Steel structure cantilever platform system for rotational flow pool open caisson construction

Abstract

The invention discloses a steel structure cantilever platform system for rotational flow pool open caisson construction, and relates to the technical field of cantilever platform systems. Comprising a plurality of overhanging main beams annularly embedded along the well wall of the open caisson, a secondary beam network installed at the tops of the main beams and arranged in the radial direction, an annular ring beam connected with the inner side ends of all secondary beams to form a closed frame, a platform bed board laid on a framework, a diagonal bracing system connected with the bottoms of the main beams and the well wall, and a safety protection system on the edge of a platform. According to the core of the method, through the design of high-position pre-burying and synchronous sinking, a platform main structure is pre-installed at the elevation higher than the underground water level when the second section of the open caisson is manufactured, and therefore a dry and stable high-altitude operation face is provided all the time in the subsequent sinking and construction process. The system fundamentally avoids the problem that a scaffold is erected in accumulated water and sludge at the bottom of a well in a traditional process, parallel working procedures are achieved, construction safety, efficiency and economical efficiency are remarkably improved, and the system is particularly suitable for deep well engineering with the high underground water level.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of cantilever platform systems, and particularly to a steel structure cantilever platform system for vortex pool caisson construction. BACKGROUND

[0002] In the field of civil construction technology, the caisson construction method is a mature and commonly used process for building deep foundations and underground structures. The core lies in first making a reinforced concrete caisson structure in the shape of a well on the ground, then excavating soil in the well, relying on the self-weight of the structure to overcome the frictional resistance of the well wall, so that the caisson gradually sinks to the designed elevation, and finally the bottom is sealed to form a stable underground space. For large vortex pool and other deep caisson projects, the existing technology generally adopts the operation mode of "segmental production and segmental sinking". Specifically, the construction of the internal support system follows an inherent process: after the caisson is completely produced in segments and sunk into place in segments, the construction personnel first need to forcibly drain and mechanically dredge the well bottom to eliminate the deep accumulated water and floating mud accumulated due to high underground water level and large seepage. After the base is processed to be relatively flat and solid, a full-frame steel pipe scaffold can be erected on it. This scaffold system serves as the core support carrier and high-altitude work platform for the subsequent concrete bottom sealing, pool wall and internal structure construction.

[0003] However, the prior art solution has many significant defects that are difficult to overcome in actual application, especially in the case of high water level and deep water working conditions. Firstly, the working environment is extremely harsh and has significant safety hazards. After the caisson sinks through the groundwater level, the bottom of the caisson becomes a catchment area, and even if continuous drainage is carried out, it is often in a slippery and muddy state. On this basis, the scaffold is erected, and the stand base is prone to slip and sink, resulting in poor overall stability of the frame body, and it is extremely inconvenient for personnel to work and materials to be transported on the slippery frame body, with a high risk of falling and even partial or even total collapse of the frame body. Secondly, the long construction period is caused by the disconnection of the working procedures. Because the erection of the internal scaffold must be started after the caisson is completely sunk into place and the drainage and bottom cleaning are completed, a serious operation gap is caused between the two key working procedures of "sinking" and "internal structure construction". This serial operation mode not only causes a large amount of idle waiting of manpower and machinery, but also directly slows down the overall construction progress, and the total construction period is thus greatly extended. Thirdly, the construction cost is significantly increased due to a number of additional operations. Continuous dewatering, water pumping and drainage, and mechanical dredging for creating working conditions require the investment of special equipment and a large amount of labor, resulting in high direct costs. At the same time, the low working efficiency in the harsh environment further increases the cost of labor and machinery. Fourthly, the final construction quality is at risk. The erection of the scaffold on the wet and soft, uneven bottom of the caisson makes it difficult to accurately control the verticality, spacing and elevation of the upright rods, which can easily cause deviations in the support system. Based on this inaccurate support system, the elevation control, cross-sectional size and concrete density of the bottom sealing concrete pouring and fine internal structure construction are difficult to guarantee, which poses a potential risk to the long-term safe use of the structure. SUMMARY

[0004] The purpose of the present disclosure is to provide a steel structure cantilever platform system for construction of a vortex pool caisson to solve the technical problems in the prior art.

[0005] To achieve the above-mentioned purpose, the present disclosure adopts the following technical solutions: The present disclosure provides a steel structure cantilever platform system for construction of a vortex pool caisson, which comprises a well wall and further comprises: A plurality of cantilever main beams are arranged in a ring around the caisson well wall and are horizontally embedded in the caisson well wall and cantilevered towards the center of the caisson; A network of secondary beams is installed on the cantilever main beams, which comprises a plurality of secondary beams arranged radially along the caisson, and the secondary beams are fixedly connected to the top of the cantilever main beams; A ring-shaped ring beam is fixedly connected to the plurality of secondary beams, which is installed at one end of the secondary beams pointing to the center of the caisson, and the ring-shaped ring beam forms a ring-shaped closed frame with the network of secondary beams; A platform deck is laid and fixed on the cantilever main beams, the network of secondary beams and the ring-shaped ring beam; a bottom bracing system comprising a plurality of bracings, one end of the bracings being connected with the bottom of the corresponding cantilever girder, and the other end being connected with the caisson wall; a safety protection system installed on the edge of the platform deck.

[0006] Optionally, the cantilever girder is made of hot-rolled H-shaped steel, and the secondary beam and the bracing are made of hot-rolled channel steel.

[0007] Optionally, the two ends of the secondary beam are respectively fully welded with the top surface of the cantilever girder and the ring beam.

[0008] Optionally, the ring beam is formed by connecting a plurality of sections of profiles through beveling welds to form a ring-shaped closed frame.

[0009] Optionally, the platform deck is a patterned steel plate, which is fixed with the secondary beam network through spot welding.

[0010] Optionally, one end of the bracing is welded with the lower flange of the cantilever girder, and a connecting plate is pre-buried in the caisson wall, and the other end of the bracing is welded with the connecting plate.

[0011] Optionally, the included angle between the bracing and the cantilever girder is °-°.

[0012] Optionally, the safety protection system comprises a plurality of guardrails fixedly installed on the platform deck, a foot plate fixedly installed between two adjacent guardrails, and a close-mesh safety net, and a plurality of crossbars are fixedly installed on the two adjacent guardrails.

[0013] Optionally, the inner side cantilever end of the cantilever girder is pre-provided with a connecting piece for connecting with a scaffold vertical rod.

[0014] Optionally, the installation elevation of the cantilever platform system is higher than the underground water level, and the distance between the final position after sinking and the design bottom sealing elevation of the caisson makes the scaffold height of the platform erected to the bottom sealing work surface within the conventional construction range.

[0015] Compared with the prior art, the beneficial effects of the present disclosure are that the platform pre-buried and the caisson are made synchronously, and serve as the operation base surface for subsequent well wall heightening, so that the processes seamlessly connect. Compared with the traditional process which must wait for the caisson to be sunk to the bottom before draining, dredging and erecting the scaffold, the total construction period is expected to be shortened by more than 30%, but the high cost of continuous drainage, large-scale dredging and mechanical station is completely saved, at the same time, the operation efficiency in dry environment is greatly improved, the labor cost is reduced, and the comprehensive cost has obvious advantages.

[0016] Further, the high risk of personnel working in deep water and muddy environment is fundamentally eliminated, and a dry, flat and stable working environment is provided for the processes such as steel binding, formwork erection and concrete pouring, so that the construction safety and the quality of engineering entity are greatly improved. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the specific embodiments of the present disclosure or the prior art, the drawings needed to be used in the specific embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present disclosure, and other drawings can be obtained by those skilled in the art without creative labor.

[0018] In the drawings: Figure 1 Structure diagram of steel structure cantilever platform system Figure 1 ; Figure 2 Structure diagram of steel structure cantilever platform system Figure 2 ; Figure 3 Structure diagram of steel structure cantilever platform system Figure 3 .

[0019] In the drawings: 1, well wall; 2, cantilever main beam; 3, secondary beam; 4, ring beam; 5, platform deck; 6, inclined brace; 7, guardrail; 8, footboard; 9, safety net; 10, crossbar. DETAILED DESCRIPTION

[0020] The technical solutions of the present application will be described in detail below with reference to the drawings. Obviously, the described embodiments are some of the embodiments of the present application, not all of the embodiments.

[0021] The components of the embodiments of the present application generally described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed application, but only represents selected embodiments of the application.

[0022] Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the present application.

[0023] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", "third" are only for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0024] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0025] Embodiment one, please refer to Figures 1 to 3 The present disclosure provides a steel structure cantilever platform system for whirlpool well sinking construction, which comprises a well wall 1, and further comprises a plurality of cantilever main beams 2 arranged in a ring shape along the well wall 1 of the sinking well, the cantilever main beams 2 are horizontally embedded in the well wall 1 of the sinking well and cantilevered to the center of the sinking well, the cantilever main beams 2 adopt hot-rolled H-shaped steel, preferably HN350x175x7x11 steel, to meet the requirements of bending and shear bearing capacity, and the inner side of the cantilevered end of the cantilever main beam 2 is provided with a connecting piece for connecting with the scaffold upright rod, such as a steel plate ear plate with bolt holes, which enables the subsequently erected scaffold upright rod to form a rigid connection with the platform main structure, greatly enhancing the overall lateral stability of the high-altitude operation system, and the core design principle is high pre-embedding: the cantilever main beams 2 are installed synchronously when the second well wall of the sinking well is made, and the top surface elevation thereof needs to be determined according to the total depth of the sinking well and the underground water level, and the core principle is to ensure that the installation and operation surface is higher than the underground water level, fundamentally avoiding the condition of well bottom water and mud, and providing a dry and stable foundation for subsequent operation.

[0026] Please refer to Figures 1 to 3The steel structure cantilever platform system in this embodiment also includes a secondary beam network installed on the cantilever main beam 2. The secondary beam network includes multiple secondary beams 3 arranged radially along the caisson. The secondary beams 3 are fixedly connected to the top of the cantilever main beam 2. The secondary beams 3 are made of hot-rolled channel steel, preferably 12.6a channel steel. The layout density of the secondary beam network is a key parameter. The spacing between the secondary beams should not be greater than 600mm to ensure that the platform deck 5 above does not have obvious deflection. Each cantilever main beam 2 is not connected to only one secondary beam, but multiple secondary beams are welded at equal intervals along the length of its cantilever section to form a many-to-many grid skeleton. This design can evenly distribute the platform load to multiple cantilever main beams 2, effectively avoiding stress concentration.

[0027] A ring beam 4 is fixedly connected to multiple secondary beams 3. The ring beam 4 is installed at the end of the secondary beam 3 pointing towards the center of the caisson. The ring beam 4 is made of multiple sections of profile, preferably 14a hot-rolled channel steel, connected by oblique welds, such as full welds at 45°, to form a closed ring frame. The ring beam 4 clamps the inner ends of all radial secondary beams together to form a highly statically indeterminate rigid planar frame, which significantly improves the integrity and deformation resistance of the platform plane and avoids instability due to excessive local stress.

[0028] The two ends of the secondary beam 3 are fully welded to the top surface of the cantilever main beam 2 and the ring beam 4, respectively. The specific connection method between the secondary beam 3 and the main beam 2 is as follows: the channel steel of the secondary beam 3 should be placed upside down with the opening facing down, so that the two sides of its web plate are fully welded to the top surface of the upper flange of the H-shaped steel of the cantilever main beam 2, with a welding height of ≥6mm. This connection method realizes the most direct and efficient transfer of vertical load.

[0029] Please see Figures 1 to 3 The steel structure cantilever platform system also includes platform slabs 5 laid and fixed on the cantilever main beam 2, secondary beam network and ring beam 4. The platform slabs 5 are made of patterned steel plates, preferably 4mm thick Q235 material. They are fixed to the secondary beam network by spot welding. The platform slabs 5 are spot welded to the top surface of the secondary beam 3. The gap between the plates should be controlled to be no more than 5mm to prevent tools from falling. The patterned steel plates provide a non-slip working surface. They work together with the dense secondary beam network below to ensure the flatness and safety of the platform surface.

[0030] Please see Figures 1 to 3The steel structure cantilever platform system also includes a bottom bracing system, which consists of multiple braces 6. One end of each brace 6 is connected to the bottom of the corresponding cantilever main beam, and the other end is connected to the caisson wall 1. The braces 6 are made of hot-rolled channel steel, preferably 12.6a channel steel. One end of each brace 6 is welded to the lower flange of the cantilever main beam 2. A connecting plate, preferably 10mm thick Q235 steel plate, is pre-embedded in the caisson wall 1. The other end of each brace 6 is welded to the connecting plate. The clamp between the brace and the cantilever main beam 2... The angle is 45°-60°, preferably 50°±5°. The bottom diagonal bracing system is a key component to ensure the stability of the root of the cantilever main beam. The diagonal bracing 6 and the cantilever main beam 2 and the embedded plate of the well wall need to be fully welded together with a welding height of ≥8mm to form a stable triangular support. This design can effectively convert part of the bending moment at the root of the cantilever main beam 2 into the axial force of the diagonal bracing 6 and transfer it to the solid well wall 1, thereby greatly reducing the bending moment and deflection of the cantilever main beam 2 itself, which is an important guarantee for the safety of the platform.

[0031] Please see Figures 1 to 3 The steel structure cantilever platform system also includes a safety protection system installed on the edge of the platform deck 5. This system comprises multiple guardrails 7 fixedly installed on the platform deck 5, toe boards 8 fixedly installed between adjacent guardrails 7, and a dense safety net 9. Multiple horizontal bars 10 are fixedly installed on adjacent guardrails 7. The safety protection system constitutes a fully enclosed working environment. The guardrails 7 are at least 1.2m high, with a spacing of no more than 1.5m between them. The toe boards 8 are at least 180mm high. The dense safety net 9 has a mesh density of ≥2000 meshes / 100cm², and is fully hung on the outside of the guardrails and securely tied. A horizontal safety net must also be laid between the inner side of the platform and the well wall to prevent the risk of personnel and objects falling.

[0032] Working principle: Through the collaborative design of high-level pre-embedded cantilevered main beam 2, building a gridded secondary beam 3 framework, setting bottom diagonal bracing 6 and ring beam 4, laying anti-slip panels and fully enclosed protection, a dry, stable and safe aerial work platform is creatively constructed in advance during the caisson sinking process. This allows the platform to sink synchronously with the caisson, realizing the parallel process of caisson sinking - platform construction - subsequent construction. It fundamentally solves a series of problems caused by traditional processes, such as harsh working environment, long construction period, poor safety and high cost, due to the erection of scaffolding in the water-filled environment at the bottom of the well. In addition, all welding nodes must be inspected according to specifications. After the platform is assembled, a static load test of 1.2 times the design load is required to check the deflection. The deflection of the main beam is ≤L / 250, where L is the cantilever length. Overloading is strictly prohibited during use, and a dedicated safety officer is assigned to monitor the process.

[0033] Example 2, as Figures 1 to 3 As shown, based on Embodiment 1, the implementation method of the steel structure cantilever platform system will be further described in detail: Given the specific working conditions and key system parameters of this project, the bottom sealing elevation of the vortex pool caisson in this project is -24.191m. The groundwater level at the site is relatively high, above -8.000m. If the traditional well bottom scaffolding process is adopted, it will face the problem of extremely deep water accumulation and dredging. This system solves this core contradiction through precise elevation positioning.

[0034] The platform elevation was determined. After comprehensive calculation, the top elevation of the platform was set at -8.000 meters. This elevation is higher than the groundwater level, ensuring that the platform assembly and subsequent work surfaces are absolutely dry. At the same time, after the platform is sunk into place, it will be located about 16 meters below the wellhead. The scaffolding erected from this point to the bottom sealing elevation of -24.191 meters will be about 16 meters high, which is within the safe erection range of conventional scaffolding. No special reinforcement is required, achieving one-time setup and full coverage.

[0035] For the layout and selection of the main beams, considering the diameter of the caisson in this project, in order to form a continuous working surface, 20 HN350×175×7×11 hot-rolled H-beams are evenly arranged around the caisson wall as cantilever main beams 2. The bearing capacity of the main beams is calculated based on a uniformly distributed load of not less than 3kN / m², including the self-weight of the scaffolding and the construction live load, to ensure a redundancy coefficient ≥1.2. The length of the outer anchorage section of the main beam is not less than 1.2m to ensure the reliability of the anchorage in the concrete, and the inner cantilever section is uniformly 1.8m to form an effective circular working surface with a width of 1.5m.

[0036] Secondary beam network and ring beam: Secondary beam 3 is made of 12.6a channel steel, with the opening facing down and fully welded to the upper flange of the main beam. The radial spacing is strictly controlled at 600mm to ensure that the 4mm thick patterned steel plate 5 has the required deflection when bearing load. The ring beam 4 is made of 14a channel steel in sections. All joints are fully welded at 45° to form a seamless closed ring, effectively tightening the inner ends of all secondary beams.

[0037] The specific workflow of this system is as follows: Step 1: Preliminary construction preparation and construction of the first section of the caisson. First, excavate a 3.5m deep pilot pit and provide support. Then, tie the reinforcing bars, set up the formwork, and pour concrete for the first section of the caisson, which is about 3-4m high. Curing is carried out until the design strength is above 75%. Step 2: Construction of the second section of the caisson and pre-embedding of the main beam system. When extending the reinforcement of the second section of the caisson wall, 20 connecting plates of cantilever main beam 2 and diagonal brace 6 are pre-embedded at an elevation of -8.000 meters. The level of the main beam needs to be calibrated with a level, and the deviation should be controlled within 3mm / m. Temporary support and fixation are required, followed by concrete pouring and curing. Step 3: With the main beam sinking and platform assembly, the first and second sections of the caisson are sunk as a whole, using a layered, balanced excavation method within the caisson to control the sinking inclination to ≤1%. Sinking continues until the area near the -8,000 meter elevation is completely dry. Then, platform assembly is efficiently completed in a dry environment: welding secondary beam 3 and ring beam 4 → spot welding and laying patterned steel plate 5 → welding bottom channel steel diagonal bracing 6, with the included angle controlled at 50°±5° → installing guardrails 7, toe boards 8, and dense safety netting 9. Step 4: Platform reuse and subsequent caisson construction. The platform is put into use immediately, and scaffolding is erected on it to complete the extension and pouring of the third section of the caisson wall. After curing, the caisson is lowered a distance, and the cycle of scaffolding erection, extension, and lowering is repeated until the caisson reaches the design elevation of -24.191m. This process realizes the parallel construction of the caisson sinking and the superstructure. Step 5: Final bottom sealing operation. After the caisson is in place, a full-span scaffold is erected directly from the stable cantilever platform to the bottom of the caisson for final bottom cleaning, pouring of bottom sealing concrete and internal structure construction. This completely avoids the struggle in mud and water that is common in traditional processes.

[0038] In this embodiment, all incoming steel sections and steel plates must have their quality assurance certificates verified and undergo sampling inspection. Welding must be performed by certified welders, welding rods must be dried, and the main load-bearing welds such as main beams, secondary beams, and diagonal braces must undergo 100% visual inspection. At least 10% of the nodes must be randomly selected for ultrasonic testing to ensure that there are no defects such as cracks or lack of fusion.

[0039] After the platform is assembled, a static load test must be conducted. A counterweight equivalent to 1.2 times the design live load, such as sandbags, is evenly stacked on the platform. After 24 hours of static loading, the deflection at 1.8m from the cantilever end of the main beam is measured. The value must not exceed 7.2mm, L / 250, L=1.8m. Only after the verification is passed can the platform be put into subsequent use.

[0040] Full-process safety monitoring: A dedicated safety officer shall be assigned to supervise the use of the platform. Overloading is strictly prohibited. The density of workers shall be ≤2 people / ㎡. During the sinking of the caisson, no personnel shall be allowed to stay under the platform. Independent guardrails must be installed around the wellhead.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this disclosure, and are not intended to limit them. Although this disclosure has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this disclosure.

Claims

1. A steel structure cantilever platform system for the construction of a vortex pool caisson includes a well wall (1), characterized in that, Also includes: Multiple cantilevered main beams (2) are arranged circumferentially along the caisson wall (1). The cantilevered main beams (2) are horizontally embedded in the caisson wall (1) and cantilevered out towards the center of the caisson. The secondary beam network installed on the cantilever main beam (2) includes multiple secondary beams (3) arranged radially along the caisson, and the secondary beams (3) are fixedly connected to the top of the cantilever main beam (2); A ring beam (4) is fixedly connected to multiple secondary beams (3). The ring beam (4) is installed at one end of the secondary beam (3) pointing towards the center of the caisson. The ring beam (4) makes the secondary beam network form a ring closed frame. Platform slabs (5) are laid and fixed on the cantilever main beam (2), the secondary beam network and the ring beam (4); Bottom bracing system, the bottom bracing system includes multiple braces (6), one end of the brace (6) is connected to the bottom of the corresponding cantilever main beam, and the other end is connected to the caisson wall (1); Safety protection system installed on the edge of the platform deck.

2. The steel structure cantilever platform system for cyclone pool caisson construction according to claim 1, characterized in that: The cantilever main beam (2) is made of hot-rolled H-beam, and the secondary beam (3) and the diagonal brace (6) are made of hot-rolled channel steel.

3. The steel structure cantilever platform system for cyclone pool caisson construction according to claim 2, characterized in that: The two ends of the secondary beam (3) are fully welded to the top surface of the cantilever main beam (2) and the annular ring beam (4), respectively.

4. The steel structure cantilever platform system for cyclone pool caisson construction according to claim 3, characterized in that: The ring beam (4) is formed by connecting multiple sections of profiles through oblique welds to form a closed ring frame.

5. The steel structure cantilever platform system for cyclone pool caisson construction according to claim 4, characterized in that: The platform slab (5) is a patterned steel plate, which is fixed to the secondary beam network by spot welding.

6. The steel structure cantilever platform system for cyclone pool caisson construction according to claim 5, characterized in that: One end of the diagonal brace (6) is welded to the lower flange of the cantilever main beam (2), a connecting plate is pre-embedded in the well wall (1), and the other end of the diagonal brace (6) is welded to the connecting plate.

7. The steel structure cantilever platform system for cyclone pool caisson construction according to claim 6, characterized in that: The angle between the diagonal brace and the cantilever main beam (2) is 45°-60°.

8. The steel structure cantilever platform system for cyclone pool caisson construction according to claim 7, characterized in that: The safety protection system includes multiple guardrails (7) fixedly installed on the platform deck (5), toe boards (8) fixedly installed between two adjacent guardrails (7), and a dense safety net (9). Multiple crossbars (10) are fixedly installed on two adjacent guardrails (7).

9. The steel structure cantilever platform system for cyclone pool caisson construction according to claim 8, characterized in that: The inner cantilever end of the cantilevered main beam (2) is pre-fitted with a connector for connecting to the scaffold uprights.

10. The steel structure cantilever platform system for cyclone pool caisson construction according to claim 9, characterized in that: The installation elevation of the cantilever platform system is higher than the groundwater level, and the distance between its final position after sinking and the design bottom sealing elevation of the caisson ensures that the scaffolding height from the platform to the bottom sealing work surface is within the normal construction range.

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