Low-Damage Bridge Columns for Post-Earthquake Serviceability
Christopher Motter, PhD – PI
Bridge columns are typically designed to behave in a ductile manner during large earthquakes, sustaining significant damage without collapse. This is not a resilient approach, as post-earthquake repair may be substantial and lead to bridge closure. The seismic performance of many of these bridges is essential to post-earthquake mobility, as bridges are relied upon as critical lifelines into urban centers after natural disasters. Bridge closure can impede emergency response, and significant financial losses may be associated with downtime of the bridge. State DOTs in Washington and Oregon recently have begun to require bridges along key emergency response lifelines to be designed to remain in-service following a Magnitude-9.0 Cascadia Subduction Zone (CSZ) earthquake. There is a need for cost-efficient, low-damage bridge columns to meet this objective. One approach, used recently by WSDOT on the SR-99 bridge, is shape memory alloy (SMA) as longitudinal column reinforcement in combination with engineered cementitious composite (ECC) in place of conventional concrete. The SMA provides post-earthquake re-centering of the column, while the ECC mitigates crushing at locations that would typically have conventional concrete. Although SMA is a more expensive material than conventional reinforcement, the SMA is only used at plastic hinge locations. While the same is true for ECC, the ECC requires a separate installation relative to casting of conventional concrete, reflecting a more significant disruption to the typical construction process. For the proposed research, SMA will be used with conventional concrete rather than ECC, with steel jackets used in the plastic hinge region to confine the concrete to prevent crushing. The steel jackets may take the place of traditional sonotube formwork at these locations, providing minimal disruption to the typical construction process. Although the approach is applicable in all seismic locations, the proposed research will focus on the response of bridge columns to CSZ earthquake demands, which produce long duration shaking. Previous research on SMA in columns has not focused specifically on long-duration earthquakes, which have more potential to induce damage based on fatigue. In the proposed research, an experimental study will be conducted, and test results will be used to characterize column response, including determination of parameters needed for column modeling. Design guidelines will be formulated to provide needed guidance to DOTs.