Gregg L. Fiegel (Cal Poly, SLO), H. Ben Mason (UC Berkeley), and Nicholas W. Trombetta (UC San Diego)

Article published for the American Society of Engineering Education (ASEE)

ABSTRACT: The paper describes our strategies and experiences in recruiting, training, advising, and mentoring five undergraduate student researchers for a large-scale experimental research project. Specific discussions focus on the development of student learning outcomes and the establishment of a recruiting program. For this project, graduate student leaders served as the primary mentors to the undergraduate researchers.

In the paper, we discuss how the graduate students prepared for their roles as research mentors. The principal investigators worked with the graduate student leaders to provide advice and training on topics such as teamwork, project management, communication, feedback, and student learning. Details of this approach are described in the paper.

The paper also includes a discussion of the methods used to assess the undergraduate students' project experiences. Examples are provided of different work products prepared by the undergraduates. Also provided are the results of a post-employment assessment survey, which was developed by the graduate student leaders and a principal investigator. The survey results indicate that the undergraduate student research experiences have been challenging and rewarding. The survey results also provide valuable feedback for the graduate student leaders. At the mid-point of the project, the graduate students are using the feedback to develop specific recommendations for managing the research project and mentoring undergraduates in the future. The recommendations are summarized in the paper.

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Shideh Dashti, Jonathan D. Bray, Juan M. Pestana, Michael Riemer, and Dan Wilson

From JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING © ASCE / JULY 2010

ABSTRACT: Seismically induced settlement of buildings with shallow foundations on liquefiable soils has resulted in significant damage in recent earthquakes. Engineers still largely estimate seismic building settlement using procedures developed to calculate postliquefaction reconsolidation settlement in the free-field. A series of centrifuge experiments involving buildings situated atop a layered soil deposit have been performed to identify the mechanisms involved in liquefaction-induced building settlement. Previous studies of this problem have identified important factors including shaking intensity, the liquefiable soil’s relative density and thickness, and the building’s weight and width.

Centrifuge test results indicate that building settlement is not proportional to the thickness of the liquefiable layer and that most of this settlement occurs during earthquake strong shaking. Building-induced shear deformations combined with localized volumetric strains during partially drained cyclic loading are the dominant mechanisms. The development of high excess pore pressures, localized drainage in response to the high transient hydraulic gradients, and earthquake-induced ratcheting of the buildings into the softened soil are important effects that should be captured in design procedures that estimate liquefaction-induced building settlement.

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Shideh Dashti, Jonathan D. Bray, Juan M. Pestana, Michael Riemer, and Dan Wilson

From JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING © ASCE / JULY 2010

ABSTRACT: The effective application of liquefaction mitigation techniques requires an improved understanding of the development and consequences of liquefaction. Centrifuge experiments were performed to study the dominant mechanisms of seismically induced settlement of buildings with rigid mat foundations on thin deposits of liquefiable sand. The relative importance of key settlement mechanisms was evaluated by using mitigation techniques to minimize some of their respective contributions. The relative importance of settlement mechanisms was shown to depend on the characteristics of the earthquake motion, liquefiable soil, and building. The initiation, rate, and amount of liquefaction-induced building settlement depended greatly on the rate of ground shaking.

Engineering design procedures should incorporate this important feature of earthquake shaking, which may be represented by the time rate of Arias intensity (i.e., the shaking intensity rate.) In these experiments, installation of an independent, in-ground, perimetrical, stiff structural wall minimized deviatoric soil deformations under the building and reduced total building settlements by approximately 50%. Use of a flexible impermeable barrier that inhibited horizontal water flow without preventing shear deformation also reduced permanent building settlements but less significantly.

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Earthquake Input Motions and Seismic Site Response in a Centrifuge Test Examining SFSI Effects

Ben Mason (UC Berkeley)
56th International Conference on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics (05.24.10)

ABSTRACT
This paper describes the ground motion selection process and reports observed seismic site response and SFSI effects during a dynamic centrifuge test (Test-1). The centrifuge test is the first in a series of tests examining the effects of SFSI in dense urban environments. The objective of Test-1 is to examine SFSI effects for two structures that are located a significant distance apart and essentially isolated. The model structures represent a three-story building founded on spread footings and a nine-story structure founded on a three-story basement. The structures are sited on a dry, dense bed of Nevada Sand. The centrifuge model is subjected to a series of shaking events that represent near-fault and “ordinary” ground motions at a site in Los Angeles. Results show that site periods degrade as ground motion intensity increases with more pronounced degradation observed for near-fault ground motions as compared with ordinary ground motions. Additionally, the results indicate the importance of kinematic effects of embedded structures when considering SFSI effects.

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Seismic Performance Assessment in Dense Urban Environments: Evaluation of Nonlinear Building Foundation Systems Using Centrifuge Tests

ZhiQiang Chen (UC San Diego)
56th International Conference on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics (05.24.10)

ABSTRACT
In dense urban areas, buildings are generally constructed in clusters, forming city blocks. New buildings are designed assuming their response is independent of adjacent buildings, which ignores potentially important structure-soil-structure-interaction (SSSI) effects. Although a few studies have revealed the significance of SSSI effects, validated simulation and design tools do not exist. In this paper, we present the results from the first in a series of centrifuge tests intended to investigate SSSI effects. Results herein are focused on the design and measured response of two model building-foundation systems placed on dense dry Nevada sand and tested at 55-g. The two models represent prototypical nine-story and three-story special moment resisting frame buildings, with the former structure supported by a three-level basement-mat and the later on isolated spread footings. Nonlinear response-history simulations are performed to aid in the design of the models, with particular attention to reproducing prototype building periods and nonlinear characteristics. Yielding of the model buildings is achieved using custom-designed fuses placed strategically throughout the superstructures. At present, the two models are placed as far apart as possible to characterize soil-structure interaction on individual buildings; subsequent experiments will move the structures in near proximity, allowing direct experimental assessment of structuresoil- structure-interaction.

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Earthquake motion selection and calibration for use in a geotechnical centrifuge

H. B. Mason (UC Berkeley); B. L. Kutter (UC Davis); J. D. Bray (UC Berkeley); D. W. Wilson & B. Y. Choy (UC Davis)

ABSTRACT: Researchers usually utilize a few previously employed ground motions or simple sinusoidal input for earthquake simulations in centrifuge tests. Given the inherent randomness of earthquake motions as well as their importance in determining seismic response, it is beneficial to use a broad suite of motions. This paper describes the earthquake motion selection and filtering processes employed for a recent series of centrifuge tests. A simple procedure is proposed for calibrating recorded ground motions for use in the University of California at Davis Center for Geotechnical Modeling centrifuge. The procedure employs an iterative frequency-domain transfer function to reasonably match the motion achieved during the test with what is targeted by the researcher. Insights about the performance of the shaking table are also made.

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Soil-Foundation-Structure Interaction Effects on Model Buildings within a Geotechnical Centrifuge

H. B. Mason (UCB), Z. Chen, K. C. Jones (UCB), N. W. Trombetta (UCSD), J. D. Bray (UCB), T. C. Hutchinson (UCSD), C. Bolisetti (UB-SUNY), A. S. Whittaker (UB-SUNY), B. Y. Choy (UCD), B. L. Kutter (UCD), and G. L. Fiegel (CalPoly-SLO)

ABTRACT: This paper describes a geotechnical centrifuge test that is part of a study investigating soil-foundation-structure interaction effects in dense urban environments. Two prototypical structures, a three-story building on spread footings and a nine-story building on a three-story basement, are located sufficiently far apart to be considered isolated from each other. The results show that kinematic soil-foundation-structure interaction is important for structures founded on deep, stiff basements. Additionally, acceleration amplification factors from the ground to roof levels of these buildings are under two and during intense motions, more than 50% of the roof drift of the shallow spread footing-supported structure is attributed to foundation movements. For lower intensity motions, the foundation movements only contribute approximately 20% of the roof drift.

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NEES City Block - Design Spectra For Project Location No.1 -

Ben Mason and Jonathan Bray

The purpose of this memorandum is to examine the seismic hazard of a selected project location for the ‘NEES City Block’ project. With this information, the research team, as well as the professional practice committee, can decide whether to make this the permanent project location, or whether another site should be selected.

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What's Fail-Safe For A Dam? -
article from MOSAIC (July/August 1979)

Geotechnical engineers seek - and find - ways to test massive structures to failure without waiting for them to fail.

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Soil-Structure/Adjacent Structure Interaction -
excerpt from Connections - The EERI Oral History Series
reprinted by permission

Vitelmo Bertero

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