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Measuring displacements in model tests typically involves contact-based sensors such as linear potentiometers, where contact between two moving parts occurs at the sensing point. The sensor's finite mass, the limited stiffness of the beams and the clamping mechanism, and the slippage and hinging of the sensor body could affect the object's response and lead to measurement errors. Also, the physical mounting rack required to hold these sensors often obstructs the view and makes significant areas unavailable for conducting some other essential investigations. The advancement in high-speed, high-resolution and reasonably priced rugged cameras makes it feasible to obtain better displacement measurements by image analysis. This paper introduces a non-contact method that works by video recording the projection of laser lines on a test object to measure static and dynamic vertical displacements. The technique produces a continuous settlement distribution along the laser line passing through multiple objects of interest. This paper presents the theory for converting laser line images to displacements. The new method's validity is demonstrated by comparing the results from other measurement techniques: hand measurements, linear potentiometers and three-dimensional stereophotogrammetry.

Earthquake-induced soil liquefaction can cause soil settlement around piles, resulting in drag load and pile settlement after shaking stops. Estimating the axial load distribution and pile settlement is important for designing and evaluating the performance of axially loaded piles in liquefiable soils. Commonly used neutral plane solution methods model the liquefiable layer as an equivalent consolidating clay layer without considering the sequencing and pattern of excess pore pressure dissipation and soil settlement. Moreover, changes in the pile shaft and the tip resistance due to excess pore pressures are ignored. A TzQzLiq numerical model was developed using the existing TzLiq material and the new QzLiq material for modeling liquefaction-induced downdrag on piles. The model accounts for the change in the pile's shaft and tip capacity as free-field excess pore pressures develop or dissipate in soil. The developed numerical model was validated against data from a series of large centrifuge model tests, and the procedure for obtaining the necessary information and data from those is described. Additionally, a sensitivity study on TzLiq and QzLiq material properties was performed to study their effect on the developed drag load and pile settlement. Analysis results show that the proposed numerical model can reasonably predict the time histories of axial load distribution and settlement of axially loaded piles in liquefiable soils both during and postshaking.

Earthquake-induced soil liquefaction can cause settlement around piles, which can translate to negative skin friction and the development of drag load and settlement of the piles. A series of centrifuge model tests were performed to assess liquefaction-induced downdrag and understand the interplay and effects of (1) pile embedment and pile-head load, (2) excess pore pressure generation and dissipation, and (3) reconsolidation and ground settlement on pile response during and postshaking. The model included a layered soil profile (clay, liquefiable sand, and dense sand) with two 635-mm-diameter instrumented piles. One pile was placed with its tip at the bottom of the liquefiable deposit; the other pile was embedded five diameters into the dense sand layer. The model was shaken with multiple earthquake motions with their peak horizontal accelerations ranging from 0.025 to 0.4 g. For each shaking event, the drag load on the piles first decreased during shaking and then increased during reconsolidation, exceeding its preshaking value. With multiple shaking events, the net drag load on the piles increased. The maximum observed drag load was found equal to the drained interface shear strength calculated from the interface friction angle of δ=30° and a lateral stress coefficient of K=1. Larger drag loads and smaller settlements were observed for the pile embedded deep in the dense sand layer. Most of the pile settlements occurred during shaking; postshaking pile settlement was less than 2% of the pile's diameter. The mechanisms behind the development of liquefaction-induced drag load on piles and settlements are described. Select ramifications concerning the design of piles in liquefiable soils are also described.

Several experimental studies have shown that rocking shallow foundations have beneficial seismic performance features: recentering and energy dissipation with little damage. A new publicly available database, “FoRDy” (Foundation Rocking—Dynamic), summarizes the results of dynamic physical model tests of single-degree-of-freedom-like structures supported on rocking foundations. It contains data from five centrifuge and three 1- g shaking table test series that were conducted at experimental facilities in the United States, Greece, and Japan. The database includes 200 model “case histories” that span a wide range of model sizes, soil and structure properties, and seismic excitations. It is compiled as the first step toward building a comprehensive dynamic rocking foundation database, and it has the potential to grow in the future. To illustrate its usefulness, the data are used to show example correlations between the peak drift ratio demand and selected ground motion intensity measures. The results suggest that peak ground velocity (PGV), peak ground displacement (PGD), and the geometric mean of the linear spectral displacement over the period range of 0.2–3 times the initial natural period predict the peak drift ratio response reliably.

Relative density has been shown to be useful for interpreting soil behaviour and for estimating the strength and other soil characteristics in geotechnical engineering. Previous studies have shown that the index void ratios (maximum and minimum void ratios) used to determine relative density depend on the particle shape and the shape of the grain size distribution. However, the effect of the median grain size on the index void ratios has not been resolved. In this study, the effects of the particle weight and the particle size relative to the inter-particle attractive forces are examined by conducting maximum void ratio (emax) tests in elevated gravity fields through the use of a centrifuge. The results indicate that both an increasing particle size and increasing gravity affect emax, providing evidence that inter-particle forces affect the packing of materials in this limit state. The change in emax, occurring in an elevated gravity field, implies that the relative densities estimated for centrifuge model experiments may not be accurate.

This paper presents a summary of the element test simulations (calibration simulations) submitted by 11 numerical simulation (prediction) teams that participated in the LEAP-2017 prediction exercise. A significant number of monotonic and cyclic triaxial (Vasko, An investigation into the behavior of Ottawa sand through monotonic and cyclic shear tests. Masters Thesis, The George Washington University, 2015; Vasko et al., LEAP-GWU-2015 Laboratory Tests. DesignSafe-CI, Dataset, 2018; El Ghoraiby et al., LEAP 2017: Soil characterization and element tests for Ottawa F65 sand. The George Washington University, Washington, DC, 2017; El Ghoraiby et al., LEAP-2017 GWU Laboratory Tests. DesignSafe-CI, Dataset, 2018; El Ghoraiby et al., Physical and mechanical properties of Ottawa F65 Sand. In B. Kutter et al. (Eds.), Model tests and numerical simulations of liquefaction and lateral spreading: LEAP-UCD-2017. New York: Springer, 2019) and direct simple shear tests (Bastidas, Ottawa F-65 Sand Characterization. PhD Dissertation, University of California, Davis, 2016) are available for Ottawa F-65 sand. The focus of this element test simulation exercise is to assess the performance of the constitutive models used by participating team in simulating the results of undrained stress-controlled cyclic triaxial tests on Ottawa F-65 sand for three different void ratios (El Ghoraiby et al., LEAP 2017: Soil characterization and element tests for Ottawa F65 sand. The George Washington University, Washington, DC, 2017; El Ghoraiby et al., LEAP-2017 GWU Laboratory Tests. DesignSafe-CI, Dataset, 2018; El Ghoraiby et al., Physical and mechanical properties of Ottawa F65 Sand. In B. Kutter et al. (Eds.), Model tests and numerical simulations of liquefaction and lateral spreading: LEAP-UCD-2017. New York: Springer, 2019). The simulated stress paths, stress strain responses, and liquefaction strength curves show that majority of the models used in this exercise are able to provide a reasonably good match to liquefaction strength curves for the highest void ratio (0.585) but the differences between the simulations and experiments become larger for the lower void ratios (0.542 and 0.515).

Many physical model tests have examined the performance of rocking foundations during cyclic and seismic loading. These tests varied in model size, testing equipment, superstructure properties, footing shape, supporting soil environment, and loading protocol. “FoRCy, Foundation Rocking database of Cyclic and Monotonic Loading” is a new database (published at https://datacenterhub.org/ ), summarizing the results of monotonic and slow-cyclic loading tests of rocking foundations. The database consists of columns identifying testing equipment and facility, soil, superstructure, and system properties, as well as loading protocol and results. The database contains 456 records (rows), each one being unique in either model configuration or loading amplitude. To illustrate its value, this article shows correlations between (1) settlement, rotation, and factor of safety with respect to bearing capacity and (2) moment and cumulative rotation for shallow footings. Data indicate that the rotation required to mobilize the moment capacity is surprisingly constant (about 0.01 radians) for a wide range of experiments.

The Liquefaction Experiments and Analysis Projects (LEAP) is an international effort to produce a set of high quality test data and to then use it in a validation exercise of existing computational models and simulation procedures for soil liquefaction analysis. A validation effort (LEAP-GWU 2015) was undertaken using a benchmark centrifuge model of a sloping deposit tested in a rigid-wall container. This article presents and discusses the shear stress-strain responses and effective stress paths of the LEAP-GW 2015 centrifuge tests and numerical predictions (including an assessment of the effects of the rigid boundaries).

LEAP (Liquefaction Experiments and Analysis Projects) is an effort to formalize the process and provide data needed for validation of numerical models designed to predict liquefaction phenomena. For LEAP-GWU-2015, one project within LEAP, an experiment was repeated at 6 centrifuge facilities (Cambridge University, Kyoto University, University of California Davis, National Central University, Rensselaer Polytechnic Institute, and Zhejiang University) and the results were shared and archived for the purposes of validation of numerical models. This paper describes the specifications for the LEAP-GWU-2015 experiment and compares the experimental results from the six facilities. The specified experiment was for uniform medium dense sand with a 5 degree slope in a rigid container subject to a ramped, 1 Hz sine wave base motion. The experiment was meant to be relatively simple to enable different facilities to produce comparable experiments. Although it cannot be claimed that identical experiments were precisely replicated on different centrifuges, it is argued that the results are similar enough that each experiment lends veracity to the set of results. A benefit of variability between experiments is that the variety enables a more general validation. Important lessons with regard to specification of future experiments for validation of numerical models are summarized. LEAP-GWU-2015 has demonstrated an approach that is a useful reference for future validation studies.

For the LEAP-GWU-2015 exercise, a relatively simple centrifuge test was conducted in parallel at 6 centrifuge facilities including the University of California Davis (UCD). The experiment consisted of a submerged medium dense clean sand with a 5° slope subjected to 1 Hz ramped sine wave base motion in a rigid container. This paper explains several details of the experiment at UCD including intended and unintended deviations from the specification and the implementation of new techniques for measurement of saturation of the centrifuge model. One unintended critical deviation was the use of pore fluid that was more viscous than specified; this had significant effect on the pore pressure dissipation time. The other important deviation from the specification was the incomplete ground motion sequence. While it is not ideal for purposes of determining the replicability of centrifuge tests, the differences between experiments diversifies the data available for validation of numerical models.

Nonlinear site response of deep offshore clay deposit plays an important role in changing the characteristics of ground motions when subjected to strong shaking, especially when different amplification behaviors of acceleration and displacement are considered. The paper describes a series of centrifuge shaking table tests and numerical simulations to investigate the behavior of deep offshore clay deposits subjected to earthquake loadings. The centrifuge model tests were performed on a slightly overconsolidated clay deposit at UC Davis. A suite of shaking tests were conducted including impulse step wave testing, frequency sweeps, a small “elastic” earthquake event and a “ductility” level large earthquake event. Accelerations, displacements and pore pressures were measured in the soils (free field) throughout the test program. For the elastic level excitations, about a 33% amplification was observed between the input acceleration at the base and the measured accelerations near the top of the clay deposit. However, for the ductility-level earthquake excitation, which had peak input acceleration at the base of 0.46g, acceleration near the top of the deposit was reduced to 0.07g. These observations are correctly simulated by DEEPSOIL with proper soil models and parameters back analyzed from the centrifuge model test. Then systematic 1-D site response analyses are performed on synthetic clay deposit models with 30 to 120 m depths using the validated DEEPSOIL program, and the amplification characteristics of acceleration and deformation induced by base excitation with different intensities and frequencies are analyzed in both time and frequency domains. The results reveal that for deep soft offshore clay deposits subjected to large earthquakes, significant acceleration attenuation may occur near the top of deposit due to soil nonlinearity and even local shear failure; however, significant amplification of displacement at low frequencies is expected regardless of the intensities of base motions, which suggests that for displacement sensitive offshore foundations and structures, such amplified low-frequency displacement response will play an important role in seismic design.

This paper describes the specifications developed by and distributed to all of the centrifuge test facilities involved in LEAP-UCD-2017. The specified experiment consisted of a submerged medium dense clean sand with a 5-degree slope subjected to 1 Hz ramped sine wave base motion in a rigid container. This document describes the detailed geometry, sensor locations, methods of preparation, quality control, shaking motions, surface markers, and surface survey techniques.

Ottawa F-65 sand (supplied by US Silica, Ottawa, Illinois) was selected as the standard sand for LEAP-UCD-2017. Between December 2017 and February 2018, each LEAP research team sent 500 g samples of sand to UC Davis for grain size analysis and minimum and maximum dry density testing. The purpose of this testing was to confirm the consistency of the sand used at various test sites and to provide updated minimum and maximum density index values. The variation of measured properties among the different samples is similar to the variation measured during repeat testing of the same sample. Modified LEAP procedures to measure index densities are used to confirm consistency of the sands, and the results from these procedures are compared to results from ASTM procedures. The LEAP procedures give repeatable results with median index densities of ρmin = 1457 kg/m3, ρmax = 1754 kg/m3. Relative densities calculated with facility-specific index densities varied by less than 4%, so we conclude that average index densities from all the sites may be used for analysis of the results. The LEAP procedures are easier to perform than the ASTM procedures and do not require specialized equipment; therefore, continued use of the LEAP procedure for frequent quality control purposes is recommended. However, the values from ASTM procedures are expected to be more consistent with values adopted in liquefaction literature in the past; therefore, we recommend using the median ASTM values for analysis of LEAP data. Index densities from ASTM procedures (ρmin = 1490.5 kg/m3, ρmax = 1757.0 kg/m3) produce relative densities that are 4 –10% smaller than the index densities from the LEAP procedures.

This paper describes how the LEAP-UCD-2017 data is organized in DesignSafe; it is intended to help users, archivers, and curators find or organize data of interest. Several key files, folders, and documents included in the archive are discussed: (1) an Excel format data template used to document much of the data and metadata for each model (sensor data, cone penetrometer data, and surface marker data as reported by the experimenters), (2) processed sensor data files with time offsets and zero and calibration corrections that facilitate comparison of consistently formatted data from various model tests, (3) plots of processed data for quick overview and comparison of results among experiments, and (4) photographs taken during construction and testing.

This paper summarizes the guidelines provided to the numerical simulation/prediction teams that participated in the LEAP-2017 prediction exercise. These guidelines are developed for the Phase 1 of the simulations that focused on the use of cyclic triaxial element tests for calibration of constitutive models that the participating teams used in their numerical simulations/predictions.

Three centrifuge experiments were performed at the University of California, Davis, for LEAP-UCD-2017. LEAP is a collaborative effort to assess repeatability of centrifuge test results and to provide data for the validation of numerical models used to predict the effects of liquefaction. The model configuration used the same geometry as the LEAP-GWU-2015 exercise: a submerged slope of Ottawa F-65 sand inclined at 5 degrees in a rigid container. This paper focuses on presenting results from the two destructive ground motions from each of the three centrifuge models. The effect of each destructive ground motion is evaluated by accelerometer recordings, pore pressure response, and lateral deformation of the soil surface. New techniques were implemented for measuring liquefaction-induced lateral deformations using five GoPro cameras and GEO-PIV software. The methods for measuring the achieved density of the as-built model are also discussed.

This paper describes the numerical sensitivity study requested prior to the December 2017 LEAP workshop. Several but not all of the simulation teams participated in this sensitivity study. The results of the sensitivity study are used to begin to map out the simulation response surfaces that relate residual displacement to PGAeff and relative density. The simulation response surfaces are compared to the corresponding response surfaces determined by nonlinear regression of the centrifuge test data. The definition of the experimental response surface allows a means to objectively reduce the influence of outliers in the experiment dataset. The residuals between the experiments and the regression surface are used to quantify the uncertainty associated with experiment-experiment variability. Some metrics for assessing the comparison between simulations and experiments are explored; it is suggested that differences in the logarithm of displacement are more meaningful than arithmetic differences. As expected, some models predicted the average displacement well and some predicted triggering of liquefaction and the shape of the response function better than others. LEAP-UCD-2017 is not a final assessment of simulation procedures; instead, the results can be used to improve simulation specifications and calibration procedures and as a stimulus for more careful review of simulation results before they are submitted.

This paper compares experimental results from every facility for LEAP-UCD-2017. The specified experiment consisted of a submerged medium-dense clean sand with a 5-degree slope subjected to 1 Hz ramped sine wave base motion in a rigid container. The ground motions and soil density were intentionally varied from experiment to experiment in hopes of defining the slope of the relational trend between response (e.g., displacement, pore pressure), intensity of shaking, and density or relative density. This paper is also intended to serve as a useful starting point for overview of the experimental results and to help others find specific experiments if they want to select a subset for further analysis. The results of the experiments show significant differences between each other, but the responses show a significant correlation, R2 ~ 0.7–0.8, to the known variation of the input parameters.

A cone penetrometer was specifically designed for the LEAP project to provide an assessment of centrifuge model densities independent from mass and volume measurements. This paper presents the design of the CPT and analyses of the results. Due to uncertainty in the specifications about how to define zero depth of penetration, about 20% of the CPT profiles were corrected to produce more accurate results. The procedure for depth correction is explained. After these corrections, penetration resistances at the representative depths of 1.5, 2, 2.5, and 3 m (prototype depth) are correlated to the reported specimen dry densities by linear regression. Using the inverse form of the linear regression equations, the density of each specimen could be estimated from the penetration resistance. Kutter et al. (LEAP-UCD-2017 comparison of centrifuge test results. In Model Tests and Numerical Simulations of Liquefaction and Lateral Spreading: LEAP-UCD-2017, 2019b) found that the density determined from penetration resistance was a more reliable predictor of liquefaction behavior than the reported density itself. Finally, the centrifuge tests at different LEAP facilities modeled the same prototype in different containers using different length scale factors (1/20 to 1/44); thus the ratio of layer thickness to cone diameter was different in each experiment. It appears that the penetration resistances are noticeably affected by container width and, to a lesser extent, resistance is affected by the length scale factor.

The experimental results of LEAP (Liquefaction Experiments and Analysis Projects) centrifuge test replicas of a saturated sloping deposit are used to assess the sensitivity of soil accelerations to variability in input motion and soil deposition. A difference metric is used to quantify the dissimilarities between recorded acceleration time histories. This metric is uniquely decomposed in terms of four difference component measures associated with phase, frequency shift, amplitude at 1 Hz, and amplitude of frequency components higher than 2 Hz (2 + Hz). The sensitivity of the deposit response accelerations to differences in input motion amplitude at 1 Hz and 2 + Hz and cone penetration resistance (used as a measure reflecting soil deposition and initial grain packing condition) was obtained using a Gaussian process-based kriging. These accelerations were found to be more sensitive to variations in cone penetration resistance values than to the amplitude of the input motion 1 Hz and 2 + Hz (frequency) components. The sensitivity functions associated with this resistance parameter were found to be substantially nonlinear.

The standard ASCE 41-13 Seismic Evaluation and Retrofit of Existing Buildings includes new provisions for linear and non-linear modeling parameters and acceptance criteria for rocking shallow foundations. The new modeling parameters and acceptance criteria were largely based on model tests on rectangular rocking foundations with a limited range of footing length to width ratio (L/B). New model test results are presented, including a systematic variation of L/B and also non-rectangular (I-shaped) footings. This new data along with previously published results are presented to validate the trilinear modeling parameters and acceptance criteria of ASCE 41-13. This paper investigates the effects of footing shape on the residual settlement, residual uplift, rocking stiffness, and re-centering. Overall, the new data supports the provisions of ASCE 41-13; however, the acceptance limits for rocking rotation of I-shaped footings could be reduced to produce performance consistent with the acceptance limits for rectangular footings.

ASCE 41-13 supports three methods of modeling the soil-structure interaction for rocking footings as components of a foundation-building system: Method 1 uses uncoupled moment, shear, and axial springs; Method 2 uses a nonlinear gapping bed of springs; and Method 3 is used for structural footings that are flexible relative to the underlying soil. New component action tables in ASCE 41-13 provide modeling parameters and acceptance criteria for nonlinear and linear analysis of shallow foundation components. The values in the component action tables for nonlinear procedures were largely based upon analysis of foundation performance in model tests on rocking foundations. The primary measure to assess foundation performance is residual settlement or uplift. The acceptance criteria for linear analysis procedures ( m-factors) were derived from the allowable rotations for nonlinear procedures. A design example is presented in an online Appendix to illustrate differences between the current and previous versions of ASCE 41 and ASCE 31.

Cone penetrometers (CPTs) are commonly used for characterising the soil properties of centrifuge models; CPT data is useful for interpretation and quality control. This paper describes the development and design of a new robust CPT device for centrifuge testing. The new device consists of a 6mm cone, an outer sleeve, and an inner rod that transmits cone tip forces to a load cell above the ground surface. The design eliminates the need for a custom submerged strain gauge bridge near the tip, significantly reducing cost.A direct comparison was performed between this CPT device and another similar device developed at the University of Cambridge. CPT’s were manufactured using the new design and then shipped to eight different centrifuge facilities, for quality control of similar experiments performed for LEAP (Liquefaction Experiments and Analysis Projects). All the centrifuge tests simulated a 4 m deep deposit of soil, all consisting of Ottawa F-65 sand with relative densities ranging between about 45 to 80%. The results obtained have been extremely valuable as an independent assessment of the density calculated from mass and volume measurements at different laboratories.

Twenty-four centrifuge model tests have been conducted at nine different geotechnical centrifuge facilities around the world as part of the international LEAP effort (liquefaction experiments and analysis projects). All of the centrifuge models represent a 4 m deep 5 degree sloping submerged sand deposit. The mean effective PGA of the input motion for all of the experiments was approximately 0.15 g and the mean relative density was approximately 65%, but the effective PGA's varied between about 0.07 g and 0.3 g, and the relative densities varied between about 40% and 75%. The test matrix was designed to enable experimental quantification of not only the median response but also the trend and sensitivity of the model response to density and shaking intensity. Quantification of the sensitivity of the response to initial conditions is a prerequisite for objective evaluation of the quality of the model test data. In other words, a discrepancy between two experiments should be evaluated after accounting for the uncertainty in the initial conditions and the sensitivity of the response to initial conditions. For the first time, a sufficient number of experiments has been performed on a similar problem to provide meaningful quantitative evaluation of the trend between PGA, density, and displacement. The sensitivity is quantified by the gradient of the trend and the uncertainty of the trend is quantified from the residuals between the fitting data and the trend.

Many sensitive clay slopes exist that have a factor of safety greater than one based on the peak strength, and a factor of safety less than one based on the remolded strength. Obviously, it is possible for shaking from an earthquake to remold and soften a sensitive clay, but there is no criteria available to help engineers determine the extent of seismic loading required to induce sufficient strain softening to trigger instability. Slopes of varying sensitivity, produced by adding a small amount of Portland cement to clays of different plasticity were tested in a centrifuge to study the static and dynamic failure mechanism for sensitive clay slopes. The properties of the clay were determined by rudimentary laboratory tests. Results are interpreted in the context of existing literature to further our understanding of the factors controlling the potential for dynamic loading to trigger the instability of sensitive clay. The findings are based on a few key concepts. First, it must be recognized that structured sensitive clay is typically stiffer than remolded clay and hence, unless softening is triggered, sensitive clay may be expected to perform better than insensitive clay of the same residual strength. Second, softening behavior, which leads to localization on a thin shear band, is counteracted to some extent by strengthening associated with increase in strain rate. The rate effect favors thick shear bands, while softening leads to thin shear bands. Another factor affecting shear band behavior is that thick bands may be undrained during dynamic shear while thin shear bands are expected to be drained during static shear. Thirdly, the slope failure mechanisms for static and dynamic loading are quite different. During static (constant) loading, large deformations initiate precisely when one failure mechanism has a factor of safety FS

Physical modeling of buildings founded on layers of liquefiable sand has produced insightful data describing ground and building performance. A new publicly available NEEShub database, “FLIQ,” summarizes data from 9 large-scale centrifuge tests with 4 different lead experimentalists, various soil profiles, 49 stations of site and structure response, and more than 60 shaking events, that is, 405 events in total. Example correlations between ground-motion intensity measures and performance measures are presented to illustrate the usefulness of the database. The relationship between PGA at the surface and base is highly variable when liquefaction is observed; however, the relationship between the cumulative absolute velocity ( CAV) at the surface and base is relatively linear, even when liquefaction occurs. Additionally, the CAV was found to correlate well with settlement and can account for settlement history. Contrary to intuition, foundation settlement in liquefied soil is not directly correlated to bearing pressure; larger bearing pressures can decrease liquefaction occurrence and related settlements. The database has potential to grow through future community input.

Summary Fluctuations in axial load imposed on a rocking footing will affect its moment capacity, the shape of its moment–rotation hysteresis, and potentially the system's seismic performance. Structural asymmetry increases the likelihood of axial load variation during earthquake excitations. To investigate this issue, a unique centrifuge testing program was carried out on low-rise frame–wall–rocking foundation systems. In this paper, the seismic behaviors of asymmetric and symmetric models from this test program are systematically compared. Experimental results reveal that placing the lateral force resisting shear wall outboard produces significant axial load fluctuation, which in turn greatly deteriorate the lateral load-carrying capacity of a foundation rocking dominated frame–wall system, particularly in its weak direction. However, it strengthens the system when loading is towards the shear wall, leading to a highly asymmetric hysteretic response. During earthquake loading, all asymmetric rocking foundation systems observe smaller peak roof accelerations, but larger peak and permanent roof drifts compared with the symmetric systems. Despite these differences in response, the axial load fluctuation and structural asymmetry do not significantly change the relative energy dissipated by the rocking foundations and inelastic structural components within each frame–wall–rocking foundation model. Copyright © 2015 John Wiley & Sons, Ltd.

Although the nonlinear behavior of rocking shallow foundations has been experimentally and numerically demonstrated as an effective tool to dissipate vibrational energy during seismic loading, the engineering community has yet to uniformly accept it as a targeted design mechanism for diffusing seismic energy in a structure. This paper presents results of a centrifuge test program that incorporated inelastic behavior into model building systems via yielding of both structural and foundation components. Three 2-story-1-bay building models were designed with similar layouts but different combinations of foundation and structural component yield strengths and were shaken with a similar suite of earthquake motions. Measurements of behavior of each of the model buildings are presented and cross-compared in terms of time history responses, hysteretic responses of the structural and foundation fuses, and maximum response parameters. A balanced design configuration, wherein the rocking foundation and struc...

A two-dimensional nonlinear dynamic finite element (FE) model was developed and calibrated against dynamic centrifuge tests to study the behavior of soil-pile-structure systems in liquefied and laterally spreading ground during earthquakes. The centrifuge models included a simple structure supported on pile group. The soil profiles consisted of a gently sloping clay crust over liquefiable sand over dense sand. The FE model used an effective stress pressure dependent plasticity model for liquefiable soil and a total stress pressure independent plasticity model for clay, beam column elements for piles and structure, and interface springs that couple with the soil mesh for soil-structure interaction. The FE model was evaluated against recorded data for eight cases with same set of baseline parameters. Comparisons between analyses and experiments showed that the FE model was able to approximate the soil and structural responses and reproduce the lateral loads and bending moments on the piles reasonably well. © 2013, Earthquake Engineering Research Institute.

Soil–foundation–structure interaction (SFSI) and structure–soil–structure interaction (SSSI) influence the seismic response of a structure. Yet, consideration of nonlinear SFSI and SSSI in design practice is lacking. In this paper data from two centrifuge tests are examined. During each test, inelastic models of (1) a low-rise frame with shallowly embedded footings and (2) a mid-rise frame with a large basement are subjected to earthquake motions. In the first test, the structures are separated. In the second test, the structures are placed next to each other. Results show that the presence of the deep basement affects the moment–rotation behavior of the adjacent shallow footings, stiffening the response in the direction of loading towards the basement. This can be attributed to the additional restraint provided by the basement. Although the presence of the basement stiffens the response, it also limits the permanent displacements of the footing, which in turn limits physical damage to the superstructure. These results suggest that in addition to considering nonlinear SFSI effects, SSSI should be considered in the design of closely clustered structures.

This paper reports the experimental results from two geotechnical centrifuge tests examining seismic soil–foundation–structure interaction of frame structures. In the first test, two three-dimensional frame structures were placed apart, and in the second test, the same frame structures were located adjacent to each other. One of the frame structures was founded on shallowly embedded spread footings, and the other was founded on a deeper basement. During the second test, seismic structure–soil–structure interaction was also examined. In this paper, the experimental set-up is described in detail, some kinematic interaction observations are made, and seismic footing response results are reported. The results of the tests indicate that the seismic response of the shallow footings of a flexible frame structure is complex. This result is important because these complexities are not well incorporated in current soil–foundation–structure interaction analysis procedures. The adjacency of two frame structures, and thus structure–soil–structure interaction, further complicates analysis procedures. In the second test, the spread footings rock, slide, and settle less when they are directly adjacent to a deep basement. These results imply that SSSI can be beneficial or detrimental, depending on the earthquake motion and the structural system. In a companion paper, the seismic response of the frame superstructures and the footing force demands are also examined.

This article presents a framework for conducting seismic system identification using geotechnical centrifuge-based data for soil-structure interaction (SSI) experimentation. The framework starts with a design step that calculates two important SSI parameters: the period-lengthening ratio and the foundation-damping ratio. An identification and approximation procedure is further developed to estimate the system parameters at a variety of boundary conditions. The framework is then applied to two centrifuge tests. The results illustrate that the proposed framework can improve both the understanding of complex seismic soil-structure response and the use of geotechnical centrifuge-based SSI test data.

From results of a recent series of centrifuge model tests, this paper investigates the effects of shape and embedment on the performance of rocking footings. Rectangular and H-shaped footin...

Many engineers are hesitant to specify rocking foundations for ordinary bridges because of the unsubstantiated notion that rocking bridges are more susceptible to instability than conventional fixed-base bridges. A parametric study using a finite element model including large deformation effects compares the performance and stability of stiff, flexible, tall, and short hinging-column and rocking-foundation systems. Eighty different ground motions, scaled using incremental dynamic analysis, were considered. Results show that, in a probabilistic sense, bridges with rocking foundations are more stable than bridges with hinging columns if their fundamental periods are the same and if base shear coefficients to initiate hinging or rocking mechanisms are the same. Maximum drifts are not much affected by changing between rocking and hinging mechanisms except near collapse, but residual drifts are smaller for rocking systems. The results also challenge the notion that rocking systems require a different design approach than hinging column systems.