Strength Calculation Features and Tests Results on Bearing Capacity and Operational Serviceability of Hollow-Core Floor Slabs of Formwork-Free Shaping in Seismic Areas
Authors:   Professor at the Department of “Building Structures” of the Faculty of “Construction of Buildings and Structures” of the Tashkent Institute of Architecture and Construction, Tashkent, Uzbekistan., Pulat* Mirzaev , Kadir Umarov ,   the Chief Engineer of the “GEO BETON TRUST” Reinforced Concrete Products Plant, Tashkent, Uzbekistan., Shavkat Mirzaev ,   Director of the Innovation Center at the Tashkent Institute of Architecture and Construction, Tashkent, Uzbekistan.
Published: June 2020

The technology of manufacturing reinforced concrete structures of long-line systems of formwork-free shaping is widely used lately in construction industry in many countries. Using this technology, industrial construction can be carried out in accordance with the requirements of modern regulatory documents that allow projects to be developed individually, and production can be reoriented in a very short time in accordance with emerging needs. This means that on the same production line it is possible to produce various structural elements of buildings and structures. Also, this technology allows the production of structures according to a wide range of products that meet operational requirements, and increases the possibility of their use in design of buildings and structures with various architectural, planning and structural decisions. Prestressed hollow-core slabs of formwork-free shaping reinforced with high-strength wire reinforcement are widely used due to the simplicity of construction and their relatively low cost, as well as their high bearing capacity, large spans and better quality. The problem of their introduction into construction industry of Uzbekistan is that the issues of designing, manufacturing and using them in construction have not been studied. Besides, the production technology of such slabs is mostly associated with the construction in non-seismic areas, and the country does not have an appropriate regulatory framework for the possibility of slab designing and production. The aim of the study is to assess the strength and serviceability of hollow-core slabs of formwork-free shaping, designed on the basis of the proposed structural solution of the slab cross section and intended for construction in seismic areas. The results of slab calculations according to the accepted methodology and the results of control tests to assess the bearing capacity, crack resistance and rigidity of slabs according to the product range ordered by the customer for the use in construction in seismic areas are given. Graphs are proposed by which it is possible to determine the values of permissible loads on slabs of various lengths with appropriate reinforcement. Based on the research results, design documentation and technical specifications for the production of hollow-core slabs of formwork-free shaping for the product range proposed by the customer were developed. The solution of design issues and the test results of the proposed floor slabs of formwork-free shaping make it possible to produce economic and technological slabs for construction in seismic areas, in which 90% of the country's population lives. Therefor the issues of optimizing the main reinforcement consumption (prestressed high-strength wire reinforcement) at class B30 concrete strength without using the non-stressed reinforcement (reinforcing products) for the product range under consideration were addressed. Theoretical and constructive solutions of the slabs were developed in accordance with the standard requirements of Uzbekistan KMK 2.03.01-96 “Concrete and reinforced concrete structures”, KMK 2.01.03 “Construction in seismic areas” and considering the Euronorm EN 1168-2005 requirements “Precast concrete. Hollow-core slabs”.