Stiffness amplification coefficient for composite frame beams considering slab spatial composite effect

Abstract

The slab spatial composite effect arises due to compatible deformation of the reinforced concrete slab with the steel beam in composite frames. This effect can significantly amplify the stiffness of composite frame beams. Current Chinese design code adopts the stiffness amplification coefficient method for the design of composite frame beams, and the equivalent moment of inertia of the composite frame beam can be calculated to conduct the global analysis. However, the current formulae are only suitable for lateral load cases and symmetric I-shaped steel section. Therefore, this study aims to propose unified design equations of the stiffness amplification coefficient considering both vertical and lateral load cases and both symmetric and asymmetric I-shaped steel sections to address the aforementioned limitations. A series of parametric finite element analyses using the beam-shell mixed element model are conducted to derive the unified design equations. The reasonability of the proposed equations is verified by comparing the critical structural indices, such as the natural vibration period, inter-storey shear, lateral displacement, bending moment, and deflection distribution of numerical examples of multi-storey composite frames. Good accuracy is obtained through the comparison between the linear beam element model modified by the proposed equations and the beam-shell mixed element model.