Patent Description:
This invention relates to barriers for guarding against entry of floodwaters into buildings.

Floodwaters are a major source of property damage. On October <NUM> and <NUM>, <NUM> tropical storm Sandy struck New York City, its suburbs, and Long Island. Supplemented by a high tide, the storm surge was approximately <NUM> feet, i.e. <NUM>, above mean low tide, overtopping seawalls and bulkheads lining Manhattan and other waterfront boroughs, flooding buildings, subway and vehicle tunnels, damaging electrical equipment, costing at least <NUM> lives, and in effect shutting down the City. Damages and economic losses across New York were estimated to be at least $<NUM> billion and in neighboring New Jersey, $<NUM> billion.

Doors and other grade level vertical openings can be guarded from entrance of water by gates that are self-actuating by the invention described in <CIT>. A problem is guarding a multi-level construction where vertically separated levels are accessed by stairs leading from one level to another. For example, if a lower floor has steps leading down to it from an entrance at street or ground level (for example, a basement, a lower level of a parking garage, or a storage area below a building mezzanine), and if due to the stairs and the construction of the building, the staired access to the lower level from the higher street or ground level cannot be closed by the solution given by <CIT>, then on the occasion of flooding waters rising at street or ground level, the lower level will be flooded. In the case of stairs descending inside a building (for instance, a foyer) to a lower level (for instance a lower floor, which could be a basement), even if a door entrance to the stairs is protected by the solution of <CIT>, water invading though a lower level such as a basement can rise though a staired access from the basement and flood the ground floor and higher levels if due to the stairs and the construction of the building, the staired access cannot be closed off from the higher level by the solution of <CIT>. In another problem, a raised entrance to a building may be accessed by a flight of stairs the construction of which in proximity to the entrance may prevent installation of the solution of <CIT> to guard the entrance.

<CIT> describes a companion stairway for application to openings which are necessary for communication between decks of, for example, ships where the openings may be companion staircases, lifts, ventilators and the like. In the companion stairway each step, or the steps as a whole, may be in the form of an airtight box. At the back or underside of the steps is provided an additional airtight chamber or float, the lower end of which may normally fit in to a recess in the deck so as to lie flush therewith and serve to steady the steps when in ordinary use. A guide is provided on one or on each side of the stairway, the sides of which may be provided with rollers, the arrangement being such that, in the event of the deck being flooded, the stairway which is hinged at the top will generally rise from the bottom and, being guided by the aforesaid guides and rollers, will eventually completely close the opening in the deck above.

<CIT> describes a prevention system for protecting urban underground facilities or subways from flood water inflow or submersion. A top-level staircase part is rotated upwards using hydraulic means to be used as an inflow water preventive staircase allowing exit from the urban underground facility via this staircase during a flood condition. Usually, at a level where this staircase part is stored, a staircase for refuge is formed by connecting the higher top step of the rotary staircase to the top step of a fixed staircase. In a small gap between a fixed staircase step surface and this movable step, a seal material is applied to completely prevent water inflow or leak through it.

Disclosed herein is a self-actuating gate that allows flood prevention in a staired multi-level construction where stairs connect a lower level or floor with a higher level or floor.

In the following detailed description of exemplary embodiments, reference is made to the accompanying drawings, which form a part hereof and in which are shown by way of illustration examples of exemplary embodiments with which the invention may be practiced. In the drawings and descriptions, like or corresponding parts are marked throughout the specification and drawings with the same reference numerals. Certain features of the invention may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in the interest of clarity and conciseness. Referring to the drawings:.

Specific details described herein, including what is stated in the Abstract, are in every case a non-limiting description and exemplification of embodiments representing concrete ways in which the concepts of the invention may be practiced. Any examples or illustrations given herein are not to be regarded in any way as restrictions on, limits to, or express definitions of, any term or terms with which they are utilized. Instead, these examples or illustrations are to be regarded as being described with respect to one particular embodiment and as illustrative only. Those of ordinary skill in the art will appreciate that any term or terms with which these examples or illustrations are utilized will encompass other embodiments that may or may not be given therewith or elsewhere in the specification and all such embodiments are intended to be included within the scope of that term or terms, as long as they fall within the scope of the invention as defined in the claims. The examples serve to teach one skilled in the art to employ the present invention as defined in the claims in virtually any appropriately detailed system, structure or manner consistent with those concepts. Language designating such non-limiting examples and illustrations includes, but is not limited to: "for example", "for instance", "e.g.", "in an embodiment". Reference throughout this specification to "an exemplary embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one exemplary embodiment of the present invention. Thus, the appearances of the phrase "in an exemplary embodiment" or similar expression in various places throughout this specification are not necessarily all referring to the same embodiment. Further, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. Various changes and alternatives to the specific described embodiments and the details of those embodiments may be made within the scope of the invention as defined in the claims. One or more of the elements depicted in the drawings can also be implemented in a more separated or integrated manner, or even removed or rendered as inoperable in certain cases, as is useful in accordance with a particular application, as long as the modification falls within the scope of the invention as defined in the claims. Because many varying and different embodiments may be made within the scope of the inventive concepts herein described and in the exemplary embodiments herein detailed, it is to be understood that the details herein are to be interpreted as illustrative and not as limiting the invention to that which is illustrated and described herein. The invention is solely limited by the scope of the appended claims.

The various directions such as "upper", "lower", "back", "front", "transverse", "perpendicular", "vertical", "horizontal", "length", "height", "width", "laterally", "proximal", "distal" and so forth used in the detailed description of exemplary embodiments are made only for easier explanation in conjunction with the drawings. The components may be oriented differently while performing the same function and accomplishing the same result as the exemplary embodiments herein detailed embody the concepts of the invention as defined in the claims, and such terminologies are not to be understood as limiting the concepts which the embodiments exemplify.

As used herein, the terms "comprises", "comprising", "includes", "including", "has", "having" or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such apparatus. As used herein, the use of the word "a" or "an" when used in conjunction with the term "comprising" (or the synonymous "having" or "including" or variants of the same) in the claims and/or the specification may mean "one", but it is also consistent with the meaning of "one or more", "at least one", and "one or more than one". That is, unless otherwise indicated, the term "or" is generally intended to mean "and/or". In addition, as used herein, the phrase "connection to" or "connected to" means joined to, either directly or through intermediate components.

In accordance with an embodiment of the invention, one level of a construction, for example a building, is guarded from flooding water coming from another level of the construction where the levels are reached by connecting stairs. A flight of stairs bridging the levels is buoyant and one end of the flight is pivotally connected to the construction adjacent one of the levels such that on occasion of presence of water in one of the levels effective to buoy the flight, the flight rotates upward on the axis of the pivot to block water from flooding at least the part of the other level past the risen flight.

For example, in an embodiment a lower level of a construction, for instance, a basement, is guarded from flooding by rising ground or street ('upper") level water where the lower level is reached from the upper level by connecting stairs. The flight of stairs bridging the levels is buoyant and an lower end of the flight is pivotally connected to the construction adjacent the lower level such that on occasion of water rising in the upper ground or street level, the flight buoyantly rotates upward on the axis of the pivot to block water from flooding the lower level.

In another embodiment, a lower level of a multi-level construction is guarded from flooding by water entering from an upper level of the construction where the lower level is reached from the upper level (or vice versa) by connecting stairs. The flight of stairs bridging the levels is buoyant and a lower end of the flight is pivotally connected to the construction adjacent the lower level such that on occasion of water entering the lower level effective to buoy the flight, the flight buoyantly rotates upward on the axis of the pivot to block water from flooding the lower level past the rotated flight and as well can block water from any further flooding of the upper level past the rotated flight.

For another example, in an embodiment an upper level of a multi-level construction is guarded from flooding by water rising from a lower level of the construction where the upper level is reached from the lower level (or vice versa) by connecting stairs. The flight of stairs bridging the levels is buoyant and an upper end of the flight is pivotally connected to the construction adjacent the upper level such that on occasion of water rising in the lower level, the flight buoyantly rotates upward on the axis of the pivot to block water from flooding the upper level.

More particularly, in these several exemplary embodiments, a self actuating flood guard comprises a buoyant flight of steps. The flight has lower and upper ends and bridges at least an upper part of a vertical distance between lower and upper levels of a construction. The flight of steps is flanked by vertical walls alongside the flight. The walls alongside the flight prevent water from flowing around the sides of the flight. The steps block fluid communication across the flight, that is, from one side of the flight to the other side of the flight. As well known, a step comprises two members, a tread, which is the horizontal member, and a riser, the vertical member. The vertical member is not an "open" riser because the flight blocks fluid communication from one side of the flight to the other.

The flood guard includes pivotation members comprising a stationary member connected to the construction adjacent one of its levels and a moveable member moveably joined to the stationary member. The moveable member is connected to one of the ends of the flight of stairs and is pivotable about a horizontal axis transverse to the flanking vertical walls, whereby upon presence of water in one of the levels effective to buoy the flight, an end of the flight remote from the axis rotates upwardly away from the lower level. At least one restraint is configured to act on the flight and prevent the flight from rotating about the axis more than a predetermined extent when the end of the flight remote from the axis rotates upwardly away from the lower level of the construction.

In an embodiment of the invention, the flood guard restraint is connected to the construction a distance above the lower end of the flight. In an embodiment, the restraint is located at least as high as the upper level.

In an embodiment of the invention, flexible lip seal gaskets are along lateral sides of the flight of width sufficient to sealingly wipe the flanking walls and prevent significant passage of water between the lateral sides of the flight and the flanking walls.

In a not claimed embodiment of the invention, the pivotation members of the flood guard are located at an end of the flight adjacent the lower level of the construction.

In an embodiment of the invention, the pivotation members of the flood guard are located at an end of the flight adjacent the lower level and the flood guard comprises an inlet on the upper level before the flight to admit water entering the upper level into the lower level under the flight.

In an embodiment of the invention, the pivotation members of the flood guard are located at an end of the flight adjacent the lower level and the restraint is connected to the construction a distance above the horizontal axis allowing the flight to rotate to a substantially vertical orientation.

In an embodiment of the invention, the pivotation members of the flood guard are located at an end of the flight adjacent the upper level.

In a not claimed embodime, the pivotation members are located at an end of the flight adjacent the upper level and the restraint is connected to the construction a distance above the lower level allowing the flight to rotate at least to a substantially horizontal orientation.

In a not claimed embodiment, the pivotation members are located at an end of the flight adjacent the upper level, the restraint is connected to the construction a distance above the lower level allowing the flight to rotate at least to a substantially horizontal orientation, and the construction comprises a stairwell in which the flight of stars is placed and in which the stairwell includes a wall transverse to the flanking walls. This transverse wall is spaced from the axis by a distance sufficiently equal to a run of the flight plus the tread of the last step that on rotation of the flight to the substantially horizontal orientation, water under the flight is blocked from entering the upper level. As well known a "run" of a flight of stairs is the horizontal distance from the first riser to the last riser (it is not the sum of the individual tread lengths if any part of the tread protrudes over the riser beneath, called a nose; if nosing is present, the treads overlap between treads).

In an embodiment of the invention, the pivotation members of the flood guard are located at an end of the flight adjacent the upper level and the restraint is connected to the construction a distance above the upper level allowing the flight to rotate to a substantially vertical orientation such that water is blocked from entering the upper level past the rotated flight.

In an embodiment of the invention in which the pivotation members of the flood guard are located at an end of the buoyant flight adjacent the upper level, the lower end of the buoyant flight rests on stationary stairs. The pivotally upwardly rotatable flight and the stationary stairs span the upper and lower levels.

In an embodiment of the invention in which the pivotation members of the flood guard are located at an end of the flight adjacent the upper level and the lower end of the flight rests on stationary stairs, and in which the flight and the stationary stairs span the upper and lower levels, an embodiment has the restraint connected to the construction a distance above said lower level and to the flight, allowing the flight to rotate to a substantially vertical orientation such that water is blocked from entering said upper level past the rotated flight.

Referring now to <FIG>, an embodiment guards from flooding a portion of an upper level (or floor) and a portion of a lower level (or floor) (e.g., a basement), each such portion being a portion distal to a source of entry of water into the levels. The embodiment, in one instance, guards such distal portions from flood waters gaining access into the construction in a portion of an upper floor remote from the distal portions. But for the flood guard, the waters from such remote source would flood all of the upper level and cascade down stairs leading from the upper level to the lower level and flood all of the lower level. In another instance, the embodiment guards such distal portions from flood waters gaining access into the construction at a portion of the lower floor remote from the distal portion of the lower floor, and but for such embodiment, the waters would flood the distal portion of the lower level and "climb" the stairs leading from the lower level to the upper level, flooding the distal portion of the upper level.

In the embodiment of <FIG>, a self actuating flood guard indicated generally by reference numeral <NUM> comprises a buoyant flight of steps <NUM>, having a lower end <NUM> and an upper end <NUM>, that bridges a vertical distance between lower level <NUM> and upper level <NUM> of a construction <NUM>. The flight of steps <NUM> is flanked by vertical walls <NUM>, <NUM>' alongside flight <NUM> below level <NUM> and vertical walls <NUM>, <NUM>' above level <NUM>. (<FIG> is a cross section between walls <NUM>, <NUM>' and <NUM>, <NUM>' so only walls <NUM> and <NUM> are seen. ) An inlet <NUM> on upper level <NUM> of construction <NUM> preceding flight <NUM> admits waters entering upper level <NUM> into lower level <NUM> under flight <NUM>. The steps of flight <NUM> block fluid communication across the flight, that is, from one side "A" of the flight to the opposite side "B" of the flight. Pivotation members <NUM> located at lower end <NUM> of flight <NUM> adjacent lower level <NUM> of construction <NUM> comprise a stationary member connected to construction <NUM> and a moveable member moveable joined to the stationary member. The moveable member is connected to lower end <NUM> of flight <NUM> and is pivotable about a horizontal axis <NUM> transverse to the flanking vertical walls <NUM>, <NUM>', whereby upon presence of water at upper level <NUM> entering lower level <NUM> though inlet <NUM>, water present under flight <NUM> (indicated by arrow "C") effective to buoy flight <NUM> upwardly, the upper end <NUM> of flight <NUM> rotates upwardly away from lower level <NUM>, rising above upper level <NUM> of the construction. The early part of the upward rotation is effected by buoyancy lifting the flight off level <NUM>, and the later part of rotation is driven more by hydrostatic force of water impressed against the underside of flight <NUM>. A restraint <NUM> is affixed to construction <NUM> situated to act on flight <NUM> to prevent flight <NUM> from rotating about axis <NUM> more than a predetermined extent when upper end <NUM> of flight <NUM> rotates upwardly away from lower level <NUM> of construction <NUM>. As shown, restraint <NUM> is connected to construction <NUM> a distance above lower end <NUM> of flight <NUM> allowing the flight to rotate to a substantially vertical orientation. As shown, restraint <NUM> is located above upper level <NUM> substantially in a vertical plane in which axis <NUM> also resides, but restraint <NUM> may be located below level <NUM>, and need not reside in such vertical plane. When end <NUM> of flight <NUM> is rotated above level <NUM> and all of flight <NUM> also rotates upwardly though vertical walls <NUM>, <NUM>' and <NUM>, <NUM>', street or ground water entering upper level <NUM> is prevented from entering the portion of level <NUM> distal to a source of water entering level <NUM> and admitted through inlet <NUM> onto level <NUM> below flight <NUM> (this distal portion is to the viewer's right of upright flight <NUM> in <FIG>). Not seen in this schematic cross section, flexible lip seal gaskets along lateral sides of flight <NUM> have width sufficient to sealingly wipe flanking walls <NUM>, <NUM>' and prevent significant passage of water between the lateral sides of flight <NUM> and flanking walls <NUM>, <NUM>'.

In the embodiment of <FIG>, using identical reference numbers for corresponding structures shown in <FIG>, a self actuating flood guard indicated generally by reference numeral <NUM>' comprises a buoyant flight of steps <NUM>, having a lower end <NUM> and an upper end <NUM>, that bridges a vertical distance between lower level <NUM> and upper level <NUM> of a multi-level construction <NUM>. The flight of steps <NUM> is flanked by vertical walls <NUM>, <NUM>' alongside flight <NUM>. (<FIG> is a cross section between walls <NUM>, <NUM>' so only one of the walls, wall <NUM>, is seen. ) Vertical walls <NUM>, <NUM>' extend above lower level <NUM> and upper level <NUM> in the multi-level construction <NUM>. An inlet <NUM> on upper level <NUM> of construction <NUM> preceding flight <NUM> admits waters entering upper level <NUM> into lower level <NUM> under flight <NUM>. The steps of flight <NUM> block fluid communication across the flight, that is, from one side "A" of the flight to the opposite side "B" of the flight. Pivotation members <NUM> located at lower end <NUM> of flight <NUM> adjacent lower level <NUM> of construction <NUM> comprise a stationary member connected to construction <NUM> and a moveable member moveable joined to the stationary member. The moveable member is connected to lower end <NUM> of flight <NUM> and is pivotable about a horizontal axis <NUM> transverse to the flanking vertical walls <NUM>, <NUM>', whereby upon presence of water under flight <NUM> (indicated by arrow "C") effective to buoy flight <NUM> upwardly, the upper end <NUM> of flight <NUM> rotates upwardly away from lower level <NUM>, rising above upper level <NUM> of the construction. The early part of the upward rotation is effected by buoyancy lifting the flight off level <NUM>, and the later part of rotation is driven more by hydrostatic force of water impressed against the underside of flight <NUM> A restraint <NUM> is affixed to construction <NUM> situated to act on flight <NUM> to prevent flight <NUM> from rotating about axis <NUM> more than a predetermined extent when upper end <NUM> of flight <NUM> rotates upwardly away from lower level <NUM> of construction <NUM>. Restraint <NUM> is connected to construction <NUM> a distance above lower end <NUM> of flight <NUM> allowing the flight to rotate to a substantially vertical orientation. As shown in the embodiment of <FIG>, restraint <NUM> is located above upper level <NUM> substantially in a vertical plane in which axis <NUM> also resides, but restraint <NUM> may be located below level <NUM>, and need not reside in such vertical plane. When end <NUM> of flight <NUM> is rotated above level <NUM>, the portion of level <NUM> distal to a source of water entering level <NUM> (to the right of upright flight <NUM> as viewed in <FIG>) is prevented from receiving additional water from that source that does not rise to a level topping end <NUM> of flight <NUM>, either during rise from level <NUM> or when flight <NUM> is fully elevated. Not seen in this schematic cross section, flexible lip seal gaskets along lateral sides of flight <NUM> have width sufficient to sealingly wipe flanking walls <NUM>, <NUM>' and prevent significant passage of water between the lateral sides of flight <NUM> and flanking walls <NUM>, <NUM>'.

Referring now to <FIG>, an embodiment guards all or at least a portion of an upper level (or floor) of multi-level construction <NUM> from flood waters gaining access into the construction in a lower level that but for the flood guard would climb stairs leading from the lower level to the upper level and flood the upper level. In <FIG> using identical reference numbers to corresponding structures shown in <FIG> and <FIG>, a self actuating flood guard indicated generally by reference numeral <NUM> comprises a buoyant flight of steps <NUM> having a lower end <NUM> and an upper end <NUM> and bridges a vertical distance between lower level <NUM> and upper level <NUM> of a multi-level construction <NUM>. The flight of steps <NUM> is flanked by vertical walls <NUM>, <NUM>' alongside flight <NUM>. Vertical walls <NUM>, <NUM>' extend at least above lower level <NUM> to upper level <NUM>. Like <FIG> and <FIG>, <FIG> is a cross section between walls <NUM>, <NUM>' so only one of the walls, wall <NUM>, is seen. The steps of flight <NUM> block fluid communication across the flight, that is, from one side "A" of the flight to the opposite side "B" of the flight. Pivotation members <NUM> located at upper end <NUM> of flight <NUM> adjacent upper level <NUM> of construction <NUM> comprise a stationary member connected to construction <NUM> and a moveable member moveable joined to the stationary member. The moveable member is connected to upper end <NUM> of flight <NUM> and is pivotable about a horizontal axis <NUM> transverse to the flanking vertical walls <NUM>, <NUM>', whereby upon entry of water onto level <NUM> (indicated by exemplary arrow "C") effective to buoy flight <NUM>, the lower end <NUM> of flight <NUM> buoyantly rotates upwardly away from lower level <NUM> of construction <NUM>. A restraint <NUM> is affixed to construction <NUM> situated to act on flight <NUM> to prevent flight <NUM> from rotating about axis <NUM> more than a predetermined extent when lower end <NUM> of flight <NUM> buoyantly rotates upwardly away from lower level <NUM> of construction <NUM>. In <FIG>, restraint <NUM> is connected to construction <NUM> a distance above lower end <NUM> of flight <NUM> allowing the flight to rotate to a substantially horizontal orientation.

In an embodiment, construction <NUM> depicted in <FIG> comprises a stairwell in which the flight of stars <NUM> is placed and in which the stairwell includes a wall <NUM> (indicated by dashed lines) transverse to flanking walls <NUM>, <NUM>', which extend above level <NUM>. Wall <NUM> is spaced from axis <NUM> by a distance sufficiently equal to the run of flight <NUM> that on rotation of flight <NUM> to substantially horizontal orientation, water in lower level <NUM> is blocked from entering upper level <NUM>. In another embodiment, restraint <NUM> is connected to construction <NUM> a distance above lower level <NUM> allowing flight <NUM> to rotate at least to a substantially vertical orientation, as in <FIG>, such that water is blocked from entering a portion of upper level <NUM>, for example, a hallway, past the vertically rotated flight <NUM>. Not seen in this schematic cross section, flexible lip seal gaskets along lateral sides of flight <NUM> have width sufficient to sealingly wipe flanking walls <NUM>, <NUM>' and prevent significant passage of water between the lateral sides of flight <NUM> and flanking walls <NUM>, <NUM>'.

Referring to <FIG>, another embodiment <NUM>, is depicted. It guards an upper level (or floor) of a construction from flood waters rising from a lower level to the upper level of a construction in which steps lead from the lower level (for example, but not limited to, ground level) to the upper level (which might be the first floor or ground floor of a building) where but for the flood guard the rising waters would flood the upper level. In <FIG>, the same reference numerals employed in <FIG> are used to indicate corresponding members. Construction <NUM> above level <NUM> may be an entrance of a building. Pivotation members <NUM> are located at an upper end <NUM> of <NUM> flight adjacent upper level <NUM> of construction <NUM>. The lower end <NUM> of a flight <NUM> rests on stationary stairs <NUM>. Flight <NUM> and stationary stairs <NUM> span upper and lower levels <NUM> and <NUM> respectively and provide access from lower level <NUM>, which may be at ground level, to upper level <NUM>, suitably into an entrance of a building construction <NUM> fronted by the stairs. On rise of water in front of the stairs buoying up flight <NUM>, end <NUM> of flight <NUM> remote from axis <NUM> rotates upwardly away from stationary stairs <NUM> on lower level <NUM>. A restraint <NUM> is connected both to construction <NUM> a distance above lower level <NUM> and to flight <NUM>, allowing flight <NUM> to rotate to a substantially vertical orientation wiping walls <NUM>, <NUM>' during rotation such that water is blocked from entering upper level <NUM> past rotated flight <NUM> (extended restraint <NUM> shown in dashed lines). Like <FIG>, <FIG> is a cross section between walls <NUM>, <NUM>' so only one of the walls, wall <NUM>, is seen. Like <FIG>, flexible lip seal gaskets (not seen in this schematic cross section) along lateral sides of flight <NUM> have width sufficient to sealingly wipe flanking walls <NUM>, <NUM>' and prevent significant passage of water between the lateral sides of flight <NUM> and flanking walls <NUM>, <NUM>'.

Claim 1:
A self actuating flood guard comprising:
a buoyant flight (<NUM>) of steps having lower (<NUM>) and upper (<NUM>) ends and bridging at least an upper part of a vertical distance between lower and upper levels of a construction, said flight (<NUM>) being flanked by vertical walls alongside the flight, said steps in said flight blocking fluid communication across the flight,
pivotation members (<NUM>) comprising a stationary member connected to said construction adjacent one of said levels and a moveable member moveably joined to said stationary member, said moveable member being connected to one (<NUM> or <NUM>) of said ends of said flight (<NUM>) and pivotable about a horizontal axis (<NUM>) transverse to said vertical walls, whereby upon presence of water at one of said levels effective to buoy said flight, an end (<NUM>) of the flight (<NUM>) remote from said axis (<NUM>) rotates upwardly away from said lower level of the construction, and
at least one restraint (<NUM>) configured to prevent the flight (<NUM>) from rotating about said axis more than a predetermined extent when said end of said flight (<NUM>) remote from said axis rotates upwardly away from said lower level of the construction, wherein the at least one restraint (<NUM>) is configured to allow the flight (<NUM>) to rotate about said axis to a substantially vertical orientation.