Soil-bridge interaction during long-duration earthquake motions

Graduation date: 2014Earthquake engineering analyses are often performed using shallow, crustal earthquake motions (e.g., 1940 El Centro). However, large areas of the world are subject to subduction zone earthquake motions (e.g., the Pacific Northwest). A subduction zone earthquake motion is characterized by its long duration (e.g., strong shaking lasts for more than a minute). Observations of unexpected bridge damage following the recent subduction zone earthquakes in Chile and Japan highlight the importance of understanding soil-bridge interaction during long-duration earthquake motions. Accordingly, the main objective of this thesis is to report the seismic response of a soil-bridge system during long-duration earthquake motions. The soil-bridge system was created within the nite-element framework OpenSees. The pile foundation was modeled using fiber-section elements (representing a reinforced concrete pile), and the pile was attached to a soil continuum, which was specified as a dense, non-liquefiable sand, by using calibrated soil springs. The bridge column was modeled using force-based fiber-section elements attached to the linear elastic bridge deck. A double span bridge was considered herein. Gap elements were used at the ends of the bridge deck to represent back ll response. The soil-bridge system was subjected to seven selected subduction zone earthquake motions and seven selected shallow, crustal earthquake motions. For each earthquake motion, the number of inelastic excursions was based on the yield rotation, θ[subscript y], corresponding to the curvature at the point of first yield of the moment-curvature analysis. The number of inelastic excursions was plotted with five earthquake intensity measures: peak ground acceleration (PGA), cumulative absolute velocity (CAV), significant duration (D₅₋₉₅), Arias intensity (I[subscript A]), and spectral acceleration (S[subscript a]). Results show a definite distinction between the two types of earthquake motions and long-duration earthquake motions are more damaging to soil-bridge systems than shallow, crustal earthquake motions with similar amplitudes and frequency contents because of the increased number of cycles of loading