Cantilever casting continuous beam closure construction method and system based on three-dimensional laser scanning monitoring

Abstract

The invention discloses a cantilever casting continuous beam closure construction method and system based on three-dimensional laser scanning monitoring, and relates to the technical field of building construction.The method comprises the steps of construction preparation, survey lofting, technical preparation, field preparation, material preparation, personnel preparation, seasonal preparation, measurement and lofting tool preparation and lofting scheme making. The method has the advantages that by means of the three-dimensional laser scanning technology, high-precision and real-time monitoring of the cantilever closure space is achieved, the accuracy of the whole construction is guaranteed, and by combining an advanced data processing and analysis method, the construction efficiency is improved. Point cloud modeling is carried out to compare errors before and after closure, the errors are compared with drawing data and total station monitoring data, each construction process is completed more finely and detailedly in the auxiliary construction process, and potential safety hazards can be found in time by comprehensively monitoring parameters such as displacement and deformation in the cantilever closure process.

Description

Technical Field

[0001] The present invention relates to the technical field of construction engineering, and particularly to a construction method and system for monitoring the closure construction of a cantilever cast continuous beam based on three-dimensional laser scanning. Background Art

[0002] With the development of bridge construction, high-pier long-span rigid frame bridges, as important transportation infrastructure, face complex terrain, climate, and construction conditions during construction. As the main construction method for rigid frame bridges, the construction quality and safety risks that the cantilever cast continuous beam needs to address are more prominent. Therefore, advanced monitoring technologies are required to ensure the safety and smooth progress of the construction process.

[0003] In the traditional construction method of cantilever cast continuous beams, total station is used as the main monitoring means, and the obtained data is single, without comparison and verification with other data. Moreover, it cannot accurately and real-time monitor the entire construction process, and cannot effectively monitor the errors generated during the construction process. If construction defects are caused, the rework cost is relatively high.

[0004] This method is a solution proposed for the monitoring requirements during the closure process of the prestressed concrete cantilever segment of the cantilever cast continuous beam. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the present invention provides a construction method and system for monitoring the closure construction of a cantilever cast continuous beam based on three-dimensional laser scanning, which solves the problems raised in the above background art.

[0006] To meet the above requirements, the present invention is achieved through the following technical solutions: A construction method for monitoring the closure construction of a cantilever cast continuous beam based on three-dimensional laser scanning, including the following steps:

[0007] S1. Construction preparation, surveying and setting out. Through technical preparation, site preparation, material preparation, personnel preparation, seasonal preparation, preparing surveying and setting out tools, and formulating a setting out plan, it is convenient to plan the site and facilitate subsequent operations and construction;

[0008] S2. Construction by the falsework method, construction of the cantilever segments with the hanging basket;

[0009] S3. Transformation of the closure segment formwork, verifying the segment linearity using three-dimensional laser scanning;

[0010] S4. Construction of the closure segment steel bars and embedded parts;

[0011] S5. Conducting three-dimensional laser scanning to detect the linearity while pouring the concrete of the closure segment;

[0012] S6. Prestressing construction of the closure segment and the whole bridge;

[0013] S7. After the completion of the bridge, the linearity of the whole bridge is verified by three-dimensional laser scanning, and the linearity assessment of the whole bridge is carried out.

[0014] Optionally, the specific operation steps of construction preparation and measurement layout in step S1 are as follows:

[0015] S1-1. Technical preparation: The construction unit needs to participate in the discussion of the preliminary design and technical design plans, and organize the compilation of the construction organization design accordingly. This is the central link of construction preparation, and all construction preparation work must be carried out according to this; Site preparation: The overall planning and progress requirements of the construction project are understood, and the situations such as land expropriation, relocation of residents, and removal of ground obstacles are clarified; Material preparation: Apply for and order the required construction machinery, equipment, and instruments, train special technical workers. In addition, construction drawing review and technical disclosure are also required to ensure that the construction drawings and technical requirements are clear; Personnel preparation: Adjust and deploy the construction force, form a new construction organization according to the characteristics of the project tasks. The construction unit shall sign contracts and relevant agreements with the construction and design units to clarify the responsibilities and authorities of division of labor and cooperation; Seasonal preparation: Understand the local natural conditions such as meteorology, hydrology, geology, and earthquake, and evaluate the adaptability of transportation and storage to construction.

[0016] S1-2. Prepare measurement and layout tools: such as measuring rulers, protractors, theodolites, layout lines, layout hammers, layout nails, prepare design drawings and site plans, measure and determine the site boundaries and terrain, including the length, width, and height data of the site to reduce errors; According to the design drawings and site measurement results, formulate a layout plan, including the position, length, and angle information of the layout line, considering factors such as the site terrain, the position and height of the building. When carrying out layout, mark the layout points on the site, connect the layout points with the layout line, and then record the layout data and check the accuracy and precision of the layout data for subsequent construction work.

[0017] Optionally, the specific operation steps of the construction of the hanging basket cantilever section in the support method construction in step S2 are as follows:

[0018] S2-1. First, carry out support production: Determine the hoisting position and support method of each steel structure component according to the design drawings, design the support form, size, and materials. The designers also need to consider the stability and safety of the frame structure, select suitable materials such as angle steel, square pipes, I-beams, bolts, etc., ensure that the material quality meets the design requirements, make a support model according to the design drawings, connect the supports using welding or connecting bolts, pay attention to the verticality and flatness of the supports, and then place the supports at the predetermined positions for installation.

[0019] S2-2. After the bracket is installed, the foundation needs to be inspected to ensure its bearing capacity. When the bearing capacity of the foundation does not meet the requirements, replacement filling treatment is required. When necessary, cast-in-place piles or driven piles are used to reinforce the foundation, and drainage ditches are set around the bracket to prevent the foundation from settling due to water immersion;

[0020] S2-3. For steel structure hoisting and concrete pouring, the bottom formwork is washed and cleaned. The concrete is poured in horizontal layers and advanced in diagonal sections. Insert type vibrators are used to compact it to ensure continuous pouring of the concrete. The concrete curing is kept moist to avoid rain, sun and exposure. Then prestressed construction is carried out, and finally the bracket is removed and the site is cleaned up;

[0021] S2-4. Then cantilever construction of the hanging basket is carried out. First, the lower structure construction of the bridge is completed, including the construction of pile foundations, pile caps and piers, and then the installation and preloading of the hanging basket are carried out;

[0022] Optionally, the specific operation steps for the modification of the closure segment formwork and the verification of the segment linearity using 3D laser scanning in step S3 are as follows:

[0023] S3-1. First, install the 3D laser scanner. Install the bracket and fixing device of the 3D laser scanner on the completed bridge deck. Use the multi-point and multi-view monitoring method based on control point transformation to measure the linearity of the cantilever segment. Utilize the bridge deck control points directly above the pier, and in combination with the control point transformation method, move the temporary control points once every 20m. Then, measure the linearity of the cantilever segment by cross-measuring at close and far distances. The horizontal scanning distance of the close-range points is within 20m, which is used to observe the detailed structure of the cantilever segment to ensure the integrity of the coordinate information of the key parts; the horizontal scanning distance of the far-range points is 50 - 80m, which is used to observe the overall structure of the cantilever segment to ensure the integrity of the point cloud of the overall model;

[0024] S3-2. Use 3D laser scanning technology to measure the linearity of the cantilever, including the deflection and deformation of the cantilever. Collect the 3D scan data of the cantilever segment, conduct data accuracy analysis, generate an accuracy report, and perform in-house processing based on the monitoring data processing method combining point cloud model stitching, random sampling, automatic simplification of members and data fusion using Cyclone software. Through the filtering of out-of-body noise points of a single monitoring point cloud and the stitching and synthesis of multiple monitoring point clouds, an overall point cloud model is formed;

[0025] S3-3. When constructing the last cantilever segment, reserve holes for the outer sliding beam, inner sliding beam and front cross beam of the hanging basket. Move the hanging basket forward, and fix the inner and outer sliding beams and the front cross beam with 32mm high-strength threaded steel through the reserved holes. Adjust the bottom formwork, side formwork and inner formwork to the designed structural dimensions;

[0026] S3-4. Before closure and locking, apply counterweights first, and use 3D laser scanning to monitor the elevation difference at both ends of the closure segment in real time, so that the elevation difference between the bottom plates of the two cantilever segments is not greater than 10 mm. Plastic water tanks are set on both sides of the closure segment, and water injection is carried out synchronously by 2 sets of 200 m high-lift pumps. The weight of the water tanks on both sides and the stored water should be equal to the weight of the concrete and the stiffening skeleton of the closure segment. Position lines for each cubic meter of water volume are marked on the outer side of the water tank wall to facilitate water discharge in coordination with the concrete placement speed, achieving the effect of weight replacement and unloading. Use 3D laser scanning to guide the on-site counterweight work: Install the scanner within 20 m outside the cantilever end, collect 3D scanning data during the cantilever counterweight process, conduct data analysis, and guide the on-site water addition process;

[0027] S3-5. For the closure segment locking, a stiffening skeleton is set externally. The stiffening skeleton is composed of embedded steel bars, embedded steel plates, and double-rolled I-beams. 4 sets of stiffening skeletons are set for each closure segment, with 2 sets arranged on the top and bottom plates of the box girder respectively. Connecting steel plates are set on the upper and lower flange plates of the two I-beams for each set of stiffening skeletons, and the I-beams are welded into a whole by the connecting steel plates. Install the stiffening skeleton, with one end welded and fixed to the embedded part first, and the other end as the adjustment end. When welding, weld the bottom plate first and then the top plate. When welding, it is required that the weld length and fullness meet the specification requirements. After the welding of the fixed end of the stiffening skeleton is completed, use a jack to jack open a displacement value at the adjustment section, and then seal and weld the adjustment end of the stiffening skeleton to complete the locking of the stiffening skeleton;

[0028] Optionally, the specific operation steps for the steel bars and embedded parts construction of the closure segment in step S4 are as follows:

[0029] S4-1. After the welding of the stiffening skeleton of the side-span closure segment is completed, the two box girders on both sides form a whole, and the temporary locking of the permanent bearings of the side-span cast-in-place segment can be released. Use tools to release the bearing limit device at the top of the transition pier to ensure that the bearing can expand and contract longitudinally freely;

[0030] S4-2. After the welding of the stiffening skeleton of the mid-span closure segment is completed, the installation of the steel bars and prestressed tendon ducts of the closure segment should be carried out immediately. Since the steel bars and prestressed ducts of the closure segment are dense and the stiffening skeleton is added, special attention should be paid to the positioning and sealing of the prestressed ducts to ensure the smoothness of the ducts;

[0031] Optionally, the specific operation steps for using 3D laser scanning to detect the linearity during the concrete pouring of the closure segment in step S5 are as follows:

[0032] S5-1. To ensure the accuracy of subsequent splicing processing, a three-dimensional laser scanner should be installed first, and there should be sufficient spatial overlap between two adjacent different scanning stations in space. The on-site setting is 50%. In order to obtain the absolute spatial coordinates of the point cloud, during the scanning operation, target points should be arranged at the scanning site. The original point cloud obtained by each station is an independent file, and the spatial position of its point cloud is also relative. It is necessary to splice the point clouds of these stations into a whole first to obtain the complete point cloud data of the closure section. The splicing of multiple scanning models is achieved through coordinate transformation. Before formally conducting point cloud deformation analysis and processing, preprocessing of the point cloud is carried out;

[0033] S5-2. Three days before the concrete pouring of the closure section, the elevation change and the length change of the closure section should be continuously observed (once every 4 hours). Temperature monitoring should be carried out 3 days in advance to determine the relationship between temperature change, elevation, and the length of the closure section, and determine the concrete pouring time. The closure time is generally selected during the period with relatively low temperature in a day, and the optimal temperature is between 15-20 °C, and it should be the same as the temperature at the time of locking, so that the poured concrete is always in a state of temperature rise and compression after pouring, avoiding the generation of tensile force due to concrete cooling, resulting in concrete cracking. Check the center line, elevation, dimensions of each part of the beam body, steel bars, formwork, supports, corrugated pipes, formwork, etc. of the closure section. After passing the inspection, the concrete construction can be carried out. Before pouring, the concrete joint surfaces at both ends should be fully roughened, wetted, and rinsed clean. Use C60 slightly expanded concrete and pump it into the formwork by a truck pump. Compact it with a handheld vibrating rod. After the concrete initial setting, cover it with plastic film and geotextile for moisture conservation until the design time;

[0034] S5-3. During the process of pouring the concrete of the closure section, use a three-dimensional laser scanner to monitor the closure alignment, guide the concrete feeding speed and the weight replacement and unloading speed. Guide the weight replacement and unloading according to the closure alignment monitored by the three-dimensional laser scanning. Conduct water release while pouring concrete. The water release speed depends on the concrete pouring speed. For every 1 m 3 of concrete poured, release 1.53 m 3 of water;

[0035] S5-4. Collect the three-dimensional scanning data during the cantilever casting process, and compare the linear offset values and perpendicularity offset values measured by the three-dimensional laser scanning and total station of each control point with the differences from the design values;

[0036] Optionally, the specific operation steps of the closure section and the full-bridge prestressed construction in step S6 are as follows:

[0037] S6-1. Before the concrete reaches the required tensile strength and before the longitudinal tendons are tensioned, remove the rigid supports at the closure joint. The removal sequence is to start with the top slab and then the bottom slab, and proceed symmetrically on both the left and right sides. When cutting, pay attention not to burn the concrete. After the weld cutting is completed, use a jack to lift the channel steel away from the embedded steel plate to ensure complete cutting. Finally, level the top surface of the embedded plate and apply cement slurry treatment at the bottom slab;

[0038] S6-2. Tension, grout, and seal the anchor heads of the remaining prestressed tendons according to the designed tensioning sequence and double-control standard to complete the system transformation of the entire bridge, and complete subsequent work such as the removal of the hanging basket according to the special construction plan;

[0039] Optionally, after the bridge is completed in step S7, verify the linearity of the entire bridge through three-dimensional laser scanning. The specific operation steps for the linearity assessment of the entire bridge are as follows:

[0040] S7-1. First, install the three-dimensional laser scanner. Four measuring points can be selected correspondingly on the upstream and downstream sides of the main pier deck of the closure beam. Since the stitching between different measuring stations is one of the main sources of point cloud model errors, the number of measuring stations should be reduced as much as possible when collecting data for the bridge. When specifically at each measuring station location, the view at this location should also be kept open to ensure the quality of the single-station bridge point cloud. At the same time, when setting up the station, the influence of the geographical environment should also be considered to ensure the safety of the surveying personnel and provide a stable working platform for the scanning equipment to the greatest extent;

[0041] S7-2. Since the measured rigid frame bridge has a large volume and due to the measurement terrain limitations, there will inevitably be some missing parts in the single-station point cloud data. The point cloud of the main beam has incomplete and sparse point cloud at the mid-span position due to the large span. For these missing parts, use the method of point cloud fitting and reconstruction to repair them. Based on the spatial characteristics of the complete point cloud around the missing part, gradually expand the scope of fitting and reconstruction until the missing part is completely fitted;

[0042] The spatial linearity of the main beam of a long-span rigid frame bridge reflects the stress state of the bridge. Extract multiple measuring points on the longitudinal measuring lines of the relevant components from the point cloud data, and then obtain the linearity of the components through multiple regression fitting of the coordinates of the measuring points. Select measuring lines on the main beam point cloud along the longitudinal direction of the bridge, and extract the longitudinal and vertical coordinates of the measuring points at equal intervals on the measuring lines. Use multiple regression fitting to obtain the linearity parameters of the main beam and compare and evaluate them with the geometric parameters of the design drawings;

[0043] The present invention provides a method and system for monitoring the closure construction of a cantilever-cast continuous beam based on three-dimensional laser scanning, having the following beneficial effects:

[0044] 1. The construction method and system for monitoring the closure of a cantilever - cast continuous beam based on 3D laser scanning utilize 3D laser scanning technology to achieve high - precision and real - time monitoring of the cantilever closure space, ensuring the accuracy of the entire construction. Combining advanced data processing and analysis methods, point cloud modeling is carried out to compare the errors before and after closure, and compared with drawing data and total station monitoring data to assist in completing each construction process more precisely and in detail during construction. By comprehensively monitoring parameters such as displacement and deformation during the cantilever closure process, potential safety hazards can be detected in a timely manner, ensuring the safety and quality of construction, thus making the construction process more accurate and reliable. By introducing advanced laser scanning technology, efficient monitoring of the cantilever closure space is achieved, improving the controllability and safety of the construction process. The application of this construction method not only meets the requirements of engineering construction for high - precision and real - time monitoring, but also introduces new scientific and technological means to the bridge construction field, promoting the modernization and intelligent development of construction monitoring technology, facilitating the scientific and precise development of construction technology, ensuring the progress of the entire construction process and greatly controlling construction costs, making the construction process safer, quality - guaranteed, scientific, cost - saving, and precise. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a schematic flow chart of the construction method for monitoring the closure of a cantilever - cast continuous beam based on 3D laser scanning of the present invention;

[0046] Figure 2 It is a schematic diagram of the 3D laser scanning principle of the present invention;

[0047] Figure 3 It is a layout diagram of linear measurement points for verifying the cantilever segment based on 3D laser scanning of the present invention;

[0048] Figure 4 It is a point cloud model diagram of the closure linearity monitoring of the cantilever based on 3D laser scanning of the present invention;

[0049] Figure 5 It is a point cloud model diagram of the completed - bridge linearity based on 3D laser scanner of the present invention;

[0050] Figure 6 (a) It is a result diagram of monitoring the bridge deck alignment based on 3D laser scanner of the present invention, Figure 6 (b) It is a result diagram of monitoring the bottom plate alignment based on 3D laser scanner of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0051] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0052] Please refer to Figure 1, the present invention provides a technical solution: a construction method for the closure of a cantilever cast continuous beam based on three-dimensional laser scanning monitoring, including the following steps:

[0053] S1. Construction preparation, surveying and setting out; through technical preparation, on-site preparation, material preparation, personnel preparation, seasonal preparation, preparing surveying and setting out tools, and formulating a setting out plan, it is convenient to plan the site and facilitate subsequent operations and construction;

[0054] S2. Construction by the falsework method, construction of the cantilever segments of the hanging basket;

[0055] S3. Transformation of the formwork for the closure segment, verifying the linearity of the segments by three-dimensional laser scanning, and measuring the linearity of the cantilever by three-dimensional laser scanning technology;

[0056] S4. Construction of the steel bars and embedded parts for the closure segment;

[0057] S5. Conducting three-dimensional laser scanning to detect the linearity while pouring the concrete for the closure segment;

[0058] S6. Prestressing construction for the closure segment and the whole bridge;

[0059] S7. After the completion of the bridge, verifying the linearity of the whole bridge by three-dimensional laser scanning and conducting a linearity assessment of the whole bridge.

[0060] Optionally, the specific operation steps for the construction preparation and surveying and setting out in step S1 are as follows:

[0061] S1-1. First, technical preparation is required: the construction unit needs to participate in the discussions of the preliminary design and technical design plans, and accordingly organize the compilation of the construction organization design, which is the central link of the construction preparation, and all construction preparation work must be carried out according to this; on-site preparation: the overall planning and progress requirements of the construction project, finding out the situations such as land expropriation, relocation of residents, and removal of ground obstacles; material preparation: applying for and ordering the required construction machinery and equipment, instruments, and training special technical workers. In addition, construction drawing review and technical disclosure are also required to ensure that the construction drawings and technical requirements are clear; personnel preparation: adjusting and deploying the construction force, forming a new construction organization according to the characteristics of the project tasks, and the construction unit needs to sign contracts and relevant agreements with the construction and design units to clarify the responsibilities and authorities of division of labor and cooperation; seasonal preparation: understanding the local natural conditions such as meteorology, hydrology, geology, and earthquake, and evaluating the adaptability of transportation and storage to construction;

[0062] S1-2. Then prepare the measuring and setting-out tools: such as measuring tapes, protractors, theodolites, setting-out lines, setting-out hammers, setting-out nails, prepare the design drawings and site plans, measure and determine the site boundaries and terrain, including the length, width, and height data of the site, and reduce errors; according to the design drawings and site measurement results, formulate a setting-out plan, including the position, length, and angle information of the setting-out lines, including considering the site terrain, the position and height of the building, mark the setting-out points on the site during setting-out, connect the setting-out points using the setting-out line, and then record the setting-out data and check the accuracy and precision of the setting-out data for subsequent construction work;

[0063] Optionally, in the construction method using the bracket method in step S2, the specific operation steps for the cantilever segment construction of the hanging basket are as follows:

[0064] S2-1. First, fabricate the brackets: Determine the hoisting positions and support methods of each steel structure component according to the design drawings, design the form, size, and materials of the brackets. The designers also need to consider the stability and safety of the frame structure, select appropriate materials such as angle steel, square tubes, I-beams, bolts, etc., ensure that the material quality meets the design requirements, fabricate the bracket model according to the design drawings, connect the brackets using welding or connecting bolts, pay attention to the verticality and flatness of the brackets, and then place the brackets at the predetermined positions for installation;

[0065] After the bracket installation is completed, it is necessary to detect the foundation to ensure its bearing capacity. When the bearing capacity of the foundation does not meet the requirements, replacement filling treatment is required. When necessary, use the methods of cast-in-place piles or driven piles to reinforce the foundation, and set drainage ditches around the brackets to prevent the foundation from being soaked by water and causing settlement;

[0066] Then, carry out the steel structure hoisting and concrete pouring, wash and clean the bottom formwork. The concrete is poured in horizontal layers and advanced in diagonal segments, and vibrated thoroughly using internal vibrators to ensure continuous pouring of the concrete. Keep the concrete moist during curing to avoid rain, sun, and exposure. Then, carry out the prestressing construction, and finally remove the brackets and clean the site;

[0067] Then, carry out the cantilever construction of the hanging basket. First, complete the construction of the lower structure of the bridge, including the construction of the pile foundation, pile cap, and pier body, and then install and preload the hanging basket;

[0068] Optionally, in the modification of the closure segment formwork in step S3, the specific operation steps for verifying the segment linearity using 3D laser scanning are as follows:

[0069] S3-1. First, install the 3D laser scanner. Install the brackets and fixing devices of the 3D laser scanner on the already built bridge deck. Use the multi-point and multi-view monitoring method based on control point transformation to measure the alignment of the cantilever segment. Utilize the bridge deck control points directly above the pier, and in combination with the control point transformation method, move the temporary control points once every 20 m. Then, conduct cross-measurements of the alignment of the cantilever segment at close and far distances. The horizontal scanning distance of the close-distance points is within 20 m, which is used to observe the detailed structure of the cantilever segment to ensure the integrity of the coordinate information of the key parts. The horizontal scanning distance of the far-distance points is 50 - 80 m, which is used to observe the overall structure of the cantilever segment to ensure the integrity of the point cloud of the overall model;

[0070] S3-2. Use the 3D laser scanning technology to measure the alignment of the cantilever, including the deflection and deformation of the cantilever. Collect the 3D scanning data of the cantilever segment, conduct data accuracy analysis, and generate an accuracy report. Based on the Cyclone software, use a monitoring data processing method that combines point cloud model stitching, random sampling, automatic simplification of members, and data fusion for in-house processing. Through the filtering of out-of-body noise points in a single monitoring point cloud and the stitching and synthesis of multiple monitoring point clouds, form an overall point cloud model;

[0071] S3-3. When constructing the last cantilever segment, reserve the reserved holes for the outer sliding beam, inner sliding beam, and front cross beam of the hanging basket. Move the hanging basket forward, and fix the inner and outer sliding beams and the front cross beam with 32 mm high-strength threaded steel through the reserved holes. Adjust the bottom formwork, side formwork, and inner formwork to the designed structural dimensions;

[0072] S3-4. Apply counterweights before closure and locking, and use 3D laser scanning to monitor the elevation difference at both ends of the closure segment in real time, so that the elevation difference between the bottom plates of the two cantilever segments is not greater than 10 mm. Set plastic water tanks on both sides of the closure segment, and use 2 synchronous 200 m high-lift water pumps to inject water. The weight of the water in the two water tanks and the storage should be equal to the weight of the concrete and the stiffening skeleton of the closure segment. Mark the position lines of the volume of water per cubic meter on the outer side of the water tank wall to facilitate draining water in coordination with the concrete pouring speed to achieve the effect of weight replacement and unloading. Use 3D laser scanning to guide the on-site counterweight work. Install the scanner within 20 m outside the cantilever end, collect the 3D scanning data during the cantilever counterweight process, conduct data analysis, and guide the on-site water addition process;

[0073] For the closure segment locking, a stiffening frame is externally provided. The stiffening frame is composed of embedded steel bars, embedded steel plates and double-rolled I-beams. Four groups of stiffening frames are arranged for each closure segment, with two groups arranged on the top and bottom plates of the box girder respectively. Connecting steel plates are provided on the upper and lower flange plates of the two I-beams for each group of stiffening frames, and the I-beams are welded into a whole by the connecting steel plates. When installing the stiffening frame, one end is first welded and fixed to the embedded part, and the other end is used as the adjustment end. When welding, the bottom plate is welded first and then the top plate. When welding, it is required that the weld length and fullness meet the specification requirements. After the fixed end of the stiffening frame is welded, a displacement value is jacked open at the adjustment section by a jack, and then the adjustment end of the stiffening frame is sealed by welding to complete the locking of the stiffening frame;

[0074] Optionally, the specific operation steps for the construction of the closure segment steel bars and embedded parts in step S4 are as follows:

[0075] S4-1. After the welding of the stiffening frame of the side-span closure segment is completed, the two side box girders form a whole, and the temporary locking of the permanent bearing of the side-span cast-in-place segment can be released. The limit device of the bearing at the top of the transition pier is released by tools to ensure that the bearing can freely expand and contract longitudinally;

[0076] S4-2. After the welding of the stiffening frame of the mid-span closure segment is completed, the installation of the closure segment steel bars, prestressed steel tendon ducts, etc. shall be carried out immediately. Since the closure segment steel bars and prestressed ducts are dense and the stiffening frame is added, special attention shall be paid to the positioning and sealing of the prestressed ducts to ensure the smoothness of the ducts;

[0077] Optionally, the specific operation steps for the three-dimensional laser scanning to detect the linearity during the concrete pouring of the closure segment in step S5 are as follows:

[0078] S5-1. To ensure the accuracy of subsequent splicing processing, a three-dimensional laser scanner shall be installed first, and there shall be sufficient spatial overlap between two adjacent different scanning stations in space, which is set to 50% on site. In order to obtain the absolute spatial coordinates of the point cloud, during the scanning operation, target points shall be arranged at the scanning site. The original point cloud obtained by each station is an independent file, and the spatial position of its point cloud is also relative. It is necessary to first splice the point clouds of these stations into a whole to obtain the complete point cloud data of the closure segment. The splicing of multiple scanning models is realized through coordinate transformation. Before the formal point cloud deformation analysis and processing, the point cloud is preprocessed;

[0079] S5-2. Three days before pouring the concrete of the joint section, the elevation change of the joint mouth and the length change of the joint section should be continuously observed (once every 4 hours). Temperature monitoring should be carried out 3 days in advance to determine the relationship between temperature change and elevation and length of the joint mouth, and to determine the pouring time of concrete. The joint time is generally selected during the period of lower temperature in a day. The optimal temperature is between 15-20℃ and should be the same as the temperature during locking, so that the poured concrete is always in a state of heating and pressure after pouring, and avoid the tension caused by concrete cooling, which leads to concrete cracking. The center line, elevation, dimensions of various parts of the beam body, steel bars, formwork, brackets, corrugated pipes, formwork, etc. of the joint section should be inspected. Only after passing the inspection can the concrete construction be carried out. Before pouring, the concrete connection surfaces at both ends should be fully roughened, moistened, and rinsed. C60 micro-expansive concrete should be used, pumped into the mold by a car pump, and vibrated and compacted by a hand-held vibrator. After the initial setting of the concrete, it should be covered with plastic film and geotextile to keep it moist and maintain until the designed time;

[0080] S5-3. During the pouring of the joint section concrete, a 3D laser scanner is used to monitor the joint linearity, guide the concrete loading speed and the weight replacement and unloading speed. The weight replacement and unloading are guided according to the 3D laser scanning monitoring of the joint linearity, and water is released while pouring concrete. The water release speed is determined according to the concrete pouring speed. Every 1m of pouring 3 Concrete, water 1.53m 3 water;

[0081] S5-4. Collect 3D scanning data during cantilever casting, and compare the linear offset values measured by 3D laser scanning and total station at each control point with the verticality offset value and the difference between the design value;

[0082] Optionally, the specific operation steps of the closure section and the prestressed construction of the entire bridge in step S6 are:

[0083] S6-1. Before the concrete reaches the tension strength requirement and the longitudinal beam is tensioned, remove the rigid support of the joint. The order of removal is the top plate first, then the bottom plate, and it should be done symmetrically. Be careful not to burn the concrete when cutting. After the weld is cut, use a jack to lift the channel steel away from the embedded steel plate to ensure that it is completely cut. Finally, level the top surface of the embedded plate and brush the bottom plate with cement slurry;

[0084] S6-2. Tension, grouting and anchoring of the remaining prestressed tendons are carried out in accordance with the designed tensioning sequence and dual control standards, and the conversion of the entire bridge system is completed. Subsequent work such as the removal of the hanging basket is completed in accordance with the special construction plan;

[0085] Optionally, after the bridge is formed in step S7, the linearity of the whole bridge is verified by three-dimensional laser scanning, and the specific operation steps for evaluating the linearity of the whole bridge are:

[0086] S7-1. First, install the 3D laser scanner. Four measuring points were selected corresponding to the upstream and downstream sides of the main pier deck of the closure beam. Since the stitching between different measuring stations is one of the main sources of point cloud model errors, the number of measuring stations should be minimized as much as possible during data collection for the bridge. When it comes to each measuring station location, the view should also be kept open to ensure the quality of the single-station bridge point cloud. At the same time, the influence of the geographical environment should be considered during station setup to ensure the safety of the surveying personnel and provide a stable working platform for the scanning equipment to the greatest extent;

[0087] S7-2. Since the volume of the measured rigid-frame bridge is large and there are inevitably some missing parts in the single-station point cloud data due to the measurement terrain limitations, and the point cloud of the main beam is incomplete and sparse at the mid-span position due to the large span, for these missing parts, the method of point cloud fitting and reconstruction is used to repair them. Based on the spatial characteristics of the complete point cloud around the missing part, the range of fitting and reconstruction is gradually expanded until the missing part is completely fitted;

[0088] S7-3. The spatial alignment of the main beam of the long-span rigid-frame bridge reflects the stress state of the bridge. Multiple measuring points on the longitudinal measuring lines of relevant components are extracted from the point cloud data, and then the alignment of the components is obtained by multivariate regression fitting of the coordinates of the measuring points. Select measuring lines on the main beam point cloud along the longitudinal direction of the bridge, and extract the longitudinal and vertical coordinates of the measuring points at equal intervals on the measuring lines. Use multivariate regression fitting to obtain the alignment parameters of the main beam and compare and evaluate them with the geometric parameters of the design drawings.

[0089] To sum up, for the construction method and system for monitoring the closure construction of the cantilever-cast continuous beam based on 3D laser scanning, during the actual application process, first, construction preparation is carried out. Through technical preparation: The construction unit needs to participate in the discussion of the preliminary design and technical design plans and organize the compilation of the construction organization design accordingly, which is the central link of construction preparation, and all construction preparation work must be carried out according to this; Site preparation: Understand the overall planning and progress requirements of the construction project, and find out the situations such as land expropriation, resettlement of residents, and removal of ground obstacles; Material preparation: Apply for and order the required construction machinery and equipment, instruments, and train special technical workers. In addition, construction drawing review and technical disclosure are also required to ensure that the construction drawings and technical requirements are clear; Personnel preparation: Adjust and deploy the construction force, form a new construction organization according to the characteristics of the project tasks. The construction unit should sign contracts and relevant agreements with the construction, design units to clarify the responsibilities and authorities of division of labor and cooperation; Seasonal preparation: Understand the local natural conditions such as meteorology, hydrology, geology, and earthquake, and evaluate the adaptability of transportation and storage to construction;

[0090] Then, prepare for the layout: prepare measuring and layout tools: such as measuring ruler, protractor, theodolite, layout line, layout hammer, layout nails, prepare design drawings and site plan, measure and determine the site boundary and terrain, including the length, width and height data of the site, and reduce errors; formulate a layout plan based on the design drawings and site measurement results, including the location, length and angle information of the layout line, including considering the site terrain, the location and height of the building, mark the layout points on the site during layout, connect the layout points with the layout line, and then record the layout data and check the accuracy and precision of the layout data to facilitate subsequent construction work;

[0091] Secondly, the support method is used for construction, and the cantilever segment of the hanging basket is constructed: the support is made: the lifting position and support method of each steel structure component are determined according to the design drawings, and the support form, size and material are designed. The designer also needs to consider the stability and safety of the frame structure, and purchase suitable materials such as angle steel, square tube, I-beam, bolts, etc., to ensure that the material and quality meet the design requirements, and make a support model according to the design drawings. The support is connected by welding or connecting bolts, and attention is paid to the verticality and flatness of the support. Then the support is placed in the predetermined position for installation. After the support is installed, the foundation needs to be tested to ensure the bearing capacity of the foundation. If the bearing capacity of the foundation is not met Replacement treatment is required when necessary. If necessary, the foundation is reinforced by cast-in-place piles or sunk piles, and drainage ditches are set around the brackets to prevent the foundation from being soaked by water and causing settlement. Then the steel structure is hoisted and the concrete is poured to wash and clean the bottom formwork. The concrete is poured horizontally in layers and pushed forward obliquely in sections. The inserted vibrator is used to compact and ensure that the concrete is poured continuously. The concrete is kept moist during maintenance to avoid rain and sun. Then the prestressed construction is carried out. Finally, the bracket is removed, the site is cleaned, and the hanging basket cantilever construction is carried out. The lower structure of the bridge is completed first, including the construction of pile foundation, abutment and pier body, and then the hanging basket is installed and prestressed.

[0092] Then the template of the joint section is transformed, such as Figure 3The verification of segment linearity using 3D laser scanning is as follows: First, install the 3D laser scanner. Install the brackets and fixing devices of the 3D laser scanner on the completed bridge deck. Use the multi-point and multi-view monitoring method based on control point transformation to measure the linearity of the cantilever segments. Utilize the bridge deck control points directly above the piers, and in combination with the control point transformation method, move the temporary control points once every 20 m. Then, measure the linearity of the cantilever segments through cross-measurements at close and far distances. The horizontal scanning distance of the close-distance points is within 20 m, which is used to observe the detailed structure of the cantilever segments to ensure the integrity of the coordinate information of the key parts. The horizontal scanning distance of the far-distance points is 50 - 80 m, which is used to observe the overall structure of the cantilever segments to ensure the integrity of the point cloud of the overall model. Measure the linearity of the cantilever using 3D laser scanning technology, including the deflection and deformation of the cantilever. Collect the 3D scanning data of the cantilever segments, conduct data accuracy analysis, and generate an accuracy report. Based on the Cyclone software, use a monitoring data processing method that combines point cloud model stitching, random sampling, automatic simplification of members, and data fusion for in-house processing. Through the filtering of out-of-body noise points in a single monitoring point cloud and the stitching and synthesis of multiple monitoring point clouds, form an overall point cloud model; When constructing the last cantilever segment, reserve the holes for the external sliding beam, internal sliding beam, and front cross beam of the hanging basket. Move the hanging basket forward, and fix the internal and external sliding beams and the front cross beam with 32 mm high-strength deformed steel bars through the reserved holes. Adjust the bottom formwork, side formwork, and internal formwork to the designed structural dimensions. Before closure and locking, apply a counterweight first, and use 3D laser scanning to monitor the elevation difference at both ends of the closure section in real time, so that the elevation difference between the bottom plates of the two cantilever segments is not greater than 10 mm. Set plastic water tanks on both sides of the closure section, and inject water synchronously through 2 high-lift pumps with a head of 200 m. The weight of the water in the two water tanks and the storage should be equal to the weight of the concrete and the stiffening skeleton in the closure section. Mark the position lines of the volume of water per cubic meter on the outer side of the water tank wall to facilitate draining water in coordination with the concrete pouring speed to achieve the effect of weight replacement and unloading. Use 3D laser scanning to guide the on-site counterweight work. Install the scanner within 20 m outside the cantilever end, collect the 3D scanning data during the cantilever counterweight process, conduct data analysis, and guide the on-site water addition process. For the closure section locking, use an external stiffening skeleton. The stiffening skeleton is composed of embedded steel bars, embedded steel plates, and double-rolled I-beams. Set 4 groups of stiffening skeletons for each closure section, with 2 groups arranged on the top and bottom plates of the box girder respectively. Connecting steel plates are set on the upper and lower flange plates of the two I-beams for each group of stiffening skeletons, and the I-beams are welded into an integral body by the connecting steel plates. Install the stiffening skeleton. One end is first welded and fixed to the embedded part, and the other end is the adjustment end. When welding, weld the bottom plate first and then the top plate. When welding, it is required that the weld length and fullness meet the specification requirements. After the welding of the fixed end of the stiffening skeleton is completed, use a jack to open a displacement value at the adjustment section, and then seal and weld the adjustment end of the stiffening skeleton to complete the locking of the stiffening skeleton;

[0093] Then, for the construction of the closure segment's steel bars and embedded parts: After the welding of the stiffening skeleton of the side-span closure segment is completed, the two side-box girders form an integral whole. The temporary locking of the permanent bearings of the side-span cast-in-place segment can be released, and the limit device of the bearings at the top of the transition piers can be removed with tools to ensure that the bearings can freely expand and contract longitudinally. After the welding of the stiffening skeleton of the mid-span closure segment is completed, the installation of the steel bars and prestressed tendon ducts in the closure segment should be carried out immediately. Since the steel bars and prestressed ducts in the closure segment are dense and the stiffening skeleton is added, special attention should be paid to the positioning and sealing of the prestressed ducts to ensure the smoothness of the ducts.

[0094] Next, during the concrete pouring of the closure segment, three-dimensional laser scanning is carried out simultaneously to detect the linearity: To ensure the accuracy of subsequent splicing processing, a three-dimensional laser scanner should be installed first, and there should be sufficient spatial overlap between two adjacent different scanning stations in the space, which is set to 50% on-site. In order to obtain the absolute spatial coordinates of the point cloud, during the scanning operation, target points should be arranged at the scanning site. The original point cloud obtained by each station is an independent file, and the spatial position of its point cloud is also relative. These point clouds of the stations need to be spliced into a whole first to obtain the complete point cloud data of the closure segment as Figure 4 shown. The splicing of multiple scanning models is realized through coordinate transformation. Before the formal analysis and processing of the point cloud deformation, the point cloud is preprocessed.

[0095] Three days before the concrete pouring of the closure segment, the elevation change and the length change of the closure gap should be continuously observed (once every 4 hours), and the temperature monitoring should be carried out 3 days in advance to determine the relationship between the temperature change, the elevation, and the length of the closure gap, and determine the concrete pouring time. The closure time is generally selected during the period with relatively low temperature in a day, and the optimal temperature is between 15 - 20 °C, and it should be the same as the temperature at the time of locking, so that the poured concrete is always in a state of temperature rise and compression after pouring, avoiding the generation of tensile force due to the concrete cooling and causing the concrete to crack. Check the center line, elevation, dimensions of each part of the beam body, steel bars, formwork, supports, corrugated pipes, formwork, etc. of the closure segment. After passing the inspection, the concrete construction can be carried out. Before pouring, the concrete connection surfaces at both ends should be fully roughened, wetted, and rinsed clean. C60 slightly expanded concrete is used and pumped into the formwork by a truck pump, and vibrated densely with a handheld vibrator. After the concrete begins to set, it is covered with plastic film and geotextile for moisture conservation until the designed time. During the process of pouring the concrete of the closure segment, a three-dimensional laser scanner is used to monitor the closure linearity to guide the concrete feeding speed and the weight replacement and unloading speed. According to the three-dimensional laser scanning monitoring of the closure linearity, the weight replacement and unloading are guided, and water is drained while pouring the concrete. The water drainage speed depends on the concrete pouring speed. For every 1 m 3 of concrete poured, 1.53 m 3 of water is drained, and the three-dimensional scanning data during the cantilever casting process is collected. The differences between the linear offset values and the verticality offset values measured by the three-dimensional laser scanning and total station of each control point and the design values are compared.

[0096] Then, for the closure segment and the prestress of the entire bridge: Before the prestressed concrete reaches the required tensile strength and before the longitudinal tendons are tensioned, remove the rigid supports at the closure joint. The removal sequence is to start with the top slab and then the bottom slab, and proceed symmetrically on both the left and right sides. When cutting, pay attention not to burn the concrete. After the weld cutting is completed, use a jack to lift the channel steel away from the embedded steel plate to ensure complete cutting. Finally, level the top surface of the embedded plate, and apply cement slurry treatment at the bottom slab. Tension, grout, and seal the remaining prestressed tendons according to the designed tensioning sequence and double-control standards to complete the system transformation of the entire bridge, and complete subsequent work such as removing the hanging baskets according to the special construction plan;

[0097] Then, conduct 3D laser scanning to verify the linearity of the entire bridge and conduct an overall bridge linearity assessment: First, install the 3D laser scanner. Four measuring points can be selected corresponding to the upstream and downstream sides of the main pier deck of the closure beam. Since the stitching between different measuring stations is one of the main sources of point cloud model errors, the number of measuring stations should be minimized as much as possible during data collection for the bridge. Specifically, the view at each measuring station location should also be kept open to ensure the quality of the single-station bridge point cloud. At the same time, the influence of the geographical environment should be considered when setting up the stations to ensure the safety of the surveying personnel and provide a stable working platform for the scanning equipment to the greatest extent (as Figure 2 shown, 3D laser scanning technology is a non-contact measurement method that obtains the three-dimensional coordinate information of the object surface by emitting a laser beam from a laser and using a sensor to receive the reflected light. The laser emits a laser beam, which is focused through a lens or a mirror. The laser beam scans the entire surface of the object at a certain speed. The scanning can be mechanical scanning, that is, achieved by the movement of the laser scanner, or linear scanning, that is, by fixing the laser scanner and using a special deflecting mirror to scan the object surface. After that, when the laser beam irradiates the object surface, it will be reflected. The sensor receives the reflected light and converts it into an electrical signal. The sensor generally uses a photodiode or a photomultiplier tube to receive the laser reflected light and convert the optical signal into an electrical signal. Then, the distance to the object surface is determined by the time-of-flight principle. It takes a certain time for the laser beam to be emitted from the laser, reach the object surface, and return to the sensor after reflection. This time is proportional to the speed of the laser beam and the distance to the object surface. The sensor measures the time difference between the emission and reception of the laser and calculates the distance to the object surface through the known value of the speed of light. Finally, the distance information of the object surface is converted into three-dimensional coordinates through coordinate transformation. During the laser scanning process, the laser scanner records the distance information at different positions when passing through different positions. These distance information corresponds to the movement trajectory of the laser scanner. By calculating and processing these distance and position information, three-dimensional coordinate data of the object surface can be generated);

[0098] Due to the large volume of the rigid frame bridge under test and the limitation of the measurement terrain, there are inevitably some missing parts in the single-station point cloud data. The point cloud of the main girder is incomplete and sparse at the mid-span position due to the large span. For these missing parts, the method of point cloud fitting and reconstruction is used to repair them. Based on the spatial characteristics of the complete point cloud around the missing parts, the scope of fitting and reconstruction is gradually expanded until the missing parts are completely fitted. The complete bridge point cloud model formed is as Figure 5 shown.

[0099] Compare the linear offset values and verticality offset values (the differences from the design values) measured by 3D laser scanning and total station, and obtain the linear offset values and verticality offset values of each segment. As shown in Table 5.2.2-1, it can be obtained from Table 5.2.2-1 that the measurement results of the cantilever segments by 3D laser scanning are approximately the same as those by total station, indicating that the application performance of 3D laser scanning technology is good, which can accurately reflect the actual construction alignment of the cantilever segments and meet the requirements of the "Construction Survey Specifications for Extra-Large-Span Highway Bridges" (JTG / T 3650-02—2019).

[0100] Table 5.2.2-1 Measurement Results of Cantilever Segments

[0101]

[0102] Collect the 3D scanning data during the cantilever casting process, compare the linear offset values and verticality offset values (the differences from the design values) measured by 3D laser scanning and total station at each control point, and summarize them in Table 5.2.6-1. It can be obtained from Table 5.2.6-1 that the monitoring results of the cantilever segments by 3D laser scanning are approximately the same as those by total station, indicating that the application performance of 3D laser scanning technology is good, which can accurately reflect the actual construction alignment of the cantilever segments.

[0103] Table 5.2.6-1 Comparison of Monitoring Effects of the Closing Segment

[0104]

[0105] Based on the Leica Cyclone software and the Cloudworx plugin, draw the profile line shape of the closure segment as required. According to the needs of deformation analysis, intercept the profiles of relevant parts of the bridge and adjust the point cloud view to the state of facing the profile directly; determine the coordinates of the control points of the closure section according to GNSS positioning and compare them with the designed point coordinates. The results are shown in Table 5.2.6-2. It can be seen that the sections where control points 1, 2, and 3 are located have completed the design and construction well, with small mileage errors, and the elevation errors are controlled within about ±1 cm; the mileage errors of the sections where control points 4, 5, and 6 are located are small, and the elevation errors are about ±0.5 cm; the mileage errors of the sections where control points 7, 8, and 9 are located are small, and the elevation errors are about ±1 cm. In summary, the mileage construction effect of the closure segment is good, but the elevation errors are relatively large and control measures need to be taken. Through the analysis of on-site measured data, it is found that the 3D laser scanner can better verify the linearity of the closure segment. The monitoring process is simple and fast, and the monitoring results are accurate and detailed, which is beneficial to guiding on-site construction.

[0106] Table 5.2.6-2 Linear Monitoring Table of the Closure Segment

[0107]

[0108] The spatial linearity of the main girder of a long-span rigid-frame bridge reflects the stress state of the bridge. Extract multiple measurement points on the longitudinal measurement lines of relevant components from the point cloud data, and then obtain the linearity of the components through multiple regression fitting of the measurement point coordinates. Select measurement lines on the main girder point cloud along the longitudinal direction of the bridge, and extract the longitudinal and vertical coordinates of the measurement points at equal intervals on the measurement lines. Use multiple regression fitting to obtain the linearity parameters of the main girder and compare and evaluate them with the geometric parameters of the design drawings. The comparison results are as Figure 6 (a) and Figure 6 (b) shown. It can be seen that by comparing the 3D laser scanning linear data with the bridge design data, the offset degree between the actual engineering construction control point coordinates and the design control point coordinates of the bridge can be obtained more intuitively and accurately, and then the subsequent bridge construction can be controlled and improved. This method has been successfully applied in the main bridge project of the Toutunhe Interchange Connecting Line of the Urumqi Ring Expressway (West Line) project and the Shanghuibin Special Bridge of the Jinan Link of the Tianjin to Weifang High-Speed Railway, creating good economic benefits and ensuring the safety, closure accuracy, and construction quality of the construction at the same time.

[0109] The above is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and all should be covered within the protection scope of the present invention.

Claims

1. A construction method for monitoring the closure of a cantilever-cast continuous beam based on 3D laser scanning, characterized in that: It includes the following steps: S1. Construction preparation and measurement lofting; S2. Construction by the support method and cantilever segment construction of the hanging basket; S3. Transformation of the closure segment formwork and verification of the segment linearity using 3D laser scanning; S4. Construction of the closure segment steel bars and embedded parts; S5. Conduct 3D laser scanning to detect the linearity while pouring the concrete of the closure segment; S6. Prestressing construction of the closure segment and the whole bridge; S7. After the bridge is completed, verify the linearity of the whole bridge through 3D laser scanning and conduct a linearity assessment of the whole bridge.

2. The construction method for closing a cantilever casting continuous beam based on three-dimensional laser scanning monitoring according to claim 1, wherein: The specific operation steps of the construction preparation and measurement lofting in step S1 are as follows: S1-1. Technical preparation: The construction unit participates in the discussion of the preliminary design and technical design plans and organizes the compilation of the construction organization design. The technical preparation includes site preparation, material preparation, and personnel preparation; the site preparation includes the overall planning and progress requirements of the construction project, finding out the situation of land expropriation, resettlement of residents, and removal of ground obstacles. The material preparation includes applying for and ordering the required construction machinery, equipment, and instruments, and training special technical workers. The personnel preparation includes adjusting and deploying the construction force, forming a new construction organization according to the characteristics of the project tasks. The construction unit shall sign contracts and relevant agreements with the construction and design units to clarify the responsibilities and authorities of division of labor and cooperation; S1-2. Prepare measurement and lofting tools: Prepare tools including measuring rulers, protractors, theodolites, lofting lines, lofting hammers, and lofting nails, and prepare design drawings and site plans; Measure and determine the site boundary and terrain, including the length, width, and height data of the site; According to the design drawings and site measurement results, formulate a lofting plan, including the position, length, and angle information of the lofting line, considering factors such as the site terrain, the position and height of the building. When conducting lofting, mark the lofting points on the site, connect the lofting points with the lofting line, record the lofting data, and check the accuracy and precision of the lofting data.

3. A method for monitoring the closure construction of a cantilever - cast continuous beam based on three - dimensional laser scanning according to claim 1, characterized in that: The specific operation steps of the construction by the support method and cantilever segment construction of the hanging basket in step S2 are as follows: S2-1. Support fabrication: Determine the hoisting position and support method of each steel structure component according to the design drawings, design the form, size, and materials of the support. The designers also need to consider the stability and safety of the frame structure, select suitable materials such as angle steel, square pipes, I-beams, and bolts to ensure that the material quality meets the design requirements. Fabricate the support model according to the design drawings, connect the supports using welding or connecting bolts, pay attention to the verticality and flatness of the supports, and then place the supports at the predetermined position for installation; S2-2. Foundation bearing capacity detection: After the support is installed, detect the foundation to ensure the bearing capacity of the foundation. When the bearing capacity of the foundation does not meet the requirements, replacement filling treatment is required. When necessary, use the method of cast-in-place piles or driven piles to reinforce the foundation, and set drainage ditches around the support to prevent the foundation from settling due to water immersion; S2-3. For the steel structure hoisting and concrete pouring, wash and clean the bottom formwork. Pour the concrete in horizontal layers and advance in diagonal segments. Use internal vibrators to tamp it densely to ensure continuous pouring of the concrete. Keep the concrete moist during curing to avoid rain, sun exposure, then conduct prestressing construction, and finally remove the support and clean the site; S2-4. The cantilever construction of the hanging basket is carried out. First, the lower structure of the bridge is constructed, including the construction of the pile foundation, the bearing platform and the pier body, and then the installation and preloading of the hanging basket are carried out.

4. A construction method for the closure of a cantilever-cast continuous beam based on three-dimensional laser scanning monitoring according to claim 1, characterized in that: In the modification of the closure segment formwork in step S3, the specific operation steps for verifying the linearity of the segment using 3D laser scanning are as follows: S3-1. Installation of the 3D laser scanner. Install the bracket and fixing device of the 3D laser scanner on the completed bridge deck. Use the multi-point and multi-view monitoring method based on the transformation of control points to measure the linearity of the cantilever segment. Utilize the bridge deck control points directly above the pier, and in combination with the control point transformation method, move the temporary control points once every 20m. Then, perform cross-measurement of the linearity of the cantilever segment at close and far distances. The horizontal scanning distance of the close-range points is within 20m, which is used to observe the detailed structure of the cantilever segment to ensure the integrity of the coordinate information of the key parts; the horizontal scanning distance of the far-range points is 50-80m, which is used to observe the overall structure of the cantilever segment to ensure the integrity of the point cloud of the overall model. S3-2. Linear measurement of the cantilever. Measure the deflection and deformation of the cantilever, collect the 3D scan data of the cantilever segment, conduct data accuracy analysis, generate an accuracy report, and perform in-house processing based on the Cyclone software using a monitoring data processing method that combines point cloud model stitching, random sampling, automatic simplification of members, and data fusion. Through the filtering of out-of-body noise points in the single monitoring point cloud and the stitching and synthesis of the multi-monitoring point clouds, an overall point cloud model is formed. S3-3. When constructing the last cantilever segment, reserve holes for the outer sliding beam, inner sliding beam, and front cross beam of the hanging basket. Move the hanging basket forward, and fix the inner and outer sliding beams and the front cross beam with 32mm high-strength threaded steel through the reserved holes. Adjust the bottom formwork, side formwork, and inner formwork to the designed structural dimensions. S3-4. Before closure locking, apply counterweights first, and use 3D laser scanning to monitor the elevation difference at both ends of the closure segment in real time, so that the elevation difference between the bottom plates of the two cantilever segments is not greater than 10mm. Set plastic water tanks on both sides of the closure segment, and use 2 synchronous 200m high-lift water pumps to inject water. The total weight of the water tanks and the stored water on both sides should be equal to the weight of the closure segment concrete and the stiffening skeleton. Mark the position lines of the volume of water per cubic meter on the outer side of the water tank wall to facilitate discharging water in coordination with the concrete pouring speed to achieve the effect of weight replacement and unloading. Use 3D laser scanning to guide the on-site counterweight work: Install the scanner within 20m outside the cantilever end, collect the 3D scan data during the cantilever counterweight process, conduct data analysis, and guide the on-site water addition process. S3-5. The joint section is locked by an external rigid frame, which is composed of embedded steel bars, embedded steel plates and double-jointed I-beams. Four groups of rigid frames are set up in each joint section, with two groups arranged on the top and bottom plates of the box girder respectively. Connecting steel plates are set on the upper and lower flange plates of the two I-beams for each group of rigid frames, and the I-beams are welded into a whole by the connecting steel plates. The rigid frame is installed, one end of which is first welded and fixed to the embedded parts, and the other end is used as the adjustment end. When welding, the bottom plate is welded first and then the top plate. When welding, the weld length and fullness are required to meet the requirements of the specifications. After the welding of the fixed end of the rigid frame is completed, a jack is used to open a displacement value in the adjustment section, and then the adjustment end of the rigid frame is sealed and welded to complete the locking of the rigid frame.

5. A construction method for the closure of a cantilever-cast continuous beam based on 3D laser scanning monitoring according to claim 1, characterized in that: The specific operation steps of the joint section steel bars and embedded parts construction in step S4 are as follows: S4-1. After the welding of the rigid frame of the side span joint section is completed, the box girders on both sides form a whole, and the temporary locking of the permanent support of the cast-in-place section of the side span can be released. The limit device of the support on the top of the transition pier can be released with tools to ensure that the support can freely expand and contract longitudinally; S4-2. After the welding of the rigid frame of the middle span joint section is completed, the installation of the joint section steel bars and prestressed steel bundle pipes should be carried out immediately, because the joint section steel bars and prestressed pipes are densely packed and the rigid frame is increased.

6. The construction method for closing a cantilever casting continuous beam based on 3D laser scanning monitoring according to claim 1, characterized in that: The specific operation steps of performing three-dimensional laser scanning and linear detection while pouring concrete at the joint section in step S5 are as follows: S5-1. Install a 3D laser scanner, and there should be enough spatial overlap between two different adjacent scanning stations, which is set to 50% on site. During the scanning operation, target points are arranged on site. The original point cloud obtained by each station is an independent file, and the spatial position of its point cloud is also relative. The point clouds of these stations are spliced into a whole to obtain the complete point cloud data of the joint section. The splicing of multiple scanning models is realized through coordinate transformation. Before the formal point cloud deformation analysis and processing, the point cloud is pre-processed; S5-2. Three days before pouring concrete at the joint section, the elevation change of the joint mouth and the length change of the joint section should be continuously observed (once every 4 hours). Temperature monitoring should be carried out three days in advance to determine the relationship between temperature change and elevation and length of the joint mouth, and to determine the pouring time of concrete. The center line, elevation, dimensions of various parts of the beam body, steel bars, formwork, brackets, corrugated pipes, formwork, etc. of the joint section should be inspected. After passing the inspection, the concrete construction can be carried out. Before pouring, the concrete connection surfaces at both ends should be fully roughened, moistened, and rinsed. C60 micro-expansive concrete should be used, pumped into the mold with a car pump, and vibrated and compacted with a handheld vibrator. After the concrete is initially set, it should be covered with plastic film and geotextile to keep it moist and maintain until the designed time; S5-3. During the process of pouring the concrete of the closure section, a three-dimensional laser scanner is used to monitor the closure alignment, guide the concrete placement speed and the weight replacement and unloading speed. The weight replacement and unloading are guided according to the closure alignment monitored by the three-dimensional laser scanning. Water is drained while pouring the concrete, and the drainage speed is determined according to the concrete pouring speed. For every 1 m 3 of concrete poured, 1.53 m 3 of water is drained; S5-4. Collect 3D scanning data during cantilever casting, and compare the linear offset values measured by 3D laser scanning and total station at each control point with the difference between the verticality offset value and the design value.

7. A construction method for the closure of a cantilever-cast continuous beam based on three-dimensional laser scanning monitoring according to claim 1, characterized in that: The specific operation steps of the closure section and the prestressing construction of the entire bridge in step S6 are: S6-1. Before the concrete reaches the required tensile strength and before the longitudinal tendons are tensioned, remove the rigid supports at the closure joint. The removal sequence is to start with the top slab and then the bottom slab, and proceed symmetrically on both the left and right sides. After the weld cutting is completed, use a jack to lift the channel steel away from the embedded steel plate to ensure complete cutting. Level the top surface of the embedded plate, and apply cement slurry treatment at the bottom slab. S6-2. Tension, grout, and seal the remaining prestressed tendons (seal the ends) according to the designed tensioning sequence and double-control standards to complete the system transformation of the entire bridge.

8. A construction method for the closure of a cantilever cast continuous beam based on 3D laser scanning monitoring according to claim 1, characterized in that: In step S7, after the bridge is completed, verify the linearity of the entire bridge through 3D laser scanning. The specific operation steps for evaluating the linearity of the entire bridge are as follows: S7-1. First, install the 3D laser scanner and select 4 measurement points corresponding to the upstream and downstream sides of the main pier deck of the closure beam. S7-2. Due to measurement terrain limitations, use the method of point cloud fitting and reconstruction. Based on the spatial characteristics of the complete point cloud around the missing part, gradually expand the range of fitting and reconstruction until the missing part is completely fitted. The spatial alignment of the main beam of a long-span rigid-frame bridge reflects the stress state of the bridge. Extract multiple measurement points on the longitudinal measurement lines of relevant components from the point cloud data, and then obtain the alignment of the components through multiple regression fitting of the measurement point coordinates. Select a measurement line on the main beam point cloud along the longitudinal direction of the bridge, and extract the longitudinal and vertical coordinates of the measurement points at equal intervals on the measurement line. Use multiple regression fitting to obtain the alignment parameters of the main beam, and compare and evaluate them with the geometric parameters on the design drawings.

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