TECHNICAL PROBLEM This hollow prefabricated reinforced concrete grilled plate solves the problem of casting flat slabs, roof slabs, stairs and similar structures. The structure can be erected manually without any supporting, because the structure is selfbearing due to casting. The structure is of a grill type with a hollow ceiling reinforced concrete block made from two separate parts. The ceiling block is produced as a final structural element; due to the prefabrication, the structure is a camber. The adaptability of the system to different forms of houses and buildings, by using a few types of precast elements, contributes to its rationality and wide applicability.

STATE OF THE ART The existing structural systems which solve, to a certain extent, the mentioned technical task are: (1) Ritter Ignance M. Mario, Plancer prefabrique P. V. no 1.877 Alger, No 1.297402, (2) Bruett Andre, Elements de planchers et planchers obtenus a 1'aide de ces elements, P. V. no 982167 France, No 1409462, (3) Ytong mixed masonry system, Portugal, Israel and Turkey.

There are no similar solutions as those obtained by this patent in civil engineering since all previous systems were not based on the significant contribution of reinforced concrete ceiling in taking over the local and global forces, stresses.

ESSENTIAL FEATURES OF THE PATENT The main features of this patent are the use of the thin doubled r/c ceiling masonry block instead of a single one, and the application of the principle of complete reinforcing of micro concrete to prefabricated girders and lateral ribs of the hollow masonry grilled slab structure.

Hence, the ceiling r/c block is constructively connected with the grill elements it takes the local and significant part of the global force without the commonly used compressive slab.

Since a hole is made between the parts of a itself block; the structures is of a light type.

Due to small weight of the structure and itself a high bearing capacity of the girder the structure needs not to be supported during erection. According to the camber of the prefabricated girder is obligatory.

DESCRIPTION OF THE DRAWINGS The drawings present a new system of hollow prefabricated reinforced grilled plates.

Each drawing shows one possible way of applying the system and does not limit the rights contained in the patent claims.

Drawing 1 shows the cross-section of a pair of r/c ceiling blocks, Drawing 2 shows the longitudinal cross-section of a hollow r/c grilled plate and r/c ceiling block, Drawing 3 shows the cross section of the prefabricated part of the main girder, Drawing 4 shows a view of the prefabricated part of the main girder, Drawing 5 shows a view of the back threshold,

DETAILED DESCRIPTION OF THE PATENT The new hollow prefabricated r/c grill plate, as presented in Figures 1-5, consists of the following elements: prefabricated r/c girder (1), down the thin part of the r/c ceiling block (2), the upper thin part of the r/c ceiling block (3), prefabricated r/c down threshold (4), prefabricated r/c back threshold (5), lateral r/c rib (6), micro concrete or cement mortar for in situ connection of the system (7) and a thin layer of cement or similar mortar (8) which is not obligatory. The thickness of the plate is over 10 cm; the recommended thickness is 15 cm. The recommended structural span is up to 10.0 m.

A prefabricated girder (1) is shown in Figures 3 and 4. It is made of two prefabricated reinforcing steel double trusses (1.3) and (1.4) strengthened by added bars (1.5) in the lower zone, and in the upper zone (1.6) which is not obligatory, and of the micro concrete body (1.1) made of fine sand, with a size smaller than 8.0 mm. The strengthened bars are choose according to the applied load and structure span.

The recommended dimensions are: the lower concrete zone d 8-9 cm and t 3 cm, the girder height H 12-20 cm and thickness dl =5 cm. The recommended chamber form is a square parabola whose midspan ordinate is 20 mm for the span of the 6.00 m.

The ceiling block shown in Figures 1 and 2 is made of two part (2) and (3). The lower part (2) is made of reinforced micro concrete with a quadratic cross section and polygonal longitudinal cross-section formed as letter U. The reinforcement is formed of at least two single bars or of an equivalent welded wire fabric. At the edge of the lower part of the ceiling block there are two notches needed for a leaning onto the concrete body of a prefabricated girder. The recommended thickness of the block shell is 2-4 cm, the block bandwidth 20-30 cm, its height 6-16 cm and length 45-75 cm.

The upper part (3) of the ceiling block is made a thin reinforced micro concrete plate with a quadratic or trapezoidal cross section. The reinforcement is formed of at least two single bars or it is formed of an equivalent welded wire fabric. The recommended thickness is 3.5-5 cm, its bandwidth 20-30 cm and length 45-75 cm.

The lateral ribs shown in drawing 2, are made of micro concrete reinforced with at least one bar in the upper and lower zones, whose mold is formed by lower threshold (4) and two back thresholds (5). The recommended rib's distance is 1.25 m.

The back threshold (6) is a prefabricated reinforced concrete member, with rectangular cross section and trapezoidal longitudinal cross section which form a closed lower block (2), which is reinforced with at least one bar. The recommended back threshold thickness is 1.5-3 cm, while its height and length are compatible to the lower ceiling block form.

The micro concrete is placed in the girder (1.2) and lateral ribs (6) channel. The ceiling blocks are connected with micro concrete or cement mortar (7). The thin layer cement or similar mortar (8) is placed over the grill and blocks (3), which is not obligatory.

The main girders (1) with lateral ribs (5), ceiling blocks (2) and (3) and in situ placed micro concrete (7) make a complete structural system.

An alternative grill plate can be cast of a prefabricated girder (1), lower ceiling block (3), lower threshold (4) and reinforcing of lateral ribs, while the rest of the volume is filled with lightweight or normal weight concrete.

INDUSTRIAL APPLICATION A successful of this patent in industry is evident. The proposed hollow prefabricated reinforced grill plate is applicable in practice as a new method for constructing various structures, such as: flat slabs, roof slabs, stairs structures and similar, based on the system of prefabrication and connection derived from this patent.