Influence of Various Reinforcing Arrangements and of Gravitation Stresses on Hysteretic Behavior of RC Sections

摘要

Seismically resistant RC structures are generally designed in accordance with response spectra. Only a few of the properties of the materials (concrete and steel) are taken into account, and the load history of the structure is practically ignored. This study proposes an analysis of the compressed concrete, the compressed and tensile reinforcement, and the entire element section under bending (including large eccentric compression) based on three-, two- and four-curve diagrams, respectively. The last-mentioned diagram for a bending element represents concrete cracking, development of inelastic deformations in the concrete compression zone, reinforcement yielding (plastic hinge), and plastic deformations of the entire section. To avoid section over-reinforcing, the reinforcement cross sections in the compressive and tensile zones must not exceed certain maximum values, which have been obtained theoretically and are presented here. A method for determining the ultimate deformation of the tensile reinforcement is presented. A problem involving a symmetrically reinforced element for structures, designed for seismic zones, is analyzed. Stress-strain relations for the RC section concrete and steel under cyclic loading are also given. The energy dissipation level is obtained for each «loading-un-loading» half cycle. It is shown that for the same peak stress, a section's total energy dissipation due to cyclic loading differs significantly from the corresponding dissipation due to static loading. The influence of gravitation stresses on RC section energy dissipation under seismic forces is examined. Non-symmetric cyclic analysis is performed. It shows that the hysteretic loop area is reduced compared to that under gravitation loading. Finally, the RC element's seismic energy dissipation capacity is formulated. The results of this study enable to get a more accurate prediction of RC sections behavior under gravitation and seismic loads.