EXPERIMENTAL INVESTIGATIONS OF THE LOSSES OF PRESTRESSING IN FINE REINFORCED CONCRETE ELEMENTS

Abstract

The article deals with late losses of prestressing of reinforcement due to shrinkage and creep in fine reinforced concrete structures. Creep deformations can several times exceed the elastic straincaused by load. The most common in practice caseof the development of concrete creep is slowly decreased creeping with timewith a rather high initial rate of the development in the first hours after loading. It is typical for stresses that do not exceed the long-term resistance of concrete. Experimental study of deformation of shrinkage and creep of fine-grained concrete allows us to compare the loss of prestressing due to concrete shrinkage and creep. Usually there is an aggregate effect of these factors, which significantly complicates the study of the processes occurring in concrete during long-term exposures. Basically, the results obtained during testing of concrete prisms are used to compare stress-related properties of concrete, but this is not enough to study the loss of prestressing due to concrete shrinkage and creep and testing should be carried out on elements reinforced with prestressed reinforcement to take into account changes in prestresses and redistribution of stresses on the height of the cross section (depth) of the element with a prolonged action of the prestressing force. The results of experimental studies of rectangular reinforced concrete beams at loadcase of different ages of t = 14, 28, 280 and 320 days are analyzed. The losses from rapid creep, shrinkage losses, total losses from shrinkage and creep are considered. The experimental data are presented in the form of graphs and tables. There was performed comparison of the experimental data with the calculated ones determined according to the current standards, and for shrinkage according to the method proposed by I.I. Ulitsky as well.