Seismic Performance of Shallow Founded Structures on Liquefiable Ground: Validation of Numerical Simulations Using Centrifuge Experiments Zana Karimi, S.M.ASCE 1 ; and Shideh Dashti, M.ASCE 2 Abstract: The results of fully coupled, three-dimensional (3D), nonlinear finite-element analyses of structures founded on liquefiable soils are compared with centrifuge experiments. The goal is to provide insight into the numerical model’ s capabilities in predicting the key en- gineering demand parameters that control building performance on softened ground for a range of structures, soil profiles, and ground motions. Experimental and numerical observations will also guide future analyses and mitigation decisions. The numerical model captured excess pore pressures and accelerations, the dominant displacement mechanisms under the foundation, and therefore building’ s settlement, tilt, and interstory drift. Both experimental and numerical results showed that increasing the structure’ s contact pressure and height=width (H=B) ratio generally reduces net excess pore pressure ratios in soil but amplifies the structure’ s tilting tendencies and total drift. The settle- ment response of a structure with a greater pressure and H=B ratio was also more sensitive to soil-structure-interaction induced forces, which could at times amplify on a denser soil with less softening. A denser soil profile also increased building’ s flexural drift in all cases by reducing excess pore pressures and rocking drift, while amplifying foundation accelerations and total drift. Numerical simulations captured these trends well. These experimental and numerical results point to the importance of taking into account a building’ s dynamic properties and overall performance in mitigation design. DOI: 10.1061/(ASCE)GT.1943-5606.0001479. © 2016 American Society of Civil Engineers. Author keywords: Liquefaction; Soil-structure-interaction; Centrifuge; Finite-element analysis. Introduction Soil liquefaction has led to excessive settlement, tilt, and lateral displacement of many buildings on shallow foundations during pre- vious earthquakes, causing damage to the structures and their nearby lifelines (e.g., 1964 Niigata, Japan; 1990 Luzon, Philippines; 1999 Kocaeli, Turkey; 2011 Christchurch, New Zealand). The existing procedures in practice for assessing liquefaction-induced settlements (e.g., Tokimatsu and Seed 1987; Ishihara and Yoshimine 1992) as- sume free-field conditions, which either completely neglect the exist- ence of the building or bring in the foundation load as an added overburden stress alone. These procedures ignore the influence of structures on static and dynamic stresses induced in the foundation soil, and the impact of soil liquefaction on building performance. These shortcomings hamper the development of mitigation strategies that enhance building performance in terms of foundation settlement and tilt as well as flexural interstory drift of the structure that is a proxy for building damage. In order to simulate more realistically the seismic response of shallow-founded structures on liquefiable soil, the stress field around the foundation, and the drainage conditions, fully coupled, three-dimensional (3D), dynamic, nonlinear numerical analyses are often warranted. These simulations can provide insight into soil nonlinearity, its interaction with the superstructure, and the building’ s settlement, tilt, period lengthening, and drift. A single time-domain analysis can evaluate the timing and location of liquefaction triggering, postliquefaction softening followed by stiffening, and the resulting accelerations and displacements imposed on structures. Nonlinear soil constitutive models developed for soil liquefaction are, however, complex with many parameters, and they are often validated against a limited set of laboratory test data that do not cover a variety of loading paths and drainage conditions. Further, interpretation of data from case histories are often associated with uncertainties due to lack of sufficient high- quality recordings of structural response as well as soil response at key locations. Physical modeling under controlled conditions can provide valuable insights into the extent and timing of soil liquefaction and its resulting consequences on the soil-foundation- structure system (e.g., Yoshimi and Tokimatsu 1977; Liu and Dobry 1997; Hausler 2002; Dashti et al. 2010a, b). Further, physi- cal model studies that cover a range of structures, soils, and ground motions enable a comprehensive evaluation and validation of advanced numerical tools, before they are used in a systematic parametric study. Centrifuge experiments performed by Dashti et al. (2010a, b) investigated the seismic response of different single-degree-of- freedom (SDOF) structures with stiff, mat foundations on a layered deposit, including a liquefiable layer. Solid-fluid, fully coupled, 3D, nonlinear finite-element numerical simulations of the centri- fuge tests were performed using the pressure-dependent, multiyield- surface, plasticity-based soil constitutive model (PDMY02) implemented in OpenSees by Elgamal et al. (2002) and Yang et al. (2003, 2008). These analyses are classified as Class C predictions, in which the results are known to the predictor prior to running the numerical simulation (Lambe 1973). Most of the previous numerical studies on soil liquefaction and its effects on structures (e.g., Elgamal et al. 2005a, b; Popescu et al. 2006; 1 Graduate Research Assistant, Dept. of Civil, Environmental and Archi- tectural Engineering, Univ. of Colorado Boulder, Boulder, CO 80309. E-mail: zana.karimi@colorado.edu 2 Assistant Professor, Dept. of Civil, Environmental and Architectural Engineering, Univ. of Colorado Boulder, Boulder, CO 80309 (corresponding author). E-mail: shideh.dashti@colorado.edu Note. This manuscript was submitted on March 26, 2015; approved on December 1, 2015; published online on February 25, 2016. Discussion per- iod open until July 25, 2016; separate discussions must be submitted for individual papers. This paper is part of the Journal of Geotechnical and Geoenvironmental Engineering, © ASCE, ISSN 1090-0241. © ASCE 04016011-1 J. Geotech. Geoenviron. Eng. J. Geotech. Geoenviron. Eng., 04016011 Downloaded from ascelibrary.org by Colorado University at Boulder on 02/26/16. Copyright ASCE. For personal use only; all rights reserved.