EXFOLIATION THE ELEMENT OF REINFORCEMENT OF THE BRIDGE STRUCTURE UNDER CYCLIC LOADING

Abstract

The problem of calculating reinforcing elements as one of the common means of repairing and restoring the serviceability of engineering structures, taking into account the fact that a large number of material-intensive bridge structures in Ukraine is close to exhausting its design resource, remains timely. Strengthening of bridge structures is necessary in cases of long-term operation without timely maintenance and capital repairs, when there are errors in the design, manufacture or execution of construction works, insufficient strength of construction materials, as well as changes in weather conditions and current regulatory documents in Ukraine.Exfoliation of the flexible hard reinforcement in conditions of plane problem under cyclic loading are researched. The development of localized zones of prefracture (weakened contact), which may correspond to the area of accumulation of  damage, partial rupture of ties, etc. are precedes the exfoliation. We assume that in the vicinity of the ends of the reinforcement, with a certain combination of amplitude values and the number of load cycles, there will be sliding delamination, which will advance along the material separation boundary from each edge to the central part. The length of the reinforcement without fragments peeled off at the ends is called the working length of the reinforcement. The coefficient of friction on the exfoliated part is assumed to be zero.Analytical dependences for changing the working length of the reinforcement depending on the amplitude of the load and the number of cycles are obtained. An energy criterion was used to construct the delamination equation, which assumes the existence of a critical value of energy necessary for the working length of the reinforcement to decrease by a unit of length, which is considered a known characteristic of the composition. For a continuous load, the solution of the problem is reduced to the Cauchy problem for a first-order differential equation, and for a cyclic – to the integration of a given function from the load parameters and the elastic and strength characteristics of the system.For a given load per cycle and a predetermined number of cycles, using the obtained formulas, it is always possible to choosethe length of the reinforcing element in such a way that its peeling does not exceed the predetermined value (or does not occur at all). The speed of exfoliation depends significantly on the initial working length of the reinforcement (it is longer for a longer one) and the maximum load per cycle. The reinforcing element in the middle part under the conditions of the problem remains connected to the base.