Lifting type construction platform for engineering

The design of the adjusting rod and support plate solves the problem of fitting the construction platform to the curved wall, ensuring the safety of the workers and the stability of the platform, and is suitable for curved wall construction in building construction.

CN223497520UActive Publication Date: 2025-10-31张斌 +2
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Patent Information

Application Number
CN202423044184.X
Authority / Receiving Office
CN · China
Patent Type
Utility models(China)
Current Assignee / Owner
Filing Date
2024-12-10
Publication Date
2025-10-31
Estimated Expiration
2034-12-10

AI Technical Summary

Technical Problem

When constructing curved walls, some parts of the existing construction platform are far from the wall, requiring workers to extend their bodies outside the platform, posing a safety hazard of falling from height.

Method used

The platform employs an adjustable rod and support plate structure. The position of the adjustable rod is adjusted according to the curvature of the wall to ensure that the edge of the support plate fits against the wall. Combined with an electric telescopic rod and lifting mechanism, the stability and safety of the platform are ensured.

Benefits of technology

This design allows the construction platform to fit snugly against the curved wall, eliminating the need for workers to extend beyond the platform and improving construction safety and platform stability.

✦ Generated by Eureka AI based on patent content.

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Abstract

The utility model relates to a lifting type construction platform for engineering. Comprising a main supporting rod, a first connecting rod, an adjusting rod, a second connecting rod, an upper side chain plate and a supporting plate. First connecting rods are arranged on the main supporting rod at intervals, and the first connecting rods are in sliding connection with the main supporting rod; an adjusting rod is installed on the first connecting rod in a sliding mode, and the adjusting rod and the main supporting rod are roughly perpendicular to each other. The two ends of each adjusting rod are each provided with a second connecting rod. The upper ends of every two adjacent second connecting rods located on the same side are hinged to the two ends of an upper side chain plate correspondingly. A supporting plate is laid on the upper side chain plate and extends in the extending direction of the adjusting rod. According to the utility model, the edge radian of the construction platform is adjusted to be the same as the bending radian of the wall body, so that the edge of the construction platform can be in full contact with the arc-shaped wall body, a worker does not need to stretch the body out of the platform when working on the construction platform, and the construction safety of the worker is effectively ensured.
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Description

Technical Field

[0001] This utility model relates to the field of construction equipment technology, and in particular to a lifting construction platform for engineering projects. Background Technology

[0002] Construction platforms are a new type of high-altitude work equipment that can replace traditional scaffolding, reduce the labor intensity of workers, improve work efficiency, and be reused. They are widely used in high-altitude operations such as exterior wall construction, curtain wall installation, insulation construction, and maintenance and cleaning.

[0003] Construction platforms mainly consist of a lifting mechanism and a platform. The platform is generally square. Due to the diverse shapes of existing buildings to be constructed or renovated, when a square platform is raised to the construction position, there are often situations where parts of the platform are far from the construction position. For example, when the exterior wall surface is concave, when the platform is raised to the construction position, the left and right ends of the platform are basically in contact with the exterior wall, but there is still a large distance between the middle of the platform and the exterior wall. When workers are working, they need to extend part of their bodies outside the platform, which poses a significant safety hazard. Summary of the Invention

[0004] To address or partially address the problems existing in related technologies, this utility model provides a lifting construction platform for engineering applications, aiming to improve the safety of workers during construction.

[0005] This utility model provides a lifting construction platform for engineering, including a main support rod, a first connecting rod, an adjusting rod, a second connecting rod, an upper chain plate, and a support plate;

[0006] The first connecting rod is provided at intervals on the main support rod, and the first connecting rod is slidably connected to the main support rod;

[0007] The adjusting rod is slidably mounted on the first connecting rod, and the adjusting rod is set approximately perpendicular to the main support rod.

[0008] Each of the adjusting rods is provided with a second connecting rod at both ends;

[0009] The upper ends of two adjacent second connecting rods located on the same side are respectively hinged to both ends of an upper chain plate;

[0010] The support plate is laid on the upper chain plate, and the support plate extends along the extension direction of the adjusting rod.

[0011] In some designs, the first connecting rod, located in the middle position, is fixedly connected to the main support rod;

[0012] Each of the remaining first connecting rods is provided with an electric telescopic rod, and the telescopic part of the electric telescopic rod is fixedly connected to its corresponding adjusting rod.

[0013] In some embodiments, the end of the adjusting rod is hinged to the middle of the second connecting rod, and the lower ends of two adjacent second connecting rods on the same side are respectively hinged to the two ends of a lower chain plate.

[0014] In some embodiments, the support plate includes an upper plate, a lower plate, a connecting plate, a movable plate, and a spring;

[0015] The upper plate and the lower plate are arranged parallel to each other and are fixedly connected by a connecting plate extending along the length direction of the support plate, thereby forming a groove between the upper plate and the lower plate. One end of the movable plate is embedded in the groove and is connected to the connecting plate by a spring.

[0016] The lower plate is hinged to the upper chain plate.

[0017] In some designs, the movable plate has a box-like structure with an open lower end. A limiting screw is threaded onto the lower plate, and the limiting screw extends into the groove and is located on the outside of the end of the movable plate that extends into the groove.

[0018] In some designs, an extension rod is slidably mounted on one end of the movable plate near the construction location, and a debris blocking plate is laid on the extension rod.

[0019] In some embodiments, the aforementioned engineering lifting construction platform further includes a lifting mechanism, which includes a base, a first upright, a movable frame, and a drive chain;

[0020] Two first uprights are arranged opposite each other on the base, and inwardly recessed guide grooves are provided on the opposite sides of the two first uprights.

[0021] The two sides of the movable frame are respectively embedded in the guide grooves of the two first uprights, and the movable frame is fixedly connected to the main support rod through the connecting rod;

[0022] The upper end of the first upright is provided with a first drive sprocket, which is driven to rotate by a first drive motor mounted on the first upright. The lower end of the first upright is provided with a second drive sprocket. The first drive sprocket and the second drive sprocket are connected by a drive chain, and one link of the drive chain is fixedly connected to the movable frame.

[0023] In some designs, the first upright includes an outer tube and an inner insert rod; the inner insert rod is slidably installed inside the outer tube.

[0024] The top of the inner rod is also provided with a chain tensioning mechanism, and the drive chain passes around the chain tensioning mechanism.

[0025] In some designs, the top of the outer tube is provided with a directional sprocket, the bottom of the inner insert rod is provided with a follower sprocket, and the drive chain passes sequentially around the first drive sprocket, the second drive sprocket, the directional sprocket, the follower sprocket, and the chain tensioning mechanism.

[0026] The second drive sprocket is driven to rotate by the second drive motor; a brake is provided on the rotating shaft of the follower sprocket.

[0027] In some embodiments, the chain tensioning mechanism includes an elastic telescopic rod fixedly installed on the upper end of the first upright. The elastic telescopic rod is arranged in a direction away from the first drive sprocket. A first redirecting wheel is rotatably installed at the end of the elastic telescopic rod away from the first drive sprocket. A second redirecting wheel is provided below the elastic telescopic rod. The drive chain forms a U-shape after passing around the first redirecting wheel and the second redirecting sprocket.

[0028] The technical solution provided by this utility model can include the following beneficial effects:

[0029] When using the construction platform described in this utility model to construct curved walls, the position of the adjusting rod can be adjusted by sliding the adjusting rod according to the curvature of the wall, so that the line connecting the ends of the adjusting rod is parallel to the curvature of the wall, thereby allowing the edge of the support plate laid on the adjusting rod to fit against the wall. When workers work on the construction platform, they do not need to extend their bodies outside the platform, effectively ensuring the safety of the workers.

[0030] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit the present invention. Attached Figure Description

[0031] The above and other objects, features and advantages of the present invention will become more apparent from the accompanying drawings, in which like reference numerals generally represent like parts.

[0032] Figure 1 This is a structural schematic diagram of the construction platform shown in an embodiment of the present utility model;

[0033] Figure 2 yes Figure 1 A schematic diagram of the structure after removing the support plate;

[0034] Figure 3 This is another structural schematic diagram of the construction platform shown in this embodiment of the utility model;

[0035] Figure 4 This is another structural schematic diagram of the construction platform shown in this embodiment of the utility model;

[0036] Figure 5 This is a schematic diagram of the structure of the support plate shown in an embodiment of the present invention;

[0037] Figure 6 This is a schematic diagram showing the connection between the platform and the lifting mechanism in an embodiment of this utility model;

[0038] Figure 7 This is a schematic diagram of the lifting mechanism shown in an embodiment of the present invention;

[0039] Figure 8 This is a transmission schematic diagram of the driving part of the lifting mechanism shown in an embodiment of the present utility model;

[0040] Figure 9 This is another transmission schematic diagram of the driving part of the lifting mechanism shown in this embodiment of the utility model;

[0041] Figure label:

[0042] 1. Main support rod; 2. First connecting rod; 21. Electric telescopic rod; 3. Adjusting rod; 4. Second connecting rod; 5. Upper chain plate; 51. Lower chain plate; 6. Support plate; 61. Upper plate; 62. Lower plate; 63. Connecting plate; 64. Movable plate; 65. Spring; 66. Limiting screw; 67. Extension rod; 7. Lifting mechanism; 71. Base; 72. First upright; 721. Outer tube; 722. Inner rod; 73. Moving frame; 74. Drive chain; 75. First drive motor; 76. First drive sprocket; 77. Second drive sprocket; 78. Chain tensioning mechanism; 79. Directional sprocket; 80. Follower sprocket. Detailed Implementation

[0043] Embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. While embodiments of the present invention are shown in the drawings, it should be understood that the present invention may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present invention will be more thorough and complete, and will fully convey the scope of the present invention to those skilled in the art.

[0044] When using a lifting construction platform to construct curved exterior walls, the platform is roughly oriented in one direction. As a result, part of the platform will be in contact with the wall on the side closest to it, while the other part will be far away from the wall. When constructing the part of the wall that is far from the platform, workers need to extend their bodies out of the platform, which poses a safety hazard of falling from a height and greatly affects the safety of the workers.

[0045] To address the aforementioned technical problems, Example 1 is provided:

[0046] Please see Figure 1 and Figure 2 This utility model provides an engineering lifting construction platform, including a main support rod 1, a first connecting rod 2, an adjusting rod 3, a second connecting rod 4, an upper chain plate 5, and a support plate 6; the main support rod 1, the first connecting rod 2, and the adjusting rod 3 are all made of steel pipes with a square cross-section, and can be made of other shapes such as circular cross-section.

[0047] The first connecting rod 2 has two through holes with roughly perpendicular extension directions. The two through holes are staggered vertically. Multiple first connecting rods 2 are provided and spaced apart on the main support rod 1. Specifically, the main support rod 1 passes through one of the through holes, thereby slidably connecting the first connecting rod 2 and the main support rod 1. The adjusting rod 3 passes through the other through hole, thereby slidably installing the adjusting rod 3 on the first connecting rod 2, and making the adjusting rod 3 roughly perpendicular to the main support rod 1.

[0048] Each adjusting rod 3 has a second connecting rod 4 extending vertically upward at both ends; the upper ends of two adjacent second connecting rods 4 on the same side are respectively hinged to the two ends of an upper chain plate 5, so that the two adjacent upper chain plates 5 can rotate relative to each other, thereby adjusting the curvature of the strip support structure composed of the upper chain plates 5.

[0049] A support plate 6 is laid on the upper chain plate 5. The support plate 6 extends along the extension direction of the adjusting rod 3, and the upper side of the support plate 6 is the range of movement for the staff.

[0050] When using the construction platform described in this utility model to construct a curved wall, the position of the adjusting rod 3 can be adjusted by sliding the adjusting rod 3 according to the curvature of the wall, so that the line connecting the ends of the adjusting rod 3 is parallel to the curvature of the wall, thereby allowing the edge of the support plate 6 laid on the adjusting rod 3 to fit against the wall. When workers are working on the construction platform, they do not need to extend their bodies outside the platform, effectively ensuring the safety of the workers. Example

[0051] Based on Example 1, such as Figure 3 As shown, in this embodiment, the first connecting rod 2 located in the middle position is fixedly connected to the main support rod 1, thereby concentrating the components such as the first connecting rod 2 and the adjusting rod 3 in the middle position of the main support rod 1, effectively preventing these components from detaching from the main support rod 1 and causing the platform to collapse.

[0052] Each of the other first connecting rods 2 is provided with an electric telescopic rod 21. The telescopic part of the electric telescopic rod 21 is fixedly connected to its corresponding adjusting rod 3. When the electric telescopic rod 21 extends, it drives the adjusting rod 3 to move, thereby adjusting the position of the adjusting rod 3. At the same time, the electric telescopic rod 21 itself also plays the role of locking the position of the adjusting rod 3, effectively ensuring the stability of the platform during use. Example

[0053] Based on Embodiment 1 or Embodiment 2, such as Figure 4 As shown, in this embodiment, the end of the adjusting rod 3 is hinged to the middle of the second connecting rod 4, and the lower ends of two adjacent second connecting rods 4 on the same side are respectively hinged to the two ends of the lower chain plate 51. The second connecting rod 4, the upper chain plate 5, and the lower chain plate 51 form a rectangular structure. Compared with the structure of only the upper chain plate 5 in the embodiment, the structure is more stable. At the same time, when one of the adjusting rods 3 breaks, the adjacent chain plate assembly can provide certain support, and the broken part will not collapse, thus improving the safety of the platform.

[0054] To further enhance the stability of the structure, diagonal braces are provided between the upper chain plate 5 and the lower chain plate 51, which correspond to each other. Example

[0055] Based on any of the above embodiments, such as Figure 5 As shown, in this embodiment, the support plate 6 includes an upper plate 61, a lower plate 62, a connecting plate 63, a movable plate 64, and a spring 65. The upper plate 61 and the lower plate 62 are arranged parallel to each other and are fixedly connected by the connecting plate 63 extending along the length direction of the support plate 6, thereby forming a groove between the upper plate 61 and the lower plate 62. One end of the movable plate 64 is embedded in the groove. One end of the spring 65 is fixedly connected to the end of the fixed plate embedded in the groove, and the other end is fixedly connected to the connecting plate 63, thereby connecting the spring 65 to the connecting plate 63. The springs 65 are arranged at intervals along the length direction of the support plate 6. With this arrangement, the overall width of the support plate 6 can be adjusted, or the width of one end of the support plate 6 can be adjusted. Specifically, if the movable plate 64 is embedded deeper in the groove, the overall width of the support plate 6 can be reduced, and vice versa. If one end of the movable plate 64 is embedded deeper and the other end is embedded less, the support plate 6 can be made to be fan-shaped, thus allowing the width of one end of the support plate 6 to be adjusted.

[0056] The lower plate 62 is hinged to the upper chain plate 5, thereby connecting the support plate 6 and the upper chain plate 5 into one unit. When the adjusting rod 3 moves, causing the support plate 6 to bend as a whole, the support plate 6 can be adjusted adaptively by utilizing its own width adjustment characteristic, making it more convenient to use. Furthermore, there are certain steps on the upper surface of the upper plate 61 and the upper surface of the movable plate 64, which increases the surface friction of the support plate 6, making it less likely for workers to slip when working on the support plate 6, thus improving the safety of workers.

[0057] Guardrails can be installed around the support plate 6 to prevent workers from falling during operation, thus further improving the safety of workers during construction. Example

[0058] Based on Example 4, such as Figure 5 As shown, in this embodiment, the movable plate 64 has a box-shaped structure with an open lower end. A limiting screw 66 is threaded onto the lower plate 62. The limiting screw 66 extends into the slide groove and is located on the outside of the end of the movable plate 64 that extends into the slide groove, thereby limiting the extension range of the movable plate 64. This effectively prevents the movable plate 64 from sliding out of the slide groove, thus avoiding the technical problem of the support plate 6 disintegrating. Example

[0059] Based on Example 5, such as Figure 5 As shown, in this embodiment, a square hole is provided at one end of the movable plate 64 near the construction position. The hole is located near the top of the movable plate 64. One end of the extension rod 67 is inserted into the hole. The inner top surface of the movable plate 64 abuts against the inserted end of the extension rod 67, thereby forming a sliding connection with the movable plate 64. A debris blocking plate is laid on the extension rod 67.

[0060] During construction, the extension rod 67 can be pulled outward and placed directly against the wall being constructed. Then, a debris blocking board can be laid on the extension rod 67 to effectively prevent mortar from falling downward during wall construction, thus improving construction safety. Example

[0061] Based on any of the above embodiments, such as Figure 6 and Figure 7 As shown, in this embodiment, an engineering lifting construction platform further includes a lifting mechanism 7. The lifting mechanism 7 is used to drive the platform described in the above embodiment to move up and down. The lifting mechanism 7 includes a base 71, first uprights 72, a moving frame 73, and a drive chain 74. Two first uprights 72 are arranged opposite to each other on the base 71, and guide grooves that are recessed inward are provided on the opposite sides of the two first uprights 72. The two sides of the moving frame 73 are respectively embedded in the guide grooves of the two first uprights 72, and thus slidably connected with the uprights, so that the moving frame 73 can move up and down. The moving frame 73 is fixedly connected to the main support rod 1 through a connecting rod.

[0062] The upper end of the first upright 72 is provided with a first drive sprocket 76, which is driven to rotate by a first drive motor 75 mounted on the first upright 72 (it is foreseeable that the first drive sprocket 76 is mounted on the output shaft of the drive motor, or the drive motor is connected to the output shaft of the reducer, and the first drive sprocket 76 is mounted on the output shaft of the reducer. At the same time, the first drive sprocket 76 and the drive motor are mounted on the first upright 72 through a crossbar that mounts two first uprights 72). The lower end of the first upright 72 is provided with a second drive sprocket 77. The first drive sprocket 76 and the second drive sprocket 77 are connected by a drive chain 74, and one link of the drive chain 74 is fixedly connected to the moving frame 73.

[0063] When the platform needs to be moved, the drive motor is powered on and rotates, which drives the first drive sprocket 76 to rotate, and then drives the platform to move through the moving frame 73.

[0064] Implementation 8:

[0065] Based on Example 7, such as Figure 8 As shown, in this embodiment, the first upright 72 includes an outer sleeve 721 and an inner insert rod 722; the inner insert rod 722 is slidably installed inside the outer sleeve 721, thereby making the height of the first upright 72 adjustable. When in use, the height of the first upright 72 is adjusted according to the construction height, and when not in use, the height of the first upright 72 is adjusted to the minimum, which is beneficial for the storage and transportation of the device.

[0066] The top of the inner rod 722 is also provided with a chain tensioning mechanism 78. The drive chain 74 passes around the chain tensioning mechanism 78. The tensioning mechanism is used to retract and extend the drive chain 74 and adjust its length to suit the use of the first upright 72 at different heights.

[0067] The chain tensioning mechanism 78 includes an elastic telescopic rod fixedly installed on the upper end of the first upright 72. The elastic telescopic rod is arranged in a direction away from the first drive sprocket 76. A first deflector is rotatably installed at the end of the elastic telescopic rod away from the first drive sprocket 76. A second deflector is provided below the elastic telescopic rod. The drive chain 74 forms a U-shape after passing around the first deflector and the second deflector.

[0068] When the first upright 72 extends, the number of drive chains 74 located on the side of the first upright 72 increases, compressing the elastic telescopic rod. Conversely, the elastic telescopic rod extends under its elasticity, thus keeping the drive chain 74 in a taut state. Example

[0069] Based on Example 8, such as Figure 9As shown, in this embodiment, the top of the outer sleeve 721 is provided with a directional sprocket 79, and the bottom of the inner insert rod 722 is provided with a follower sprocket 80. The drive chain 74 passes through the first drive sprocket 76, the second drive sprocket 77, the directional sprocket 79, the follower sprocket 80, and the chain tensioning mechanism 78 in sequence. The second drive sprocket 77 is driven to rotate by the second drive motor. A brake is provided on the rotating shaft of the follower sprocket 80.

[0070] During normal operation, the first drive motor 75 acts as the active drive, while the second drive motor follows.

[0071] When the length of the first upright 72 needs to be adjusted, the second drive motor acts as the active drive, and the first drive motor 75 follows (specifically, it reverses, and the linear velocity of the reverse speed is equal to the speed at which the first upright 72 rises). The brake locks the follower sprocket 80. When the second drive motor is activated, since the directional sprocket 79 is in a high position, it lifts the follower sprocket 80 upward, thereby driving the inner rod 722 upward, thus achieving the purpose of adjusting the height of the first upright 72, making the adjustment more convenient.

[0072] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A lifting construction platform for engineering projects, characterized in that: It includes a main support rod, a first connecting rod, an adjusting rod, a second connecting rod, an upper chain plate, and a support plate; The first connecting rod is provided at intervals on the main support rod, and the first connecting rod is slidably connected to the main support rod; The adjusting rod is slidably mounted on the first connecting rod, and the adjusting rod is set approximately perpendicular to the main support rod. Each of the adjusting rods is provided with a second connecting rod at both ends; The upper ends of two adjacent second connecting rods located on the same side are respectively hinged to both ends of an upper chain plate; The support plate is laid on the upper chain plate, and the support plate extends along the extension direction of the adjusting rod.

2. The lifting construction platform for engineering applications according to claim 1, characterized in that: The first connecting rod, located in the middle position, is fixedly connected to the main support rod. Each of the remaining first connecting rods is provided with an electric telescopic rod, and the telescopic part of the electric telescopic rod is fixedly connected to its corresponding adjusting rod.

3. The lifting construction platform for engineering applications according to claim 1, characterized in that: The end of the adjusting rod is hinged to the middle of the second connecting rod, and the lower ends of two adjacent second connecting rods on the same side are respectively hinged to the two ends of a lower chain plate.

4. The lifting construction platform for engineering applications according to claim 1, characterized in that: The support plate includes an upper plate, a lower plate, a connecting plate, a movable plate, and a spring; The upper plate and the lower plate are arranged parallel to each other and are fixedly connected by a connecting plate extending along the length direction of the support plate, thereby forming a groove between the upper plate and the lower plate. One end of the movable plate is embedded in the groove and is connected to the connecting plate by a spring. The lower plate is hinged to the upper chain plate.

5. The lifting construction platform for engineering applications according to claim 4, characterized in that: The movable plate has a box-like structure with an open lower end. A limiting screw is threaded onto the lower plate. The limiting screw extends into the slide groove and is located on the outside of the end of the movable plate that extends into the slide groove.

6. The lifting construction platform for engineering applications according to claim 5, characterized in that: An extension rod is slidably installed at one end of the movable plate near the construction position, and a debris blocking plate is laid on the extension rod.

7. The lifting construction platform for engineering applications according to claim 1, characterized in that: Also includes A lifting mechanism, comprising a base, a first upright, a movable frame, and a drive chain; Two first uprights are arranged opposite each other on the base, and inwardly recessed guide grooves are provided on the opposite sides of the two first uprights. The two sides of the movable frame are respectively embedded in the guide grooves of the two first uprights, and the movable frame is fixedly connected to the main support rod through the connecting rod; The upper end of the first upright is provided with a first drive sprocket, which is driven to rotate by a first drive motor mounted on the first upright. The lower end of the first upright is provided with a second drive sprocket. The first drive sprocket and the second drive sprocket are connected by a drive chain, and one link of the drive chain is fixedly connected to the movable frame.

8. The lifting construction platform for engineering applications according to claim 7, characterized in that: The first upright includes an outer tube and an inner insert rod; the inner insert rod is slidably installed inside the outer tube. The top of the inner rod is also provided with a chain tensioning mechanism, and the drive chain passes around the chain tensioning mechanism.

9. A lifting construction platform for engineering applications according to claim 8, characterized in that: The top of the outer tube is provided with a directional sprocket, the bottom of the inner insert rod is provided with a follower sprocket, and the drive chain passes through the first drive sprocket, the second drive sprocket, the directional sprocket, the follower sprocket, and the chain tensioning mechanism in sequence. The second drive sprocket is driven to rotate by the second drive motor; a brake is provided on the rotating shaft of the follower sprocket.

10. A lifting construction platform for engineering applications according to claim 8 or 9, characterized in that: The chain tensioning mechanism includes an elastic telescopic rod fixedly installed on the upper end of the first upright. The elastic telescopic rod is arranged in a direction away from the first drive sprocket. A first redirecting wheel is rotatably installed at the end of the elastic telescopic rod away from the first drive sprocket. A second redirecting wheel is provided below the elastic telescopic rod. The drive chain forms a U-shape after passing around the first redirecting wheel and the second redirecting sprocket.