'ϊ'ecnnical field

Tne object of the invention is a bearing grid of a formwork for a dome over a reinforced concrete rank, which serves to carry vertical working load from concreting formwork and from the working platfoim. The bearing grid , according to the pre¬ sent invention , will find its application - among others - in erection of reinforced concrete domes for tanks in sewage treatment plants. State of -cechnique In tne majority of currently used practical solutions , the firictior. of basic bearing elements of formwork is performed oy conventional free-standing tubular scaffolds . Vertical loads from formwork, concrete and working platforms are carried by props wnose height differentiates up to 20 m, as in the case of concrete tanks for sewage treatment plants . Stability of the whole scaffolding system was ensured by three-dimensio¬ nal scaffold lattice , made of props , longitudinal and cross bars, and vertical and horizontal bracings . All connections between particular lattice bars are ensured by conventional joints. In case of construction of a dome over the cylindri¬ cal part of a sewage treatment plant tank, the lattice is formed through a regular circumferential partition in horizon¬ tal plane into sectors 7 ,5 wide , with props spaced every 1 ,30 m. In vertical plane , partition of the inner space of the tank into levels , assumes their height as 2 ,0 m in the cylindrical part , 2,25 in the sub-dome part and 0,75 ^ in the bottom f nnel .

The main drawback of such free-standing scaffolding system, it is its high material and labour consumption index , and its toilsome erection and dismantling. Moreover, the function of thai; scaffolding is limited proncipally to concreting of a "cank dome , without any possibility of carrying OUΌ other orks inside tne tank /finisning works , insulation, sealing/ .

Disclosure of the invention

The purpose of the invention is to remove - or at least to reduce considerably - inconvenie ces encountered in the course of concreting of a tank dome . In order to reach tnac goal , tnere was set a task to elaborate a concept of cons¬ t-ruction of a formwork bearing a grid for a dome over a re¬ inforced concrete tank which would enable elimination of la¬ bour - consuming scaffolding syεtem in the space from the tank bottom to a level at the heigh of about 10 m. The bearing grid of the formwork for a dome over a reinfor¬ ced concrete tank, according to the invention , has bearing elements circumscribed on the network of a number of regular polygons inscribed subsequently one into anotner and turned subsequently in relation one to another by the same angle , so that respective sides every second polygon in the netv/ork are parallel to each other, whereas the whole network has at least two axes of symeti-y. The comers of the biggest poly¬ gon are mounted in bearing seats. Bearing elements are arran¬ ged in steps and each subsequent element is supported solely on the element placed one step down. The bearing grid, accor¬ ding to τ;he invention, does not require additional bracings aε it is rigid by itself and forms a rigid horizontal struc¬ ture . Erection and dismantling of the grid is very simple . Snore description of tne drawing The object of the invention is presented aε an example given in tne Fig. 1 whicn presents the bearing grid of a formwork seen from above , whereas the Fig. 2 presents vertical section of the grid in its axis. In the presented example , regular po¬ lygons are formed by squares, turned one to another by 5 . Principal use of the invention

Bearing elements , 2, ^, , , §. °^ ^tile S ^r --&- according to the invention , are circumscribed on the network of squares inscribed one into anotner and turned subsequently by -ή in relation to eacn other. The biggest bearing elements _ form discountable binding joists with reinforcing elements £. and

. The bearing elements 2 are formed by four i^ beams placed on the binding joists 1_ and fixed to them by means of simple dismountable joints. On the erected four bea¬ ring elements 2 is placed subsequent storey composed of. four bearing elements 2 and so on, until * storey com¬ poεed of bearing elements 6 is placed on bearing elements _• The squares of particular storeys are connected with each other in a disconnec table way in order to facilitate their dismantling and they are turned one to another by

10 45° _• The bearing elements 1_ are connected in a disconnec- table a^ with one another and their corners are placed in support seats 2 in in-situ cast reinforced concrete walls of the upper part of the cylindrical tank in a sewage treat¬ ment plant . The seats 2 are cut out in the concrete walls

-1 0 ,9 a thick and they are furnished with support plates 10. 1h.e working space of the grid , which has a stepped struc¬ ture , is laid out by bottom planes of circular sectors, formed between tank walls and binding joists 1_ and top pla¬ nes of the network of triangles arranged in steps . Those

20 planes are filled with radial beams. The radial beams car¬ ry loads from props _11_ during concreting . The geometrical network of the grid , composed of triangles , assures a nigh degree of rigidity and stability of the whole structural system. Shoring and formwork for the dome is placed on wor- 5 king platform, above the bearing grid.

Another variant of the grid , according to the invention, has bearing elements circumscribed on the network of hexa¬ gons inscribed one into another and turned subsequently by an angle of 5O ⁰ . Also in that variant of the grid , vertical

30 and horizontal loads irom the formwork are carried to the cast-in -place reinforced concrete walls of the tank through heel joints and suport seats cut out in those walls.