Portland State University. Department of Civil & Environmental Engineering
Date of Award
Master of Science (M.S.) in Civil & Environmental Engineering
Civil and Environmental Engineering
1 online resource (xx, 119 pages)
Effective-stress nonlinear dynamic analyses (NDA) were performed for piles in liquefiable sloped ground to assess how inertia and liquefaction-induced lateral spreading combine in long-duration vs. short-duration earthquakes. A parametric study was performed using input motions from subduction and crustal earthquakes covering a wide range of earthquake durations. The NDA results were used to evaluate the accuracy of the equivalent static analysis (ESA) recommended by Caltrans/ODOT for estimating pile demands. Finally, the NDA results were used to develop new ESA methods to combine inertial and lateral spreading loads for estimating elastic and inelastic pile demands.
The NDA results showed that pile demands increase in liquefied conditions compared to nonliquefied conditions due to the interaction of inertia (from superstructure) and kinematics (from liquefaction-induced lateral spreading). Comparing pile demands estimated from ESA recommended by Caltrans/ODOT with those computed from NDA showed that the guidelines by Caltrans/ODOT (100% kinematic combined with 50% inertia) slightly underestimates demands for subduction earthquakes with long durations. A revised ESA method was developed to extend the application of the Caltrans/ODOT method to subduction earthquakes. The inertia multiplier was back-calculated from the NDA results and new multipliers were proposed: 100% Kinematic + 60% Inertia for crustal earthquakes and 100% Kinematic + 75% Inertia for subduction earthquakes. The proposed ESA compared reasonably well against the NDA results for elastic piles. The revised method also made it possible to estimate demands in piles that performed well in the dynamic analyses but could not be analyzed using Caltrans/ODOT method (i.e. inelastic piles that remained below Fult on the liq pushover curve). However, it was observed that the pile demands became unpredictable for cases where the pile head displacement exceeded the displacement corresponding to the ultimate pushover force in liquefied conditions. Nonlinear dynamic analysis is required for these cases to adequately estimate pile demands.
Nasr, Jonathan, "Development of a Design Guideline for Bridge Pile Foundations Subjected to Liquefaction Induced Lateral Spreading" (2018). Dissertations and Theses. Paper 4160.