Work Platform for Construction of Pipelines

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the construction of pipelines. More particularly, the present invention is directed to a work platform which can be selectively mounted on top of a manhole casing and provides a stable standing surface for an operator to access the manhole during construction thereof.

2. Background

Underground pipelines, and in particular, non-pressurized, gravity-flow pipelines, such as, for example, water, sewer, and storm sewer pipelines, are typically constructed from prefabricated segments which are laid into a trench excavated along the desired path of the pipeline. Vertical, silo-like structures called “manholes” are connected between adjacent pipeline segments and provide access for inspection, maintenance, and cleaning of the pipeline. Like the pipeline, manholes are also constructed from prefabricated sections referred to as “casings”, “manhole casings”, or “manhole sections”. These casings are adapted to be stacked on top of each other to form the silo-like structure of the manhole. Typically, each casing will include one or more male and/or female ends which interlock with the male or female end of an adjacent casing to couple the casings together.

During construction, it is often necessary for an operator to access the top or interior of the manhole before the trench surrounding the manhole is filled in. For example, gravity-flow pipelines typically require tight alignment and slope control to ensure consistent free flow of wastewater therethrough. Changes to slope and horizontal alignment of a pipeline segment typically only occur at a manhole and are performed using a construction laser and surveying equipment. The construction laser is generally mounted at the bottom of the manhole and the surveying equipment is mounted at the top of the manhole.

Traditionally, an operator would stand on top of the manhole or stand on top of a board placed over the manhole to operate the surveying equipment. This creates a significant fall hazard particularly when the trench is more than a few feet deep. Additionally, an operator must descend into the manhole to mount and adjust the construction laser. However, because the operator must descend into the manhole before the trench has been filled in, it is often difficult or impossible to set up and use rescue hoists or cranes in the event the laser operator must be rescued from the manhole.

Accordingly, there exists a need for a work platform which can be selectively mounted on top of a manhole casing and provides a stable standing surface for an operator to access the manhole during construction of the pipeline.

SUMMARY OF THE INVENTION

In a first embodiment thereof, the present invention is directed to a work platform that mounts on top of a manhole casing comprising a cylindrical exterior surface and a central bore having a cylindrical bore interior surface. The work platform can comprise a deck/frame structure and a cylindrical interlock lip secured to the deck/frame structure. The cylindrical interlock lip can include a cylindrical lip exterior surface and a cylindrical lip interior surface. The cylindrical interlock lip can be sized and shaped to either nest/fit snugly into the central bore with the cylindrical lip exterior surface circumscribed by and extending parallel and closely adjacent to the cylindrical bore interior surface or to nest/fit snugly around the manhole casing with the cylindrical lip interior surface circumscribing and extending parallel and closely adjacent to the cylindrical casing exterior surface. In use, when the work platform tips or slides relative to the manhole casing, the cylindrical interlock lip engages either the cylindrical bore interior surface or the cylindrical casing exterior surface for thereby preventing the work platform from tipping or sliding off of the manhole casing.

Preferably, the cylindrical lip exterior surface has a lip exterior diameter, the cylindrical lip interior surface has a lip interior diameter, the cylindrical bore interior surface has a bore interior diameter, and the cylindrical casing exterior surface has a casing exterior diameter. When the cylindrical interlock lip is sized and shaped to nest/fit snugly into the central bore, the lip exterior diameter is preferably not more than 1″, and yet more preferably, not more than 0.5″, less than the bore interior diameter. When the cylindrical interlock lip is sized and shaped to nest/fit snugly around the manhole casing, the lip interior diameter is preferably not more than 1″, and yet more preferably, not more than 0.5″, greater than the casing exterior diameter.

Preferably, the deck/frame structure includes an access window which aligns with and provides access to the central bore. The cylindrical interlock lip is preferably selectively coupled to the deck/frame structure and circumscribes the access window. Yet more preferably, the work platform further comprises a ring-shaped coupler disc that is secured to the deck/frame structure and the cylindrical interlock lip is selectively secured to the coupler disc.

In a second embodiment thereof, the work platform can comprise a pair of concentric first and second cylindrical interlock lips. The first cylindrical interlock lip can include a cylindrical lip exterior surface and can be sized to nest/fit snugly into the central bore with the cylindrical lip exterior surface circumscribed by and extending parallel and closely adjacent to the cylindrical bore interior surface. The second cylindrical interlock lip can include a cylindrical lip interior surface and can be sized to nest/fit snugly around the manhole casing with the cylindrical lip interior surface circumscribing and extending parallel and closely adjacent to the cylindrical casing exterior surface. In use, the first and second cylindrical interlock lips engage the cylindrical bore interior surface and the cylindrical casing exterior surface for thereby preventing the work platform from tipping or sliding off of the manhole casing.

Preferably, the manhole casing further includes an annular alignment protrusion extending upwardly from an upper end of the manhole casing. An annular interlock slot is defined between the cylindrical lip interior surface and the cylindrical lip exterior surface, and the annular alignment protrusion is received into the annular interlock slot and engages the first and second cylindrical interlock lips to prevent the work platform from tipping or sliding off of the manhole casing.

In a third embodiment thereof, the work platform comprises a plurality of arc-shaped interlock lips that are secured to the deck/frame structure and are configured to either nest/fit snugly into the central bore or to nest/fit snugly around an upper end of the manhole casing. In use, the arc-shaped interlock lips engage either the cylindrical bore interior surface or the cylindrical casing exterior surface for thereby preventing the work platform from tipping or sliding off of the manhole casing.

Preferably, the work platform includes three or more inner arc-shaped interlock lips and three or more outer arc-shaped interlock lips. The three or more inner arc-shaped interlock lips are configured to nest/fit snugly into the central bore and engage the cylindrical bore interior surface. The three or more outer arc-shaped interlock lips are configured to nest/fit snugly around the manhole casing and engage the cylindrical casing exterior surface.

Preferably, the inner and outer arc-shaped interlock lips can be arranged in parallel, concentric pairs that sandwich a portion of the manhole casing therebetween, or the inner and outer arc-shaped interlock lips can be offset circumferentially from each other and form a staggered ring.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features of this invention and the manner of attaining them will become more apparent, and the invention itself will be better understood by reference to the following description of the embodiments of the invention, taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a perspective view of a work platform mounted on top of a manhole located within a trench and connected to a pipeline;

FIG. 2 is a front elevation view of the work platform, the manhole, and the pipeline;

FIGS. 3-5 are cross section views of the work platform, the manhole, and the pipeline taken along the line 3-3 shown in FIG. 2 wherein the manhole is shown in different stages of construction;

FIG. 6 is an exploded cross section view of the manhole shown in FIG. 5;

FIG. 7 is a perspective view of the work platform shown in FIG. 1;

FIG. 8 is another perspective view of the work platform;

FIG. 9 is a perspective view of the work platform wherein the mounting collar has been removed for greater clarity;

FIG. 10 is an exploded cross section view taken along the line 10-10 shown in FIG. 3 illustrating the work platform being lowered onto the intermediate manhole casing;

FIG. 11A is a cross section view showing the work platform mounted on top of the intermediate manhole casing;

FIG. 11B is a magnified detail view of circled Detail 11B;

FIG. 12 is another exploded cross section view showing the mounting collar in an exploded state with the coupler disc and fasteners exploded apart from the cylindrical interlock lip;

FIGS. 13A-B are exploded perspective views of the mounting collar shown in FIG. 12;

FIGS. 13C-D are side elevation and bottom plan views of the mounting collar;

FIG. 14 is a perspective view of a work platform having a mounting collar configured to interlock with a reducer casing or a riser casing;

FIG. 15 is another perspective view of the work platform shown in FIG. 14;

FIG. 16A is a cross section of the work platform taken along the line 16-16 shown in FIG. 5;

FIG. 16B is a magnified detail view of circled Detail 16B;

FIG. 17 is a perspective view of a work platform having a mounting collar with a cylindrical interlock lip configured to be received over the annular alignment protrusion of a manhole casing;

FIG. 18A is a cross section of the work platform taken along the line 16-16 shown in FIG. 5;

FIG. 18B is a magnified detail view of circled detail 18B;

FIG. 19 is a perspective view of a work platform having a mounting collar with a pair of concentric cylindrical interlock lips;

FIG. 20A is a cross section of the work platform taken along the line 16-16 shown in FIG. 5;

FIG. 20B is a magnified detail view of circled Detail 20B;

FIG. 21 is a perspective view of a work platform having a mounting collar with three arc-shaped interlock lips that are configured to fit into the central bore of a manhole casing;

FIG. 22 is a bottom plan view of the work platform shown in FIG. 21;

FIG. 23 is a perspective view of a work platform having a mounting collar with three arc-shaped interlock lips that are configured to fit over the annular alignment protrusion of a manhole casing;

FIG. 24 is a bottom plan view of the work platform shown in FIG. 21;

FIG. 25 is a perspective view of a work platform having a mounting collar with parallel concentric arc-shaped interlock lips;

FIG. 26 is a bottom plan view of the work platform shown in FIG. 21;

FIG. 27 is a perspective view of a work platform having a mounting collar with offset concentric arc-shaped interlock lips; and,

FIG. 28 is a bottom plan view of the work platform shown in FIG. 27.

Corresponding reference characters indicate corresponding parts throughout several views. Although the exemplification set out herein illustrates certain embodiments of the invention, the embodiments disclosed below are not intended to be exhaustive or to be construed as limiting the scope of the invention to the precise form disclosed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring initially to FIGS. 1-5, a work platform constructed in accordance with the principles of the present invention is shown and designated by the numeral 10. The work platform 10 is adapted to be selectively mounted on top of a manhole 12 and provides a stable standing surface for an operator to access the manhole 12 during construction of a pipeline 14. Pipelines 14, such as, for example, a water, sewer, or storm sewer pipelines, are commonly constructed from prefabricated pipeline segments 16 which are laid into a trench 18 excavated along the desired path of the pipeline. Manholes 12 are hollow, silo-like structures which are connected between the pipeline segments 16 and include a central chamber 20 which provides access for inspecting, maintaining, or cleaning the pipeline 14.

Like pipelines 14, manholes 12 are typically constructed from a plurality of prefabricated sections 22 which are commonly referred to as “casings”, “manhole casings”, or “manhole sections”. The manhole casings 22 are hollow and include central bores 24 which together form the manhole's central chamber 20. These manhole casings 22 can be manufactured in a variety of sizes and shapes as may be necessary or desirable. For example, as best seen in FIGS. 5 and 6, a manhole 12 can comprise a barrel-shaped base casing 22a which connects to the pipeline segments 16 and forms the base of the manhole 12, a cylindrical intermediate casing 22b which stacks on top of the base casing 22a, a cone-shaped reducer casing 22c which stacks on top of the intermediate casing 22b, and one or more cylindrical riser casings 22d which stack on top of the reducer casing 22c and form the neck of the manhole 12.

The manhole casings 22 are preferably configured to interlock with each other. More particularly, as best seen in FIG. 6, the base casing 22a can include an upper male end 26 having an annular alignment protrusion 28 which adapted to be received into and interlock with an annular alignment recess 32 formed in the lower female end 30 of the intermediate casing 22b. Similarly, the intermediate casing 22b can include an upper male end 26 having an annular alignment protrusion 28 which is adapted to be received into and interlock with an annular alignment recess 32 formed in the lower female end 30 of the reducer casing 22c and the reducer casing 22c can include an upper male end 26 having an annular alignment protrusion 28 which is adapted to be received into and interlock with an annular alignment recess 32 formed in the lower female end 30 of a riser casing 22d. Configuring the base, intermediate, reducer, and riser casings 22a, 22b, 22c, 22d to interlock with each other ensures that the casings 22a, 22b, 22c, 22d are properly aligned with each other and remain aligned after the trench 18 is filled in.

During construction of a pipeline 14, it is often necessary for an operator to access the central chamber 20 of the manhole 12 before the trench 18 is filled in. For example, pipelines 14, and in particular, non-pressurized, gravity-flow pipelines, such as, for example, water, sewer, and storm sewer pipelines, typically require tight alignment and slope control to ensure consistent free flow of wastewater therethrough. Each pipeline segment 16 generally has a uniform pipe diameter, slope, and horizontal alignment and changes to slope and horizontal alignment typically only occur at the manholes 12 between the pipeline segments 16. The uniform slope and horizontal alignment between manholes 12 ensure that wastewater flows freely through the pipeline 14 and prevents any solids suspended in the wastewater from settling within the pipeline.

Changes to slope and horizontal alignment are generally made using a construction laser (not shown) which mounts in the bottom of the manhole chamber 20 and surveying equipment (not shown) which mounts at the top of the manhole 12. The surveying equipment is used to align the construction laser with survey markers (not shown) which are placed on the surface of the ground and define the desired path for the pipeline segment 16. The construction laser is then used to coordinate the excavation of the trench 18 and align the pipeline segments 16 along the desired path.

The work platform 10 is adapted to be selectively mounted on top of a manhole casing 22 and provides a stable surface for an operator to stand on while operating the surveying equipment or before descending into the manhole 12. In the present exemplary embodiment, the work platform 10 includes a deck/frame structure 34 and a mounting collar 36 which is secured to the deck/frame structure 34. The deck/frame structure 34 supports the weight of an operator and their equipment and the mounting collar 36 is used to couple the work platform 10 to a manhole casing 22.

The work platform 10 preferably also includes a jib crane 38 which is mounted to the deck/frame structure 34 (see FIG. 7) and one or more catwalks 40 (FIGS. 3-5) which can be coupled to the deck/frame structure 34. The jib crane 38 can be used to for lowering equipment and personnel into the manhole chamber 20 and also as a safety lift for rescuing an operator from the manhole chamber 20 in the event of an accident. The catwalks 40 form a bridge that allows an operator to access the work platform 10 from the edge of the trench 18. Preferably, the work platform 10 and its components are constructed from a high strength materials such as, for example, steel, aluminum, or other high strength metallic materials.

Turning to FIGS. 7-9, the deck/frame structure 34 includes a floor panel 42 which an operator can stand on while using the work platform 10. The floor panel 42 includes an access window 44 that aligns with the central bore 24 of a manhole casing 22 and allows an operator to climb down through the access window 44 to access the manhole chamber 20. The deck/frame structure 34 also includes legs 46 which are secured to and extend downwardly from the floor panel 42, handrails 48 which are secured to the floor panel 42 and extend upwardly along the perimeter of the deck/frame structure 34, and self-closing gates 50 which are secured to the handrails 48. The legs 46 support the work platform 10 when it is not in use, and the handrails 48 and self-closing gates 50 form a barrier around the perimeter of the platform 10 to help prevent an operator from falling or slipping off of the platform or through the access window.

As best seen in FIGS. 10-13, the mounting collar 36 includes an annular coupler disc 52 and one or more cylindrical interlock lips 54. The annular coupler disc 52 is a ring-shaped bracket that secures to the deck/frame structure 34 and circumscribes the access window 44. The cylindrical interlock lips 54 are secured to and extends downwardly from the coupler disc 52 and are adapted to engage and interlock with the manhole casing 22 for coupling the work platform 10 thereto.

In a first embodiment (FIGS. 7, 8, and 10-12), the mounting collar 36 includes a single cylindrical interlock lip 54 that is configured to nest/fit snugly into the manhole casing's central bore 24. More particularly, the cylindrical interlock lip 54 includes a cylindrical lip exterior surface 54ES having a lip exterior diameter 54DE. The casing central bore 24 includes a cylindrical bore interior surface 24IS having a bore interior diameter 24DI. The interlock lip 54 is sized such that the lip exterior diameter 54DE is slightly smaller than the bore interior diameter 24DI. This allows the interlock lip 54 to be inserted and nest/fit snugly into the central bore 24 with the lip exterior surface 54ES being circumscribed by and extending parallel and closely adjacent to the bore interior surface 24IS (see FIGS. 11A-B). Preferably, the lower outboard edge 56 of the interlock lip 54 is beveled to help align the interlock lip 54 as it is inserted into the central bore 24.

In use, the cylindrical interlock lip 54 prevents the platform 10 from tipping or falling off of the manhole casing 22. Specifically, if the work platform 10 begins to tip/pivot, the cylindrical interlock lip 54 will pivot within the casing's central bore 24 and will engage and abut/wedge against the bore interior surface 24IS. By abutting/wedging against the bore interior surface 24IS, the cylindrical interlock lip 54 is prevented from continuing to pivot and, hence, prevents the work platform 10 from tipping/pivoting and potentially tipping or sliding off of the manhole casing 22.

Of course, variations in the manufacturing process can cause the manhole casing central bores 24 to vary slightly in diameter. To account for these variations, manhole casings 22 are typically manufactured to fit within specified manufacturing tolerances. For example, a manhole casing 22 with a manufacturing tolerance of +1% and a nominal central bore diameter of 48″ could have a central bore 24 that is between 47.5″ and 48.5″ wide.

To ensure the platform 10 can be used with all manhole casings 22 that meet the specified manufacturing tolerances, the lip exterior diameter 54DE is preferably slightly less than the minimum diameter 24Dmin of the central bore 24. (See FIG. 11B). However, to ensure the interlock lip 54 properly engages the bore interior surface 24IS when the platform 10 tips/pivots, the lip exterior diameter 54DE preferably is not more than 1″, and yet more preferably, not more than 0.5″, less than the bore minimum diameter 24Dmin. Additionally, the longitudinal height 54H of the cylindrical interlock lip 54 should be configured such that, in the event the work platform 10 begins to tip/pivot to one side, the cylindrical interlock lip 54 will still engage the bore interior surface 24IS and prevent the work platform 10 from tipping or sliding off of the manhole casing 22 even if the central bore 24 is on the wider end of the specified tolerance range.

For example, as mentioned above, a manhole casing 22 having a manufacturing tolerance of +1% and a nominal central bore diameter of 48″ could have a central bore 24 that is between 47.5″ and 48.5″ wide. To ensure that the cylindrical interlock lip 54 nest/fits snugly into the central bore 24 of each manhole casing 22 that meets the +1% manufacturing tolerance, the lip exterior diameter 54DE is preferably slightly less, but not more than 1″, and yet more preferably, not more than 0.5″, less, than the 47.5″ minimum diameter 24Dmin. Additionally, to ensure the interlock lip 54 engages the bore interior surface 24IS even if the bore interior diameter 24DI is 48.5″ (i.e., the maximum bore diameter that meets the +1% manufacturing tolerance), the longitudinal height 54H of the interlock lip 54 is preferably 12″ or more.

Preferably, as best seen in FIGS. 11B, 12, and 13A-D, the cylindrical interlock lip 54 is manufactured separately from the coupler disc 52 and is selectively secured to the coupler disc bottom surface 52B by, for example, one or more fasteners 60. Specifically, the cylindrical interlock lip 54 includes an annular mounting flange 66. The annular mounting flange 66 is formed at the upper end 64 of the cylindrical interlock lip 54 and is adapted to extend through the access window 44 and abut against the coupler disc bottom surface 52B. The coupler disc 52 and the mounting flange 66 include respective fastener bores 62a, 62b which align with each other and are adapted to receive and engage the fasteners 60 for securing the cylindrical interlock lip 54 to the coupler disc 52.

Preferably, the interlock lip 54 can be removed and replaced with other sizes or configurations of interlock lips 54 such that the work platform 10 can be mounted on top of a variety of different manhole casings 22 having different sizes, shapes, and/or configurations. For example, as best seen in FIGS. 5 and 6, the upper end of the reducer casing's central bore 24 and the central bores 24 of the riser casings 22d are narrower than the central bores 24 of the base casing 22a and the intermediate casing 22b. To allow the work platform 10 to be mounted on top of a reducer casing 22c (FIG. 4) or a riser casing 22d (FIGS. 5 and 16A-B), a narrower cylindrical interlock lip 54′ that is sized and shaped to nest/fit snugly into the central bore 24 of a reducer casing 22c or a riser casing 22d must be used. This narrower cylindrical interlock lip 54′ includes a wider mounting flange 66′ that extends radially outwardly from the interlock lip upper end 64 and engages and is secured to the coupler disc 52.

Of course, the mounting collar 36 is not limited to the configurations described hereinabove, and yet other configurations of the mounting collar 36 may be used as necessary or desirable. For example, in a second embodiment (FIGS. 17 and 18A-B), a mounting collar 36′ includes a cylindrical interlock lip 54″ that is sized and shaped to nest/fit snugly around the annular alignment protrusion 28 of a manhole casing 22. Specifically, as mentioned above, the manhole casings 22 are preferably configured to interlock with each other and include an annular alignment protrusion 28 that is configured to be received into and interlock with the annular alignment recess 32 of an adjacent casing 22. The annular alignment protrusion 28 includes a cylindrical protrusion exterior surface 28ES having a protrusion exterior diameter 28DE. The cylindrical interlock lip 54″ includes a cylindrical lip interior surface 54IS having a lip interior surface diameter 54DI. The lip interior surface diameter 54DI is sized to be slightly larger than the protrusion exterior surface diameter 28DE such that the alignment protrusion 28 nests/fits snugly inside of the interlock lip 54′ with the protrusion exterior surface 28ES being circumscribed by and extending parallel and closely adjacent to the lip interior surface 54IS. In the event the work platform 10 begins to tip/pivot, the alignment protrusion 28 abuts/wedge against the lip interior surface 54IS and thereby prevent the work platform 10 from tipping or sliding off of the manhole casing 22.

In this embodiment, the longitudinal height 54H′ of the cylindrical interlock lip 54″ is preferably configured to match the longitudinal height 28H′ of the annular alignment protrusion 28 (FIG. 18B). Matching the lip height 28H′ to the protrusion height 28H allows the cylindrical interlock lip 54″ to mimic the function of a manhole casing alignment recess 32 which helps to ensure the alignment protrusion 28 properly engages the lip interior surface 54IS in the event the work platform 10 begins to tip/pivot. Additionally, the lower inboard edge 58 of the interlock lip 54″ is preferably beveled to make it easier to align and receive the cylindrical interlock lip 54′ over the casing's annular alignment protrusion 28.

In a third embodiment (FIGS. 19 and 20A-B), a mounting collar 36″ includes a pair of concentric cylindrical interlock lips 54a, 54b. The inner interlock lip 54a includes a cylindrical lip exterior surface 54as having a lip exterior diameter 54DE′. The outer interlock lip 54b includes a cylindrical lip interior surface 54bs that extends parallel to the inner lip exterior surface 54as and has an outer lip interior diameter 54DI′. An annular interlock slot 68 is defined between the inner lip exterior surface 54as and the outer lip interior surface 54bs.

The cylindrical interlock lips 54a, 54b are sized and shaped such that the annular alignment protrusion 28 of a manhole casing 22 can be received into and captured within the annular interlock slot 68. Specifically, the inner interlock lip 54a is sized such that the lip exterior diameter 54DE′ is slightly less than the central bore interior diameter 24DI and the outer interlock lip 54b is sized such that the lip interior diameter 54DI′ is slightly greater than the alignment protrusion's exterior diameter 28DE. This configuration allows the alignment protrusion 28 to next/fit snugly into the annular interlock slot 68 with inner interlock lip 54a nested/fit snugly into central bore 24 and the outer interlock lip 54b nested/fit snugly around the alignment protrusion 28. By configuring the interlock lips 54a, 54b such that the annular alignment protrusion 28 nests/fits snugly into the interlock slot 68, tipping or pivoting the work platform 10 will cause the annular alignment protrusion 28 to wedge between the interlock lips 54a, 54b and lock the work platform 10 in position, thereby preventing the work platform from tipping or sliding off of the manhole casing 22.

In a fourth embodiment (FIGS. 21-28), a mounting collar 36″ “′ can include a plurality of arc-shaped interlock lips 70a, 70b that can be arranged in a variety of patterns and configurations as may be necessary or desirable for coupling the work platform 10 to a manhole casing 22. For example, as shown in FIGS. 21 and 22, the mounting collar 36”′ can include three or more inner arc-shaped interlock lips 70a that are configured to nest/fit snugly into a casing's central bore 24 and function like the cylindrical interlock lip 54 shown in FIGS. 11A-B. Specifically, the inner arc-shaped interlock lips 70a include arc-shaped exterior surfaces 72a and are configured such that, when the work platform 10 is mounted on a manhole casing 22, the arc-shaped exterior surface 72a of each interlock lip 70a faces towards and is positioned closely adjacent to the bore interior surface 24IS. In the event the work platform 10 begins to tip/pivot, one or more of the inner arc-shaped interlock lips 70a will engage and abut/wedge against the bore interior surface 24IS for thereby preventing the work platform 10 from tipping or sliding off of the manhole casing 22.

Alternatively, as shown in FIGS. 23 and 24, the mounting collar 36″ “′ can include three or more outer arc-shaped interlock lips 70b that are configured to be nest/fit snugly around a casing's annular alignment protrusion 28 and function like the cylindrical interlock lip 54” shown in FIGS. 18A-B. Specifically, the outer arc-shaped interlock lips 70b include arc-shaped interior surfaces 72b and are configured such that, when the work platform 10 is mounted on a manhole casing 22, the arc-shaped interior surface 72b of each interlock lip 70b faces towards and is positioned closely adjacent to the protrusion exterior surface 28ES. In the event the work platform 10 begins to tip/pivot, one or more of the outer arc-shaped interlock lips 70b will engage and abut/wedge against the alignment protrusion 28 for thereby preventing the work platform 10 from tipping or sliding off of the manhole casing 22.

As shown in FIGS. 25-28, the mounting collar 36″″ can also be configured to include three or more inner arc-shaped interlock lips 70a and three or more outer arc shaped interlock lips 70b. In use, the interlock lips 70a, 70b are configured to function like the concentric cylindrical interlock lips 54a, 54b shown in FIGS. 19 and 20A-B. Specifically, the inner arc-shaped interlock lips 70a include arc-shaped exterior surfaces 72a and are configured such that, when the work platform 10 is mounted on a manhole casing 22, the arc-shaped exterior surface 72a of each interlock lip 70a faces towards and is positioned closely adjacent to the bore interior surface 24IS. The outer arc-shaped interlock lips 70b include arc-shaped interior surfaces 72b and are configured such that, when the work platform 10 is mounted on a manhole casing 22, the arc-shaped interior surface 72b of each interlock lip 70b faces towards and is positioned closely adjacent to the protrusion exterior surface 28ES. In the event the work platform 10 begins to tip/pivot, one or more of the inner arc-shaped interlock lips 70a and one or more of the outer arc-shaped interlock lips 70b will engage and abut/wedge against the bore interior surface 24IS and the protrusion exterior surface 28ES for thereby preventing the work platform 10 from tipping or sliding off of the manhole casing 22.

Preferably, the inner and outer arc-shaped interlock lips 70a, 70b can be arranged as may be necessary or desirable to ensure one or more interlock lips 70a, 70b abut/wedge against the bore interior surface 24IS or the protrusion exterior surface 28ES for thereby preventing the work platform from tipping or sliding off the manhole casing 22. For example, as shown in FIGS. 25 and 26, the inner and outer arc-shaped interlock lips 70a, 70b can be aligned in parallel, concentric pairs that sandwich a portion of the casing's annular alignment protrusion 28 therebetween. Alternatively, as shown in FIGS. 27 and 28, the inner and outer arc-shaped interlock lips 70a, 70b can be offset from each other at regular circumferential intervals whereby the inner and outer arc-shaped interlock lips 70a, 70b together form a staggered ring that interlocks with the alignment protrusion 28.

While this invention has been described as having an exemplary design, the present invention may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles.