Quantifying the influence of elliptical ring geometry on the degree of restraint in a ring test

A novel elliptical ring test method has been proposed to replace the traditional circular ring test method for the purpose of shortening test duration for assessing cracking tendency of concrete and more conveniently examining crack evolution in concrete rings. To further explore the mechanism of this new test method, a numerical model was established to analyse stress development and crack initiation in concrete rings in which a fictitious temperature field simulated the externally applied mechanical effects of concrete shrinkage on concrete causing the same strain as shrinkage does. The proposed numerical model was validated against experimental results and was then used to evaluate the effects of ring geometry on the degree of restraint to concrete. Moreover, a series of numerical experiments were conducted to derive the expression of the degree of restraint to elliptical rings. Through the error analysis of the degree of restraint on concrete properties and ring geometry, the expression was verified so that it can be used to calculate the degree of restraint provided by the internal steel ring. According to the derived expression, the restrained elliptical ring test can be designed to quantitatively simulate the service condition of concrete in an engineering structure more accurately.