WORKER SUPPORT APPARATUS FOR CONICAL ROOF CONSTRUCTION

An apparatus supporting workers assembling a conical roof includes a central support column, a pivot frame pivotally supported at a top end of the support column, and a stair assembly having an upper end coupled to the pivot frame such that the stair assembly is pivotal together with the pivot frame relative to the support column. The lower end of the stair assembly is supported on wheels for rolling on the building floor. A worker support platform is also carried on the pivot frame to pivot with the stairs. A roof support frame extends above the pivot frame, in fixed relation to the support column to support an apex of the conical roof thereon while the stairs and platform remain pivotal. This arrangement ensures that the stair assembly can be easily aligned with any selected rafters of the roof during construction while remaining safely supported relative to the support column.

FIELD OF THE INVENTION

The present invention relates to a work support apparatus arranged to support workers thereon when constructing a conical roof of a building, for example the roof of a grain storage bin having rafters that taper upwardly and radially inwardly from a perimeter edge to an apex of the roof, so that workers on the work support apparatus can perform work along the rafters of the conical roof.

BACKGROUND

A common type of storage building or silo for storing grain and the like includes an upright cylindrical perimeter wall that is enclosed at a top end by a conical roof that tapers upwardly and radially inwardly from a perimeter edge to an apex of the roof. In this instance, it is a known practice to assemble the rafters and exterior sheathing forming the conical roof near ground level or on a suitable foundation followed by lifting of the assembled roof in stages to construct sequential annular bands of the cylindrical perimeter wall below the roof at the various stages of lifting. Assembly of the conical roof typically involves use of a scaffold to support a fixed platform for workers in proximity to the apex of the roof together with a stair assembly for accessing the platform. One known stair assembly is supported at an upper end for rolling movement on the platform and at a lower end for rolling movement on the foundation. The rolling contact of the stair assembly relative to the platform is unconstrained such that the stair assembly can potentially roll over edges of the platform causing considerable damage and potential severe injury to workers.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided a method of constructing a conical roof of a building, the method comprising:providing a worker support apparatus comprising (i) a support column having a bottom end and a top end, (ii) a pivot frame pivotally supported on the support column in proximity to the top end of the support column, and (iii) a stair assembly extending longitudinally between a lower end of the stair assembly supported on wheels and an upper end of the stair assembly;mounting the support column to extend upwardly from the bottom end supported on a floor of the building to the top end in proximity to an apex of the conical roof such that the pivot frame is pivotal relative to the support column about a vertical pivot axis;coupling the top end of the stair assembly to the pivot frame such that (i) the stair assembly is pivotal together with the pivot frame relative to the support column about said vertical pivot axis, and (ii) the lower end of the stair assembly is in proximity to a perimeter of the conical roof with the wheels arranged for rolling movement in a circumferential direction about the vertical pivot axis of the support column;rotating the stair assembly about the vertical pivot axis between a plurality of circumferentially spaced apart working locations and supporting workers on the stair assembly while constructing respective portions of the conical roof at each of the working locations.

The method may further include providing a worker platform supported on the support column in proximity to the top end in which the worker platform has a horizontal upper supporting surface arranged to support workers thereon and in which the worker platform is supported on the pivot frame for rotation relative to the support column about the vertical pivot axis together with the stair assembly.

The method may further include providing a worker platform supported on the support column in proximity to the top end in which the worker platform has a horizontal upper supporting surface arranged to support workers thereon and in which an uppermost tread at the upper end of the stair assembly is supported in proximity to a perimeter edge of the worker platform.

The method may further include (i) providing a roof support frame supported on the top end of the support column such that the pivot frame is supported on the support column at a location spaced below the roof support frame, and (ii) supporting the apex of the conical roof on the roof support frame.

The method may further include releasing the stair assembly from the pivot frame by an upward sliding movement of the upper end of the stair assembly relative to the pivot frame.

According to a second aspect of the invention there is provided a worker support apparatus for use with a conical roof of a building, the apparatus comprising:a support column having a bottom end arranged to be supported on a floor of the building and being arranged to extend upwardly from the bottom end to a top end of the support column located in proximity to an apex of the conical roof;a pivot frame pivotally supported on the support column in proximity to the top end of the support column such that the pivot frame is pivotal relative to the support column about a vertical pivot axis;a stair assembly extending longitudinally between an upper end and a lower end of the stair assembly;the upper end of the stair assembly being arranged to be coupled to the pivot frame such that the stair assembly is pivotal together with the pivot frame relative to the support column about said vertical pivot axis; andthe lower end of the stair assembly being supported on wheels arranged for rolling movement in a circumferential direction about the vertical pivot axis of the support column.

Providing a pivot frame which is rotatable relative to the support column relative to which the top end of the stair assembly can be coupled so that the stair assembly pivots relative to the support column ensures that the stair assembly is constrained to a pivotal movement about an upright axis of the support column. This ensures that the stair assembly remains safely supported relative to the support column while also ensuring that the stair assembly can be easily aligned with any selected rafters of the roof assembly during construction by simply pivoting the stair assembly about the upright pivot axis of the support column.

Preferably a worker platform is supported on the support column in proximity to the top end in which the worker platform has a horizontal upper supporting surface arranged to support workers thereon. The worker platform is preferably supported on the pivot frame for rotation relative to the support column about the vertical pivot axis together with the stair assembly. Preferably an uppermost stair tread at the upper end of the stair assembly is supported in proximity to a perimeter edge of the worker platform.

Preferably the stair assembly is releasably coupled to the pivot frame. In this instance, the pivot frame may include a first mating connector and the upper end of the stair assembly may include a second mating connector arranged for releasable connection with the first mating connector to support the stair assembly on the pivot frame, in which the second mating connector is releasable from the first mating connector by upward sliding movement of the second mating connector relative to the first mating connector.

The support column may comprise a plurality of modular sections arranged to be stacked with one another such that the support column is adjustable in height by adding or removing one of the modular sections relative to the support column.

The support column may further comprise (i) a base portion at the bottom end for engaging the floor of the building, (ii) a mounting portion near the top end for pivotally supporting the pivot frame thereon, and (iii) an intermediate portion comprising a singular pole formed in one or more sections to extend vertically between the base portion and the mounting portion.

When the support column comprises (i) a base portion at the bottom end for engaging the floor of the building, (ii) a mounting portion near the top end for pivotally supporting the pivot frame thereon, and (iii) an intermediate portion formed in one or more sections to extend vertically between the base portion and the mounting portion, the base portion may further comprise a lifting assembly arranged to lift the intermediate portion of the support column supported on the base portion relative to the floor of the building.

Preferably the support column is arranged to be supported by guy wires extending between the support column and the floor of the building.

The apparatus may further include a roof support frame supported on the top end of the support column in which the roof support frame is arranged to support the apex of the conical roof thereon. The pivot frame is preferably supported on the support column at a location spaced below the roof support frame such that the pivot frame is pivotal relative to the roof support frame about the vertical pivot axis of the support column. The roof support frame may comprise a plurality of radial support arms extending radially from the vertical pivot axis of the support column. The radial support arms are preferably adjustable in length such that the roof support frame is adjustable in diameter.

When the roof includes a loading opening at the apex including a circular rim, the apparatus may further comprise a roof support collar arranged to be supported on the support arms concentrically with the vertical pivot axis, in which the roof support collar includes an annular upper supporting surface arranged to support the circular rim of the loading opening of the roof thereon.

DETAILED DESCRIPTION

Referring to the accompanying figures, there is illustrated a worker support apparatus generally indicated by reference numeral10. The apparatus10is particularly suited for supporting workers during construction of a conical roof12of a building14, for example a grain storage bin as shown in the accompanying figures.

In the illustrated example, the roof12tapers upwardly and radially inwardly from a circular perimeter edge16at the bottom where the roof is supported on a cylindrical perimeter wall18of the bin, to a central apex20at the top of the bin. A loading opening22is provided at the apex where a circular rim24forms the perimeter boundary of the loading opening. A hatch cover is typically subsequent mounted over the opening22to form a lid over the opening upon completion of the bin construction. The roof further includes a plurality of rafters26which extend radially between the perimeter edge16and the circular rim24at the apex20of the roof at circumferentially spaced positions about the roof. Subsequent to assembly of the rafters, suitable sheathing material28spans the top side of the rafters to form the outer boundary of the roof.

For larger bins, the bin is typically supported on a suitable foundation30such as a concrete base defining a main floor of the constructed bin. In some instances, an access passage may be provided within the concrete base below the main floor of the bin with a central passage communicating vertically between the access passage below the main floor and the hollow interior of the bin. In this instance the lower boundary of the access passage below the bin forms an auxiliary floor surface spaced below the main floor of the bin.

Construction of the roof of the bin is typically accomplished at ground level as shown inFIG.1in which the rafters are connected between the circular rim24at the apex and an upper portion32of the cylindrical wall of the bin which is also initially assembled at ground level. Once the rafters are assembled, the sheathing material28can be mounted onto the rafters as further shown inFIG.1. Once the roof is complete, the roof is then raised relative to the foundation in stages. A plurality of lifting cylinders34are provided at circumferentially spaced positions about the bin structure for actuation by a common hydraulic circuit to uniformly lift the roof by a prescribed amount relative to the foundation. The prescribed amount corresponds to the height of one annular portion of the cylindrical wall18of the bin. Each stage of the bin wall construction thus involves lifting of the roof by the prescribed amount, followed by construction of one annular portion of the cylindrical wall as shown inFIG.2. Upon completion of one annular portion of the cylindrical wall, the lifting cylinders34are then reattached to the newly constructed annular portion to lift the roof by the prescribed amount once more to permit construction of a subsequent portion of the cylindrical wall of the bin. A completed cylindrical bin constructed according to the present invention is illustrated inFIG.3.

The worker support apparatus10according to the present invention is primarily used while the roof remains under construction at ground level as shown inFIG.1. As shown inFIG.4, the apparatus10generally includes (i) a central support column36arranged to substantially span the height of the conical roof between a floor surface of the foundation and the apex of the roof during the initial assembly stage ofFIG.1, (ii) a pivot frame38which is pivotally mounted on the support column in proximity to the top end thereof so as to be pivotal about a vertical pivot axis relative to the support column, (iii) a roof support frame40mounted in fixed relation to the support column36at the top end thereof at a location spaced above the pivot frame38for supporting the circular rim24at the apex of the roof thereon during roof construction, and (iv) a stair assembly42extending longitudinally between an upper end44arranged to be fixed onto the pivot frame38for pivotal movement of the stair assembly with the pivot frame about the vertical pivot axis of the support column and a lower end46supported for rolling movement along a corresponding floor surface of the bin structure in a circumferential direction about the vertical pivot axis of the support column.

The support column36generally includes (i) a base portion48at the bottom end for being engaged upon a floor surface of the bin, (ii) a mounting portion50at the top end which supports the pivot frame38and the roof support frame40thereon, and (iii) an intermediate portion52formed in modular sections54stacked to form a singular pole connected between the base portion48at the bottom of the column and the mounting portion50at the top of the column.

The base portion includes two floor beams56mounted perpendicularly to one another to form a stable base lying a common horizontal plane for engagement on the floor surface of the bin. An inner post58extends vertically upward from the intersection of the two floor beams in fixed relation to the floor beams. An outer sleeve60has a cross-section which matches the cross-section of the inner post58and includes an inner dimension closely matching the outer dimensions of the inner post58such that the outer sleeve60can be slid over top and along the inner post58received therein.

A lift assembly of the base portion comprises two hydraulic actuators62which are mounted parallel to the inner post at diametrically opposing sides thereof so that each hydraulic actuator is connected at a bottom end to one of the floor beams and at a top end on a crossbar that is fixed to the outer sleeve60at an intermediate location along the height thereof. The actuators62are connected to a common hydraulic circuit such that the actuators can be activated together to commonly lift the outer sleeve60relative to the inner post50on the floor being56. In this instance, a plurality of modular sections of the intermediate portion of the support column can be selected to be near to the desired height of the apex of the roof and assembled to locate the roof support frame40in close proximity to the desired height of the apex. The lift assembly can then be used to further extend the support column and raise the roof support frame40to the desired height relative to the conical roof of the building.

The modular sections54of the support column each comprise an elongate tubular sleeve which is hollow and open at both ends. A plurality of couplers64are provided for connecting each end of each modular section to an adjacent modular section or the base portion below or mounting portion above. Each coupler comprises an elongate post having outer dimensions closely matching the inner dimensions of the sleeves of the modular sections54to permit the post to be slidably inserted into the abutted ends of two modular sections54. A stop collar66is provided at a central location along the post forming the coupler in which the collar66has an outer dimension closely matching the outer dimension of the sleeves54. In this manner the collar66functions as a stop which controls the amount of insertion of the post of the coupler64into each of the two sleeves54being coupled by the coupler. The coupler64can be coupled to the top end of the outer sleeve60of the base portion in the same manner. The coupler64can also be coupled in the same manner by insertion into the open bottom end of a corresponding main sleeve68of the mounting portion above.

The mounting portion50of the support column includes the main sleeve68thereof at a central location which has cross-sectional dimensions similar to the sleeves54of the intermediate portion52. The main sleeve68of the mounting portion supports a bearing plate70at an intermediate location on the main sleeve in the form of a circular plate which is welded about the main sleeve68. The bearing plate lies perpendicular to the vertical pivot axis of the support column and defines an upward facing annular bearing surface that supports a pivot sleeve72of the pivot frame rotatably thereon. The pivot sleeve72has an outer diameter which is equal to or less than the outer diameter of the bearing plate so that a bottom annular rim of the pivot sleeve72is fully engaged upon the upper bearing surface of the bearing plate70.

An inner circular rim74having an outer diameter closely matching the inner diameter of the pivot sleeve72is mounted on the upper surface of the bearing plate70to concentrically locate the pivot sleeve72relative to the bearing plate70. The circular rim74is thus received into an open bottom end of the pivot sleeve72. An upper centering plate76is welded to the main sleeve68at a location spaced above the bearing plate70in alignment with the top of the pivot sleeve72. The outer diameter of the upper centering plate76is approximately equal to the inner diameter of the pivot sleeve while being mounted so that the top of the centering plate76is substantially flush with the top edge of the pivot sleeve. In this manner the outer peripheral edge of the centering plate is rotatably engaged with an inner surface of the pivot sleeve72to assist in concentrically locating the pivot sleeve72relative to the main sleeve68while permitting relative rotation therebetween. The mounting of the pivot sleeve72about the main sleeve68by the bearing plate70and the upper centering plate76effectively defines a pivot coupling between the pivot frame and the mounting portion50of the support column. The pivot sleeve72span substantially the full height of the pivot coupling.

The roof support frame40includes a centre post78having an outer dimension which closely fits within the inner dimension of the main sleeve68of the mounting portion of the column therebelow. The centre post78is square in cross-section to mate with a corresponding square cross-section of the main sleeve68below to form a non-rotatable mating connection therebetween. This is similar to the mating non-circular cross-sectional shapes of the modular sections54of the intermediate portion of the support column and the posts of the couplers64connecting the modular sections of the support column from the base portion48to the mounting portion50so that all of the components have a square cross-section to be coupled non-rotatably relative to one another from the bottom of the base portion to the top of the roof support frame with the exception of the rotatably support of the pivot frame.

The roof support frame40further includes a stop collar80which is fixed about the exterior of the centre post78at a location spaced upwardly from the bottom end thereof. The stop collar has an outer dimension which is approximately equal to the outer dimension of the main sleeve68such that the stop collar is abutted with the top end of the main sleeve68and the bottom portion of the centre post78is received within the main sleeve68by a prescribed overlapping amount. A majority of the centre post78extends above the stop collar to the top end of the support frame.

Four radial arms82extend radially outward from the top end of the centre post78at evenly spaced apart positions in the circumferential direction such that the four radial arms are offset 90 degrees apart from one another. Each radial arm82is a hollow tube protruding perpendicularly and radially outward from the centre post. An extension tube84is slidably received through the open end of the main tube of each radial arm82and supports a hook flange86at the outer end thereof which protrudes upwardly above the top side of the corresponding radial arm82to form an upwardly protruding flange that functions to hook a portion of the circular rim24of the apex of the roof thereon in some instances. A suitable setscrew threaded through the hollow tube of each radial arm or a latch pin inserted through cooperating apertures in the extension tube84and the corresponding radial arm82permits the extension tube to be fixed at a selected position relative to the radial arm for adjusting the length of the radial arms and in turn adjusting an overall diameter of the roof support frame.

When the circular rim at the apex of the roof includes a depending flange, the depending flange may be directly engaged upon the radial arms82while being retained by the hook flanges86. Alternatively, as shown in the illustrated embodiment, when the circular rim24of the roof has a sloped bottom surface, an adapter may be provided for centering the rim24relative to the roof support frame40. The adapter comprises a roof support collar88having a diameter which is matched to the diameter of the rim of the bin roof. Different sizes of adapters may be provided for different bin sizes. The collar88of the adapter is positioned on the radial arms of the roof support frame with the position of the hook flanges86selected to contain and concentrically locate the collar88relative to the roof support frame.

A plurality of support flanges90are provided at spaced positions about the perimeter of the roof support collar88. Each support flange90comprises a top plate which is sloped downwardly and radially outwardly from an inner end supported on the outer side of the collar88to an outer end spaced radially outward from the collar, and a bottom plate below the top plate. The bottom plate of the support flange90extends horizontally outward from the collar88at a location spaced below the top plate to an outer end joined to the outer end of the top plate to rigidly support the top plate relative to the collar. The top plates of the support flanges90collectively form a conical support surface matching the slope of the circular rim24of the bin roof supported thereon.

The pivot frame38further includes two main beams92which are supported spaced apart and parallel to one another at diametrically opposing sides of the vertical pivot axis to lie in a common horizontal plane that is perpendicular to the pivot axis. The main beams92are supported relative to the pivot sleeve72of the pivot frame by a pair of connecting arms94respectively. The connecting arms94extend radially outward from the pivot sleeve72at diametrically opposed locations to lie along a common diametrical axis relative to the pivot axis. Each connecting arm94mounts a respective one of the main beams92at an outer end thereof so that the beam extends perpendicularly across the end of the connecting arm94. An additional brace arm96is connected between each connecting arm94and a location on the pivot sleeve directly above the connection of the corresponding connecting arm94to the pivot sleeve. The connecting arms94and the main beams92collectively form an H-shaped subframe mounted externally on the pivot sleeve72of the pivot coupling.

At one end of the subframe formed by the main beams92there is formed a coupling arrangement for connecting the upper end of the stair assembly onto the pivot frame. An upright collar98is mounted on one end of each of the main beams92. Each collar extends about an upright axis having an open top end defining a first mating connector arranged to receive a corresponding second mating connector100of the stair assembly therein.

More particularly, the upper end of the stairs is supported on a horizontal crossbeam102forming the upper end of the stair assembly. Two posts extend vertically downward from laterally opposing ends of the crossbeam102to define the second mating connectors100. The posts100are vertically oriented when the stair assembly is supported at the desired slope in an assembled configuration. The posts100mate with the collars98on the pivot frame for vertical sliding movement therebetween such that the stairs are coupled to the pivot frame by sliding the second mating connectors100of the stair assembly vertically downward into the open top ends of the collars98forming the first mating connectors on the pivot frame. Releasing the stair assembly from the pivot frame involves sliding the second mating connectors100vertically upward and out of the collars98forming the first mating connectors on the pivot frame. The posts100are fixed onto the crossbeam102at a horizontal spacing corresponding to the spacing between the collars98for alignment therebetween.

The apparatus10further includes a worker platform104which is mounted on the pivot frame to pivot together with the stair assembly and the pivot frame about the vertical pivot axis relative to the support column. The worker platform104defines an upper supporting surface arranged to support workers thereon during construction of the roof. The worker platform104includes a perimeter floor portion106in the form of a rigid sheet having a central opening therein so that the rigid sheet is generally annular about the opening. The sheet is mounted onto the top side of the main beams so as to be horizontally oriented. The perimeter floor portion106spans the full length and full width of the pivot frame to protrude outwardly therefrom in a cantilevered manner along two opposing sides and along one end longitudinally opposed from the coupling arrangement where the stairs are connected. The rigid sheet forming the perimeter floor portion106can be joined to the top side of the main beams of the pivot frame by various means including connecting flanges, support braces108or gussets of various forms. The perimeter floor portion106forms an annular perimeter portion of the upper supporting surface of the worker platform that supports workers thereon.

An edge flange110is mounted about the perimeter of the floor portion106to form a lip protruding upwardly above the upper supporting surface that supports workers thereon. The edge flange110extends about the full perimeter of the worker platform with the exception of a gap in the perimeter that is aligned with the stairs between the two collars98forming the coupling arrangement to the stair assembly.

A railing assembly is also mounted about the perimeter of the floor portion106with the exception of the gap in the perimeter that is aligned with the stairs as described above. The railing assembly includes a plurality of posts112which are fixed to the edge flange110to extend upwardly therefrom and a plurality of railing members114connected between adjacent ones of the posts at different elevations while remaining open at the gap between the first mating connectors98for the stair assembly.

The worker platform further includes a plurality of floor panels116which enclose the central opening in the perimeter floor portion106. The floor panels116each comprise an elongate member which is mounted to extend in a lateral direction to be supported at opposing ends on the top side of the two main beams92respectively. The floor panels fit within the cavity defined by the perimeter floor portion106so that the floor panels are fully surrounded by the perimeter floor portion106. Each floor panel spans the width of the cavity in the lateral direction that is perpendicular to the beams92. A sufficient number of floor panels are provided so that the floor panels are abutted side-by-side in the longitudinal direction of the beams92so that the collective width of all the floor panels fits closely within the longitudinal dimension of the cavity in the perimeter floor portion106to constrain the floor panels in the longitudinal direction of the beams92.

The floor panels116each include a flat upper surface lying in a common plane with the other panels and in a common plane with the perimeter floor portion106so that the floor panels116and the perimeter floor portion106collectively define the entirety of the upper supporting surface of the worker platform that supports workers thereon. Each floor panel is formed of a rigid sheet material formed in an inverted U shape in cross-section so as to comprise a top bridge plate spanning the length of the floor panel between the opposing ends and two side flanges depending down from opposing sides of the bridge plate along the full length of the floor panel so that the side flanges of the panels are engaged upon the top side of the main beams92in a mounted position.

The stair assembly42includes two stringers118which collectively span the full length of the stair assembly in the longitudinal direction between an upper end at the crossbeam102and an opposing lower end joined by a lower crossbeam120. The stringers are formed in modular sections which can be readily attached to one another or disassembled for transport. Furthermore, the number of modular sections connected between the upper and lower ends of the stair assembly can be adjusted to vary the overall length of the stair assembly according to the size of the bin being constructed. Each modular section includes a plurality of stair treads122connected laterally between the two stringers so that the sections of the stringers and the treads connected therebetween form a fixed rigid frame. A suitable railing structure124is also mounted along both sides of each modular section of the stair assembly so that the railing extends upward from the stringers118respectively.

An uppermost modular section of the stair assembly supports the upper crossbeam102spanning between the two stringers thereof, while a lowermost modular section of the air assembly supports the bottom crossbeam120extending between the two stringers of that modular stair section. Intermediate modular sections of the stair assembly between the top and bottom sections are otherwise substantially identical to one another and interchangeable with one another. In the mounted position of the stair assembly, an uppermost tread among the stair treads122is located in close proximity to a perimeter edge of the worker platform104at a similar elevation to one another.

The bottom crossbeam120is supported along the bottom of the stringers to extend laterally across the width of the stair assembly and protrude outwardly beyond the stringers at both opposing ends of the bottom crossbeam120. A vertical leg126extends downward from each end of the bottom crossbeam120to supports an axle at the bottom end of each leg which in turn supports a dual wheel set128thereon for rolling movement along the floor surface of the bin while supporting the bottom end of the stringers spaced above the floor. The dual wheels at each end of the bottom crossbeam120are oriented for rolling movement perpendicularly to the longitudinal direction of the stair assembly corresponding to a circumferential direction about the vertical pivot axis of the upright support column.

The apparatus10is typically provided in the form of a kit of parts ready to be assembled such that the kit of parts can be readily transported between different job sites. Before construction of the roof begins, a centre of the bin is located on the bin floor so that the support column can be assembled on the bin floor in concentric alignment with the desired location of the cylindrical wall of the bin and the roof thereabove. The support column is assembled in sections stacked one above the other with the worker platform104fixed onto the mounting portion and the pivot frame rotatably supported on the mounting portion of the support column. A set of guy wires130are connected between the intermediate portion of the support column and the floor surface of the bin foundation at a plurality of circumferentially spaced positions to maintain the support column in a vertical orientation relative to the bin structure.

The stair assembly can then be assembled and attached to the pivot frame at the upper end by inserting the second mating connectors of the stair assembly vertically downward into the collars98forming the first mating connectors on the pivot frame. Using access provided by the stairs, the railings and the floor panels of the worker platform can then be mounted in place followed by attachment of the roof support member onto the top end of the support column.

Once the apparatus has been assembled, construction of the roof begins by positioning the circular rim for the apex of the roof on the roof support member at the top of the apparatus. The stairs are positioned at a slope corresponding approximately to the slope of the roof so that the stairs can be located immediately below each rafter being assembled from the perimeter edge to the apex of the roof. Upon assembly of each rafter, the stair assembly is rotated about the vertical pivot axis of the support column to the next rafter location to permit assembly of the next rafter while workers are supported on the stair assembly and/or the worker platform104. Once all of the rafters have been assembled, the stair assembly can then be further pivoted to each rafter location for ease of attachment of exterior sheathing onto the exterior of the rafters. Once all of the sheathing has been mounted and the construction of the roof is complete, the apparatus10can be disassembled and the remainder of the cylindrical wall of the bin is constructed by jacking up the roof in stages using the perimeter lift cylinders34as described above.