Abstract:
A scaffold to which form plates for forming a concrete wall can be fastened is suitable for circular constructions and includes a polygonal frame which is vertically adjustable along supports. The frame, is angularly adjustable at the corners, of plural straight frame portions, each of which is a separate part attached to the adjacent frame portions.

Description:
FIELD AND BACKGROUND OF THE INVENTION 
     The invention relates to a scaffold for forms of circular constructions of concrete or the like, including a horizontally aligned substantially annular polygonal frame for a working platform. The frame has an upper chord and a lower chord connected by means of truss bars and is vertically adjustably mounted, preferably on three pillar-like supports. 
     DESCRIPTION OF THE PRIOR ART 
     A known device for erecting structures, preferably of closed circumference, such as silos, swimming pools, aging towers or the like, of castable materials, e.g. concrete, includes a vertically adjustable working platform. This working platform is mounted on three extensible tubes and mounts an annular lattice beam to which are fixed radial outwardly or inwardly extending supports on which is suspended the external or internal form. As construction progresses, the working platform is lifted together with the suspended forms, when the cast concrete has set. 
     It is a disadvantage of known working platforms that a separate platform must be provided for each working diameter. 
     SUMMARY OF THE INVENTION 
     It is the object of the invention to provide a scaffold in which the working platform can be adapted to different diameters of constructions. 
     According to the invention this is achieved by providing a polygonal frame which is angularly adjustable at its corners and by providing each portion of the polygonal frame between two corners as a separate part releasably linked, preferably screwed, to the adjacent frame portions. 
     Preferably upper and lower chords of the portions are joined at the corners in a fork-like manner by connecting flanges arranged alternately against each other in the mounted position. 
     Hence, the frame portions can be separated at each corner, and by inserting a further frame portion or a number of frame portions the diameter of the frame can be increased as desired, or similarly decreased by removing frame portions. By adjusting the angles at the other corners the polygonal frame can be adapted to the continuous shape of a circle. 
     It is a further disadvantage of conventional scaffolds that the extensible tubes serving as supporting columns are arranged within the ring of the working platform, and displacement of the working platform, i.e. detaching from and fastening to the guide tubes, is time-consuming and dangerous as these operations can only be carried out below the working platform. 
     It is a further object of the invention to provide a scaffold which eliminates this disadvantage. 
     According to the invention this is achieved in that the frame portions rest with their outer sides against the supports and are linked thereto. 
     It is advantageously provided that the two connecting flanges at one end of the upper and lower chord portions are angularly arranged to the longitudinal axis of the upper and lower chord portions. Acceptable tolerances are therefore possible in the production of the frame portions. 
     An embodiment of the invention provides that the connecting flanges are provided with holes for connecting screws which lie at least partially on a circular arc. Some of these holes are slots. Advantageously, one hole is positioned at the center of the circular arc. 
     A further embodiment provides that the connecting flange at one end of each of the upper and lower chord portions is divided into internal and external flange parts arranged at the two sides of the upper or lower chord portion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following an embodiment of the invention will be described in more detail with reference to the attached drawings, in which 
     FIG. 1 is a schematic vertical sectional view of a scaffold according to the invention and the form belonging thereto, 
     FIG. 2 is a schematic top view thereof, 
     FIG. 3 is a diagramatic perspective view of a portion of the working platform according to the invention, 
     FIG. 4 is a side view of a frame portion, 
     FIG. 5 is a top view of a frame portion, 
     FIG. 6 is an enlarged view of details A, B of FIG. 4, the ends of the frame portions shown adjacent each other, 
     FIG. 7 is a sectional view along line C--C of FIG. 6, 
     FIG. 8 is a plan view of a connection between frame and support, 
     FIG. 9 is a schematic view of the engaging portions of upper and lower chords, 
     FIG. 10 shows a top view of a further embodiment of a frame portion, and 
     FIG. 11 is a side view of the latter-mentioned frame portion. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1 a wall under construction is shown at 1. A form skin 2, which may for example be of steel, light metal or of wood or plastic material, rests directly against the inner and outer surfaces of the wall 1. 
     Profiled steel beams 3 of a mounting scaffold are held by external polygonal rings 4 and are bolted thereto. 
     As can be seen from FIG. 2, each external or internal ring 4 consists of ring portions 8 which are hingedly linked at corners 9. 
     For reasons of stability, each ring portion 8 is preferably formed by an I-beam. A rectangular tube could equally be used but the use of the I-beam offers advantages with respect to fast fixing when the ring 4 is adapted to a new diameter. 
     At the corners 9 the link joint can be formed either by an axle or by bending the lower parallel flange of the I-beam. 
     The internal form has substantially the same construction as the external form. Next to the form skin 2 are the vertical steel beams 3 which are held by polygonal rings 4. 
     The inner polygonal rings 4, are vertically adjustable. 
     In the interior of the rings 4 of the internal form there are three pillar-like supports 5 for a working platform 6 carried by a polygonal frame 16, which is a truss comprising an upper chord 17, a lower chord 18 and vertical and inclined bars 19,20. 
     The frame 16 is formed by separate frame portions 16&#39;. Each frame portion 16&#39; comprises a static load-bearing vertical bar 19 a supplemental bar 21. In the illustrated embodiment upper chord portions or members 17&#39; and lower chord portions or members 18&#39; are formed by rectangular tubes, as are the vertical bars 19 and the inclined bars 20. A different profile, e.g. I-shaped, could also be used if it has the required resistance to buckling. 
     The frame 16 is formed by frame portions 16&#39; which are bolted together. Each upper chord portion 17&#39; and each lower chord portion 18&#39; is at its two ends provided with connecting flanges 22, 23 alternately engaging into each other, as can be seen in FIG. 9, so that each connecting flange 22 contacts a respective connecting flange 23. 
     The individual frame portions 16&#39; are bolted together at the connecting flanges 22, 23. 
     As can be seen in FIG. 5, the connecting flanges 22 are angularly arranged to the longitudinal axis of the upper or lower chord portions 17&#39;,18&#39;. Each connecting flange 23 includes two separated parts, one each on each side of the upper and lower chords 17, 18. 
     Each connecting flange 22, 23 is provided with holes 24, 25 through which connecting bolts extend, a number of the holes being slots 25 lying on a circular arc about a circular fastening hole 24. 
     It is obvious that by removing the bolts connecting plural frame portions 16&#39;, one or more portions can be removed and the angles at the corners of the polygonal ring can be adjusted to form a frame 16 of a smaller diameter. 
     It is equally possible to open the frame 16 at a joint between two frame portions 16&#39; and to insert new frame portions 16&#39; to increase the diameter of the frame. 
     As can particularly be seen from FIGS. 2 and 8, the pillar-like supports 5, which are I-shaped members, rest externally against respective frame portions 16&#39; of the frame 16. Each such frame portion 16&#39; has holding means 26 at its upper chord portion 17&#39; embracing a flange 5&#39; of the I-shaped support 5, and the upper chord portion 17&#39; is connected with the flange 5&#39; through this holding means 26, e.g. by being bolted thereto. The second flange 5&#34; of the I-shaped support 5 is in similar or equal manner connected with the rings 4 of the form scaffold. This connection can also be effected by means of bolts, for example. 
     Due to the fact that the supports 5 laterally rest against the frame 16 as well as against the rings 4, the form scaffold and the mounting scaffold form a unitary structure. The mounting scaffold is vertically guided in the form scaffold. This arrangement eliminates the need for the working platform to be fastened at its lower side. Moreover, the supports 5 can be secured against buckling directly at the concrete wall, thereby avoiding the need for dangerous operations below the working platform which otherwise would be required. 
     To increase the static load-carrying capacity of the frame 16, each frame portion 16&#39; can (as illustrated in FIGS. 10 and 11) be a three-dimensional truss. 
     The frame portions 16&#39; advantageously are trapezoidal shaped, when viewed from the top.