No abstract

Earthquake response of multi-story reinforced concrete moment resisting frames are calculated considering the deformation of the beam-column joints modeled with rigid panels, uniaxial springs for concrete, steel and bond-slip representing the non-linear coupling of moments, axial forces and shear in members framing into the joint. The variation of the frames includes the column-to-beam strength ratio and the joint hoop reinforcement ratio which are neglected in the current design practice in Japan as structural design criteria affecting the seismic safety. Five synthesized base motions conformed to maximum considered design spectrum and five observed base motions are used. It is revealed that the design parameters of beam-column joint have significant influences. Particularly, the maximum story drift ratio significantly exceeds the current design criteria due to concentration of lateral deflection in some cases due to beam-column joint deformation caused by the mechanism known as joint hinging.

This paper extends a kinematic model named nine DOF model proposed by one of the authors which could predicts the moment capacity and moment at balanced failure of reinforced concrete beam-column joints. The original model is applicable to interior beam-column joints of which the geometric and loading conditions are equal and symmetric about a diagonal line of the joint. The extension reduced the limitations and allows for different sectional dimensions and reinforcement of beam and column and different forces on the beams and columns. The results from the extended model compared to experimental results and the model gave accurate prediction.

The results of nonlinear dynamic analysis on the seismic response of reinforced concrete moment resisting frames in which beam-column joints are damaged are reported. In the analysis, beam-column joints are modeled with the simplified macro-element of beam-column joints to simulate the nonlinear behavior after the yielding of beam-column joints. The analytical results indicate that yielding of beam-column joints, which occurs in the beam-column joints with low column-to-beam strength ratio, induces the story collapse mechanism. The seismic acceleration levels of collapse are lower than the case of beam-column joints which do not yield.

This paper extends a kinematic model named nine DOF model proposed by one of the authors which could predicts the moment capacity and moment at balanced failure of reinforced concrete beam-column joints to apply the model to exterior beam-column joints. Four failure mechanisms of exterior joints caused by moments on the joints are assumed and formulas for calculating moment capacities of exterior joints are derived based on the model and assumed failure mechanism. In the calculation, the yielding of longitudinal bars of beam and columns and lateral reinforcing bars in joints is assumed. The results from the proposed formula compared to experimental results gave accurate prediction.