Bridge rectangular high pier sliding and combining formwork

Abstract

The utility model discloses a bridge rectangular high pier slip and turn over combination form, including outer frame body, hydraulic pressure jacking system, inner turning over form, hydraulic pressure jacking system is four groups of through core type jack, and the lower end of each group of through core type jack is located in pier column, and the upper portion of through core type jack is provided with crossbeam and can jacking to crossbeam, and the outer end head of crossbeam is connected with outer frame body through outer mould frame pull rod, and the middle lower end of crossbeam is provided with inner mould pull rod and is used for connecting with inner turning over form. The system is composed of four parts of form system, hydraulic pressure climbing system, protection system and support system: form system adopts modularization design; hydraulic pressure climbing system ensures form stable promotion through synchronous control; protection system integrates full -enclosed safety net and wide -width operation platform, and guarantees high -altitude operation safety; support system adopts high -strength steel frame body, and ensures overall stability. System design gives consideration to the efficiency of slip form and the economy of turn over form, is applicable to complex working conditions such as high pier, large -span bridge etc.

Description

Technical Field

[0001] This utility model relates to the field of construction of rectangular high piers for bridges, specifically to a sliding and flipping combined formwork for rectangular high piers for bridges. Background Technology

[0002] As my country's highway planning extends into inland mountainous areas, the proportion of high-pier bridges is increasing, posing numerous challenges to traditional high-pier construction techniques. The formwork flipping method involves high-altitude operations and poor appearance quality; the slipform method struggles to balance speed and quality; and the climbing formwork method is prohibitively expensive. Existing techniques cannot simultaneously meet the requirements of low risk, high efficiency, high quality, and low cost, thus hindering the development of high-pier bridge construction in mountainous areas. This paper aims to study the key technologies of a combined slipform and flipping formwork system for rectangular high-pier bridges to address the shortcomings of traditional techniques and promote the upgrading of bridge construction technology.

[0003] 1. Shortcomings in existing high pier construction technology and the necessity of project approval 1.1 Shortcomings of existing process technology Currently, the construction of high bridge piers in China mainly relies on three processes: flip-form, slip-form, and climbing form. Each process has significant differences in characteristics and has unavoidable shortcomings: (1) Flip-form process, which is based on the cyclic lifting of 3-4 sections of steel formwork, has an equipment investment cost of only 50% of that of climbing formwork. However, it requires frequent lifting of formwork by tower crane, resulting in high risk of high-altitude operations. According to industry statistics, the accident rate of flip-form construction is 2.8 times that of climbing formwork. At the same time, misalignment is prone to occur at the splicing of formwork, and the defect rate of concrete appearance quality exceeds 15%, which increases the cost of later repairs and project cost. (2) Slip-form process, which uses a hydraulic system to drive the continuous lifting of formwork, can achieve an average daily construction height of 2.5m, which is 40% higher than flip-form and has a good safety protection system. However, the core contradiction of this process lies in the "conflict between speed and quality" - in order to ensure the construction progress, the formwork needs to be climbed before the concrete initially sets (usually 4-5 hours after pouring). The friction between the formwork and the surface of the incompletely set concrete causes scratches, resulting in a concrete appearance quality qualification rate of only 80%. Some projects need to invest an additional 3%-5% of the cost for appearance repair. (3) Climbing formwork process, which uses attached lifting frame and fixed formwork, does not require high-altitude hoisting operations, greatly improves the safety factor, and there is no friction between the formwork and the concrete surface during the climbing process, with an appearance quality qualification rate of over 95%. However, the purchase and installation costs of climbing formwork equipment are high, with a single pier construction cost of about 400,000-550,000 yuan, which is 80% higher than that of flip formwork. For mountainous projects with a large number of high piers, the economic shortcomings are particularly prominent.

[0004] 1.2 Necessity of Project Establishment The urgent need to resolve the contradictions in the construction of high piers in mountainous areas: After my country's highway planning extends to inland mountainous areas, the proportion of high pier bridges has increased significantly, but the existing technology cannot simultaneously meet the construction requirements of "low risk, high efficiency, high quality and low cost". Taking the Anjing Expressway project as an example, if climbing formwork is used to construct 43 high piers, an additional cost of about RMB 8.4 million will be required; if slip formwork is used, the cost of repairing the appearance of concrete will account for 3.2% of the total construction cost of the square piers; and the safety risk of using flip formwork is too high. The slip-flip combined formwork system can effectively balance the four objectives and resolve the construction contradictions. (1) The "Technical Specification for Safety of Highway Engineering Construction" (JTGF90-2015) and the "Standard for Quality Inspection and Evaluation of Highway Engineering" (JTGF80 / 1-2017) put forward higher requirements for the construction of high piers, and the traditional technology is no longer suitable for the needs of industry development. The development of the slip-flip combined formwork system is an important path to promote the upgrading of bridge construction technology and realize "green construction". [1] (2) The practical need to enhance the core competitiveness of enterprises: Sichuan Road & Bridge East China Construction Co., Ltd., as a top-level general contracting enterprise for highway engineering construction, has accumulated rich experience in the field of mountain bridge construction. Through the research of this project, core technologies with independent intellectual property rights will be formed, which can further consolidate the enterprise's technical advantages in the field of high pier construction and provide support for subsequent market expansion.

[0005] 2. Analysis of the limitations of traditional template systems 2.1 Shortcomings of the mold-making system Formwork flipping consists of 3-4 layers of formwork, constructed by flipping it layer by layer, relying on manual assembly, disassembly, and hoisting. Its main problems are: first, high safety risks, as construction workers must work on the outside of the formwork with rudimentary protective measures, posing a significant risk of falls from heights; second, low construction efficiency, with each layer requiring 8-10 hours to assemble and disassemble, and heavily influenced by weather conditions; and third, misalignment is prone to occur at formwork joints, resulting in significant deviations in the flatness of the concrete surface, requiring subsequent grinding and repair. In the early trials on the Anjing Expressway, the construction of pier No. 65 using formwork flipping took 35 days, and three obvious misalignments appeared on the surface.

[0006] 2.2 Defects of the sliding mode system Slip-form construction uses hydraulic jacks to lift the entire formwork, enabling continuous construction. However, it has two major drawbacks: First, the concrete appearance quality is poor. When the formwork rises, it rubs against the unset concrete, creating longitudinal scratches. In the past, after slip-form construction was used on construction sites, the surface scratches were 2-3 millimeters deep, increasing repair costs by 80,000 yuan. Second, it requires extremely high control over the concrete slump. Deviations in slump can easily lead to grout leakage or formwork jamming, resulting in a low tolerance for errors during construction.

[0007] 2.3 Disadvantages of the climbing model system Climbing formwork uses the wall as support and a climbing frame to raise and lower the formwork, offering good safety and quality assurance. However, it is less economical, with each set of climbing formwork equipment costing approximately 500,000 yuan, three times that of roll-up formwork; moreover, the climbing frame is complex to install and requires a long preparation time, limiting its applicability in projects with tight schedules. The feasibility study for the Anjing Expressway shows that if climbing formwork were used exclusively, the formwork cost alone would increase by more than 8 million yuan. Utility Model Content

[0008] Therefore, to address the aforementioned shortcomings, this utility model provides a sliding-formwork combined with formwork for rectangular high piers of bridges. This application focuses on the construction of rectangular high piers of bridges and proposes a sliding-formwork combined with formwork system to address the shortcomings in safety, quality, and cost of existing flip-form, slip-form, and climbing formwork processes.

[0009] This utility model is implemented as follows: a rectangular high pier sliding and flipping combined template for bridges is constructed, characterized in that the template consists of an outer frame, a hydraulic jacking system, and an inner flipping template; the hydraulic jacking system consists of four sets of through-type jacks, the lower end of each set of through-type jacks is located in the pier column, the upper part of the through-type jacks is provided with a crossbeam that can lift the crossbeam, the outer end of the crossbeam is connected to the outer frame through an outer formwork tie rod, and the lower middle part of the crossbeam is provided with an inner formwork tie rod for connecting with the inner flipping template. The jacking by the hydraulic jacking system can drive the outer frame and the inner flipping template to rise and fall along the pier column. The top surface of the outer frame forms an upper operating platform, and the lower end of the outer frame forms a lower operating platform. A ladder is provided between the upper and lower operating platforms to facilitate personnel to go up and down to the upper and lower operating platforms. After personnel enter the lower operating platform, it is used for pier column repair after jacking.

[0010] According to the present invention, a rectangular high pier sliding and tilting combined template for bridges is characterized in that the outer frame is composed of multiple segments, and the whole is located around the corresponding pier column, surrounding the pier column.

[0011] According to the present invention, a rectangular high pier sliding and overturning combined formwork for bridges is characterized in that the inward overturning formwork is located inside the outer frame.

[0012] According to the present invention, a rectangular high pier sliding and tilting combined template for bridges is characterized in that: there are two sets of crossbeams, and an electric control platform is provided on the two sets of crossbeams.

[0013] According to the present invention, a bridge rectangular high pier sliding and overturning combined template is characterized in that: a guardrail is set on the upper operating platform and a railing is set at the lower operating platform.

[0014] This application focuses on the construction of rectangular high piers for bridges, addressing the shortcomings of existing slipform, tilting formwork, and climbing formwork processes in terms of safety, quality, and cost. It proposes a combined slipform and tilting formwork system. This system integrates the advantages of both slipform and tilting formwork, optimizing spatial layout through BIM simulation, verifying the structure using Midas, and innovating the design of key components. The application also studies construction techniques, clarifying process planning, technological innovation, and key points of quality control. Pilot application on the Anjing Expressway demonstrates significant advantages in efficiency, quality, cost, and safety. Further improvements and refinements have led to the development of a construction manual, providing new ideas and standardized guidance for high pier construction.

[0015] This utility model has the following advantages: The slipform combined formwork system takes the "slipform climbing system and flipform formwork system" as its core, and optimizes and combines them for coordinated construction operations: the entire formwork and climbing system relies on a hydraulic system to uniformly slide the formwork system, completing the cyclic pouring work before the initial setting of concrete, constructing the initial structure, shortening the construction period, and reducing joints; the concrete pouring process adopts an improved flipform process, using a hydraulic lifting device to lift the outer platform system as a whole, lifting the formwork, flipping the formwork, and then inspecting and pouring. All operations are completed within the construction platform, avoiding the risks of high-altitude disassembly and assembly, and reducing labor intensity. The system consists of four parts: a formwork system, a hydraulic climbing system, a protective system, and a support system; the formwork system adopts a modular design; the hydraulic climbing system ensures stable lifting of the formwork through synchronous control; the protective system integrates a fully enclosed safety net and a wide operating platform to ensure safety during high-altitude operations; the support system uses a high-strength steel frame to ensure overall stability. The system design takes into account the efficiency of slipform and the economy of flipform, and is suitable for complex conditions such as high piers and long-span bridges. Attached Figure Description

[0016] Figure 1 This is a diagram of the overall implementation structure of this application; Figures 2-4 This is a side view of the overall structure of this application; Figure 5 This is a schematic diagram of the ladder in this application; Figure 6 This is a schematic diagram of the structural components of the external frame in this application; Figure 7 This is a schematic diagram of the electrical control platform structure in this application. Detailed Implementation

[0017] The following will be combined with the appendix Figures 1-7 This utility model will be described in detail, and the technical solutions in the embodiments of this utility model will be clearly and completely described. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of this utility model.

[0018] This utility model provides a rectangular high pier sliding and tilting combined template for bridges, such as... Figures 1-7 As shown, it can be implemented in the following manner: The template consists of an outer frame 1, a hydraulic jacking system 5, and an inward-turning template 6; the hydraulic jacking system 5 consists of four sets of through-type jacks, with the lower end of each set of through-type jacks located in the pier column. A crossbeam 7 is installed on the upper part of the through-type jacks and can lift the crossbeam 7. The outer end of the crossbeam 7 is connected to the outer frame 1 through the outer formwork tie rod 2. An inner formwork tie rod 3 is installed at the lower middle part of the crossbeam 7 for connection with the inward-turning template 6. The top surface of the outer frame 1 forms an upper operating platform 1-1, and the lower end of the outer frame 1 forms a lower operating platform 1-2. A ladder 8 is installed between the upper operating platform 1-1 and the lower operating platform 1-2 to facilitate personnel to go up and down to the upper and lower operating platforms. After personnel enter the lower operating platform, it is used for the repair of the pier column after jacking.

[0019] In the implementation of this application, the outer frame 1 is composed of multiple segments, and its entirety is located around the corresponding pier, surrounding the pier.

[0020] In the implementation of this application, the inward-turning template 6 is located inside the outer frame 1.

[0021] In the implementation of this application, there are two sets of crossbeams 7, and an electrical control platform 4 is installed on each set of crossbeams 7.

[0022] In the implementation of this application, a guardrail 9 is installed on the upper operating platform 1-1, and a railing 10 is installed at the lower operating platform 1-2.

[0023] The implementation principles of this application will be explained in detail below; Research on the Design of Tilting Combined Template System 1. Overall system design concept: The slipform-turning combined formwork system centers on a "slipform climbing system and a turning formwork system," optimizing and merging them for coordinated construction: the entire formwork and climbing system utilizes a hydraulic system to uniformly lift the formwork system, completing cyclic pouring before the concrete initially sets, constructing the initial structure, shortening the construction period, and reducing joints; the concrete pouring process employs an improved turning formwork technology, using a hydraulic lifting device to lift the outer platform system as a whole, lifting the formwork, turning it over, and then inspecting and pouring. All operations are completed within the construction platform, avoiding the risks of high-altitude disassembly and assembly, and reducing labor intensity. This system consists of four parts: a formwork system, a hydraulic climbing system, a protective system, and a support system. The formwork system adopts a modular design; the hydraulic climbing system ensures stable formwork lifting through synchronous control; the protective system integrates a fully enclosed safety net and a wide operating platform to ensure safety during high-altitude operations; and the support system uses a high-strength steel frame to ensure overall stability. The system design balances the efficiency of slipform and the economy of turning formwork, making it suitable for complex conditions such as high piers and long-span bridges.

[0024] 2. BIM-based spatial layout optimization A 1:1 BIM model of the pier and formwork system was constructed using Revit software, accurately reproducing structural dimensions and spatial relationships through 3D visualization technology. Collision detection was used to optimize formwork splicing nodes, hydraulic jacks, and frame layout, proactively identifying and resolving component interference issues to reduce on-site rework. To address the issue of air bubbles easily forming at the corners of rectangular piers, curved transition formwork was designed. This streamlined structure improves the flowability of concrete during pouring, effectively reducing surface defects. Based on the BIM model, processing drawings for formwork panels, ribs, and connectors were automatically generated, clearly defining dimensional tolerances and welding requirements, controlling processing errors to within 2 millimeters. Through the linkage between BIM and CNC machining equipment, precise formwork manufacturing was achieved, improving the overall assembly quality of the formwork and providing a reliable guarantee for subsequent construction.

[0025] 3. Structural verification based on Midas Nonlinear structural analysis of the formwork system was conducted using MidasGen software to simulate the stress state under the most unfavorable working conditions: firstly, the lateral pressure generated during concrete pouring, calculated as 48 kN / m² based on a C40 concrete slump of 180 mm; secondly, the self-weight and construction load during the formwork climbing process, with a total load considered at 2.5 kN / m². The calculation results show that the maximum deflection of the formwork panel under lateral pressure is 1.8 mm, far less than the standard allowable limit of 3 mm; the maximum force on the hydraulic jack is 120 kN, and jacks with a rated lifting capacity of 150 kN are selected, achieving a safety factor of 1.25; the stability coefficient of the scaffold uprights is 2.3, higher than the standard requirement of 1.5, meeting the strength, stiffness, and stability requirements. Through structural calculations, the reliability of the formwork system under extreme working conditions was verified, providing theoretical support for construction safety.

[0026] 4 Key Component Optimization Design The formwork panel is made of 6mm thick Q235 steel plate, with a surface roughness reduced to Ra≤6.3μm after polishing, significantly reducing concrete adhesion and improving surface quality after demolding. The ribs are made of #8 channel steel, arranged laterally at 300mm intervals to form a grid-like reinforcement structure, increasing the panel's bending stiffness by 40%. The hydraulic climbing system incorporates synchronous control technology, using a PLC controller to adjust the climbing speed of the four jacks in real time, with an error controlled within 0.5mm / s, effectively preventing formwork tilting or jamming. The safety system includes a fully enclosed flame-retardant safety net and a 1.2-meter-wide steel operating platform, surrounded by double guardrails and fall arrestors, forming a comprehensive safety protection system. The formwork connectors use a combination of high-strength bolts and pins, ensuring connection strength while facilitating quick assembly and disassembly, comprehensively improving construction efficiency and safety.

[0027] Research on construction technology of slip-over combined formwork 1. Construction process planning The construction process is rigorous and orderly, divided into six key steps. The first step is the treatment of the construction joint at the connection with the foundation cap. This requires meticulous treatment, strictly adhering to the standardized construction process of "chising, cleaning, moistening, and brushing." The quality of the construction joint is crucial to the tightness of the connection between the pier and the foundation. The second step involves the construction of the initial solid section and the chamfered section using slipform construction. First, the slipform climbing system and formwork system are professionally installed, followed by continuous concrete pouring while simultaneously raising the slipform, efficiently completing the lower 5 meters of construction. The third step is the installation of the standard section formwork. First, the inner chamfered formwork is removed, then the standard section inner formwork is installed, and the hydraulic device is carefully adjusted to ensure smooth subsequent construction. The fourth step involves concrete pouring using a pump, poured in layers, with each layer thickness strictly controlled at 300mm. During vibration, an immersion vibrator is used, and the vibration time is precisely controlled at 20-30 seconds. The fifth step is the formwork raising. After the concrete strength reaches 2.5MPa, the hydraulic system is activated to raise the entire formwork, with a single raising height of 1.2 meters. The sixth step is maintenance and acceptance, which involves water curing for at least 7 days, with a comprehensive quality inspection conducted after every 4 floors are completed. [3] .

[0028] 2 Core Construction Technology Innovations This process achieves several technological breakthroughs. Firstly, it utilizes synchronous climbing control technology. This technology, employing displacement sensors, can accurately monitor the formwork's tilt in real time. If the tilt exceeds 3mm, the PLC controller automatically adjusts the jack speed for precise correction, ensuring the formwork remains stable throughout the climbing process and significantly improving construction accuracy and safety. Secondly, it controls the timing of concrete pouring. A rebound hammer precisely tests the concrete strength, and the formwork is only lifted after the concrete strength meets design requirements, effectively preventing premature lifting that could damage the concrete surface and ensuring structural quality. Thirdly, it employs formwork joint treatment technology. High-quality rubber sealing strips are used to fill formwork gaps, and a release agent is carefully applied before pouring. These measures effectively reduce grout leakage and adhesion, resulting in a smoother concrete surface and improved project appearance and overall performance.

[0029] 3 Key Points of Construction Quality Control Construction quality control is integrated throughout the entire construction process, with specific key points at several critical stages. During formwork installation, a high-precision total station is used to calibrate the formwork position, strictly controlling the axial deviation to within 10mm to ensure accurate installation. In the concrete pouring stage, slump and pouring speed must be strictly controlled; insufficient slump or excessively fast or slow pouring speeds can lead to concrete segregation or over-vibration, affecting structural strength and durability. During formwork lifting, professional personnel carefully inspect the hydraulic system to ensure synchronized operation of all jacks, preventing deformation or damage due to asynchrony. During the curing stage, maintaining continuous moisture on the pier surface is crucial to effectively prevent cracks caused by rapid evaporation. Simultaneously, a comprehensive "three-inspection system" is established: self-inspection, mutual inspection, and handover inspection. Each process can only proceed to the next stage after passing inspection, ensuring construction quality from a systemic perspective.

[0030] Effectiveness verification study 1. Engineering Application Overview To fully verify the practical effectiveness of the slip-formwork combined with formwork construction technology, three representative rectangular high piers (Nos. 67, 68, and 86) were carefully selected in the AJLJ-02 section of the Anjing Expressway for pilot application. These three piers have significantly different heights, at 35 meters, 42 meters, and 50 meters respectively, comprehensively reflecting the applicability of this technology in the construction of high piers of varying heights. During the application process, key indicators such as construction period, concrete quality, and cost consumption were monitored comprehensively and in real time. Simultaneously, to objectively evaluate the advantages of this technology, a detailed comparison was made with traditional slip-formwork and climbing formwork techniques. [4] This method allows for accurate data acquisition of the performance of the slip-over combined formwork construction technique in actual projects, providing solid data support for subsequent technical improvements and promotion.

[0031] 2. Application Effect Analysis From the perspective of construction efficiency, the No. 86 pier was constructed using a combined slip-over and formwork system, taking only 25 days, 20 days shorter than the formwork turning process and 5 days shorter than the climbing formwork process, significantly improving construction speed and effectively shortening the project duration. Regarding concrete quality, the three pilot piers performed excellently, with surface flatness deviations strictly controlled to less than 3mm, and no scratches, misalignments, or other quality defects. The appearance quality score was over 95 points, far exceeding the 75 points of the slip-over construction. In terms of cost, each set of the slip-over and formwork system cost approximately 250,000 yuan, a 50% saving compared to the climbing formwork process. The total construction cost of the three piers was 1.7 million yuan less than that using the climbing formwork process, demonstrating a significant economic advantage. In terms of safety, no safety accidents occurred during the entire construction process, and the high-altitude operation protection compliance rate reached 100%, superior to the formwork turning process, providing reliable safety guarantees for construction personnel.

[0032] 3. Technological Improvement and Perfection Some problems were also discovered during practical application. Insufficient guiding accuracy during formwork lifting affected construction precision. After improvements were made by adding guide rails, the deviation was significantly reduced to less than 1mm. Additionally, the hydraulic system operated unstably in low-temperature environments; replacing it with low-temperature resistant hydraulic oil successfully adapted to the complex environment of large diurnal temperature variations in mountainous areas. To address these issues, the project team further optimized the technical solution, ultimately developing a comprehensive construction technical manual to provide standardized guidance for the widespread application of this technology.

[0033] Research on key technologies for a sliding-over combined formwork system for rectangular high piers of bridges has successfully overcome the limitations of traditional processes, achieving multi-dimensional improvements in construction efficiency, quality, cost, and safety. Pilot applications have validated the system's significant advantages, providing an efficient, economical, and safe solution for the construction of high-pier bridges in mountainous areas. The resulting construction manual, refined through technological improvements, provides a standardized basis for the widespread adoption of this technology. In the future, with continuous technological advancements, the sliding-over combined formwork system is expected to be applied in more bridge projects, driving the industry towards green and intelligent construction and helping my country's transportation infrastructure construction reach a new level.

[0034] The above description of the disclosed embodiments enables those skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A sliding and tilting combined formwork for rectangular high piers of bridges, characterized in that; The template consists of an outer frame (1), a hydraulic jacking system (5), and an inward-turning template (6). The hydraulic jacking system (5) consists of four sets of through-type jacks. The lower end of each through-type jack is located in the pier column. A crossbeam (7) is installed on the upper part of the through-type jack and can lift the crossbeam (7). The outer end of the crossbeam (7) is connected to the outer frame (1) through an outer formwork tie rod (2). An inner formwork tie rod (3) is installed at the lower middle part of the crossbeam (7) for connecting with the inward-turning template (6). The hydraulic jacking system (5) can lift the outer frame (1) and the inner flip template (6) together along the pier. The top surface of the outer frame (1) forms an upper operating platform (1-1), and the lower end of the outer frame (1) forms a lower operating platform (1-2). A ladder (8) is set between the upper operating platform (1-1) and the lower operating platform (1-2) to facilitate personnel to go up and down to the upper and lower operating platforms. After personnel enter the lower operating platform, it is used for the repair of the pier after jacking.

2. The bridge rectangular high pier sliding and tilting combined template according to claim 1, characterized in that; The outer frame (1) is composed of multiple segments, and its whole is located around the corresponding pier, surrounding the pier.

3. The sliding and tilting combined formwork for rectangular high piers of bridges according to claim 1, characterized in that; The inward-turning template (6) is located inside the outer frame (1).

4. The bridge rectangular high pier sliding and tilting combined template according to claim 1, characterized in that; There are two sets of crossbeams (7), and an electric control platform (4) is installed on each set of crossbeams (7).

5. The bridge rectangular high pier sliding and tilting combined template according to claim 1, characterized in that; A guardrail (9) is installed on the upper operating platform (1-1), and a railing (10) is installed on the lower operating platform (1-2).

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