The macromodel, by which the beam and column are simulated by fiber beam elements, has been extensively used in the progressive collapse analysis of reinforced concrete (RC) frames due to its high computing efficiency as compared to the solid element model. However, there exist some problems that need to be solved to improve the accuracy of the macromodel. One typical issue is to develop an accurate beam-column joint model. In current practice, the beam-column joint is as part of the rectangular frame with rigid elements, neglecting the shear damage and bending moment distribution in the core region of the joint, although they are crucial to progressive collapse analysis. In this paper, a new macromodel that considers the shear damage and bending moment distribution in the core region of the beam-column joint is developed for the progressive collapse analysis of RC frame structures under blast loads. Nonlinear springs are used in the joint connection interfaces to consider the force transfers from the beams or columns to the joint. Also, nonlinear shear springs are used in the core region of the joint, whose characteristics are derived based on the actual force-deformation relationship of the sub-assemblage due to joint shear distortion, to model the shear damage of the joint under blast loading. The proposed beam-column joint macromodel is validated with the available test data in the literature. The results indicated that the proposed macromodel for beam-column joints is more accurate than the traditional beam-column joint macromodel, while the computing efficiency remains almost unchanged in progressive collapse analysis of RC structures, especially when the RC frame structures are seriously damaged or collapse under blast loadings.
POST-EARTHQUAKE CAPACITY EVALUATION OF RC FRAME STRUCTURES WITH MULTI-STORY FLEXURAL WALLS