reinforcement of the keys with 4Ø3Вr1 (Fig. 5) was proposed on the basis of the
minimum reinforcement percentage of reinforced concrete 0.05%. The proposed
spatial cage with three-level reinforcement has additional possibilities for its
attachment to the girder cage.
Figure 5. Improved connection of circular hollow-core slabs with a monolithic girder
in a precast-cast-in-place overlapping:
1 ‒ slab bearing sections; 2 ‒ monolithic girder; 3 ‒ keys;
4 ‒ cylindrical reinforcement cages; 5 ‒ key size limiter
Meanwhile, in all the above-mentioned structures, the reinforcement of the keys
is not used as the working reinforcement of the monolithic bearing girder. There is a
proposal to improve the connecting slabs with a girder in precast-cast-in-place
overlapping (Fig. 6).
Its essence consists in the use of longitudinal reinforcement keys as cross
reinforcement girder. The double functional purpose of the working reinforcement
reduces the steel content and contributes to an increase in the strength of the girder in
an inclined section. The key longitudinal reinforcement in the place of entry into the
volume of the girder bends down or up at different angles, depending on its position
relative to the sections of the girder near the supports and specified by the design
scheme for placement of inclined cracks. Its effective work is ensured by fastening to
the girder cage.
The uncapital ungirder system KUB-2.5 consists of vertical multi-storey columns
without protruding support parts, overlapping slabs and connections or shear walls.
Overlapping construction in such buildings consist of three types of precast reinforced
concrete slabs with a thickness of 160 mm and dimensions of 2.98 × 2.98 m:
overcolumned, intercolumned and middle column (Fig. 7). The concrete monolithing
of the seams between the slabs with a width of 20 mm is carried out without the
formwork installation.
Recommendations for the improvement of this structural system developed in
PoltNTU. Their essence lies in the fact that due to the introduction of reinforced
concrete shear walls and foundations for them, it became possible to significantly
reduce the vertical load on the columns of the lower floors and thereby increase the
number of floors from 12 to 16.
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