Rotational stiffness and moment-rotation response for embedded transfer connections in steel-reinforced concrete vertically irregular structures

The rotational stiffness and moment-rotation response of transfer connections are critical parameters in the design of steel-reinforced concrete vertically irregular structures under seismic conditions. The recently proposed partially embedded transfer connection with wing wall (PETC-WW) and the conventional embedded connection (EC) have been studied in terms of moment resistance and economic performance. However, there is a lack of design guidelines for full-range behaviour for these connections under seismic conditions. This paper presents an analytical framework for the prediction of rotational stiffness and moment-rotation curves of PETC-WW and EC. Firstly, stress distributions of PETC-WW and EC at the elastic stage are assumed based on the failure modes of the test specimens, and the initial rotational stiffness is derived using Timoshenko beam theory. Secondly, a four-parameter moment-rotation model, incorporating established moment resistance models, is employed and simplified to predict moment-rotation curves of PETC-WW and EC. The predicted results are compared with test and finite element (FE) analysis results reported in the literature. For the rotational stiffness of PETC-WW and EC, it is shown that the mean ratios of tested-to-predicted values are 0.99 and 0.91, respectively, with the corresponding coefficients of variation of 0.082 and 0.039. Similarly, for the moment-rotation curves of PETC-WW and EC, the predictions generally agree well with those from the test and FE results. The analytical framework proposed in this work serves as an alternative but more advanced method compared to those conventionally simplified ones based on the assumptions of either rigid or pinned connections, for predicting the mechanical behaviour of transfer connections. The framework is also feasible to be integrated into macro-level simulations of multi-story steel-reinforced concrete vertically irregular structures under both static and dynamic loading conditions using FE software such as OpenSEES and SAP2000, thereby enhancing computational and analytical efficiency.