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This paper presents the earthquake response of three low-rise frame-wall-foundation centrifuge building models, including a structural hinging-dominated, foundation rocking-dominated, and balanced design model. The models were designed such that the capacities of the dominant inelastic elements varied; however, each was subjected to a similar sequence of earthquake shaking in a 30-g centrifuge environment to facilitate comparison. Experimental results reveal that the traditional frame-wall building with a strong foundation (i.e., a hinging-dominated system) has the least potential to recover from displacements induced during earthquake shaking. As a result, this system suffered the most significant residual deformation. In contrast, systems with rocking foundations sustained a smaller peak roof acceleration, residual drift, and peak base shear despite the relatively larger peak transient drift demand. Consistent with slow cyclic test results, dissipated hysteretic energy was reasonably distributed amongst superstructure and substructure inelastic components in the balanced model during moderate and high intensity shaking. [ABSTRACT FROM AUTHOR]

The mechanism of foundation rocking has received much attention recently due to its appealing seismic resistant features, namely, self-centering tendency and energy dissipation capability. It is well recognized, however, that other inelastic mechanisms will contribute to a system's seismic resistance. Considering the strength difference between a rocking footing and a shear wall structural fuse, and the system symmetry, six different two-story-two-bay frame-wall-foundation building models were constructed and tested in a geotechnical centrifuge. In this paper, the test program and experimental results when the models were subjected to slow cyclic loading are presented. A companion paper presents results from the dynamic phase of testing. Results indicate that, with the aid of foundation rocking, the system behaves in a ductile and stable manner with no strength degradation, even when the model is pushed to a drift of more than 2.5%. Importantly, when structural and foundation component strengths are approximately equal, the hysteretic energy is reasonably distributed among the superstructure inelastic components and the rocking foundations. Finally, numerical analyses predictions demonstrate comparable local and global response to measurements obtained during the experiments. [ABSTRACT FROM AUTHOR]

Two geotechnical centrifuge tests were designed to elicit the influence of soil-foundation-structure interaction (SFSI) and structure-soil-structure interaction (SSSI) effects on the seismic demands of an inelastic frame structure founded on individual spread footings. Four experimental cases were considered: (1) SFSI of an individual inelastic frame structure (baseline case); (2) in-plane SSSI between the frame structure and a large elastic wall structure designed to respond predominately in a rocking mode; (3) anti-plane SSSI between the frame and wall structures; and (4) combined in-plane and anti-plane SSSI between the frame structure and two wall structures. Results from Cases 1, 2, and 4 are analyzed considering 13 demand parameters. The peak seismic demands from the baseline case are compared to the peak demands from the SSSI cases to elicit the impacts of building adjacency. The number of earthquake motions that resulted in increases or decreases in the seismic demands in the frame structure are tracked for the SSSI cases. For these tests, SSSI consistently results in increased peak foundation moment and foundation base shear demands, regardless of the geometric layout of the structures. These increases propagate throughout the superstructure, resulting in increases in moment, shear and curvature ductility demands in the structural components. SSSI effects are observed to be most significant for low-to-moderate intensity earthquake motions, suggesting that particular consideration should be given to the likelihood of SSSI for highly probable earthquakes. [ABSTRACT FROM AUTHOR]

Many of the older bridges in the United States have no original contract documents available, and about 26,000 bridges that are rated as scour critical have unknown foundation conditions. Thus, no information is available regarding the type, depth, geometry, or material of these scour critical bridge foundations. The unknown bridge foundations pose a significant problem to bridge owners because of safety concerns. This paper presents the determination of an unknown bridge foundation depth at Forth Worth, Texas. The bridge was supported by driven steel H-piles. Three nondestructive testing (NDT) techniques were utilized: (1) the parallel seismic (PS) method, (2) the sonic echo (SE) method, and (3) resistivity imaging (RI). The main objective of this present study was to compare the suitability of NDT techniques to determine the unknown bridge foundation depth. Based on the field test results, both PS and RI methods provided foundation depth close to actual foundation depth. However, the SE method was determined to be unsuitable for determining the unknown steel H-pile depth. [ABSTRACT FROM AUTHOR]

The mechanisms that control the seismic liquefaction performance of shallow foundations are identified for the special, still common case of a clay crust separating the foundation from the liquefied ground. For that purpose, foundation response is first analyzed with the nonlinear dynamic finite-difference method and consequently evaluated in connection with published field and experimental evidence. Insight is given into the excess pore-pressure buildup under the foundation, the seismic settlement accumulation, the static-bearing capacity degradation, and the inertia-induced interaction with the superstructure. It is thus shown that a naturally or artificially created nonliquefiable soil crust may effectively mitigate the detrimental effects of liquefaction and allow for a performance-based design of surface foundations, without additional improvement measures. [ABSTRACT FROM AUTHOR]

Recent studies have highlighted the beneficial role of foundation uplifting and the potential effectiveness of guiding the plastic hinge into the foundation soil by allowing full mobilization of bearing capacity during strong seismic shaking. With the inertia loading transmitted onto the superstructure being limited by the capacity of the foundation, this concept may provide an alternative method of in-ground seismic isolation: the so-called rocking isolation. Attempting to unravel the effectiveness of this alternative design method, this paper experimentally investigates the nonlinear response of a surface foundation on sand and its effect on the seismic performance of an idealized slender single-degree-of-freedom structure. Using a bridge pier as an illustrative prototype, three foundation design alternatives are considered, representing three levels of design conservatism. Their performance is investigated through static (monotonic and slow-cyclic pushover) loading, and reduced-scale shaking table testing. Rocking isolation may provide a valid alternative for the seismic protection of structures, providing encouraging evidence in favor of the innovative idea of moving foundation design toward a less conservative, even unconventional, treatment. [ABSTRACT FROM AUTHOR]

This engineering educational module on the behavior of piles in soft clays during earthquake loading sought to introduce engineering as a viable career to eighth graders and teach students how geotechnical engineers design foundations in marginal soils to minimize damage to infrastructure during earthquakes. This module could also be used at various educational levels, from elementary to middle and high school, as well as at the undergraduate level, with appropriate modifications. A 5-h module was created to simulate the real-world behavior of piles in soft clays during earthquake loading and visually show the improvement in how these same piles behave after being stabilized with a deep-soil-mixing technique. In this module, soft soil was simulated using Jell-O, piles were simulated using Slim Jims, and soil stabilization was simulated using peanut butter, marshmallows, or cheese. Each student group had to design a stabilization procedure to improve the behavior of the piles. The students competed to see who could design a stabilized pile with the least amount of deflection for the least amount of money. An abbreviated module was also administered to a group of middle-school science and mathematics teachers. The students' and teachers' learning and perceptions were assessed by administering pre- and post-assessment questions, which were matched. [ABSTRACT FROM AUTHOR]

This paper reports on the seismic performance of three geosynthetic-reinforced segmental retaining wall systems backfilled with a silty sand mixture, using a shaking table excited by 1995 Kobe earthquake loadings. The preparation of the backfill mixture and its properties, the tested wall configurations, the reinforcement layouts and instrumentations, and the observed wall performance are described. Visual observations and test results indicate that walls having 0.4-m vertical reinforcement spacing, backfilled with soil containing a large percentage of fines, performed better than those having good-quality sandy soil under otherwise identical conditions. Vertical spacing of 0.8 m with removal of interlocking facing blocks in one of the walls did not lead to global collapse under repeated applications of the Kobe earthquake loadings. Only localized shear failure behind the top block layer was observed as the top facing blocks tended to topple. The good performance was attributable to apparent cohesion in the soil mixture stemming from soil matrix suction and true cohesion. Because this apparent cohesion is affected by the moisture content, its existence must be ensured by providing proper drainage to prevent seepage into the backfill. Considering the risk associated with the use of apparent cohesion, its exclusion from design is recommended. [ABSTRACT FROM AUTHOR]