Testing of axial-moment-rotation response for skewed flat radial joints in precast concrete segmental tunnel linings

An experimental study has been conducted to examine the rotational stiffness and flexural strength of skewed flat radial joints in full-scale precast concrete tunnel lining systems when subjected to combinations of moment and axial load applied within the circumferential cross-section of the tunnel. The full-scale specimens were procured from a U.S. tunnel project and consist of steel fiber reinforced concrete segments measuring 1.98 m by 0.46 m with an 8(degrees) skew angle at their radial joints. Those joints are experimentally subjected to moment-rotation demands at axial load levels ranging from 674 to 2250 kN/m. The contact face of each specimen included the as- designed rubber gaskets, and the joints were examined with and without radial joint bolts (which are commonly used during installation of the segments but sometimes are removed prior to the initiation of tunnel operation depending on the anticipated loading and traffic demands). The experimental results were compared against analytical models for joint moment-rotation developed by Janssen, which are commonly used in tunnel design practice. Test results from this program demonstrated a significantly higher flexural capacity than predicted by Janssen's model, with measured results 2.5 times greater than predicted when the hoop stress is at 2.85 % of the design compressive strength (i.e. the "low" axial load level, 674 kN/m), and 1.7 times greater when the hoop stress is at 9.50 % of the design compressive strength (i.e. the "high" axial load level, 2250 kN/m). The elastic rotational stiffness of the tested joints increased with the applied axial load, whereas Janssen's model indicates a constant stiffness until joint opening regardless of the axial force level. Specifically, the tested rotational stiffness is approximately 70 % less than Janssen's computed value at the low axial load level and then converges to Janssen's value at the higher axial load level. The presence of radial bolts is shown to have negligible effect on initial rotational stiffness, and the bolts only have minor influence at large rotations greater than 0.002 rad.