# Ultimate Compressive Strains and Reserves of Bearing Capacity of Short RC Columns with Basalt Fiber
## 6 Conclusions  
This experimental study was aimed at studying the effect of a particular type of fiber on the strength and strain properties of concrete. The use of high-strength reinforcement in ordinary concrete is useless due to the limitations of the deformability of the compressed zone of concrete. The introduction of coarse basalt fiber into the concrete composition increases the ultimate tensile strength of the concrete. The condition for the compatibility of work of concrete and reinforcement bars makes it possible to use reinforcement of a higher strength class, capable of increasing the bearing capacity of the column with increased deformability. Simultaneously, for calculating the bearing capacity, it is possible to use the value of the ultimate stresses in the reinforcement 520 MPa, which is 30% higher than the standard value in SP 63.13330.2018 [30]. Considering this factor in the calculation and design will make it possible to achieve greater bearing capacity and efficiency of structures due to the possibility of using reinforcing steel bars with higher resistance. The addition of 10% fiber from coarse basalt fiber increased fine-grained concrete's actual strength with a design strength of 25.0 MPa on ordinary crushed stone by 9.0%, and structural expanded clay concrete of the same design strength up to 12%. Dispersed fiber reinforcement had a positive effect on the scale factor. Thus, the difference in cube strength parameters made of expanded clay concrete with an edge from 7.07 to 15.0 cm reached 7.2%, and in similar ones with fiber from 1.9 to 3.6. The \"narrowing\" of the specified parameter is explained by the introduction of fiber, which creates a \"reinforced\" cage around the expanded clay grains, preventing its premature crushing. It was found that the load level corresponding to the formation of microcracks when testing prisms made of structural expanded clay FRC was from 29 to 42% higher than that of ordinary expanded clay concrete. The increase \(\varepsilon_{b}\) in prism samples with fiber on a conventional aggregate was 12%, and on expanded clay, 26%. Ultimate compressive strains in BFRC concrete of columns with combined reinforcement were higher than in similar specimens without fibers. Under axial compression, the absolute values \(\varepsilon_{bR}\) in the uprights on a light aggregate increased by 1.42 times, and on a heavy one by 1.19 times. In the case of eccentric compression with a relative eccentricity of 0.6, the values \(\varepsilon_{bR}\) increased even more, while their absolute values 3.6\(\cdot 10^{-3}\) in the expanded clay FRC samples reached, and in similar ones without fibers 2.4\(\cdot 10^{-3}\). Under axial compression, the addition of 10% fiber in the samples of expanded clay concrete and heavy concrete increases the ultimate stresses in the reinforcement in compression \(\sigma_{sc}\) by 18.1 and 12.3%, respectively. With an eccentric load application, the ultimate compressive stresses in the reinforcement of the compressed zone increased even more (samples with the codes KK-1 and KKF-1). The absolute values \(\sigma_{sc}\) in high-strength reinforcement class A1000 at forces of 0.98\(N_{u}\) reached 520 MPa, exceeding the standardized SP 63.13330.2018 by up to 30%, and in column specimens reinforced with hot-rolled steel of class A400 increased to 19%. At the same time, at the same load level (the forces perceived by the structures during their operation were taken \(N=0.7N_{u}\) as the baseline), the actual compressive stresses in reinforcement and concrete in FRC samples were lower than in similar resistant ones without fibers. Analysis of the results of testing short columns for axial compression showed that prototypes with fiber reinforcement, all other things being equal, had peak load values that were 11-12% higher than those with conventional reinforcement. At the same time, the degree of increase in the bearing capacity of the test racks did not significantly depend on the type of concrete.