Manhole cover structure having load-distributing rib structure

Abstract

The present invention discloses a manhole cover structure (100) having a load-distributing rib structure, comprising: a ring-shaped side plate (110) of a certain height that is seated on the upper edge of a manhole frame (10) that is connected to a sewage or wastewater pipe; a top plate (120) that extends from the top of the side plate (110) and is formed in a curved circular shape to cover the manhole space; and a rib member (130) formed on the bottom surface of the top plate (120) to distribute and support the load applied from the top plate (120), thereby efficiently distributing and supporting the load applied from the outside to the side plate (110) through the distribution of compressive stress of the curved top plate (120) and the grid-shaped reinforcing structure of the rib member (130).

Description

Technology Field

[0001] The present invention relates to a manhole cover structure having a load-distributing rib structure capable of efficiently distributing external loads through a combined structure of a curved top plate and a grid-shaped rib member. Background Technology

[0003] As is well known, a manhole is an inspection opening formed on the surface for the inspection and maintenance of various underground buried pipelines, such as water and sewage pipes, communication conduits, power conduits, and gas pipelines. A manhole cover is a structure that covers the entrance of such a manhole, and manhole covers are installed above urban infrastructure, such as roadways, sidewalks, parking lots, and plazas, and are used in environments where they are directly exposed to the traffic load of vehicles and pedestrians.

[0004] Meanwhile, conventional manhole covers are generally manufactured from thick cast iron or cast steel in a flat shape, and their structure typically supports the wheel load from vehicle traffic solely through the thickness of the plate. While these flat manhole covers are easy to manufacture due to their simple shape, securing the required strength necessitates making the plate thick, which consequently leads to a problem of excessive weight increase per cover.

[0005] As such, an excessive increase in the weight of manhole covers places a heavy physical burden on workers when manually lifting them during inspections, raising the risk of work safety accidents. Furthermore, there were limitations in that maintenance costs increased significantly in the case of wide-area infrastructure where numerous manholes are distributed.

[0006] In addition, since the vehicle traffic load is transmitted intensively through the contact surface between the wheel and the manhole cover, in the case of a flat manhole cover, the wheel load is concentrated in a part of the flat plate, making it easy for local bending stress and shear stress to occur.

[0007] In particular, there was a limitation in that stress concentration was intensified at the boundary where the outer edge of the flat plate rests on the manhole frame, raising concerns about the formation of microcracks; these microcracks gradually grew due to repeated loading from vehicle traffic and progressed into fatigue cracks, leading to the premature failure of the manhole cover.

[0008] Meanwhile, due to the recent trend of increasing cargo transport capacity, the frequency of heavy-duty vehicles weighing over 100 tons, such as container trucks, dump trucks, and trailers, passing through road infrastructure is increasing. To cope with this heavy-duty environment, the KS D 3695 standard requires manhole covers to be rated for a load class of up to 100 tons.

[0009] However, there was a limitation in that it was unrealistic in terms of weight because, in order to satisfy an applied load of 100 tons with a simple flat manhole cover, the thickness of the flat plate had to be excessively increased. Prior art literature

[0011] Korean Registered Patent Publication No. 10-2052884 (Pressure regulating device for manhole cover, Jan. 22, 2020) Korean Registered Patent Publication No. 10-2448675 (Multi-purpose safety handle with fall prevention function when manhole cover detaches and easy access during manhole inspection, Sep. 29, 2022) The problem to be solved

[0012] The technical problem that the concept of the present invention aims to solve is to provide a manhole cover structure having a load-distributing rib structure that efficiently distributes and supports a load applied from the outside to the side plate through the distribution of compressive stress of the curved top plate and the lattice-type reinforcing structure of the rib member. means of solving the problem

[0014] To achieve the aforementioned objective, an embodiment of the present invention provides a manhole cover structure having a load-distributing rib structure, comprising: a ring-shaped side plate of a certain height that is seated on the upper edge of a manhole frame communicating with a sewage or wastewater pipe; a top plate that extends from the upper end of the side plate and is formed in a curved circular shape to cover the manhole space; and a rib member formed on the lower surface of the top plate to distribute and support the load applied from the top plate.

[0016] Here, the top plate is formed with an arc-shaped cross-section having a constant curvature from the center of the top plate toward the outer edge, thereby distributing the load received from the outside as compressive stress along the arc shape.

[0018] Additionally, the arc-shaped cross-section of the top plate is formed to have a constant radius of curvature (R), wherein the radius of curvature (R) is formed within a range of 5 to 25 times the outer diameter (D) of the top plate, and the arc deflection amount (h), defined as the distance between the vertex of the arc shape of the top plate and a virtual straight line connecting the outer end of the top plate, can be formed within a range of 1 / 200 to 1 / 40 of the outer diameter (D) of the top plate.

[0020] In addition, the rib member comprises a plurality of radial ribs extending radially from the bottom surface of the top plate to the center of the top plate to the side plate, and a plurality of concentric ribs arranged in multiple concentric shapes concentrically with the center of the top plate along the radial direction and intersecting with the radial ribs to be integrally combined, thereby enabling the load applied from the top plate to be distributed and transmitted to the side plate through a grid-type reinforcing structure formed by the plurality of radial ribs and the plurality of concentric ribs.

[0022] In addition, the radial ribs are formed with a tapered structure in which the thickness at the side plate side is greater than the thickness at the center side of the top plate, and the cross-sectional area increases toward the side plate side, and the concentric ribs can be formed such that the thickness of the concentric ribs placed on the outer side is greater than or equal to the thickness of the concentric ribs placed on the inner side. Effects of the invention

[0024] According to the present invention, by efficiently distributing external loads through a combined structure of a curved top plate and a grid-type rib member, it is possible to achieve lightweighting while ensuring sufficient rigidity even under heavy loads of 100 tons, and by effectively suppressing the occurrence of fatigue cracks in a repetitive load environment through a curved surface treatment structure of an outer ring reinforcement part and a stress concentration relief part, it is possible to simultaneously ensure durability and safety. Brief explanation of the drawing

[0026] FIGS. 1 and FIGS. 2 respectively illustrate a manhole cover structure having a load-distributing rib structure according to an embodiment of the present invention. FIG. 3 illustrates a rib member of a manhole cover structure having the load-distributing rib structure of FIG. 1. Figure 4 illustrates a cross-sectional structure of a manhole cover structure having the load-distributing rib structure of Figure 1. Figure 5 illustrates a cross-sectional view of a manhole cover structure having the load-distributing rib structure of Figure 3. FIG. 6 illustrates a modified example of a manhole cover structure having the load-distributing rib structure of FIG. 1. Specific details for implementing the invention

[0027] Hereinafter, embodiments of the present invention having the aforementioned features will be described in more detail with reference to the attached drawings.

[0029] A manhole cover structure (100) having a load-distributing rib structure according to an embodiment of the present invention comprises a ring-shaped side plate (110) of a certain height that is seated on the upper edge of a manhole frame (10) that communicates with a sewage or wastewater pipe, a top plate (120) that extends from the top of the side plate (110) and is formed in a curved circular shape to cover the manhole space, and a rib member (130) formed on the bottom surface of the top plate (120) to distribute and support the load applied from the top plate (120), and the main point is to efficiently distribute and support the load applied from the outside to the side plate (110) through the distribution of compressive stress of the curved top plate (120) and the grid-shaped reinforcing structure of the rib member (130).

[0031] Hereinafter, with reference to FIGS. 1 to 6, a manhole cover structure (100) having a load-distributing rib structure of the above configuration will be specifically described as follows.

[0033] First, the side plate (110) is formed in a ring shape of a certain height so as to be seated on the upper edge of a manhole frame (10) that is connected to a sewage or wastewater pipe. Referring to FIGS. 1 and 3, the manhole frame (10) is an annular structure installed at the upper end of a pipe buried on the ground surface, and a seating surface (11) is formed on the upper edge of the manhole cover structure of the present invention to be seated thereon. The side plate (110) is fitted and coupled to the seating surface (11) at a certain depth so that its outer circumference can be stably supported by the manhole frame (10).

[0034] That is, the side plate (110) has a cylindrical ring structure that stands upright at a certain height along the outer circumference of the top plate (120), and is formed by extending downward from the outer edge of the top plate (120) to form the end portion of a load transfer path that distributes the load transmitted through the top plate (120) to the seating surface (11) of the manhole frame (10).

[0035] Here, the side plate (110) may be formed by being integrally connected to the top plate (120) at the top, and the outer end of the rib member (130), which will be described later, may be connected to the inner side to accommodate the load transmitted from the rib member (130).

[0036] For example, the outer diameter of the side plate (110) may be formed to approximately ø648 mm depending on the specifications of the applied conduit, and the height of the side plate (110) may be formed to approximately 50 mm, and the height of the side plate relative to the outer diameter of the manhole cover structure may be formed within the range of 1 / 15 to 1 / 10, but the exemplified dimensions are examples of one embodiment and may be changed depending on the specifications of the applied conduit and infrastructure environment.

[0037] Accordingly, through the side plate (110), the manhole cover structure is stably seated on the manhole frame (10), thereby stably securing the end of the load transfer path that transmits the load distributed from the top plate (120) and the rib member (130) to the manhole frame (10).

[0039] Next, the top plate (120) extends from the top of the side plate (110) and is formed in a curved circular shape to cover the manhole space. Referring to FIGS. 1 and FIGS. 3, the top plate (120) extends inward from the top edge of the side plate (110) and is formed in a circular shape that covers the entire opening of the manhole.

[0040] Here, the top plate (120) is not a simple flat plate shape, but is formed in a curved shape to have an arc-shaped cross-section with a certain curvature from the center outward, so that the center of the top plate (120) has a curved structure in the shape of a dome or vault that is raised upward by a certain distance compared to the outer periphery.

[0041] For example, the top plate (120) is formed with an arc-shaped cross-section having a constant curvature from the center of the top plate (120) toward the outer edge, so that a load applied from the outside, that is, from the top of the top plate (120), is distributed along the arc-shaped cross-section into a compressive stress component and an in-plane membrane stress component, and the bending stress concentrated in the center of the top plate (120) can be reduced.

[0042] Specifically, the arc-shaped cross-section of the top plate (120) is formed to have a constant radius of curvature (R), wherein the radius of curvature (R) can be formed within a range of 5 to 25 times the outer diameter (D) of the top plate (120), and the arc deflection amount (h) or curvature height (h), defined as the distance between a virtual straight line connecting the vertex of the arc shape and the outer end, can be formed within a range of 1 / 200 to 1 / 40 of the outer diameter (D) of the top plate (120).

[0043] For example, when the outer diameter (D) of the top plate (120) is formed to be ø648mm, the radius of curvature (R) of the arc-shaped cross-section can be selected within the range of 3,200mm to 16,000mm, and the deflection amount (h) of the arc can be selected within the range of 3.2mm to 16.2mm.

[0044] In this way, if the radius of curvature (R) is formed to be less than 5 times the outer diameter (D), the protrusion of the top plate (120) is excessive, and there is a concern that the impact of the wheel will be concentrated in a local area when a vehicle passes, and if it exceeds 25 times, the effect of dispersing compressive stress due to the arc shape may be insufficient.

[0045] In addition, if the deflection amount (h) is less than 1 / 200 of the outer diameter (D), the effect of the arc shape is similar to a flat plate structure, so the distribution of compressive stress may be insufficient, and if it exceeds 1 / 40, the height difference with the road surface is excessive, which may reduce vehicle trafficability and pedestrian safety.

[0046] The aforementioned numerical range is an example of one embodiment and may be appropriately changed depending on the application environment and required stiffness.

[0048] Additionally, the thickness of the top plate (120) can be formed uniformly along the arc-shaped cross-section, for example, the thickness of the top plate (120) can be formed to be 15 mm and cast integrally with the rib member (130) described later, or the thickness at the center of the arc can be formed smaller than the thickness at the outer edge to be advantageous for stress distribution.

[0050] Meanwhile, on the upper surface of the top plate (120), anti-slip protrusions or surface patterns may be formed to prevent slipping when a vehicle passes, and identification characters may be displayed to identify the type of pipe to be applied. For example, in the case of a drainage type for sewage, "STORM" may be displayed in the center of the top plate (120), and in the case of a sealed type for sewage, "SEWAGE" may be displayed so that the worker can intuitively identify the type of pipe by its appearance.

[0051] Accordingly, through the top plate (120), the wheel load applied from the outside is converted into compressive stress along the arc-shaped cross-section and distributed to the side plate (110), thereby greatly improving rigidity under the same weight conditions compared to a simple flat plate, and can satisfy the high load requirement of 100 tons without excessively increasing the thickness of the flat plate.

[0053] Next, the rib member (130) is formed on the bottom surface of the top plate (120) to distribute and support the load applied from the top plate (120). Referring to FIGS. 3 to 5, the rib member (130) is a reinforcing member that protrudes downward by a certain height from the bottom surface of the top plate (120) to form a grid-shaped reinforcing structure, and forms an intermediate part of the load transfer path that distributes and transmits the load transmitted from the top plate (120) to the side plate (110).

[0054] That is, the rib member (130) may be configured to include a plurality of radial ribs (131) extending radially from the center of the top plate (120) to the side plate (110), and a plurality of concentric ribs (132) arranged in multiple concentric shapes spaced apart from each other along the radial direction with the center of the top plate (120) concentrically, and intersecting with the radial ribs (131) to be integrally joined.

[0055] Here, a plurality of radial ribs (131) are straight ribs extending radially from the center of the top plate (120) toward the side plate (110), and can be arranged at equal intervals along the circumferential direction of the top plate (120).

[0056] Specifically, the plurality of radial ribs (131) can be formed into eight and arranged at 45° intervals relative to the center of the top plate (120).

[0057] Additionally, the plurality of concentric ribs (132) are annular ribs arranged in multiple radially spaced apart from each other along a plurality of concentric circles sharing the center of the top plate (120), and can be integrally combined by intersecting orthogonally with the radial ribs (131) to complete a grid-type reinforcing structure.

[0058] Specifically, the multiple concentric ribs (132) are arranged in a triple arrangement of a central concentric, a middle concentric, and an outer concentric, so that each concentric can be firmly joined at the intersection point where it intersects the radial rib (131).

[0059] For example, the radial ribs (131) and concentric ribs (132) can both be formed to protrude from the bottom surface of the top plate (120) to a height of 40 mm to 60 mm, and the joint portion can be formed integrally with the top plate (120) and the side plate (110) during the casting process to be completed as a single structure without separate fastening members.

[0061] Meanwhile, although not shown, the radial rib (131) can be formed with a tapered structure in which the thickness on the side plate (110) side is greater than the thickness on the center side of the top plate (120), and the cross-sectional area increases as it goes toward the side plate (110).

[0062] Specifically, the thickness of the radial rib (131) at the center is formed to be 12 mm and the thickness at the outer side is formed to be 20 mm, so that the cross-sectional area gradually increases toward the outer side, thereby reflecting a stress distribution characteristic in which the amount of accumulated load increases toward the outer side, and thus the rigidity of the entire rib member (130) can be distributed in a balanced manner.

[0064] Additionally, the concentric ribs (132) may be formed such that the thickness of the concentric ribs positioned on the outer side is greater than or equal to the thickness of the concentric ribs positioned on the inner side.

[0065] For example, the thickness of the central concentric rib is formed to be 12 mm, the thickness of the middle concentric rib is 12 mm, and the thickness of the outer concentric rib is 14 mm, so that it can be configured to effectively accommodate the cumulative load that increases toward the outside.

[0067] Additionally, the ratio between the thickness (t) of the top plate (120) and the protrusion height (H) of the rib member (130) can be formed to be limited within a certain range, specifically, the protrusion height (H) of the rib member (130) can be formed within a range of 2 to 5 times the thickness (t) of the top plate (120).

[0068] Here, the protrusion height (H) of the rib member (130) can be defined as the vertical distance from the bottom surface of the top plate (120) to the bottom of the rib member (130), and the thickness (t) of the top plate (120) can be defined as the distance between the top surface and the bottom surface of the top plate (120). If the protrusion height (H) of the rib member (130) is less than twice the thickness (t) of the top plate (120), the reinforcing effect on the bottom surface of the top plate (120) is insufficient, making it difficult to effectively suppress bending deformation in the central part of the top plate (120). Conversely, if the protrusion height (H) of the rib member (130) exceeds five times the thickness (t) of the top plate (120), there is a possibility of uneven shrinkage, uneven cooling, or increased stress concentration at the base of the rib member (130) during the casting process. Accordingly, by limiting the protrusion height (H) of the rib member (130) to 2 to 5 times the thickness (t) of the top plate (120), sufficient reinforcement height can be secured through the rib member (130) without forming the top plate (120) excessively thick.

[0069] Through this, the wheel load acting on the top plate (120) is primarily distributed through the curved top plate (120) and secondarily supported through the rib member (130), so that the central sagging and local bending stress of the manhole cover structure (100) can be effectively reduced.

[0071] Meanwhile, the rib member (130) is not limited to a grid-type reinforcing structure composed of radial ribs (131) and concentric ribs (132), and may further include auxiliary truss ribs (not shown) in some grid areas between the radial ribs (131) and concentric ribs (132), and the auxiliary truss ribs may be configured to be arranged along the diagonal direction of the grid area to further multiplex the load distribution path.

[0072] Accordingly, through the rib member (130), the load distributed from the top plate (120) is transmitted to the side plate (110) via multiple paths through the lattice-type reinforcing structure, thereby improving the uniformity of stress distribution compared to a single reinforcing member, and the tapered structure of the radial and concentric ribs effectively accommodates the accumulated load that increases toward the outside, thereby ensuring a balanced stiffness distribution throughout the lattice.

[0074] Alternatively, as illustrated in FIG. 6, the side plate (110) may further include an outer ring reinforcement (140) formed to extend a certain width from the outer circumference of the top plate (120) and form a closed annular structure along the outer edge of the top plate (120). The outer ring reinforcement (140) is formed in the shape of a reinforcing ring that forms a closed annular structure along the outer circumference of the top plate (120) from the upper side of the side plate (110), and may be configured to support the concentrated load by distributing it in both the width direction and the circumference direction when the wheel load of the vehicle is concentrated in the outer edge area of ​​the top plate (120).

[0075] Here, the outer ring reinforcement (140) can be formed by being cast integrally with the side plate (110) to partially increase the thickness of the side plate (110), and its width can be formed to be approximately 55 mm and its height to be approximately 50 mm, thereby securing a cross-sectional area capable of sufficiently accommodating the concentrated load transmitted from the outer edge of the top plate (120) to the side plate (110).

[0076] Accordingly, through the outer ring reinforcement (140), even if the wheel load is concentrated on the outer edge of the top plate (120), the concentrated load is evenly distributed in the circumferential direction along the closed ring structure of the outer ring reinforcement (140) and transmitted to the side plate (110) and manhole frame (10), thereby relieving local stress concentration in the outer edge area.

[0078] Additionally, a curved stress concentration relief portion (not shown) may be formed in at least one of the joint where the bottom surface of the top plate (120) meets the side plate (110) or the outer ring reinforcement (140), and the joint where the rib member (130) meets the bottom surface of the top plate (120).

[0079] Here, the stress concentration relief section may be configured to include a rib joint curved surface treatment section formed by rounding a fillet in the corner area where the side of the rib member (130) and the bottom of the top plate (120) are joined at a right angle, and an outer ring lower curved surface treatment section formed by rounding a fillet in the corner area where the bottom of the top plate (120) and the side plate (110) or the outer ring reinforcement section (140) are joined at a right angle.

[0080] Specifically, the stress concentration relief section can be formed by processing the corners of each joint into an arc shape with a certain radius of curvature. For example, curved processing with a radius of curvature ranging from 5 mm to 20 mm can be applied to the corners of the joints. In right-angle joints, when a load is applied, stress trajectories tend to concentrate at the corners and become crack initiation sites. However, if the corners are treated as curved surfaces, the stress trajectories flow smoothly along the curved surface, thereby dispersing local stress concentration.

[0081] Accordingly, through the stress concentration relief section, the starting point of fatigue cracks occurring at right-angle joints in a repetitive loading environment due to vehicle traffic can be eliminated in advance, thereby extending the fatigue life of the entire manhole cover structure.

[0083] In addition, a packing (not shown) for preventing noise, odor, and shaking may be further attached to the seating surface (11) where the manhole cover structure and the manhole frame (10) of the present invention are joined. For example, the packing may be formed as an annular gasket made of EPDM (Ethylene Propylene Diene Monomer) material and may be attached so as to be inserted into the lower surface or outer surface of the side plate (110) or the lower part of the outer ring reinforcement (140). It may be configured to absorb micro-vibrations and shocks between the manhole cover structure and the manhole frame (10) when a vehicle passes, thereby reducing noise, and in the case of a sealed type for sewage, to block odors generated inside the manhole from leaking out.

[0085] Additionally, the manhole cover structure of the present invention may be formed as a drainage type for sewage or a sealed type for wastewater depending on the type of pipe to which it is applied. In the case of the drainage type for sewage, a plurality of drainage holes (12) (see FIG. 1) through which rainwater and rainwater can pass are formed in a multi-line circumferential pattern, a grid pattern, or a honeycomb pattern to provide a path for the inflow of rainwater. In the case of the sealed type for wastewater, the top plate (120) is formed as a closed surface without drainage holes, and the aforementioned EPDM packing is coupled to the seating surface (11) of the side plate (110) to prevent wastewater from leaking out or external foreign matter from entering the manhole.

[0086] That is, the manhole cover structure of the present invention may ensure compatibility between the drainage type and the sealed type by applying the basic skeletal structure of the side plate (110), top plate (120), and rib member (130) to both types in common, while only varying the presence or absence of a drainage hole and the presence or absence of a packing connection in the top plate (120).

[0088] Meanwhile, the material of the manhole cover structure of the present invention can be formed from ductile cast iron capable of simultaneously securing tensile strength and ductility. For example, the side plate (110), top plate (120), and rib member (130) can be integrally cast from ductile cast iron of KS standard FCD600 grade to secure superior tensile strength and impact resistance compared to flat gray cast iron, and can be configured to suppress crack propagation even under repeated impact loads caused by vehicle traffic.

[0090] Accordingly, the manhole cover structure having a load-distributing rib structure according to the present embodiment can be configured as a lightweight structure of 68 kg, as it does not rely on a simple increase in plate thickness, while securing rigidity capable of accommodating a high load of 100 tons through the compressive stress distribution action of the curved top plate (120) and the multi-path reinforcement action of the grid-shaped rib member (130).

[0092] Through the configuration of a manhole cover structure having such a load-distributing rib structure, the wheel load resulting from vehicle traffic is distributed as compressive stress along the arc-shaped cross-section of the curved top plate (120), and the distributed load is evenly transmitted to the side plate (110) through multiple paths of the grid-shaped rib member (130), and local stress concentration in the outer edge area and fatigue cracks in the corner area are effectively suppressed by the outer ring reinforcement (140) and the stress concentration relief part, thereby ensuring good durability even in a repetitive load environment.

[0094] Accordingly, by configuring a manhole cover structure having a load-distributing rib structure as described above, external loads can be efficiently distributed through a combined structure of a curved top plate and a grid-type rib member, thereby achieving lightweighting while ensuring sufficient rigidity even under heavy loads of up to 100 tons. Additionally, durability and safety can be simultaneously ensured by effectively suppressing the occurrence of fatigue cracks in a repetitive load environment through the curved treatment structure of the outer ring reinforcement and the stress concentration relief section, and a basic frame applicable to both types—a drainage type for sewage and a closed type for wastewater—can be provided, thereby improving type compatibility and component standardization.

[0096] The embodiments described in this specification and the configurations illustrated in the drawings are merely the most preferred embodiments of the present invention and do not represent all of the technical ideas of the present invention; therefore, it should be understood that various equivalents and modifications that can replace them may exist at the time of filing this application. Explanation of the symbols

[0098] 10: Manhole frame 11: Seating surface 12: Drainage hole 100: Manhole cover structure 110: Side panel 120: Top panel 130: Rib member 131: Radial rib 132: Concentric rib 140: Outer ring reinforcement

Claims

Claim 1 A ring-shaped side plate of a certain height that rests on the upper edge of a manhole frame communicating with a sewage or drainage pipe; and a top plate that extends from the top of the side plate and is formed in a curved circular shape to cover the manhole space; and a rib member formed on the bottom surface of the top plate to distribute and support a load applied from the top plate; wherein the rib member comprises a plurality of radial ribs extending radially from the bottom surface of the top plate to the center of the top plate to the side plate, and a plurality of concentric ribs arranged in multiple concentric shapes concentric to the center of the top plate along the radial direction, spaced apart from each other, and integrally joined by intersecting the radial ribs, thereby distributing and transmitting the load applied from the top plate to the side plate through a grid-type reinforcing structure formed by the plurality of radial ribs and the plurality of concentric ribs, wherein the protrusion height (H) of the rib member is formed within a range of 2 to 5 times the thickness (t) of the top plate, and the side plate further comprises an outer ring reinforcing part formed to extend from the outer circumference of the top plate by a certain width to form a closed annular structure along the outer edge of the top plate, and the outer ring The reinforcing member is formed in the shape of a reinforcing ring that forms a closed ring along the outer circumference of the top plate at the upper side of the side plate, configured to distribute and support the concentrated load in both the width direction and the circumference direction when the wheel load of the vehicle is concentrated in the outer edge area of ​​the top plate, and a curved stress concentration relief member is formed at least one of the joint where the bottom surface of the top plate meets the side plate or the outer ring reinforcing member, and the joint where the rib member meets the bottom surface of the top plate, and the stress concentration relief member comprises a rib joint curved surface treatment part formed by rounding with a fillet in the corner area where the side of the rib member and the bottom surface of the top plate are joined at a right angle, andA manhole cover structure having a load-distributing rib structure, comprising an outer ring lower curved surface treatment portion formed by rounding the corner area where the bottom surface of the top plate and the side plate or the outer ring reinforcement portion are joined at a right angle, wherein the stress concentration relief portion is formed by processing the corners of each joint portion into an arc shape with a certain radius of curvature, and the curved surface processing is applied to the corners of the joint portion with a radius of curvature in the range of 5mm to 20mm. Claim 2 A manhole cover structure having a load-distributing rib structure, wherein, in claim 1, the top plate is formed with an arc-shaped cross-section having a constant curvature from the center of the top plate toward the outer edge, thereby distributing the load received from the outside as compressive stress along the arc shape. Claim 3 A manhole cover structure having a load-distributing rib structure, wherein, in claim 2, the arc-shaped cross-section of the top plate is formed to have a constant radius of curvature (R), the radius of curvature (R) is formed within a range of 5 to 25 times the outer diameter (D) of the top plate, and the arc deflection amount (h), defined as the distance between a virtual straight line connecting the vertex of the arc shape of the top plate and the outer circumference end of the top plate, is formed within a range of 1 / 200 to 1 / 40 of the outer diameter (D) of the top plate. Claim 4 delete Claim 5 A manhole cover structure having a load-distributing rib structure, wherein, in claim 1, the radial rib is formed with a tapered structure in which the cross-sectional area increases toward the side plate side, such that the thickness at the side plate side is greater than the thickness at the center side of the top plate, and the concentric rib is formed such that the thickness of the concentric rib disposed on the outer side is greater than or equal to the thickness of the concentric rib disposed on the inner side.

Images