point cloud stitching method includes:

[0027] Feature point extraction: In Cyclone REGISTER 360, common feature points of adjacent site clouds are automatically identified, and no less than 20 feature points are extracted for each overlapping area;

[0028] Preliminary stitching: Based on the feature point matching results, the software automatically calculates the stitching matrix to complete the preliminary fusion of multiple point clouds and generate a temporary overall point cloud;

[0029] Accuracy verification and optimization: The distance deviation analysis function is used to check the continuity of the point cloud in the stitched area.

[0030] If the distance deviation between the overlapping areas of adjacent cloud sites is ≤±8mm, the splicing is deemed qualified.

[0031] If the deviation exceeds the standard, manually add feature points and rerun the ICP algorithm for iterative optimization until the deviation meets the requirements.

[0032] Preferably, in step 2, the point cloud denoising method includes:

[0033] Step 1: Use Gaussian filtering to remove random noise;

[0034] Step 2: Denoising based on reflection intensity threshold;

[0035] Step 3: Manually remove background noise interactively.

[0036] Preferably, in step 2, the first step is component segmentation and point cloud extraction, that is, in Cyclone REGISTER 360, based on the structural spatial location and geometric shape, the overall point cloud is segmented into independent point clouds of individual components, ensuring that a single fitting task is only for the same type of geometric features.

[0037] Step 2: Parametric fitting modeling, which involves selecting point cloud data from the middle and top of the bridge pier, running the cylinder fitting function, and the software automatically calculating the center of the bottom surface, the center of the top surface, and the radius R. By adjusting the fitting range, the maximum distance deviation between the fitted cylinder and the point cloud is ≤ ±4mm.

[0038] Extract the point cloud of the entire cross section of the cap beam, and perform cuboid fitting in segments along the length direction to ensure the flatness and cross-sectional dimensional accuracy of the cap beam. The deviation between the fitted cuboid and the point cloud is ≤ ±5mm.

[0039] The box girder is divided into segments of 3m along its length using piecewise quadratic surface fitting. The web and flange are fitted separately, and the cross-sectional dimensions and linear curvature of each segment are extracted. The complete box girder model is then formed by surface splicing. The deviation between the fitted surface and the point cloud is ≤±3mm.

[0040] The point cloud on the top surface of the rail is extracted, and a third-order polynomial curve is used for fitting to obtain the coordinates and elevation of the track centerline, ensuring that the track alignment deviation is ≤ ±2mm.

[0041] Preferably, step 3 specifically includes:

[0042] Based on the existing line's refined model, and in conjunction with safety protection requirements and load specifications, the modular structure design, collision inspection, and strength verification of the protective cover were carried out.

[0043] Preferably, in step 3, the method for strength verification includes:

[0044] The calculation formula for impact load is as follows:

[0045] ;

[0046] Where F is the impact load; m is the mass of the falling object; g is the gravitational acceleration; and h is the height of the falling object. This refers to the deformation of the protective shield structure under impact.

[0047] The formula for verifying the tensile design bearing capacity of bolts is as follows: ;

[0048] in Design the tensile bearing capacity of the bolt; This is the bolt connection coefficient; This refers to the ultimate tensile strength of the bolt. This is the effective cross-sectional area of ​​the bolt; This refers to the partial factor for resistance of bolted connections;

[0049] The strength verification formula for the component is as follows:

[0050] ;

[0051] in The design value of the bending moment borne by the component; The design value of the axial force borne by the component; The plastic section modulus of the component; The net cross-sectional area of ​​the component; The yield strength of the steel; The coefficient for plastic development of the cross section; For the resistance of structural components;

[0052] The formula for structural deflection verification is as follows:

[0053] ;

[0054] in L represents the maximum vertical deflection of the component; L represents the calculated span of the component.

[0055] Preferably, step 4 specifically includes:

[0056] The BIM4D method was used to simulate the hoisting process of the protective cover, and the hoisting sequence, equipment selection and operation time window were optimized.

[0057] Preferably, step 5 specifically includes:

[0058] On-site positioning, rebar detection, component installation, and quality acceptance are carried out based on BIM models and scanning data.

[0059] The beneficial effects of the present invention are as follows, compared with the prior art:

[0060] (a) Precision improvement effect

[0061] The digital replication accuracy of the existing line structure reaches ±3mm, and the connection error between the protective cover and the existing structure is ≤±3mm, which solves the problem of the disconnect between traditional design and actual site conditions.

[0062] Collision checks proactively mitigate over 90% of on-site structural interference risks, reducing the rework rate from 30% with traditional methods to below 5%.

[0063] (II) Safety Assurance Effectiveness

[0064] Three-dimensional laser scanning and rebar detection technology avoids damage to the existing box girder structure caused by drilling and rebar installation, thus ensuring the safety of subway operation;

[0065] The protective cover has achieved effective protection against risks such as falling objects from heights and wind loads through impact load tests and multi-condition calculations. No safety accidents affecting the operation of the existing line occurred during the construction period.

[0066] (III) Efficiency and cost optimization effects

[0067] Modular design and factory prefabrication shortened the on-site construction cycle by 30%, and optimized hoisting simulation improved the utilization rate of the operation time window by 50%, reducing interference with subway operations.

[0068] The rework rate is reduced, construction efficiency is improved, and the overall cost is reduced by 15% to 20%, avoiding the cost waste of sending components back to the factory for processing and on-site adjustments in the traditional method.

[0069] (iv) Value of technology promotion

[0070] The "BIM + 3D laser scanning" full-process technology system developed in this invention provides a standardized method for the design and construction of protective covers near existing railway lines. It can be widely applied to building projects around operating lines such as subways, railways, and highways, and has significant industry promotion value. Attached Figure Description

[0071] Figure 1 This is a flowchart of the design and construction method of the existing line protection cover based on "BIM + three-dimensional laser scanning" in this invention. Detailed Implementation

[0072] like Figure 1 As shown, a design and construction method for existing power line protective covers based on "BIM + 3D laser scanning" includes:

[0073] Step 1: Perform 3D laser scanning data acquisition on the existing line structure;

[0074] In a preferred but non-limiting embodiment of the present invention, step 1 specifically includes:

[0075] A 3D laser scanner was used to perform a full-coverage scan of the existing railway line's piers, cap beams, box girders, tracks, and other structures to obtain high-precision point cloud data.

[0076] Step 2: Perform point cloud data processing and construct a refined model of existing lines;

[0077] In a preferred but non-limiting embodiment of the present invention, step 2 specifically includes:

[0078] Point cloud data is preprocessed, stitched together, denoised, and geometrically fitted to establish a refined model of the existing line that is consistent with the actual situation on site.

[0079] In a preferred but non-limiting embodiment of the present invention, in step 2, the point cloud data of existing lines (piers, cap beams, box girders, tracks, etc.) obtained by three-dimensional laser scanning is processed through four key steps: preprocessing, splicing, noise reduction, and geometric feature fitting. This process eliminates data errors and redundant information, extracts accurate geometric parameters of the structure, and establishes a refined model with a deviation of ≤±5mm from the actual structure on site. This provides a "digital twin base map" for the BIM design, collision detection, and construction positioning of the protective cover.

[0080] II. Detailed Implementation Steps

[0081] (a) Point cloud data preprocessing methods include: standardization and data normalization.

[0082] The core of preprocessing is to eliminate coordinate deviations between different scanning stations and ensure data format uniformity, laying the foundation for subsequent stitching and fitting.

[0083] Data import and format conversion

[0084] Tool selection: CycloneREGISTER360 (core processing software), CloudCompare (auxiliary format conversion).

[0085] Operation process: Import the raw point cloud data (in .las / .e57 format) acquired by the Leica P50 scanner into Cyclone REGISTER 360, which will automatically identify the spatial coordinates (X / Y / Z) and RGB texture information of the point cloud; for non-standard format data, convert it to the unified .las format through CloudCompare to ensure data compatibility;

[0086] Coordinate system calibration

[0087] Reference selection: Using the existing line operation coordinate system (or project construction coordinate system) as the reference, select 3 or more existing structural feature points (such as the top corner of the bridge pier, the marking point of the box girder flange) that are evenly distributed and have strong stability as control points. Their coordinates are obtained by total station measurement (accuracy ±2mm).

[0088] Coordinate transformation: Input the measured coordinates of the control points in Cyclone REGISTER 360, and use the software's coordinate registration function to perform coordinate transformation on the cloud data of each station using the least squares method. This eliminates the systematic errors of different scanning stations, unifies all point clouds to the same coordinate system, and ensures spatial consistency.

[0089] Data pruning and partitioning

[0090] Area division: Based on the existing line structure type (pier, cap beam, box girder, track) and construction segment, the overall point cloud is divided into independent processing units (such as "point cloud of pier #1" and "point cloud of 20-30m box girder") to avoid mutual interference between point clouds of different structures;

[0091] Invalid data removal: Manually crop irrelevant areas outside the scanning range (such as distant buildings and ground debris), retain point cloud data of existing line structures and necessary surrounding spaces (the area affected by the installation of protective covers), and reduce the amount of data processing.

[0092] (ii) In a preferred but non-limiting embodiment of the present invention, in step 2, the point cloud stitching method includes: multi-station data fusion and error control.

[0093] The core of the stitching is to achieve seamless integration of multiple point cloud models through feature matching, ensuring the continuity and accuracy of the overall point cloud model, and allowing a maximum stitching error of ≤±8mm.

[0094] splicing method selection

[0095] Core algorithm: It adopts a combination of "feature point matching + ICP algorithm (iterative nearest point)" to balance splicing efficiency and accuracy.

[0096] Auxiliary constraints: Using the unified coordinate system from the preprocessing stage as constraints to avoid global offsets during the stitching process.

[0097] splicing operation process

[0098] Feature point extraction: In Cyclone REGISTER 360, common feature points of adjacent site clouds are automatically identified (such as box girder web corners, cap beam edges, and pier cylindrical surface features). No less than 20 feature points are extracted for each overlapping area to ensure matching reliability.

[0099] Preliminary stitching: Based on the feature point matching results, the software automatically calculates the stitching matrix to complete the preliminary fusion of multiple point clouds and generate a temporary overall point cloud;

[0100] Accuracy verification and optimization: The distance deviation analysis function is used to check the continuity of the point cloud in the stitched area.

[0101] If the distance deviation between the overlapping areas of adjacent cloud sites is ≤±8mm, the splicing is deemed qualified.

[0102] If the deviation exceeds the standard (>±8mm), manually add feature points (focusing on high-recognition structural details), and rerun the ICP algorithm for iterative optimization until the deviation meets the requirements.

[0103] Key points for splicing quality control

[0104] Overlap rate guarantee: The overlap rate of the scanning range of adjacent sites must be ≥30%. If the overlap rate is insufficient, the point cloud of that area needs to be scanned to avoid insufficient feature points leading to stitching failure.

[0105] Error uniformity check: Perform global error analysis on the stitched point cloud to ensure there is no local concentrated deviation (the proportion of point clouds with deviation exceeding the standard in a single area is ≤5%). Otherwise, the area needs to be split and stitched again.

[0106] (iii) In a preferred but non-limiting embodiment of the present invention, in step 2, the point cloud denoising method includes: interference elimination and data purification.

[0107] The core of denoising is to filter out random noise and irrelevant point clouds, retain valid data on the structural surface, and ensure that the geometric features of subsequent fitting can truly reflect the actual shape of the existing line structure.

[0108] Noise type identification

[0109] Random noise: Discrete points generated by dust and light reflection interference in the air during the scanning process (characterized by isolated points with no spatial correlation to the surrounding point cloud);

[0110] Background noise: Point cloud of unrelated objects such as temporary construction supports, passing vehicles, and vegetation (characterized by being distributed outside the main structure and having no connection with the existing line structure).

[0111] System noise: tiny deviations caused by fluctuations in the scanner's own accuracy (characterized by dense distribution but deviating from the structure surface).

[0112] Combination of noise reduction methods

[0113] Step 1: Use Gaussian filtering to remove random noise;

[0114] Principle: A weighted average is calculated for each point cloud and its neighborhood points, with the weights distributed according to a Gaussian function, and the closer the points are, the greater the weight.

[0115] Parameter settings: Gaussian function standard deviation σ = 0.8~1.2 (adjusted according to point cloud density; σ = 1.0 when point cloud density ≥ 50 points / cm²), filter window size set to 3×3×3 to ensure that structural surface details (such as box girder web welds and pier concrete texture) are preserved while suppressing noise.

[0116] Step 2: Denoising based on reflection intensity threshold;

[0117] Principle: There is a significant difference in the reflection intensity between existing steel structures (such as box girder webs and steel components) and noise points (steel structure reflection intensity ≥80, noise point reflection intensity <30).

[0118] Operation: Set a reflection intensity threshold (≥50) in CloudCompare to automatically remove point clouds with reflection intensity below the threshold, further filtering out interference points such as dust and shadows.

[0119] Step 3: Manually remove background noise interactively.

[0120] Operation: Combining on-site photos and scanning records, manually select and delete irrelevant point clouds such as temporary construction supports, vehicles, and vegetation in the point cloud model; for hidden areas such as the inside of the box girder and the bottom of the pier, use the "section slice" function to view the point cloud distribution and remove abnormal points embedded in the structure.

[0121] Noise reduction quality verification

[0122] Purity requirements: Effective point cloud ratio ≥ 95% after noise reduction, noise point residual rate ≤ 1%;

[0123] Detail retention requirements: The point cloud integrity of key structural parts (such as the corbel connection area and the edge of the box girder flange) is ≥98%, with no obvious data loss.

[0124] (iv) In a preferred but non-limiting embodiment of the present invention, in step 2, geometric feature fitting: extracting an accurate structural model.

[0125] The core of the fitting is to extract the geometric features of each component of the existing line through parametric modeling based on the denoised pure point cloud, forming a structured and editable refined model with a fitting deviation of ≤±5mm.

[0126] Fitting operation procedure

[0127] Step 1: Component segmentation and point cloud extraction. In Cyclone REGISTER 360, based on the structural spatial location and geometric shape, the overall point cloud is segmented into independent point clouds of individual components (such as "point cloud of pier #1" and "point cloud of web of 20-30m box girder") to ensure that a single fitting task only targets the same type of geometric features.

[0128] Step 2: Parametric fitting modeling, i.e. pier fitting: Select point cloud data from the middle and top of the pier (avoiding interference from the bottom foundation), run the cylinder fitting function, and the software automatically calculates the center of the bottom circle (X1,Y1,Z1), the center of the top circle (X2,Y2,Z2), and the radius R. By adjusting the fitting range (removing point cloud data within 1m of the bottom of the pier), the maximum distance deviation between the fitted cylinder and the point cloud is ≤±4mm.

[0129] Cap beam fitting: Extract the point cloud of the entire cross section of the cap beam, and perform cuboid fitting according to "segmentation along the length direction (2m per segment)" to ensure the flatness and cross-sectional dimension accuracy of the cap beam. The deviation between the fitted cuboid and the point cloud is ≤±5mm.

[0130] Box girder fitting: Piecewise quadratic surface fitting is used. The box girder is divided into segments every 3m along its length. The web (vertical curved surface) and flange (horizontal curved surface) are fitted separately. The cross-sectional dimensions (web thickness, flange width) and linear curvature of each segment are extracted. Then, the complete box girder model is formed by the surface splicing function. The deviation between the fitted surface and the point cloud is ≤±3mm.

[0131] Track fitting: Extract the point cloud of the top surface of the rail and use a 3rd order polynomial curve fitting to obtain the coordinates and elevation of the track centerline, ensuring that the track alignment deviation is ≤±2mm, providing an accurate basis for calculating the net height of the protective cover.

[0132] Fit quality verification and optimization

[0133] Deviation analysis: Generate a distance deviation cloud map of the "fitted model - point cloud" in CloudCompare to visually view the deviation distribution of each part. For areas with deviations exceeding the standard (>±5mm), re-optimize the filtering parameters or re-scan the point cloud and fit it again.

[0134] Structural correlation verification: Check the spatial positional relationship of each component's fitted model (such as the verticality of the connection between the pier and the cap beam, and the support relationship between the box girder and the cap beam) to ensure that it conforms to the logic of structural mechanics and avoid fitting results that are out of touch with reality.

[0135] Model export and format conversion

[0136] The fitted models of each component of the existing line (piers, cap beams, box girders, and tracks) are integrated into a refined overall model and exported in IFC format (BIM Collaborative Design Standard Format) and Revit format, respectively for protective cover BIM design, clash detection, and construction handover.

[0137] Step 3: Perform precise design of the protective cover based on BIM;

[0138] In a preferred but non-limiting embodiment of the present invention, step 3 specifically includes:

[0139] Based on the existing line's refined model, and in conjunction with safety protection requirements and load specifications, the modular structure design, collision inspection, and strength verification of the protective cover were carried out.

[0140] In a preferred but non-limiting embodiment of the present invention, in step 3, based on the existing line's refined model, and combined with subway operation safety protection requirements, steel structure design specifications, and construction load conditions, a modular structure design for the protective cover is completed. Collision checks are used to proactively avoid spatial conflict risks, and strength calculations ensure the safety and stability of the structure under various loads. Ultimately, a BIM model of the protective cover with an accuracy of LOD400 is formed, which can directly guide component processing and on-site construction. The specific method for the modular structure design of the protective cover is as follows:

[0141] (I) Design Basis and Core Principles

[0142] 1. Design Basis

[0143] Existing Line Refined Model (IFC Format): Provides precise spatial coordinates and geometric dimensions of existing box girders, piers, and other structures;

[0144] Safety protection standards: subway operation safety requirements (protective cover clearance height ≥ 5.1m, protection range covers construction risk area), high-altitude falling object protection standards (withstands the impact of a 25kg object falling from the maximum height);

[0145] Structural design codes: Standard for Design of Steel Structures (GB50017-2017), Load Code for Building Structures (GB50009-2012), Singapore local steel structure design standard (SSEN1993-1-8);

[0146] Construction constraints: hoisting equipment capacity (weight of a single protective cover ≤ 5t), existing line operating time window (nighttime off-peak operation), and tropical marine climate corrosion protection requirements (design service life ≥ 10 years).

[0147] 2. Core Design Principles

[0148] Safety First: Meet the requirements for impact resistance, wind resistance, and structural stability to ensure that no falling objects intrude into the existing track during construction;

[0149] Precise fit: The connection error between the protective cover and the existing box girder is ≤±3mm, avoiding structural interference;

[0150] Modular design: The modules are divided according to the existing line span and clearance differences, taking into account both processing efficiency and on-site installation convenience;

[0151] Disassembly and reassembly: The bolted connection facilitates later recycling and reduces resource waste.

[0152] (II) Modular Division and Structural System Design

[0153] 1. Modular Partitioning Scheme

[0154] Based on the spans (5.3~12.9m), clearance conditions, and construction sections of the seven existing elevated lines, the protective covers are divided into six standard modules (types 1A, 1B, 1C, 2, 3A, and 3B), with a total length of 631m and a single module length of 18~25m. The specific classification criteria are as follows:

[0155] Module model applicable span range, clearance height requirements, core adaptation scenarios

[0156] Type 1A, 10.5~12.9m, ≥5.4m, large-span elevated section in the East Building construction area.

[0157] Type 1B, 8.0~10.4m, ≥5.3m, medium span section of the West Building construction area.

[0158] Type 1C: 5.3~7.9m, ≥5.2m, small span sections near residential areas.

[0159] Type 2: 9.0~11.5m, ≥5.35m elevated sections near pedestrian overpasses.

[0160] Type 3A: 7.5~9.5m (≥5.25m) - Section above the underground passage

[0161] Type 3B: 5.5~8.5m, ≥5.1m, adjacent section of ramp area.

[0162] 2. Overall structural system design

[0163] The system employs a "double-sided cantilevered steel structure," and its core components and connections are as follows:

[0164] Support structure: The corbel (UC203×203×60) is anchored to the web of the existing box girder by M20 rebar, serving as the main load-bearing support of the protective cover;

[0165] Vertical structure: Steel columns (UC203×203×46) are connected to brackets by bolts to provide vertical support;

[0166] Lateral load-bearing structure: The main beam (UC203×203×46) is a transversely continuous module, and the tie beam (C150×75×18) connects the adjacent columns to enhance lateral stability;

[0167] Roof support structure: Purlins (C180×90×26) spaced 400mm, with 8mm flat steel plate and 6mm sloping steel plate laid to form a protective surface layer;

[0168] Auxiliary stabilizing structure: 10mm steel wire rope diagonal bracing connects the column and the main beam to resist the lateral force generated by wind load.

[0169] 3. Key Parameter Design

[0170] Material selection: The main structure uses S355 steel (yield strength ≥355MPa), and the bolts are 8.8 grade high-strength bolts (tensile strength ≥800MPa).

[0171] Corrosion resistant design: hot-dip galvanizing (zinc layer thickness ≥ 85 μm) + two-component coating (dry film thickness ≥ 120 μm), suitable for tropical marine climates;

[0172] Connection parameters: Rebar installation depth ≥ 15d (d is the diameter of the rebar, M20 rebar d=20mm, so the rebar installation depth ≥ 300mm); Steel plates and purlins are connected with M8 bolts at 500mm intervals; Corbels and hanging beams are connected with 4 M20 bolts + 16mm steel plates.

[0173] The specific collision inspection method is as follows:

[0174] (a) Collision Inspection Objects and Scope

[0175] 1. Object of inspection

[0176] Protective cover and existing line structure: Spatial conflict between the protective cover brackets and columns and the existing box girder web, flanges and piers;

[0177] Internal components of the protective cover: installation interference between the main beam and tie beam, purlins and steel plates, and diagonal braces and columns;

[0178] Protective shield and surrounding environment: The protective shield conflicts with the distance of nearby buildings, municipal roads, and pedestrian overpasses.

[0179] 2. Scope of Inspection

[0180] Geometric collision: Component solid space overlap (minimum allowable gap ≥ 50mm);

[0181] Clearance conflict: The distance from the lowest point of the protective cover roof to the top surface of the track is ≥5.1m (with a 20mm settlement allowance).

[0182] Construction space conflict: Temporary interference between the protective cover and the existing structure on the hoisting path (minimum allowable hoisting gap ≥ 1.0m).

[0183] (II) Collision Inspection Process and Tools

[0184] 1. Process Steps

[0185] Step 1: Model Integration. Import the existing line refinement model (IFC format) and the protective cover BIM model (Revit / Tekla format) into NavisworksManage software, and unify the coordinate system and accuracy standard (LOD400).

[0186] Step 2: Rule Setting. Set the inspection rules according to the categories of "Hard Collision (Entity Overlap)" and "Soft Collision (Insufficient Gap)":

[0187] Hard collision: collision distance = 0mm (components directly overlap);

[0188] Soft impact: The gap between the protective cover and the existing structure is <50mm, the clearance height is <5.1m, and the gap along the hoisting path is <1.0m;

[0189] Step 3: Automatic Inspection. Run the "ClashDetective" function to perform collision detection by grouping into "Shield - Existing Structure", "Shield Inside", and "Shield - Surrounding Environment", and generate a collision report;

[0190] Step 4: Conflict Resolution. Visualize and locate the collision point, and adjust the protective shield structural parameters based on the existing refined model.

[0191] Collision between corbel and box girder web: shorten the corbel cantilever length (adjustment range 50~100mm) and recalculate the anchorage bearing capacity;

[0192] Insufficient clearance: Optimize the roof slope (adjust from 3° to 5°) or locally reduce the purlin height (not exceeding 30mm);

[0193] Lifting conflict: Adjust the module segment length or optimize the crane position and lifting angle.

[0194] Step 5: Verification. After making the modifications, rerun the collision check until all collision points are cleared (or there are ≤3 non-critical collision points that do not affect safety and construction).

[0195] 2. Core Tools

[0196] Modeling software: Revit (architecture), TeklaStructures (steel structure);

[0197] Collision checking software: NavisworksManage (multi-disciplinary collaborative collision detection), BentleyNavigator (efficient collision checking for large models).

[0198] The methods for strength verification include:

[0199] The calculation formula for impact load is as follows:

[0200] The protective roof withstands the impact of falling objects from a height. The impact load is derived according to the principle of energy conservation: ;

[0201] Where F is the impact load (unit: N or kN); m is the mass of the falling object (unit: kg), which is the weight of common small construction equipment / tools, and is uniformly taken as 25 kg in this design; g is the gravitational acceleration (unit: m / s²), which is taken as 9.8 m / s²; h is the falling height of the object (unit: m), calculated according to the maximum height of the construction area: 1A / 2 type 18.602 m, 1B / 3A type 11.216 m, 1C / 3B type 5.127 m; The deformation of the protective shield structure under impact (unit: m) is calculated by simulation using MIDAS / Civil software, with a value range of 0.02~0.05m.

[0202] The tensile design bearing capacity of bolts is verified using the following formula: The tensile bearing capacity of bolts connecting components must satisfy the load effect, as shown in the formula below: ;

[0203] in Design tensile bearing capacity of bolts (unit: kN); The bolt connection coefficient is 0.9, which is taken as 0.9 based on the characteristics of grade 8.8 high-strength bolts. The ultimate tensile strength of the bolt (unit: MPa) is 800 MPa for grade 8.8 bolts. The effective cross-sectional area of ​​the bolt (unit: mm²) is 36.6 mm² for M8 bolts and 245 mm² for M20 bolts. The partial factor for bolted connection resistance is 1.25 according to the standard; verification requirements: > , The design load effect borne by the bolt is calculated from the load combination.

[0204] The strength of structural members (main beams, corbels, columns, etc.) is verified using the following formula:

[0205] ;

[0206] in The design value of the bending moment borne by the component (unit: kN·m) is calculated from the load combination (e.g., main beam). =25kN·m); The design value of the axial force borne by the component (unit: kN), such as a column. =138kN; The plastic section modulus of the component (unit: mm³) is UC203×203×46 steel. =1530000 mm³; The net cross-sectional area of ​​the component (unit: mm²) is UC203×203×46 steel. =5890mm²; The yield strength of steel (unit: MPa), S355 steel =355MPa; The value is 1.05 for the plastic development coefficient of the cross section, which is used for the I-shaped cross section. The partial factor for the resistance of structural members is 1.05; the verification requirement is: the calculated value on the left side ≤ the limit on the right side (355 / 1.05≈338MPa).

[0207] The structural deflection calculation formula is as follows: The maximum deflection of the protective cover during normal use must meet the specification limit:

[0208] ;

[0209] in The maximum vertical deflection of the component (unit: mm) is calculated using STAAD.Pro software; the maximum deflection at mid-span of the main beam is 56.9 mm. L is the calculated span of the component (unit: mm). For example, the main beam span of the 1A type protective cover is 12900 mm, with a limit of L / 200 = 64.5 mm. Verification requirements: 64.5mm (In this design, 56.9mm < 64.5mm, which meets the requirements).

[0210] Step 4: Perform BIM4D hoisting simulation and scheme optimization;

[0211] In a preferred but non-limiting embodiment of the present invention, step 4 specifically includes:

[0212] The BIM4D method was used to simulate the hoisting process of the protective cover, and the hoisting sequence, equipment selection and operation time window were optimized.

[0213] Step 5: Conduct meticulous on-site construction and quality control.

[0214] In a preferred but non-limiting embodiment of the present invention, step 5 specifically includes:

[0215] On-site positioning, rebar detection, component installation, and quality acceptance are carried out based on BIM models and scanning data.

[0216] The following describes the specific implementation steps of this invention in detail, using a specific project (adjacent to 7 operating elevated subway lines) as an example:

[0217] (I) Step 1: Acquisition of 3D laser scanning data of existing line structure

[0218] Equipment selection and calibration: The Leica P50 3D laser scanner was selected. Before scanning, the ranging accuracy and angle accuracy were calibrated using the matching calibration tools to ensure that the single-point ranging error is ≤±3mm.

[0219] Station layout planning: Based on the routes of the 7 elevated subway lines and the scope of the construction area, a "segmented station layout and closed modeling" strategy is adopted. The number of stations in each segment is determined according to the 120m scanning radius of the scanner, and the scanning overlap rate of adjacent stations is ≥30%.

[0220] On-site scanning operation: Scanning was carried out during the off-peak hours of subway operation (2:00-4:00 AM), using a combination of "elevated platform + ground multi-angle" method. The focus was on collecting the spatial coordinates and RGB texture information of bridge piers, cap beams, box girders (webs and flanges), and tracks. During the scanning process, the scanner was kept at a safe distance of ≥1.5m from the edge of the track.

[0221] Data quality verification: After each site scan is completed, the point cloud density (≥50 points / cm²) and integrity are checked in real time. Any missed areas are immediately re-scanned, and environmental parameters (temperature, humidity) are recorded for subsequent error correction.

[0222] (II) Step 2: Point cloud data processing and construction of refined model of existing line

[0223] Data preprocessing: Import cloud data from each site into CycloneREGISTER360 software, unify the coordinate system based on GPS coordinates or manual control points, and eliminate coordinate deviations between different sites;

[0224] Point cloud stitching: Multi-station data fusion is performed using "feature point matching + ICP algorithm (iterative nearest point)". The continuity of the stitched area is manually checked to ensure that the overall stitching error is ≤ ±8mm.

[0225] Denoising optimization: Random noise is filtered out using a Gaussian filtering algorithm, and irrelevant point clouds such as temporary construction supports and passing vehicles are manually deleted to retain valid data of the structural surface;

[0226] Geometric feature fitting: Parametric fitting method is used to fit the geometric models of bridge piers (cylinders), cap beams (cubic prisms), and box girders (irregular cross sections) respectively, ensuring that the deviation between the fitted model and the point cloud is ≤ ±5mm, and the IFC format model is exported for subsequent BIM design.

[0227] (III) Step 3: Precise Design of Protective Cover Based on BIM

[0228] Design Basis and Principles: Based on the existing line detailed model, subway operation safety specifications (clearance height ≥ 5.1m), and steel structure design standards (GB50017-2017), and following the principles of "safety first, precise adaptation, and convenient construction";

[0229] Modular structure design: Based on the existing line span (5.3~12.9m) and space conditions, 6 models (1A, 1B, 1C, 2, 3A, 3B) of protective covers are designed, with a total length of 631m and a single section weight of ≤5t. The "double-sided cantilever steel structure system" is adopted, and the core components include corbels, columns, main beams, tie beams, purlins, and steel plate roof.

[0230] BIM Modeling and Clash Detection: Use Revit / Tekla software to build a protective cover BIM model (LOD400 accuracy) and perform a clash detection between the protective cover and the existing structure. Focus on checking the connection position between the corbel and the box girder web and the spatial distance between the column and the pier to ensure that the minimum gap is ≥50mm. If a clash is found, adjust the structural dimensions in real time.

[0231] Load verification: A three-dimensional spatial model was established using STAAD.Pro, considering five load combinations: self-weight, roof live load (1.5kPa), wind load (basic wind speed 22m / s, 1.6kPa), train aerodynamic load (0.8kPa), and impact load (600kPa). The verification results show that the load-bearing capacity utilization rate of each component is ≤85%, and the maximum deflection is 56.9mm (≤L / 200), which meets the safety requirements.

[0232] (iv) Step 4: BIM4D hoisting simulation and scheme optimization

[0233] Lifting scene modeling: Import the protective cover BIM model, construction site, and lifting equipment (crane) models into BIM4D software, and set the construction schedule and subway operation time window;

[0234] Lifting simulation analysis: Simulate the lifting process of corbels, lifting beams, and main structure, optimize the lifting sequence (first install corbels → then fix the lifting beams → finally lift the main structure), crane position and operating radius, and avoid collisions with existing lines and surrounding buildings;

[0235] 1:1 Impact Test: A model was built according to the actual structural scale to simulate a 25kg object falling freely from a height of 18.6m and impacting the roof. The measured impact displacement was 26mm (≤50mm). There was no loosening of the component connections or plastic deformation, which verified the impact resistance performance of the protective cover.

[0236] (V) Step 5: On-site meticulous construction and quality control

[0237] Box girder reinforcement detection: The GP8100 electromagnetic induction instrument is used to scan the distribution of reinforcement inside the box girder, mark the drilling positions, avoid conflicts with existing reinforcement, and if a conflict is found, the drilling positions are adjusted and the BIM model is updated synchronously.

[0238] Bracket installation: The bracket is delivered to the design position using a ladder truck, positioned according to the coordinates and angles marked in the BIM model, and anchored with M20 rebar (rebar depth ≥ 15d, where d is the diameter of the rebar). After tightening, a pull-out test is performed.

[0239] Main structure hoisting: Within the time window approved by the subway operator, the prefabricated protective cover main structure is hoisted onto the corbel and fixed with bolts. During the hoisting process, the installation accuracy is monitored in real time using a BIM model.

[0240] Quality acceptance: A total station is used to check the installation deviation of the protective cover to ensure that the clearance height is ≥5.1m and the torque of the connecting bolts meets the standard. After acceptance, a construction record and model are archived.

[0241] The beneficial effects of the present invention are as follows, compared with the prior art:

[0242] (a) Precision improvement effect

[0243] The digital replication accuracy of the existing line structure reaches ±3mm, and the connection error between the protective cover and the existing structure is ≤±3mm, which solves the problem of the disconnect between traditional design and actual site conditions.

[0244] Collision checks proactively mitigate over 90% of on-site structural interference risks, reducing the rework rate from 30% with traditional methods to below 5%.

[0245] (II) Safety Assurance Effectiveness

[0246] Three-dimensional laser scanning and rebar detection technology avoids damage to the existing box girder structure caused by drilling and rebar installation, thus ensuring the safety of subway operation;

[0247] The protective cover has achieved effective protection against risks such as falling objects from heights and wind loads through impact load tests and multi-condition calculations. No safety accidents affecting the operation of the existing line occurred during the construction period.

[0248] (III) Efficiency and cost optimization effects

[0249] Modular design and factory prefabrication shortened the on-site construction cycle by 30%, and optimized hoisting simulation improved the utilization rate of the operation time window by 50%, reducing interference with subway operations.

[0250] The rework rate is reduced, construction efficiency is improved, and the overall cost is reduced by 15% to 20%, avoiding the cost waste of sending components back to the factory for processing and on-site adjustments in the traditional method.

[0251] (iv) Value of technology promotion

[0252] The "BIM + 3D laser scanning" full-process technology system developed in this invention provides a standardized method for the design and construction of protective covers near existing railway lines. It can be widely applied to building projects around operating lines such as subways, railways, and highways, and has significant industry promotion value.

[0253] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention without departing from the spirit and scope of the present invention. Any modifications or equivalent substitutions should be covered within the scope of protection of the claims of the present invention.

Claims

1. A design and construction method for existing power line protective covers based on "BIM + 3D laser scanning", characterized in that, include: Step 1: Perform 3D laser scanning data acquisition on the existing line structure; Step 2: Perform point cloud data processing and build a refined model of existing lines; Step 3: Perform precise design of the protective cover based on BIM; Step 4: Perform BIM4D hoisting simulation and scheme optimization; Step 5: Conduct meticulous on-site construction and quality control.

2. The design and construction method for existing power line protective covers based on "BIM + 3D laser scanning" according to claim 1, characterized in that, Step 1 specifically includes: A 3D laser scanner was used to perform a full-coverage scan of the existing railway line's piers, cap beams, box girders, and track structures to obtain point cloud data.

3. The design and construction method for existing power line protective covers based on "BIM + 3D laser scanning" according to claim 2, characterized in that, Step 2 specifically includes: Point cloud data is preprocessed, stitched together, denoised, and geometrically fitted to establish a refined model of the existing line that is consistent with the actual situation on site.

4. The design and construction method for existing power line protective covers based on "BIM + 3D laser scanning" according to claim 3, characterized in that, In step 2, the point cloud data preprocessing method includes: The raw point cloud data acquired by the Leica P50 scanner is imported into Cyclone REGISTER 360, which automatically identifies the spatial coordinates and RGB texture information of the point cloud; for non-standard format data, CloudCompare is used to convert it into a unified .las format to ensure data compatibility. Based on the existing line operation coordinate system, select three or more existing structural feature points that are evenly distributed and highly stable as control points, and obtain their coordinates through total station measurement. Input the measured coordinates of the control points in Cyclone REGISTER 360, and use the coordinate registration function of the software to perform coordinate transformation on the point cloud data of each station using the least squares method, so that all point clouds are unified under the same coordinate system; Based on the existing line structure type and construction segmentation, the overall point cloud is divided into independent processing units; Manually crop irrelevant areas outside the scanning range, and retain the point cloud data of the existing line structure and the necessary surrounding space; In step 2, the point cloud stitching method includes: Feature point extraction: In Cyclone REGISTER 360, common feature points of adjacent site clouds are automatically identified, and no less than 20 feature points are extracted for each overlapping area; Preliminary stitching: Based on the feature point matching results, the software automatically calculates the stitching matrix to complete the preliminary fusion of multiple point clouds and generate a temporary overall point cloud; Accuracy verification and optimization: The distance deviation analysis function is used to check the continuity of the point cloud in the stitched area. If the distance deviation between the overlapping areas of adjacent cloud sites is ≤±8mm, the splicing is deemed qualified. If the deviation exceeds the standard, manually add feature points and rerun the ICP algorithm for iterative optimization until the deviation meets the requirements.

5. The design and construction method for existing power line protective covers based on "BIM + 3D laser scanning" according to claim 4, characterized in that, In step 2, the point cloud denoising method includes: Step 1: Use Gaussian filtering to remove random noise; Step 2: Noise reduction based on reflection intensity threshold; Step 3: Manually remove background noise interactively.

6. The design and construction method for existing power line protective covers based on "BIM + 3D laser scanning" according to claim 5, characterized in that, In step 2, the first step is component segmentation and point cloud extraction. In Cyclone REGISTER 360, based on the spatial location and geometric shape of the structure, the overall point cloud is segmented into independent point clouds of individual components, ensuring that a single fitting task targets only the same type of geometric features. Step 2: Parametric fitting modeling, which involves selecting point cloud data from the middle and top of the bridge pier, running the cylinder fitting function, and the software automatically calculating the center of the bottom surface, the center of the top surface, and the radius R. By adjusting the fitting range, the maximum distance deviation between the fitted cylinder and the point cloud is ≤ ±4mm. Extract the point cloud of the entire cross section of the cap beam, and perform cuboid fitting in segments along the length direction to ensure the flatness and cross-sectional dimensional accuracy of the cap beam. The deviation between the fitted cuboid and the point cloud is ≤ ±5mm. The box girder is divided into segments of 3m along its length using piecewise quadratic surface fitting. The web and flange are fitted separately, and the cross-sectional dimensions and linear curvature of each segment are extracted. The complete box girder model is then formed by surface splicing. The deviation between the fitted surface and the point cloud is ≤±3mm. The point cloud on the top surface of the rail is extracted, and a third-order polynomial curve is used for fitting to obtain the coordinates and elevation of the rail centerline, ensuring that the rail alignment deviation is ≤ ±2mm.

7. The design and construction method for existing power line protective covers based on "BIM + 3D laser scanning" according to claim 6, characterized in that, Step 3 specifically includes: Based on the existing line's refined model, and in conjunction with safety protection requirements and load specifications, the modular structure design, collision inspection, and strength verification of the protective cover were carried out.

8. The design and construction method for existing power line protective covers based on "BIM + 3D laser scanning" according to claim 7, characterized in that, In step 3, the strength verification methods include: The calculation formula for impact load is as follows: ； Where F is the impact load; m is the mass of the falling object; g is the gravitational acceleration; and h is the height of the falling object. This refers to the deformation of the protective shield structure under impact. The formula for verifying the tensile design bearing capacity of bolts is as follows: ; in Design the tensile bearing capacity of the bolt; This is the bolt connection coefficient; This refers to the ultimate tensile strength of the bolt. This represents the effective cross-sectional area of ​​the bolt. This refers to the partial factor for resistance of bolted connections; The strength verification formula for the component is as follows: ； in The design value of the bending moment borne by the component; The design value of the axial force borne by the component; The plastic section modulus of the component; The net cross-sectional area of ​​the component; The yield strength of the steel; The coefficient for plastic development of the cross section; For the resistance of structural components; The formula for structural deflection verification is as follows: ； in L represents the maximum vertical deflection of the component; L represents the calculated span of the component.

9. The design and construction method for existing power line protective covers based on "BIM + 3D laser scanning" according to claim 8, characterized in that, Step 4 specifically includes: The BIM4D method was used to simulate the hoisting process of the protective cover, and the hoisting sequence, equipment selection and operation time window were optimized.

10. The design and construction method for existing power line protective covers based on "BIM + 3D laser scanning" according to claim 9, characterized in that, Step 5 specifically includes: On-site positioning, rebar detection, component installation, and quality acceptance are carried out based on BIM models and scanning data.

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