The invention relates to a tensioning device for frame pieces, according to German Offenlegungsschrift No. 2,049,245 published Apr. 13, 1972, including a tensioning wedge and a tensioning element.
In this publication, there is described a shuttering which does not, however, always have to be used for boarding purposes only but can also be used in cases where building site walls are erected as a protection against the weather, etc. This publication shows, for example in FIG. 3, a specially formed frame piece profile which comprises a longitudinal bead as well as outer legs which extend parallel to the shuttering board. This frame piece profile has, in its legs which are vertical to the shuttering board, holes through which a tensioning element in the shape of a stressing bolt passes, which bolt has a longitudinal slot. This construction has the following disadvantages:
(a) For tensioning purposes, it is necessary to punch holes into the frame pieces. These holes necessitate an additional operation and weaken the moment of resistance of the frame pieces.
(b) Prior to tensioning, attention has to be paid that the two holes of both juxtaposed frame pieces are aligned so that the tensioning element pulls in the desired direction. In other words, careful attention has to be paid to alignment both on the building site and during production.
(c) A sleeve has to be placed into the holes in order to ensure that the concrete will not run into the frame piece profile. It is true, attempts have been made to prevent the concrete from doing so by filling the hollow portion of the frame piece with a wooden profile. However, this is expensive.
(d) It presents difficulties to connect together shuttering panels which are staggered in height relative to one another because attention has to be paid to the hole pattern. Steps can therefore only be realised with difficulty and frequently outside the shuttering system.
(e) The holes dictate the tensioning location, which sometimes does not coincide with the optimum tensioning location.
(f) Prior to tensioning, attention has to be paid that the shuttering elements are flush because otherwise the concrete surfaces sometimes project forward or backward by several millimeters. The flushness which has initially been established may be lost again during tensioning.
(g) Access to the wedges is difficult when they are driven in. If one is not careful, one hits the frame piece because the wedges bear closely against the frame piece, and this applies particularly to those legs which form a corner with the shuttering board. In practice, the tensioning element is placed in such a way that the wedges extend obliquely from the front top to the rear bottom. However, this means that when the wedges are released there is practically no room for the hammer, for the wedge point is after all even more inaccessible than the wedge head.
It is the object of the invention to indicate a tensioning device which is cheap while suitable for the building site, stands harsh handling and, while suitable for the frame piece system mentioned at the beginning, eliminates all the aforementioned disadvantages.