Adaptation of The Eligehausen Model to Experimental Results of Shear Stress at The Steel-Cement Mortar Interface Tests

This paper presents an adapted version of the Eligehausen bond–slip model aimed at more accurately reproducing the mechanical response of ribbed steel–cement mortar interfaces observed in direct shear tests reported in previous studies. The proposed approach introduces a refined analytical formulation that overcomes key limitations of existing bond–slip laws, particularly their inability to adequately describe the nonlinear adhesion and slip behavior characteristic of steel–mortar composite interfaces. The objective of this research is to develop a constitutive law that more reliably characterizes the shear stress–slip relationship and reflects the actual adhesion mechanisms identified experimentally. A series of direct shear tests was conducted on high-strength cement mortar cast between two steel plates. The resulting stress–deformation curves were analyzed to identify the governing parameters of the interfacial bond mechanism. The Eligehausen model was implemented and calibrated using MATLAB through an iterative optimization procedure designed to minimize discrepancies between experimental and analytical results. The calibrated model demonstrates a significantly improved agreement with the experimental stress–slip responses compared to the original formulation. In particular, it successfully captures both the nonlinear ascending branch and the subsequent softening behavior, which are not adequately represented by existing models. The study introduces modified equations that enhance the physical interpretation of adhesion and frictional mechanisms at the steel–mortar interface. The proposed constitutive model provides a more accurate description of shear loading behavior and enables more reliable numerical simulations of steel–mortar composite connections. Keywords: Steel–cement mortar interface; Bond–slip behavior; Adhesion mechanisms; Direct shear test; Constitutive modeling.