Peculiarities of construction and operation of monolithic slabs of frame buildings

Abstract

Annotation. In recent years, in the construction of residential and public buildings, the frame system with prefabricatedmonolithic flat disks of floors, formed by hollow-core slabs and hidden girders in the plane of overlap, has increasingly become used. Hollow core prestressed slabs in the overlap are united by monolithic reinforced concrete girders hidden in the plane of overlap and supported on monolithic columns. Joint work of prefabricated reinforced concrete slabs with monolithic girders is ensured by the release of the working reinforcement, concrete keys and monolithic interlacing inserts. The column spacing can be up to 8.4 m both along and across the building, and the column grid can have an irregular structure in design with variable spans in any building column lines. Hollow core floor slabs must have openings on both sides with a depth of 100 ± 10 mm. The purpose of this research is the experimental verification of technical solutions to ensure joint work of prefabricated hollow-core slabs with hidden monolithic girders and verification of calculation model in the environment of the software complex "Lira-CAD" and the introduction of this system on the territory of Ukraine. To achieve the goal, there was made a calculation of a nine-story a cast-in-place and precast frame building of a Housing and office complex in Kyiv with the subsequent experimental justification. Calculation shows that the outlets of the working armature and key ensure the perception of design loads under idealized operating conditions. However, in the real conditions of work there will be bending moments on the supports of the slabs, while the upper zone of plates (joints of plates with beams) doesn’t have the reinforcement to accept them, meaning that, there are prerequisites for breaking the integrity of the section. This is due to the uneven deformations of the foundations. Thus, the presence of projectures from the slabs ensures the safety of the operation of the support units of the slabs of prefabricated-monolithic overlap. In order to confirm the possibility of safe operation of this building and to obtain reliable output for the application of the used structural scheme in the future, a slab fragment in real facility was tested at the maximum realization of the irregular deformation of the foundations of the building (the construction of all elements of the frame, the arrangement of the external wall fence of the internal partitions and floors). A representative section of the floor was selected for the testing according to the size of the project load projected. The obtained data were used for verification of the operational suitability of the floor. Conclusions: Analysis of deflections of a precast-monolithic overlap cell showed that the excess of permissible deflections occurred at a load level of structures 1.2 times higher than the operational load. In calculating the reinforced concrete structures of floor slabs and monolithic beams of the building, it was found that: the designs of floor slabs and monolithic girders are sufficient for the accepting the design loads; concrete keys of joints of slabs and girders are capable of accepting design loads only in the ideal conditions of their work; in real conditions of work during the implementation of estimated slab settlements, the floor slabs will be kept in working position due to projectures of operating reinforcement of slabs in the girders. Units of connection of slabs and girders should be performed only with the use of projectures of operating reinforcement of slabs in a girder.