Numerical investigation of a novel concrete-to-steel column splice in mixed structures in height

Abstract

Buildings in which the type of structural material changes between their stories are referred to as mixed-in-height structures. Typically, these buildings have concrete structures in lower stories and steel structures in upper stories. Valuable investigations have been conducted on mixed-in-height structures to explore their seismic response and changes in structural natural period due to the sudden change in the lateral stiffness at transition level and mass irregularity, but scant attention has been given to the connection between steel and concrete structures at varying heights. Given the geometrical limitations of existing concrete structures, the dimensions of steel columns in supplementary stories must align with those of reinforced concrete columns. Consequently, building codes have not yet provided guidelines for proper connection details and effective load transfer from upper steel to lower concrete structures which is crucial due to the abrupt changes in stiffness and force transfer mechanisms in such splice connections. Thus, this study considers Numerical investigation on two full-scale laboratory tested specimens, with similar details but different axial loads, and numerical analysis of a new connection between a concrete and a steel column at the transition level. This research examines the aforementioned connection under two boundary conditions. Furthermore, after validating the numerical models with experimental specimens, axial load parameters, relative percentage of reinforcement to concrete area, and the force–displacement diagrams are presented. Finally, a numerical model of a three-story column in a frame is analyzed using finite element analysis under lateral load, and the sequence of plastic hinge formation is studied. The practicality and effectiveness of the proposed splice was verified herein. Furthermore, the average value of ductility (µ) was calculated to be 5.5, while exhibiting negligible overstrength factor (Ω). Similar response parameters were calculated for F-AL-R2 (43.2 kN/mm, 21.1 kN/mm) and F-AL-R3 (43.8 kN/mm, 22 kN/mm), indicating that the influence of increased rebar percentage diminishes at higher values. The analysis demonstrates that column connection failure did not occur, and the sequence of hinge formation was from top to bottom, validating the suitable performance of the proposed connection.