The limit value of plasticity coefficient of reinforcement under seismic loads

Abstract

Plastic deformations develop in bending reinforced elements under seismic loads. In calculation of reinforced concrete constructions by spectral method they are taken into account only at the stage of seismic loads determination by introduction of reducing coefficients. But the development of plastic strains in bending elements leads to appearance of cracks, which don’t close after changing the internal forces sign. Due to it the work height of a section decreases, and the strength of elements reduces during subsequent loading cycles. The experimental evaluation of the influence of plastic strains on the stress-strain state of beams under low-cycle alternating effects of high intensity has been carried out. The first group of beams, considered as reference, was loaded with a monotonously increasing load until complete destruction. The other groups of beams were loaded by the monotonically increasing load up to the specified value of plastic deformations was reached. Then they were unloaded and loaded by the force of the opposite sign up to destruction. The stress-strain state of normal sections at all stages of loading was studied. It has been discovered that when changing the sign of load the through cracks are formed which close later if the plastic deformations of reinforcement are not large. The limit value of plasticity coefficient in the first semi cycle of loading preventing the formation of non-closing through cracks when changing the sign of internal forces has been determined.