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Introduction. The method of strengthening the reinforced concrete structures is chosen depending mainly on the cost and timeframe of the performed work. In each specific case, the decision is made depending on the load, type of defects, operational features, etc. Apart from the direct costs of inspection, strengthening project design, materials, lifting and transport services and the cost of strengthening works proper, there is a number of additional costs related to the technological features of the work performed. Among the new methods of strengthening, the method of external strengthening with the composite carbon materials can be particularly emphasised. Compared to the previously developed methods of strengthening with the reinforced concrete and metal, the composite systems are easily transportable and do not incur additional costs. The aim of this study is to determine the method of strengthening most rational for the compressed structures. Materials and methods. The authors have examined three methods of strengthening the compressed reinforced concrete structures. In the frame of the research a numerical experiment has been carried out, in which a reinforced concrete column was strengthened at different strengthening coefficients from 1.1 to 2.0, i.e., from 10 to 100% of strength increase. The estimations of the cost of strengthening the column by three methods of strengthening have been carried out: jacketing using the reinforced concrete, metal and composite materials. After carrying out thirty variants of calculation, a table presenting all specifications and quantities of the materials has been drawn up. At the final stage of the research, the total cost of each method under investigation has been estimated based on the prices of the selling companies. Results. The analysis of strengthening with the reinforced concrete revealed that at most of the strengthening coefficients the achieved structural reinforcement is minimal. Under the high loading levels strengthening with the metal is not economically expedient, as it implies the use of the large-section angles. The composite material systems of external strengthening are very material-consuming at all load increasing coefficients. Taking into account the high cost of materials, this method is basically the least economically expedient. Discussion and conclusion. Based on the results obtained, the efficiency of three most common methods of strengthening the reinforced concrete compressed columns was analysed. Proposals on the rational design of the strengthening systems for the eccentrically compressed reinforced concrete poles under the different eccentricities of load applied have been developed.
Georgiev et al. (Tue,) studied this question.