Initial stiffness of connection joining I-beam to concrete-filled multicellular steel tube wall

Concrete-filled multicellular steel tube (CF-MCST) wall is widely used in China in recent years. In the companion paper, the moment capacity of the connection joining an I-beam to a CF-MCST wall was studied. Realizing that the insight into the connection's stiffness would greatly benefit performing a fine structural analysis, this paper aims to propose a theoretical approach for approximating the rotational stiffness of the connection. Finite Element (FE) model is first established for analysis, which is validated by using the experimental results extracted from previous studies. In order to attain the stiffness resulting from the endplate and the wall individually, an additional companion FE model is employed, where the endplate's deformation is negligible by using an extreme great value for the Young's modulus of the endplate and the connection's rotation is therefore mainly attributed to the wall's local deformation near the connection. For the stiffness accounting for the deformation of the endplate, the stiffness accounting for the local deformation of the wall, and the connection's stiffness, parametric study is then performed via the validated FE models whose geometrical parameters falling into the range conventionally taken in the engineering. Based on the FE analysis results, the abstracted mechanical model is proposed, resulting in semi-empirical formulas where partial parameters are identified by the means of regression analysis. It is found that enlarging the geometrical parameters would improve the connection's stiffness. Among the parameters, the beam height has the most significant effects on the connection's stiffness. Accordingly, increasing the beam height first is suggested for the aim of enhancing the connection's stiffness. The comparison of the results obtained via the FE analyses and that obtained via the proposed theoretical approach shows a good agreement, and the error is <10% regarding the connection's stiffness.