CA2504363A1

CA2504363A1 - Adjustable and transportable scaffolding

Info

Publication number: CA2504363A1
Application number: CA002504363A
Authority: CA
Inventors: Daniel Grenon; Marco Robidoux; Richard Boucher
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-07-27
Filing date: 2005-04-06
Publication date: 2006-01-27
Also published as: WO2006010247A1; US20090026013A1

Abstract

An adjustable and transportable scaffolding is described. It comprises an adjustable leg support mechanism for a scaffolding having vertical corner frame members connected to horizontal frame members and cross-braces. The mechanism comprises an open-ended sleeve adapted to receive a support rod therethrough and wherein the support rod has at least a horizontal toothed edge section and a bottom support foot. A tooth engaging member is pivotally secured to the sleeve and has a tooth engaging head biased against the toothed edge inside the sleeve for supporting the sleeve about the support rod while permitting upward displacement of the sleeve about the rod. The tooth engaging head can be unbiased from the toothed edge of the support rod to permit downward displacement of the sleeve about the rod. A
locking member is provided to lock the tooth engaging head in arresting position with the toothed edge. The sleeve is also securable for support engagement of one of the corner frame members of the scaffolding.

Description

ADJUSTABLE AND TRANSPORTABLE SCAFFOLDING
The present invention relates to an adjustable and transportable scaffolding and more particularly to an s adjustable leg support mechanism which provides ease of leveling a scaffolding on an irregular ground support surface.
Scaffolding devices comprising interconnectable tubular frame members are well known in the art whereby to io support people and material in an elevated position whereby to facilitate working on structures such as building structures or working adjacent elevated ceilings. When working on scaffolding outdoors, often the ground area adjacent the structure is irregular and it is therefore i5 necessary before climbing such scaffolding or building such scaffolding that the ground be preferably level or else the vertical corner posts of the scaffolding are shimmed by using all sorts of material whereby the space of the scaffolding lies substantially in a planar horizontal plane.
2o A problem with such shimming is that often it becomes disengaged and this can cause the scaffolding to collapse resulting in injuries to personnel working on such structures.
Another disadvantage of scaffolding is that once 25 erected they are difficult to transport to relocate at a different site. Usually the entire scaffolding structure is disassembled and re-assembled at the new site where again it may be required to shim the corner vertical post to re-level the structure prior to assembly thereof.
3o Solutions have been proposed to remedy these problems and reference is made to U.S. Patent 4,171,033 which proposes such solutions. One solution is to mount the scaffolding on wheels which may be retracted, as illustrated in U.S. Patent 5,937,967. In order to maintain the working

- 2 -platform of the scaffolding substantially horizontal at a desired position, telescopic legs have also been proposed as described and shown in U.S. Patent 4,171,033. However, such proposed solution is very time-consuming and is permanently s adapted to a specific scaffolding platform. There is therefore a need to also provide a scaffolding which incorporates features of adjustability and transportability and which is easy to disassemble and assemble and which can be transported by small transport vehicles such as a pick-up to truck or the like small vehicles . There is also a need to provide an adjustable and transportable scaffolding which is safe to use and which can be erected very quickly and easily displaceable from site to site.
It is therefore a feature of the present invention is to provide an adjustable and transportable scaffolding which substantially overcomes the disadvantages of the above mentioned prior art and which provides for the required needs.
Another feature of the present invention is to 2o provide an adjustable leg support mechanism which is securable to vertical corner posts of a scaffolding structure and which is easy to connect thereto, which is quick and easy to adjust by a single person.
Another feature of the present invention is to 2s provide an adjustable leg support mechanism to which is connectable wheels whereby to transport and displace and assembly scaffolding from site to site.
Another feature of the present invention is to provide a scaffolding and wherein the wheels can be 3o displaced about the scaffolding corner posts for ease of displacing the scaffolding.
According to a still further feature of the present invention there is provided a support foot for a

- 3 -scaffolding which is slidingly displaced over a ground support surface even when covered with snow.
According to the above features, from a broad aspect, the present invention provides an adjustable leg s support mechanism for a scaffolding having vertical corner frame members connected to horizontal frame members and cross-braces. The mechanism is characterized in that it comprises an open-ended sleeve adapted to receive a support rod therethrough and wherein the support rod has at least a io longitudinal toothed edge section and a bottom support foot.
A tooth engaging member is pivotally secured to the sleeve and has a tooth engaging head biased against the toothed edge inside the sleeve for supporting the sleeve about the bottom support rod while permitting upward displacement of 15 the sleeve about the rod. Means is provided to unbias the tooth engaging head from the toothed edge to permit downward displacement of the sleeve about the rod. Arresting means is provided to lock the tooth engaging head in arresting position with the toothed edge. Attachment means is 2o provided for securing the sleeve for support engagement with one of the vertical corner frame members of a scaffolding.
According to another broad aspect of the present invention there is provided a support foot for a scaffolding having vertical corner posts. The support foot is 25 characterized by a slide plate having a bottom ground engaging face and opposed upwardly angled end flanges. A
vertical connector is disposed substantially central on a top wall of the slide plate for removable connection with a lower end section of a vertical corner post.
3o A preferred embodiment of the present invention will now be described with reference to the accompanying drawings in which:
FIGURE 1 is a simplified side view, partly fragmented, showing a section of a scaffolding and to which

- 4 -is secured an adjustable leg support mechanism to each of two vertical corner posts of the scaffolding for ease of adjustment of the scaffolding on an irregular ground surface;
FIGURE 2 is a side view, partly sectioned, illustrating the construction of the open-ended sleeve and some of its component parts for displaceable connection about a support rod;
FIGURE 3 is a top view of the open-ended sleeve to substantially as illustrated in Figure 2;
FIGURE 4 is a side view illustrating the support sleeve and its rod connector and attachment means to secure to a vertical connecting post of a scaffolding structure;
FIGURE 5 is a side section view similar to Figure 2 but showing the support rod having a serrated edge and extending through the open-ended sleeve;
FIGURE 6 is a side view, partly sectioned, of the sliding foot plate and its vertical connector to secure to the bottom of a hollow corner frame member of a 2o scaffolding;
FIGURE 7A is a side view showing the support rod secured to the foot plate;
FIGURE 7B is an end view of Figure 7A;
FIGURE 8 is a partly sectioned side view of the sleeve showing a support wheel secured thereto as well as an adjustable rod connector secured to the sleeve;
FIGURE 9 is a top view illustrating the construction of the arcuate horizontal lock flange;
FIGURE 10 is a side view of Figure 9 illustrating 3o the disposition of the lock flange relative to a pivot connecting flange secured to the open-ended sleeve;
FIGURE 11 is a top view showing an adjustable leg support mechanism with the attachments as shown in Figure 8 and secured to a telescopic horizontal rod;

- 5 -FIGURE 12 is a side view showing the other side of a tandem arrangement of two adjustable leg support mechanisms with wheels secured together by the telescopic rod;
FIGURE' 13 is a top view illustrating the construction of a carriage assembly secured to the adjustable leg support mechanism of a tandem arrangement;
and FIGURE 14 is a view similar to Figure 13 but io showing the wheels interconnected to the adjustable leg support mechanism at different angles with respect to the corner post of a scaffolding whereby to pull the scaffolding sideways or at an angle.
Referring now to the drawings and more i5 particularly to Figure 1, there is shown generally at 10, typical scaffolding structure constructed of tubular frame members. Only a bottom end section of a scaffolding structure is illustrated and it comprises of vertical corner frame members 11 and 11' connected to horizontal frame 2o members 12 and to cross-braces 13, as is well known in the art, whereby to construct a stable and rigid scaffolding assembly. Usually the bottom section of a scaffolding assembly is assembled on a ground surface 14 with the vertical corner frame members shimmed to level the lower 25 section. After being leveled, further sections 15 are assembled on top of the bottom section.
The present invention provides for an adjustable leg support mechanism 20 which is connectable to one or more of the vertical corner frame members 11. The adjustable leg 3o support mechanism will now be described with further reference to Figures 2 to 5.
The adjustable leg support mechanism 20 comprises an open-ended sleeve 21 which is adapted to receive a support rod 22 therethrough and wherein the support rod 22

- 6 -has at least a longitudinal toothed edge section 23 and is adapted to secure to a bottom support foot 24, as illustrated in Figure 6. A tooth engaging member 25 is pivotally secured to the sleeve 21 and has a tooth engaging head 26 which is biased against the toothed edge 23 inside the sleeve 22 for supporting the sleeve about the support rod 22 at a desired location therealong. The tooth engaging member is a ratchet-like member and permits upward displacement of the sleeve 21 about the support rod 23 by to simply pulling the sleeve upwardly along the rod 22.
The tooth engaging head 26 is mounted on a pivot pin 27 and is provided with a lever arm 28 integrally formed therewith and which constitutes a means to unbias the tooth engaging head from the toothed edge 23 to permit downward i5 displacement of the sleeve 21 about the rod 22. The lever 28, due to its own weight, biases the tooth engaging head inwardly of a rectangular passage of the open-ended sleeve through an aperture 30 formed in a side wall 31 of the sleeve 21. It is pointed out that the support rod 22 is of 2o square cross-section and received in close sliding fit within the rectangular passage 29 of the sleeve.
As shown in Figure 5, the saw tooth formations 23 each define a horizontal support ledge 32 and an outwardly sloping wall section 33. The tooth engaging head 26 has an 25 engaging projection 34 which is of wedge-shaped formation and defines a flat bottom wall 35 for seated engagement on a support ledge 32 of the saw tooth formation and a rearwardly sloping upper wall 36 for frictional sliding engagement against the outwardly sloping wall section 33 when the 3o sleeve is retracted upwardly along the support rod and thereby providing the ratchet effect.
As better illustrated in Figures 2 and 3, the tooth engaging head 26 is pivotally secured by the pivot pin 27 which is supported between a pair of support flanges 37 secured to the sleeve 21 and hereinshown as forming an integral part thereof extending beyond the rectangular passage 29. In order to disconnect the sleeve from the support rod, it is merely necessary to pull the lever arm 28 s upwardly in the direction of arrow 38, as shown in Figure 2 thereby causing the wedge shape formation 34 to retract outwardly of the rectangular passage 29 through the aperture 30.
With further reference to Figures 2 and 5, there to is illustrated an arresting means in the form of a locking lever 40 which is hingedly connected to the sleeve support flanges 37 by a pivot connection 41 and the locking lever 40 has an arresting formation 42 for removable engagement with the tooth engaging head 26 to prevent displacement of the i5 lever arm 28 and disengagement of the engaging projection 34 with the toothed edge section 23 of the support rod 22.
This locking lever has a finger engaging formation 43 to provide disconnection of the arresting formation 42 from a notch 44 provided in a rear top portion of the tooth 2o engaging head 26.
As shown in Figures 3 and 4, a rod connector 50 in the form of a tubular member is secured to the sleeve 21 for connection to a transverse tubular rod 51, as will be described later in detail, whereby to interconnect two 25 opposed leg support mechanisms 20 together as illustrated in Figure 1.
Attachment means in the form of a vertical connecting post 52 is also secured to the sleeve and herein to the connector 50 on a top wall thereof and projects 3o upwardly on a vertical axis which is parallel to the longitudinal axis 53 of the sleeve. The connector 50 extends on a transverse longitudinal axis 54. The vertical post 52 is structured for release engagement with a hollow tubular end section 55 of a vertical corner frame member, _ g _ herein a hollow tubular frame member 11 as illustrated in Figure 6.
The sleeve 21 is further provided with locking means in the form of a spring-bias lock pin 56 which is spring-biased inside the rectangular passage 29 by a spring 57 whereby to lock the support rod with the sleeve at one or more predetermined positions as dictated by holes 58 provided in a wall 59 of the support rod opposed to the toothed edge section 23. Accordingly, when the sleeve is to displaced upwardly or downwardly it will be arrested from the displacement when the pin enters one of the holes 58 delimiting the upward and downward projectory of the sleeve over the support rod 22. The lock pin 56 is further provided with a retracting finger engaging head 59 to i5 disengage the pin 56 from the hole 58. This pin is constantly urged against the wall 59 of the support rod and slides therealong during the displacement bf the sleeve thereabout.
Referring now to Figure 8 it can be seen that a 2o support wheel 60 is also securable to the sleeve by support means herein an attachment sleeve 61 projecting along the horizontal axis 54 and secured thereto by a lock pin 62.
The wheel is mounted with its planar axis of rotation 63 extending parallel to the longitudinal axis 53 of the sleeve 25 and transverse to the axis 54. By removing the lock pin 62 the wheel is easily removable from the bracket or attachment sleeve 61 permanently secured to the open-ended sleeve 21.
Referring now to Figures 8 to 12, there is shown a further embodiment wherein the rod connector 50 is 3o constructed differently than that illustrated in Figures 3 and 4. As hereinshown, the rod connector comprises a horizontal lock flange 70 which is secured to the sleeve 21 and has an arcuate outer edge 71 (see Figure 9) provided with two or more locking cavities 72 disposed therealong. A

_ g _ pivot connecting flange 73 is secured to the sleeve 21 and is disposed a predetermined distance above the horizontal lock flange 70 and extends parallel thereto. Both the lock flange and pivot flange are provided with through bores 70' and 73', respectively, to receive a pivot pin 74 therethrough, see Figure 8. The horizontal rod 51 is provided with a transverse bushing 75 at an end thereof and constitutes a rod connector which is simply connected between the lock flange and the pivot connecting flange by io the pivot pin 74 as illustrated in Figure 8. As also shown in Figure 8, the vertical connecting post 52 is herein secured adjacent the connecting end of the horizontal rod 51 for release engagement with the hollow tubular end 55 of a vertical corner frame member of a scaffolding assembly.
i5 A position arresting pin 76 interconnects the rod connector or rod end 51' to the lock flange 70 when the pin is received in one of the locking cavities 72. The position arresting pin 76 is provided with finger engaging means in the form of a tap handle 77 to retract the arresting pin 2o from one of the locking cavities for disengagement therewith.
As can be seen from Figures 11 to 12, the transverse tubular rod 80 is a telescopic rod for adjustment with scaffolding having vertical corner posts spaced at 25 different distances from one another. This telescopic tubular rod 80 is capable of adjusting the spacing between two vertical post connectors 52 at opposed ends of the tubular rod whereby to interconnect two opposed leg support mechanisms 20 in a tandem arrangement. The lock pin 81 3o interconnects the two pipe sections 80' and 80" together, once the tubular rod 80 is of proper length. A handle 82 is connected to the tubular rod 80 to facilitate the horizontal adjustment of the tandem arrangement by simply providing a means to pull up on the opposed leg support mechanisms whereby the sleeve 21 rides up on the respective support rods 22. The level 83 secured to the top of the tubular rod indicates the proper level of the rod. Of course a further level, not shown, could also be mounted transverse to the level 83 to provide for the leveling along the transverse axis or in a transverse plane when the tandem arrangement is connected to a scaffolding assembly.
With reference now to Figures 13 and 14 there is shown the construction of a carriage frame 85 which is 1o secured to carriage connectors 86 and 86' each secured to a respective one of the wheel attachment sleeves 61 and 61~.
The carriage connectors 86 and 86' are each constituted by an elongated flange 87 having a slot 88 therein to receive a free end of a carriage frame connecting rod 89 attached thereto by a connecting pin element 90 whereby to permit displacement of the connecting end of the connecting rods 89 along the flange 86.
As hereinshown, the carriage frame 85 has a pair of these connecting rods 89 and 89' connected to a pivoting 2o frame 91 which is pivotally connected at an end 92 to the tubular rod 80. The other end of the connecting rods 89 and 89~ are pivotally attached to a forward end of the pivotal frame 91 on pivot connections 93 and 93', respectively. A
handle 94 is secured to the free end of the pivotal frame 91 whereby to provide ease of pulling a scaffolding secured to the tandem arrangement. As shown in Figure 3, the wheels 60 of the tandem arrangement are disposed transverse to the tubular rod 80 but these can swivel about the ends of the tubular rod by adjusting the angle of the wheels by 3o withdrawing the lock pin 76 from engagement with the horizontal locking flange 70 and displacing the wheels by pushing laterally on the pulling handle 94 until the lock pin 76 falls into the adjacent locking cavity 72 whereby both wheels can be locked at an angular position. As shown in Figure 14, the wheels have been displaced 90 degrees about the ends of the tubular rod 80 whereby a scaffolding structure can be easily pulled sideways.
Referring now to Figures 6, 7A and 7B, there will be described the construction of the bottom support foot 24 which is secured at the bottom of the corner post 11 of a scaffolding assembly. As hereinshown, the support foot is formed from a metal plate which is configured to form a sliding plate defining a contacting bottom wall 100 for to sliding displacement on a support surface. This slide plate also has opposed outwardly angled end flanges 101 to permit the displacement of the scaffolding over an irregular ground surface as these angled end flanges provide for the sliding plate to slide over objects or irregularities on a ground surface. They also provide for the scaffolding to be easily displaced on a snow covered surface.
The center of the bottom wall 100 of the plate has a cavitated section 102 whereby to permit the engagement the securement of a vertical connector 103 herein constituted as 2o a vertical connecting post of the type as previously described. The vertical connector 103 is disposed substantially central on the top wall 104 of the slide plate and provides removable connection with the lower hollow end section 55 of the corner post 11. It is provided with spring-loaded prongs 105 to engage within the locking holes 106 provided in the end section 55 of the corner posts 11.
Such interconnection is well known in the art. Accordingly, the present invention also encompasses a novel support foot structure for connection directly to the scaffolding.
Referring now to Figures 7A and 7B, there is shown the slide plate as previously described but wherein the support rod 22 is secured thereto at a lower end 22' by a suitable connecting means. Therefore, in order to render a scaffolding assembly easily displaceable over ground surface, a tandem arrangement is secured to one pair of corner posts of a rectangular scaffolding assembly and the other pair of corner posts are connected directly to a respective one of the sliding plates.
s As above described, the present invention provides an adjustable leg support mechanism which can be easily assembled and disassembled in component parts for ease of transport and storage. Also, some of the component parts are considered to be optional, such as the support wheels or to the carriage frame and the support wheels can be adapted to the leg support mechanisms only when required. When it is required to transport a scaffolding assembly the sleeve 21 is disconnected form the toothed edge of the support rod 22 and the sleeve is lowered therealong until the support wheel is rests on the ground surface. The support rod 22 is then pulled upwardly above the ground surface and the sleeve is relocked thereto to maintain the support foot or slide plate 24 elevated from the ground surface. The tandem arrangement is then supported on its opposed support wheel 60.
2o It is within the ambit of the present invention to cover any obvious modifications of the preferred embodiment described herein, provided such examples fall within the scope of the appended claims.

Claims

CLAIMS,

1. An adjustable leg support mechanism for a scaffolding having vertical corner frame members connected to horizontal frame members and cross-braces, said mechanism being characterized in that it comprises an open-ended sleeve adapted to receive a support rod therethrough and wherein said support rod has at least a longitudinal toothed edge section and is adapted to secure to a bottom support foot, a tooth engaging member pivotally secured to said sleeve and having a tooth engaging head biased against said toothed edge inside said sleeve for supporting said sleeve about said bottom support rod while permitting upward displacement of said sleeve about said rod, means to unbias said tooth engaging head from said toothed edge to permit downward displacement of said sleeve about said rod, arresting means to lock said tooth engaging head in arresting position with said toothed edge and attachment means for securing said sleeve for support engagement with one of said vertical corner frame members of a scaffolding.

2. An adjustable leg support mechanism as claimed in claim 1 characterized in that said means to unbias said tooth engaging head is a lever arm formed integral with said tooth engaging head, said tooth engaging head having an engaging projection projecting through an aperture inside said open-ended sleeve.

3. An adjustable leg support mechanism as claimed in claim 2 characterized in that said sleeve has a substantially rectangular cross-section for receiving therethrough said support rod which is of substantially square cross-section, said toothed edge section being constituted by a plurality of saw tooth formations formed along a side wall of said support rod and facing said aperture of said sleeve.

4. An adjustable leg support mechanism as claimed in claim 3 characterized in that said saw tooth formations each define a horizontal support ledge and an outwardly sloping wall section, said engaging projection having a wedge shape formation defining a flat bottom wall for seated engagement on said support ledge and a rearwardly sloping upper wall for frictional sliding engagement against said outwardly sloping wall section of said tooth.

5. An adjustable leg support mechanism as claimed in claim 4 characterized in that said tooth engaging head is pivotally connected by a pivot connection between a pair of support flanges secured to said sleeve on opposed sides of a side wall of said sleeve having said aperture, said wedge-shaped formations being biased against said saw tooth formations by the weight of said lever arm, said lever arm when displaced upwardly about said pivot connection causing said wedge shape formation to retract through said aperture.

6. An adjustable leg support mechanism as claimed in claim 2 characterized in that said arresting means is a locking lever hingedly connected to said sleeve and having an arresting formation for removable engagement with said tooth engaging head to prevent displacement of said lever arm and disengagement of said engaging projection with said toothed edge section of said support rod.

7. An adjustable leg support mechanism as claimed in claim 1 characterized in that said bottom support foot is a slide plate for sliding displacement on a ground support surface.

8. An adjustable leg support mechanism as claimed in claim 1 characterized in that there is further provided a rod connector secured to said sleeve for connection to a transverse tubular rod interconnecting two opposed leg support mechanisms together.

9. An adjustable leg support mechanism as claimed in claim 1 characterized in that said attachment means is a vertical connecting post for release engagement with a hollow tubular end of said vertical corner frame member.

l0. An adjustable leg support mechanism as claimed in claim 1 characterized in that there is further provided locking means to automatically lock said support rod with said sleeve at one or more predetermined positions.

11. An adjustable leg support mechanism as claimed in claim 10 characterized in that said locking means is a spring-biased lock pin secured to said sleeve and having a spring-biased rod urged against a side wall of said support rod for engagement in a hole formed in said side wall at said one or more predetermined positions.

12. An adjustable leg support mechanism as claimed in claim 1 characterized in that there is further provided a support wheel secured to wheel support means secured to said sleeve, said wheel having its planar axis of rotation extending parallel to said sleeve.

13. An adjustable leg support mechanism as claimed in claim 12 characterized in that said wheel is removably secured to said wheel support means which is constituted by a wheel support bracket secured to said sleeve.

14. An adjustable leg support mechanism as claimed in claim 12 characterized in that there is further provided a rod connector secured to said sleeve for connection to a transverse tubular rod for interconnecting two opposed leg support mechanisms together in tandem arrangement, a carriage frame connector secured to said wheel support means, each of said two opposed leg support mechanisms adapted for interconnection with carriage frame connecting rods to displace said tandem arrangement on said support wheels.

15. An adjustable leg support mechanism as claimed in claim 14 characterized in that said rod connector is pivotally secured to said sleeve, and a vertical connecting post secured to said rod connector for release engagement with a hollow tubular end of said vertical corner frame member, and lock means for arresting said wheel support means at a desired angular portion relative to said sleeves of said tandem arrangement to displace said tandem arrangement along a desired direction.

16. An adjustable leg support mechanism as claimed in claim 15 characterized in that said carriage connector is an elongated flange having a slot therein to receive a connecting pin element secured to a connecting end of said carriage connecting rods to permit displacement of said connecting end along said slot, said carriage connecting rods being pivotally secured at a remote end to a control arm to effect said displacement of said tandem arrangement.

17. An adjustable leg support mechanism as claimed in claim 15 characterized in that said lock means comprises a horizontal lock flange secured to said sleeve and having an arcuate outer edge provided with two or more locking cavities disposed therealong, a pivot connecting flange spaced above said lock flange and extending parallel thereto, said rod connector being pivotally connected between said lock flange and said pivot connecting flange by a pivot pin, and a position arresting pin spring-biased against a top peripheral edge of said lock flange and secured to said rod connector, said position arresting pin interconnecting said rod connector to said lock flange when received in one of said locking cavities.

18. An adjustable leg support mechanism as claimed in claim 17 characterized in that said position arresting pin is provided with finger engaging means to retract said arresting pin from one of said locking cavities for disengagement.

19. An adjustable leg support mechanism as claimed in claim 15 characterized in that said rod connector is a connecting end of said transverse tubular rod.

20. An adjustable leg support mechanism as claimed in claim 19 characterized in that said transverse tubular rod is a telescopic rod having interconnection means.

21. An adjustable leg support mechanism as claimed in claim 19 characterized in that a leveling device is secured to said transverse tubular rod to assist in locking a scaffolding tubular structure secured to said tandem arrangement.

22. A support foot for a scaffolding having vertical corner posts, said support foot being characterized by a slide plate having a bottom ground engaging face and opposed upwardly angled end flanges, and a vertical connector disposed substantially central on a top wall of said slide plate for removable connection with a lower end section of said corner posts.

23. A support foot as claimed in claim 22 characterized in that said vertical connector is a vertical connecting post for release engagement within a hollow end of said corner posts, said corner posts being hollow tubular posts having at least one lock pin receiving holes for receiving therein a spring-biased lock pin projecting from said vertical connecting post.