Strength of conventional and damaged reinforced concrete beams strengthened by carbon plastic under the action of a small load of high levels

Abstract

Most span reinforced concrete structures experience repeated loads of various sizes and signs, that is, a complex stress-strain state. During operation or during hostilities, span reinforced concrete structures experience significant damage and a significant decrease in bearing capacity, especially when a low-cycle repeated load is applied. In this regard, there is a need to restore their performance and/or to increase bearing capacity. The current design standards do not contain recommendations for determining the residual bearing capacity of such structures and calculating their amplification. Known methods for restoring performance and strengthening the structure by increasing the cross section by attaching additional metal or reinforced concrete elements to them. But the methods for calculating this gain are also imperfect. It is proposed to restore the operability of these structures by strengthening their stretched parts of the CFRP, and the experimental studies will form the basis for improving the deformation method for calculating their bearing capacity. Obviously, the main reason for the decrease in the bearing capacity of prototypes under low cycle alternating load is the violation of the structure of concrete, especially in the supporting areas, its softening and partial loss of adhesion to the reinforcement. The greatest increase in residual deformations in concrete and transverse reinforcement of the research beams of the first and third series is observed in the first two to three cycles and, as a rule, they stabilize until the fifth or sixth cycle. And in some samples with a minimum class of concrete and the number of transverse reinforcement, these deformations did not stabilize and they collapsed in 6 ... 9 cycles from reaching fatigue strength or a possible decrease in their strength parameters due to statistical error in determining the breaking load of high levels. The prototype fifth-series beams reinforced with external composite reinforcement deformed almost elastically until they reached their ultimate state in compressed concrete or stretched metal or composite reinforcement. The presence of external carbon fiber reinforcement in the lower stretched zone of the beams in series 5 and on their supporting sections allows to increase their bearing capacity in comparison with similar series 3 beams at the same low-cycle load, on average, 1.7 times and partially change the nature of their destruction.