Grounds for the decision to strengthen reinforced concrete structures after short-term impulse loads, using Alluriquin HPP as an example

Introduction. Floorings of the turbine hall and installation sites of the HPP (PSS) are one of the most important reinforced concrete structures, as during operation they are subjected to significant process duties, including those not provided for by the project. Thus, during the testing of crane equipment on the floor surface of the installation site of the Alluriquin HPP under construction, the cargo weighing 22 tons fell, under the influence of which the floor slab was punched, which required a comprehensive study of the condition of the reinforced concrete structure of the floor and the surrounding area of the failure of structures, as well as the development of measures to strengthen the damaged structure. Materials and Methods. Visual and instrumental studies of the stress and strain state (SSS) of the reinforced concrete structure of the turbine hall slab and surrounding structures were carried out with the use of optical devices (MPB-3 reading microscope), Schmidt hammer to determine the strength of concrete structures, as well as the “reinforcement load removal” method to determine the actual stresses in the reinforcement of structures. Results. The punching of the reinforced concrete floor of the installation site with vertical displacements of the edges of through cracks up to 12 mm, as well as the system of cracks formed during the fall of cargo was revealed. The actual stresses in the reinforcement are determined by the “reinforcement load removal” method. On the basis of finite element modeling the actual condition of structures during the period of cargo fall and after the removal of the load is obtained. On the basis of the analysis of results of field and design studies the schematic diagram of strengthening of structures by carbon composite materials is developed. Conclusions. The actual SSS of the reinforced concrete floor of the installation site and its support structures during the period of the cargo fall and after the termination of the impulse load is established. The vertical displacement of the edges of the crack of the floor punching was 17.5 mm during the period of the fall of the load and 12 mm after the removal of the impulse load. Crack opening width in reinforced concrete structures in the cargo drop area reached 2 mm. At the moment when the cargo fell on the floor slab, the values of stresses in the reinforcement cage reached 200 MPa; after the impact — 76.2 MPa. With a view of the subsequent safe operation of the reinforced concrete floor and surrounding structures the basic schemes of their strengthening by external reinforcement on the basis of carbon fiber have been developed, which have been proved by calculation.