Date of Award
Doctor of Philosophy (PhD)
Recent earthquakes have shown that even buildings designed according to local seismic regulations may suffer damage due to liquefaction. This is because the mechanisms that lead to a loss of building serviceability due to liquefaction are not well understood and considered in the design of structures. The current state-of-practice for estimating liquefaction-induced building settlement is primarily based on procedures that assume free-field conditions and are known to be unreliable, because they do not account for changes in stress distribution, flow patterns, and soil-foundation-structure interaction.
In this research, results from centrifuge experiments are used to: 1) gain insight into the underlying mechanisms of deformation near structures on softened ground; and 2) validate and evaluate the capabilities and shortcoming of an advanced numerical tool, which are then employed in a parametric study.
Solid-fluid, fully-coupled, nonlinear, effective stress, 3D, finite element analyses are performed in the OpenSees platform. The key Engineering Demand Parameters (EDPs) of interest that quantify the performance of the soil-foundation-structure system (e.g., excess pore pressures, accelerations, and settlements, foundation tilt, and transient inter-story drift) were compared numerically and experimentally. For the cases considered, numerical predictions compared fairly well with experimental results, with the exception of free-field settlement and permanent foundation tilt.
A numerical parametric study, validated against experiments was then performed, in which different soil, structural, and ground motion Input Parameters (IPs) were systematically varied to investigate the influence and relative importance of different IPs, and to search for and identify optimum Intensity Measures (IMs) that minimized the variability and uncertainty in estimating different EDPs. The extent of excess pore pressure generation (EDP = ru,peak) in the free-field and near the structure was significantly influenced by relative density and thickness of the liquefiable layer. These factors along with the foundation contact pressure and area were shown to significantly influence building settlements. Spectral acceleration at the initial period of the site as well as Arias Intensity were identified as optimum IMs for predicting ru,peak and foundation settlement, respectively. Additional simulations validated against case histories will be necessary to develop a probabilistic method for predicting the performance of structures on softened ground.
Karimi, Zana, "Seismic Performance of Shallow-Founded Structures on Liquefiable Ground: an Experimental and Numerical Study" (2016). Civil Engineering Graduate Theses & Dissertations. 442.