Result of observing the formation of stresses in the concrete of a buttress dam during its construction

Abstract

It is known that so-called technological stresses forming during construction have a considerable effect on the behavior of massive concrete structures.Control of the formation of these stresses is one of the ways to promote the creation of reliable economical structures.For instance, the results of field investigations revealed the possibility of creating preliminary compression of the upstream face of a dam by regulating the conditions of grouting the joints between columns [i]. This article elucidates the possibility of using the stresses occurring in concrete during its hardening for these purposes.Vertical stresses and strains in a concrete element of the simplest configuration in the form of a 5-m-thick wall were examined for determining the regularities of formation of the indicated stresses.This wall was the buttress of one of the sections of the Andizhan dam [2, 3].The temperature and deformations of the concrete were measured by embedded remote transducers.String transducers of the All-Union Industrial Association for Automation of Power Plants (Soyuzenergoavtomatika) were used: for temperature, type PTS-60 with a measurement range from --20 to 60~ and for strains, type PLDS-400 with a 400-mm base and measurement ranges from --200 to 50 and from --50 to 200 • 10 -5 units of strain. The error of the transducers is 2% of the measurement limit. The apparatus was arranged in the buttress in transverse horizontal lines, three measuring points in each line (Pig~ i). The strain gauges were installed both singly (lines I, II, V) and as rosettes (lines III, IV).The single strain gauges were arranged vertically at the intersection with the horizontal block joints formed after a long interruption in concreting.The strain-gauge rosettes, oriented parallel to the faces of the wall, consist of two mutually perpendicular gauges at the face and of four (a "fan" rosette) on the axis of the wall.Furthermore~ the results of observations of the stresses near the upstream face of the dam at measuring points 4-6 were obtained. Here the measurements were taken by means of "fan" rosettes consisting of four strain gauges oriented parallel to the face with a fifth one perpendicular to the plane of the "fan."The results of the observations were processed with the use of a computer.The stresses in the concrete were determined from the readings of the strain gauges arranged as rosettes by means of a specially developed program.The calculations were performed on the basis of the theory of an elastico-creeping body with the use of A. V. Shvetsov's method of numerical solution of the fundamental integral equation, which was tested experimentally in [4].Stresses in concrete begin to occur when it reaches a certain strength.Investigations [5] showed that the process of the increase of strength is determined by the composition of the concrete, conditions of its transport, compaction, maturing, etc. However, the effect of the actual construction conditions on the characteristics of this process have been inadequately investigated.This hi...