Analytical Model for Initial Rotational Stiffness of Steel Beam to Concrete-Filled Steel Tube Column Connections with Bidirectional Bolts

Abstract

The initial rotational stiffness of connections is important for the design of semirigid frames. However, most current studies on steel beam to concrete-filled steel tube column connections with bidirectional bolts are based on experimental tests, and theoretical analysis and numerical analysis are rarely reported. As a result, there is no suitable analytical model for calculating the initial stiffness of the connection. Based on the component method, this paper proposes an analytical model to predict the initial stiffness of the connection. It is considered that the connection rotation is mainly induced by deformations of the endplate in bending, column flange in bending, bolts in tension, and panel zone in shear. Moreover, the effects of the endplate in bidirectional bending and bolt pretension are taken into consideration. Then, the prediction results based on the proposed analytical model are compared with experimental results to verify its accuracy, and comparison results indicate that the proposed analytical model can predict the initial rotational stiffness of steel beam to concrete-filled steel tube column connection well. In addition, bolt diameter and endplate thickness are the most influential parameters that affect the initial stiffness of the connection. It also provides a way for such connections to be designed as rigid connections. Finally, the proposed analytical model can be applied with good precision in elastic analysis and serviceability calculations in the design of semirigid steel-concrete composite frames. It can be applied to four types of connections: stiffened extended endplate connections, nonstiffened extended endplate connections, flush endplate connections, and T-stub connections. The proposed analytical model saves substantial resources and workload in experiments and simulations.