Multi-scale modeling for deformation mechanism analysis of composite joint substructures

• A multiscale model of the composite joint substructure is developed.
• The multiscale model is validated by extensive experimental results.
• The DCP diagram is introduced to analyze the deformation mechanism.
• A fiber model for slab composite effect under bidirectional loading is proposed.
• Mode I and II parameters for the crack model of the core concrete are presented.

Analyzing the deformation mechanism of composite joint substructures in a concrete filled steel tubular (CFST) column-composite floor frame structural system is essential to assessing its overall seismic performance and failure mode. Conventional microscopic and discrete finite element models have several problems hindering application for the deformation mechanism analysis. To address these problems, the present study develops a multi-scale modeling approach of the composite joint substructure. Two critical issues in the multi-scale modeling is first discussed: (i) modeling the slab spatial composite effect under bidirectional earthquake loading using efficient fiber beam–column elements and (ii) key parameters of the concrete crack model for simulating the spatial shear behavior of the composite joint core. The proposed multi-scale model is validated by several tested plane and spatial composite joint substructures. Finally, the deformation-component-proportion (DCP) diagram, which can be calculated directly from the displacement results of the proposed multi-scale model, is introduced to analyze the deformation mechanism of the composite joint substructure. The proportions of the beam flexural, column flexural and joint core shear deformations in the total deformation corresponding to different story drift angles and different story drift direction angles can be illustrated by the DCP diagram so that the failure mode of the composite joint substructure can be clearly revealed in any possible earthquake incident direction. The proposed multi-scale modeling approach offers a powerful tool for assessing the deformation mechanism of composite joint substructures.