SEISMIC BEHAVIOR INDICES OF OLD TYPE REINFORCED CONCRETE MEMBERS

The study reviews the existing methods for estimation of the peak and residual shear strength of columns and the main parameters that affect their shear drift capacity.Shear force effects on the behavior of the columns seem to be significant as shear influences the flexural behavior of columns and encourages failure mechanisms that are more brittle, especially for columns which are shear critical (columns over-reinforced in flexure, short columns).The methods that have been developed up until now for the estimation of shear strength vary, but in all cases contributions from separate mechanisms of resistance, namely the contribution of concrete, web reinforcement and axial load are recognized.In establishing the degradation of shear strength under seismic load reversals the decomposition of concrete cover, the diagonal strut cracking of the element and the yielding or slip of the longitudinal reinforcement are determined.Another important parameter which must be taken into account in experimental results for the calibration of previous methods in establishing the rate of strength degradation as well as the residual strength is the contribution of axial load to the load-carrying capacity loss, with increasing displacement.This phenomenon is shown to be significant and for that reason separation from the other mechanisms of degradation will be essential in revision and refinement of design expressions for shear, necessary in assessment procedures.An analytical investigation of the relationship between shear drift capacity, transverse reinforcement, aspect ratio and axial load is presented in the paper.