Evaluation of Cyclic Deterioration and Post-Peak Behavior of RC Beam-Column Joint Assemblages by 3-D FE Analysis

Nonlinear finite element analyses on the RC beam -column joint specimens failing in shear tested under cyclic lateral loading were conducted to investigate their fracture modes and post peak behaviors such as cyclic deterioration and shear resistance mechanism. The analyses were performed especially by paying attention to spatial discretization, modeling of bond behavior and type of loading. Furthermore, a macro -scale model for predicting the joint capacity proposed by Shiohara is reviewed and validity of his hypotheses are rigorously investigated through comparison of the observed and calculated results. Beam-column joint assemblage in the RC moment -resisting framed structures is a critical seismic element because its behavior under severe earthquake motions has a significant effect on failure mechanism and strength and deformation capacity of the building structures. Thus, many experimental studies have been conducted to understand failure and resistant mechanisms of the beam-column joints so far. The current seismic codes provides the upper limit of input shear to the joint to avoid the joint failure; that is, degradation of the story shear and localization of the shear deformation to the joint (ACI 1995, AIJ 1994 and SANZ 1995). Allowable limit of the input shear is expressed by a simple empirical formula in terms of the compressive strength of concrete. Kitayama et al. conducted the cyclic lateral loading test on the interior beam-column joint specimens with different bond properties of longitudinal steel bars in the beam through the joint. In addition, the earthquake response analyses with the simplified framed model were carried out using two kind of hysteresis models; one is a regular Takeda model and the other is a modified Takeda model characterized by a significant effect of the bond slip on a shape of the hysteresis (Kitayama et al. 1987). Consequently, they derived several recommendations on the limitation by the so-called bond index indicating bond deterioration of rebars, the limitation of the ratio of rebar diameter in the beam to width of the column expressed in terms of the yielding strength of rebar and the compressive strength of concrete, the limitation of the input shear for