# Ultimate Compressive Strains and Reserves of Bearing Capacity of Short RC Columns with Basalt Fiber
## 4 Results of Testing Short Columns  
### Load Bearing Capacity  
All 10 samples of short columns, following the experimental studies program (series of tests no. 2), were tested by short-term loading until fracture. Six columns were tested for axial compression, two with relative eccentricity \(e_{0}/h=0.15\), and two with eccentricity \(e_{0}/h=0.6\). The failure of specimens without fiber reinforcement under axial application of an acting force was caused by the concrete crushing in compression in the middle of the columns. Immediately before the destruction of the concrete in the compressed zone, the formation of cracks was observed. Longitudinal cracks appeared, and the concrete cover was punctured in the middle part of the sample. In specimens reinforced with fiber with a centrally applied force, the nature of the destruction was identical. However, the moment of appearance of cracks in concrete along the longitudinal reinforcement corresponded to higher compressive stresses \(N/N_{u}=0.88\)-\(0.92\), and the width of their opening was significantly smaller. Figure 6 shows the fracture of two samples tested for the action of a compressive force with eccentricities \(e_{0}/h=0.15\) and \(e_{0}/h=0.6\) (codes KKF-0.15 and KKF-0.6)  
Under the action of a longitudinal force with a small relative eccentricity \(e_{0}/h=0.15\), the section of the element had an insignificant tensile zone. Accordingly, the reinforcement \(A_{s}^{1}\) was subjected to compression, and the reinforcement \(A_{s}\), located at the face further from the longitudinal force, was subjected to tension. The element crushing, in this case, began from the side of the compressed zone, while the second case was observed when the condition \(\xi>\xi_{R}\) was met (where \(\xi=x/h_{0}\) is the relative height of the concrete compression zone, \(x\) is a coordinate and \(h_{0}\) is the cross-sectional height, and \(\xi_{R}=x_{R}/h_{0}\) is the boundary value of the relative height of the concrete compression zone, \(x_{R}\) is a coordinate in tensile zone). Figure 5: The stress–strain diagram (compression test results for prism specimens): 1, 3—heavy concrete and expanded clay concrete; 2, 4—also with fiber. With an eccentric application of a force with small eccentricities, the crushing of expanded clay basalt fiber reinforced concrete (BFRC) of short columns, as well as in the samples described above, occurred from the concrete crushing in compression zone, while the stress in the reinforcement further from the line of action of the external force did not reach the yield point. A general view of the prototype during testing is shown in Figure 1. Actual strains (both compression and tension) in specimens with conventional reinforcement varied from 7.0 to 13%, and in models with combined reinforcement, from 11.7 to 28%. The columns tested with a relative eccentricity \(e_{0}/h=0.6\) failed due to reaching the ultimate stresses in the tensile reinforcement. The achievement of ultimate stresses in the compressed zone of concrete was observed almost simultaneously. Figure 6: Photo of failure specimens: (**a**) KKF-0.15; (**b**) KKF-0.6. The theoretical bearing capacity of the columns under axial compression was determined by the formula:  
\[N_{u}^{theor}=R_{b}A_{b}+R_{sc}A_{stot} \tag{1}\]  
where \(R_{b}\) and \(R_{stot}\) are the calculated resistance of concrete and reinforcement; \(A_{b}\) and \(A_{stotb}\) are the cross-sectional area of the sample and the total area of the longitudinal reinforcement.