A multilayer thermo-elastic damage model for the bending deflection of the tunnel lining segment exposed to high temperatures

For a shield tunnel structure in fire, the thermal-mechanical behavior of tunnel lining segments plays a key role in determining the failure process. Due to the restriction at the segment ends, secondary stress will be induced, and this is particularly the case when the temperature distribution is non-uniform over the cross-section, thus further worsening the adverse effect on the structure. Existing studies on the thermal-mechanical behavior of tunnel lining have mainly focued on the complex nonlinear and non-elastic behavior of the concrete, whereas little attention has been paid to the application in engineering. In this study, a multilayer thermo-elastic damage model is proposed to analyze the bending behavior of the tunnel lining segment exposed to high temperature. The temperature distribution on the cross-section is described by a piecewise function. The contributions of the concrete and bolts are modelled equivalently by a set of springs. A multi-scale thermal damage model is introduced to describe the damage evolution of concrete with temperature. Various boundary conditions, including a statically determinate segment, a statically indeterminate segment with two hinged ends and a segment with two fixed ends, are considered. To verify the analytical model, four-point bending tests have been conducted with reduced-scale specimens. Test results indicate that this multilayer model can well predict the response of the tunnel lining segment under or after high temperature. The model is suitable in the fire protection design of the tunnel lining segment.