The paper presents the results of experimental investigations performed by the authors on the casting position factor. It was proved that at the height of reinforced concrete elements there are different bond conditions. Moreover, the bond depends on concrete mechanical properties, element height as well as concrete mix composition and consistency. The experiments also showed the advisability of determining the casting position factor separately for bars from normal concrete and those from high–performance concrete (HPC). The analysis of investigation results has shown that “good” bond conditions are a relative concept and depend on, among other things, element height. The higher the element the better the concrete to lower bars bond. Consequently, elements of considerable height (higher than 600 mm) demonstrate a bigger difference between concrete to upper bars bond and concrete to lower bars bond.

A method of calculating the deflections of steel plate-concrete composite beams is proposed. In the hybrid work of such beams the properties of reinforced concrete and composite structures are combined. This convention should be followed in considering their ultimate capacity and serviceability limit state. The proposed solution has been verified in experimental studies performed by the authors. Good compatibility of theoretical calculations and experimental results has been obtained. It allows the theoretical solution to be used in the analysis of other cases with parameters different than those of the discussed beams. In the experiments done by the author six beams of total length of 5.20 m and theoretical length of 5,00 m were used. The cross section was rectangular, 0.24 m in width and 0.49 m in height. The steel plate 4.74 m long was 6.10 and 16 mm thick. The diameter of the flexible connectors was 13 mm. Their spacing varied between 80 and 200 mm. Owing to the flexibility of the connectors the interface slip between the steel and concrete parts was included in the theoretical solutions. The results of an in-depth analysis indicate that the deflections of steel plate-concrete composite beams are affected by the compressive strength of concrete and the yield point of steel as well as connectors’ diameter and spacing. This impact varies, that of the yield point of the steel from which the plate is made being the highest.

The aim of the paper was to assess the bending strength of steel plate - concrete composite members, based on an experimental study performed by the authors together with theoretical and numerical analyses. The values of the mechanical parameters of the materials the beams were made from were adopted on the basis of the tests results. The proposed solutions have been verified by experiment. For this purpose the results of tests performed by the authors and other researchers have been used. The former ones are original, and the way of their presentation makes them applicable by other researchers. Following the results it can be stated that with respect to bending strengths from the experimental study the results obtained from the theoretical analysis are underestimated 6,6 % on average. The results based on the numerical analysis, on the other hand, are overestimated by - 7,5 % on average. The results of the theoretical and numerical analyses indicate that the interface slip between the steel plate and concrete part affect the bending strength of steel plate-concrete composite beams only slightly (about 2% on average).

In recent years, carbon fibres have been extensively used to strengthen concrete structures. In most cases, the lamination process is carried out using epoxy resin as matrix. In some cases, especially when strengthen structural elements made of weak concrete, it is possible to replace the epoxy resin with an inorganic, cement matrix, while at the same time maintaining a sufficient efficiency of strengthen understood as the percentage increase in the compressive strength of concrete samples due to the applied reinforcement in relation to the reference concrete. In these studies, elements of carbon fibres mats that are reinforced with a cement matrix were used as the starting product for fibre recovery. The laminate, which was used to reinforce concrete elements, was detached from the concrete surface and subjected to processing in order to obtain clean carbon fibre scraps without cement matrix. Then, the obtained carbon material, in shaped form, was used to strengthen self-compacting, high performance, fibre reinforced concrete (SCHPFRC). For comparative purposes, this concrete was also strengthened by carbon fibre mats (with one and three layers of CFRP). Each samples were tested in uniaxial compression test. The compressive strength of concrete reinforced with 1 and 3 layers of CFRP was higher by 37.9 and 96.3%, respectively, compared to the reference concrete. On the other hand, the compressive strength of concrete reinforced with 1 and 3 layers of carbon fibre scrapswas higher by 11.8 and 40.1%, respectively. Regardless of the reinforcement technique used, the composite elements showed a higher deformability limit in comparison plain concrete. The obtained results showed that it is possible to reuse carbon fibre to strengthen structural elements made of SCHPFRC effectively, using simple processing methods.