Resilient seismic design of precast segmental bridge columns with resettable sliding joints

Abstract

In an attempt to extend the application of cost-effective precast segmental bridge column construction technologies to regions of moderate to high seismicity whilst fulfilling the latest resilience-based seismic design concept, the resilient design of precast segmental bridge columns incorporating resettable sliding joints has been explored and investigated experimentally and numerically. In the search for a way to achieve seismic resilience in segmental structures, varying non-emulative structural systems are examined. Incidentally, similar arrangements of semi-rigid rocking joints are extensively found in many ancient Chinese timber pagodas. The flexibility of these timber pagodas and their ability to reset after being disturbed have helped them survive numerous earthquakes over the centuries. Following a rethink of the design strategy in the light of inspirations from ancient Chinese timber pagodas, the design of resettable sliding joints should have the following features: (i) interface with gentle guide key; (ii) durable low-friction concrete contacts; and (iii) partially debonded tendons. A component-level kinetic parametric study has been carried out on a sliding model comprising a block on a W-shaped gently keyed sliding surface to investigate its resetting responses at the post-peak stages of various earthquake excitations. The results show that a sliding system with a W-shaped smooth surface with gentle slope θ (5°≤θ≤8°) and low coefficient of friction (COF) μ (0.05≤μ≤0.1) can provide superior post-peak resetting performance while assuring sufficient seismic isolation ability during the peak stages of the design seismic events. Direct shear testing with suitable modification has been conducted to validate the feasibility of providing durable low-friction concrete contacts. The results indicate that a low COF at around 0.05 for untreated original concrete interface can be achieved with durability using high-performance PTFE grease lubricant under contact pressures up to 40 MPa. Simplified cyclic bond tests have been conducted to validate the practicality of the partially debonded tendon system. The results suggest that the strand performs elastically under relatively large transverse displacements. To understand the overall seismic responses of precast segmental columns with hybrid sliding and rocking joints, system-level conceptual shaking table testing has been conducted on seven typical scaled-down (1:12) precast segmental column models. Tailor-made 3D printed molds have been used for easy preparation of the segments for fabrication of scaled-down specimens of precast segmental column for conceptual shaking table testing. An advanced 3D motion capture system has been used for accurate non-contact measurement of displacements. The findings from the previous component-level studies are used for the design of columns with resettable sliding joints (RSJs). The experimental results confirm the occurrence of beneficial moderate rocking behavior, evenly distributed sliding behavior and excellent resetting performance in columns with RSJs under various seismic conditions. The proposed design of precast segmental column with RSJs is expected to achieve seismic resilience with excellent seismic isolation and system-level post-peak resetting performance under various types of earthquake conditions. Simplified numerical modeling of the shaking table tests based on rigid body assumption has been carried out in the OpenSees environment. Comparison between numerical and experimental results shows reasonable agreement.