SUMMARYThis paper presents an analytical solution for the prediction of internal forces and displacements of a jointed segmental precast circular tunnel lining. The e!ects of joint sti!ness on the performance of the tunnel lining are discussed. The &force method' is used to determine the internal forces and displacements of jointed tunnel lining. Five shield-driven tunnel cases are adopted to study the e!ects of joint sti!ness, soil resistance, joint distribution and joint number on the internal forces and displacements of circular tunnels. Laboratory model tests are conducted to verify the proposed analytical solution.
This paper presents a new method of determining the correction factor to approximate a jointed, shield-driven tunnel lining as a continuous ring structure under plane strain conditions. An earth pressure distribution pattern is proposed which is developed based on the long-term behavior of shallow tunnels constructed in soft clays as observed in the field. The "force method" was used to determine the internal forces and displacements of jointed, shield-driven tunnels. Either the vertical or the horizontal displacement of the tunnel lining can be used as a common matching parameter. Factors such as joint stiffness, soil resistance, joint distribution, number of joints, and tunnel geometry can be considered by the proposed method. Simplified design equations for the estimation of equivalence factors are also proposed for the typical tunnel lining geometry of urban subway tunnels. The proposed equivalence method was evaluated by comparing it with the results of laboratory tests.Key words: shield-driven tunnel, jointed segmental lining, effective bending rigidity ratio, equivalence factor, lining internal force, earth pressure distribution.
A set of benchmark, medium scale, shaking table tests on corroded reinforced concrete (RC) columns is conducted with the aim of investigating the effects of corrosion damage on the nonlinear dynamic behaviour of RC bridge piers. The experimental programme consists of an uncorroded control specimen and two corroded RC column specimens, with identical structural details. An accelerated corrosion procedure is used to corrode the RC columns. The uncorroded and corroded specimens are subjected to far-field long duration ground motion excitations. The two corroded columns had 51% and 65% average mass loss ratios. The testing sequence includes slight, extensive, and complete damage levels, followed by an aftershock to examine the cascade effect on the nonlinear dynamic response of the proposed RC columns. The experimental results show that corrosion changes the failure mode of the RC columns, and has a significant negative impact on the residual strength (about 50% mass loss results in about 80% strength reduction) and drift capacity of RC columns.
This paper reports the results of a set of benchmark medium-scale shaking table tests to investigate the significance of the non-stationary characteristics of ground-motion on nonlinear dynamic responses and the structural damage of reinforced concrete (RC) columns. To examine the influence of ground-motion characteristics, four RC columns are tested under (1) near-field without pulse, (2) near-field pulse-like, and (3) far-field groundmotions. These ground-motion records were spectrally matched by the reweighted Volterra series algorithm without changing non-ergodic characteristics. To explore the confinement effects, two sets of column specimens are designed to represent the modern well-confined and older lightly-confined RC columns. Each column is tested in slight, extensive and complete damage limit states. Then aftershock excitations are conducted to investigate the performance of severely damaged RC columns. Low amplitude white-noise tests are conducted on pristine columns and after each damage limit state experiment to detect natural frequency variant of damaged columns using transfer function estimate. Furthermore, using time-frequency analysis, the real-time variant frequency of test specimens is estimated. The significant duration of ground-motions accounting for the effect of nonstationary characteristics of ground-motion is also estimated by time-cumulative damage analysis of the test results. Finally, the time-variant stiffness degradation of RC columns is estimated.
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