Experimental and Analytical Modeling of Shield Segment under Cyclic Loading

Because of the lack of adequate monitoring performance data for shield tunnel segments from either laboratory testing or in situ measurement, it is difficult to improve the current segment design codes. As a result, overdesign or excessive use of reinforcement in tunnel linings is common. To overcome these segment design inadequacies, this study aimed to investigate the bending behavior of RC members based on measured strain data and the modeling results from a proposed analytical model, which takes into account section nonlinearity resulting from concrete tensile cracking and the actual effective moment of inertia. The cyclic four-point loading test was performed on a RC beam with an embedded optical fiber sensor and on a smart tunnel lining segment, in which two vibrating wire strain gauges with thermistors were welded into a rebar cage on either side of the neutral axis. The measured strain data for the rectangular beam subject to concrete curing and subsequent four-point loading justify the applicability of the optical fiber sensor. The results of the load-moment relationship obtained from the model were found to be in good agreement with the theoretical solution, verifying the correctness of the proposed analytical model. This model has been proposed to predict the bending behavior of the smart tunnel lining segment. The modeled load-deformation relationship matched reasonably well with the measured strain data, except for the modeled results of tensile strain after cracking. This discrepancy may have been caused by either the influence of the concrete tensile cracking on the local bonding condition at the concrete-sensor interface or the modeling difference of concrete tensile behavior. Despite the discrepancy between the modeling results and the measured strain data after cracking, the statistical parameters justify the application of the proposed analytical model to RC segment design and to the design of recently developed composite segments.