Slab spatial composite effect in composite frame systems. II: Equivalent stiffness and verifications

Based on the research of the companion paper, the influence of the slab spatial composite effect on the lateral stiffness and internal force distributions of composite frame structures has been investigated. The critical factors influencing the equivalent stiffness of composite beams are firstly analyzed using beam-shell mixed element models. Furthermore, a parametric analysis is conducted to derive a simplified design formula of the composite beam stiffness amplification coefficient. The methods for considering the slip effect at the steel–concrete interface have also been discussed. Several regular and irregular composite frame system models with different parameters are used to sufficiently verify the reasonability of the proposed formula in this paper. It can be found that the proposed “line” element composite beam frame model considering the slab spatial composite effect can accurately predict the periods of natural vibration, the seismic story shear forces, the lateral displacements, the story drifts and the internal forces of composite beams etc. However, the model using the formula proposed by Eurocode 4 or neglecting the slab spatial composite effect may give unsatisfactory predictions. Finally, five experimental programs of the composite frames are selected to validate the design methods proposed in this and the companion paper. It can be concluded that the proposed design method in this research can be used to more accurately consider the influence of the slab spatial composite effect in the routine design practice of composite frame systems compared with other methods proposed in the literature and the current design codes.

► Stiffness amplification coefficient is defined to derive composite beam stiffness.
► Main factors influencing the stiffness amplification coefficient are obtained.
► Design formula of the stiffness amplification coefficient is proposed.
► Methods for considering the slip effect are discussed.
► Proposed methods in two papers are verified by numerical and test results.