PRESTRESSING OF CONCRETE STRUCTURES USING THE DURING – TENSIONING METHOD

Abstract

The improvement of building structures, development of alternative methods of prestressing, expansion of the boundaries of technological approaches create opportunities for the rational use of construction materials, contribute to increasing efficiency in construction. Such methods are based on physical laws, provisions of theoretical and building mechanics, resistance of materials and take into account the properties of building materials and the practice and experience of manufacturing and operating building structures. Prestressed concrete structures are usually manufactured according to post-or pretensioning technology. There are a great number of proposals as to the application of these technologies. The majority of them are well studied, and some of the best ones find their practical use. Almost all these suggestions can be united according to the principle of the steel prestressing transfer, namely onto the strong hardened concrete. The possibilities of manufacturing more effective prestressed reinforced concrete structures in the limited frames of the single principle are in many respects exhausted. Many specialists think it is the reason for slowing down progress in this direction. We need here qualitative transition to new concepts in the sphere of prestressed concrete to have precedents for rapid flourishing of ideas and developments. The author has proposed and put into practice the principle of prestressing transfer onto the freshly placed concrete mix of structures. In this case prestressing is transferred already at the stage of cement concrete mix. The new production technology has led us to the possibility of increasing concrete strength in prestressed structures up to 50-70 per cent. It is achieved due to the compressing of unset concrete mix during the operation of steel tensioning. A wide range of research and practical studies has shown that the given technology provides necessary steel pretensioning and uniform or predetermined concrete mix compaction as well as further hardening of concrete in a structure. Taking the experimental research data as a basis, we can state that the self-organization of concrete structure at the stage of mix prestressing, effective bond between concrete and steel, preservation of the force of prestressing – all this becomes a guarantee for high strength and quality of the concrete elements proposed. Industrial application of prefabricated bridge elements with prestressing onto the concrete mix has proved the expediency of the method developed.