Mechanical properties and constitutive model of filling medium in hot casting socket at elevated temperatures

Abstract

Hot casting sockets have been commonly applied in the prestressed structures to anchor steel cables. However, the study on the fire behaviour of hot casting sockets is limited, particularly in relation to the thermo-mechanical properties of the filling medium. This paper experimentally investigates the mechanical properties of a zinc copper alloy (employed as the filling medium) at varying target temperatures. A comprehensive range of stress–strain curves are obtained by using a digital image correlation measurement system. The elastic modulus, proportional limit, effective yield strength and ultimate strength are presented and compared to those of steel cables. It is found that the strain hardening effect diminishes as the temperature increases. Reduction factors of elastic modulus, effective yield strength and ultimate strength of the zinc copper alloy are smaller than those of steel cables at elevated temperatures, indicating the vulnerability of the filling medium in fire scenarios. Mathematical formulas of reduction factors of mechanical properties are proposed. Furthermore, a novel constitutive model is proposed by modifying the Johnson-Cook model. Parameters involved in the stress–strain relationship are determined by the smooth round bar test results, whereas those in the failure criterion are determined by the notched round bar test results. Finally, the modified constitutive model is applied in a finite element model, and the numerical results have good agreement with the test results.