Partuta V. Bearing capacity and deformability of monolithic reinforced concrete slabs with inserts in two directions

At present, monolithic reinforced concrete floors and other solid-section plate structures are mainly used in construction practice, which leads to significant overconsumption of concrete during their manufacture. However, the analysis of scientific research results showed that concrete and reinforced concrete are very energy-intensive materials, so reducing any cost is an important national economic issue. The relevance of scientific research is related to important problems of material economy in the design of reinforced concrete slab structures. The problem of preserving the environment is becoming more and more urgent. Portland cement is the most energy-intensive component of concrete, the production of which is accompanied by significant CO2 emissions. Therefore, reducing the use of cement leads to a significant saving of natural resources and a significant reduction of CO2 emissions. This especially applies to reinforced concrete structures, in particular, monolithic reinforced concrete floors in buildings of various purposes, monolithic foundation slabs, and monolithic reinforced concrete span structures of bridges of small and medium spans. An alternative to solid monolithic reinforced concrete slabs is slabs with cavity-forming inserts, which make it possible to significantly reduce the consumption of concrete and therefore to reduce the weight of the slabs and the number of working fittings. In general structural solutions, there are mainly slabs with one-way or two-way arrangement of cavity-forming inserts. Most of the conducted studies concern slabs (mainly overlaps) with unidirectional arrangement of inserts. In the dissertation, a program and methodology of experimental research was developed, according to which 3 types of main test samples of brands with cross-shaped beams and 4 types of linear beams, which consist of cross-beams, were designed. Linear reinforced concrete beams were loaded by 2 concentrated forces located symmetrically from the zone of pure bending. Cross-test beams were loaded with 4 concentrated forces. The method of experimental measurements of the deformations of the upper face of concrete test samples using an optical-digital system and the method of applying the acoustic emission method when testing test samples are also presented. The results of tests of linear and cross-sectional samples according to indicators of load-bearing capacity and deformability analyzed. The nature of the destruction showed that concrete strengthening occurs at the intersection of the beams due to biaxial compression. The load-bearing capacity of the test samples of linear beams is lower compared to their load-bearing capacity in the composition of cross beams. Deformations of concrete and reinforcement of linear beams are greater than their deformations in cross-sectional test samples. The use of the speckle-correlation method made it possible to detect the nature of the change in the stress-strain state of compressed concrete on the upper face of the cross beams in the area of their intersection and to fix them at the pre-destruction stages. The results of calculating the strength of normal cross-sections of linear test samples using the deformation method are presented. The results of modeling the stress-strain state of linear beams and cross-sectional test samples in the "Lira" software complex are shown, as well as the visualization of the destruction of cross-sectional test samples, which confirms the nature of the destruction of test samples. The simulation of the work of linear and transverse samples in PC "Lira" showed a fundamental difference in the SDS of the beams in the area of their intersection. They are smaller at the intersection of beams measuring 10×10 cm (hereafter CS) and larger in areas adjacent to the CS section. General recommendations for the calculation of slab-reinforced concrete structures with bidirectional arrangement of inserts, taking into account biaxial compression, have been developed. The technical, economic, and environmental efficiency of plate structures with the bidirectional arrangement of inserts and the implementation of work results are given. Thus, the dissertation solved an important scientific and practical task related to the current problems of material, resource, and energy saving, as well as environmental safety. For the first time, experimental and theoretical studies of cross beams confirmed the strengthening of compressed concrete in the cross-section of the beams, which must be taken into account when calculating and designing monolithic reinforced concrete slab structures with bidirectional arrangement of inserts. The use of cavity-forming inserts makes it possible to significantly (up to 26-32%) reduce the consumption of concrete, the production of which is accompanied by a significant depletion of material resources and environmental pollution, and to reduce the consumption of reinforcement by up to 12%.