A METHOD OF PRESTRESSING REINFORCED CONCRETE STRUCTURES THAT INCREASES THEIR STRENGTH

Abstract

The study considers and analyzes technologies of prestressing of reinforced concrete structures known in wide construction practice. Technological methods of manufacturing prestressed reinforced concrete structures are divided by the method and time of tensioning of steel, by methods of its placement and pretension and by fastening of pretention bars in concrete. According to the method and time of tensioning of steel all prestressed structures are combined into two groups: elements with pretentioning before placing of concrete and elements with posttensioning on hardened concrete. Such methods of prestressing, as a rule, do not compact concrete mix and therefore reserves of durability, water and frost resistance of materials remain unused. In the presented work the original practical way of preliminary tension of steel of reinforced concrete products is developed; it includes well-known operations: playcing of steel in the form, tension of steel, the subsequent fixing of steel elements. What distinguishes the proposed method is that in order to increase the degree of prestressing of the structure and its strength, the ends of steel bars are fixed with anchors on the moving ends of the form, and their tension is performed by rapid rotation of the concrete-filled closed form with simultaneous compaction of concrete. The tension of steel is performed as follows. The form, filled with concrete mixture with some excess in the throat, rotates quickly. Under the action of centrifugal forces, the mixture is distributed and thrown to the moving ends of the form, compacted and due to the action of pressure pushes the ends apart. Since the steel bars are fixed at the ends of the form by anchors, they are strained. In the central part of the form, the concrete mixture is compacted with a vibrating piston. Static load onto the piston is transmitted by a hinge. Thus, the tensioning of bars and compaction of concrete occur simultaneously in one operation. After concrete reaches the required strength, the form is removed from the structure. A method of simultaneous prestressing and pressing of reinforced concrete structures has been developed. This method is carried out using the action of centrifugal forces. Dependences for determination of technological parameters – speed of rotation of the form with concrete mix, value of pressure and pretensioning of steel are provided. This new mechanical method of tensioning of steel on concrete mix, which is carried out due to the action of centrifugal forces, is added to the existing classification of methods of manufacturing prestressed reinforced concrete structures.