Characterization of rocking shallow foundations using centrifuge model tests

Deng, Lijun; Kutter, Bruce L.

doi:10.1002/eqe.1181

Cited by 91 publications

(25 citation statements)

References 23 publications

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“…However, the response at the bases of the heavily and the lightly loaded foundations differ substantially: uplifting of half the base takes place under light (vertical) loading, while compression is still transmitted under the whole heavily loaded base. This is reminiscent of the response of surface foundations that has been amply demonstrated both theoretically and experimentally (Paolucci et al, 2008;Anastasopoulos et al, 2010aAnastasopoulos et al, , 2012Deng & Kutter, 2012): uplifting dominates with large FS V , whereas soil yielding and failure mechanisms dominate with small FS V .…”

Section: Tensionless Potentially Sliding Interface (Tsi) Mq Envelopementioning

confidence: 89%

Static and cyclic undrained response of square embedded foundations

Ntritsos¹,

Anastasopoulos²,

GAZETAS³

2015

Géotechnique

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Results of a three-dimensional finite-element study for the effect of embedment on the undrained bearing capacity, the elastic stiffness, and the cyclic behaviour of square-in-plan foundations are presented. Uniaxial horizontal (Q) and pure-moment (M) limit loads, as well as the respective elastic stiffnesses (K HH and K MM ) are obtained, and simplified models are developed to interpret the observed trends. The substantially different role of embedment in increasing elastic stiffness and in increasing ultimate loads is interpreted in simple soil mechanics terms. Extensive comparisons are made with the two-dimensional results for a strip foundation. Combined (QM) loading capacities are obtained and presented as 'interaction' diagrams; the significance of the vertical load (N ) is also addressed. The importance of the type of contact between the foundation interfaces (vertical or horizontal) with the surrounding or underlying soil is explored. A substantial reduction in all capacities is shown when the interfaces are tensionless and of limited shear (sliding) resistance (TSI), compared with the capacities for the ideal case of fully bonded contact (FBC). The cyclic moment-rotation (M-θ) response of embedded foundations carrying a simple slender structure is investigated parametrically. It is found that the monotonic loading curves provide approximately the envelope for the cyclic M-θ loops. But the shape of these loops and the ensuing settlement of the foundation are both functions of the factor of safety (FS V ) against vertical bearing capacity. In case of surface and shallowly embedded foundations with high values of FS V (i.e. with light loading or on very stiff soil) the loops pass nearly through the centre (M ¼ θ ¼ 0) of the coordinate axes and the residual settlement is negligible; both are a consequence of the predominantly geometric non-linearity in the form of separation of the walls and uplifting of the base from the soil. On the contrary, with low FS V values (heavy loading or soft soil) and deeper relative embedment, broad hysteresis loops and accumulating settlement are the rule -a product of material inelasticity of the soil, under limited soil-foundation detachment.

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Section: Tensionless Potentially Sliding Interface (Tsi) Mq Envelopementioning

confidence: 89%

Static and cyclic undrained response of square embedded foundations

Ntritsos¹,

Anastasopoulos²,

GAZETAS³

2015

Géotechnique

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“…T 1 is also the duration of the longest episode of the corresponding sequence. If the amplitude of the first uplift episode is equal to the initial vertical displacement of the footing, that is, there is no energy dissipated because of the first impact, T 1 of the rigid system can be estimated using Equation (9). In the study of Housner [2], Equations (9) and (10) were proposed to determine the free vibration period of a rigid rocking block.…”

Section: Free Vibration Involving Upliftmentioning

confidence: 99%

“…In the study of Housner [2], Equations (9) and (10) were proposed to determine the free vibration period of a rigid rocking block. If the amplitude of the first uplift episode is equal to the initial vertical displacement of the footing, that is, there is no energy dissipated because of the first impact, T 1 of the rigid system can be estimated using Equation (9).…”

Section: Contact Forces On a Rigid Base Following Footing Upliftmentioning

confidence: 99%

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Experimental assessment of contact forces on a rigid base following footing uplift

Chen

Larkin

Chouw

2017

Earthq Engng Struct Dyn

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Summary A number of investigations in the recent decades have shown that footing uplift can reduce the seismic loading on a structure. Guidelines to design a structure with seismic uplift capability have been proposed. However, these studies mainly focus on the structural response and neglect the impact forces on the footing from re‐contact between the footing and the supporting medium. A small number of computational studies of the induced forces on the footing have been performed. This paper presents the results of free vibrations and shake table tests on a single degree‐of‐freedom model of a bridge pier with footing uplift on a rigid base. Two support conditions are considered, that is, footing fixed to the base and footing free to uplift on a rigid base. Load cells were placed at the interface of the footing and rigid base to measure the contact forces during structural vibration. The footing responses of both flexible and rigid structures due to free vibration are compared. The results show that the flexibility of the structure has significant effects on footing uplift duration and amplitude and reduces the contact force, in some cases very significantly. The flexible structure was also subjected to harmonic base excitations. It is found that varying the characteristics of the excitation changes the uplift amplitude but does not affect the contact force significantly. Copyright © 2017 John Wiley & Sons, Ltd.

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“…The importance of understanding the foundation's capacity is elevated when a designer wants to incorporate the foundation rocking mechanism into the seismic design of structures to improve the system's performance [e.g. ]. Inelastic soil–foundation–structure–interaction (SFSI), particularly when the foundation is allowed to uplift, has inherent capabilities to dissipate seismic input energy as well as introduce a self‐centering tendency, each of which has been demonstrated by numerous experiments and numerical studies [e.g.…”

Section: Background and Research Scopementioning

confidence: 99%

Effect of earthquake‐induced axial load fluctuations on asymmetric frame–wall–rocking foundation systems

Liu

Hutchinson

Kutter

et al. 2015

Earthq Engng Struct Dyn

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SUMMARYFluctuations 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 framewall-rocking foundation model. Copyright © 2015 John Wiley & Sons, Ltd. KEY WORDS: axial load fluctuation; frame-wall structure; foundation rocking; asymmetry; nonlinear soilstructure interaction; seismic testing; centrifuge modeling 1. BACKGROUND AND RESEARCH SCOPE BackgroundArchitectural aesthetics or building functionality often leads to requirements for large open bays in buildings. Structural shear walls, however, are highly successful at minimizing interstory drift demands induced by an earthquake. Many buildings require a compromise between these two competing design issues and therefore are constructed of mixed systems, i.e. walls and frames, with multiple load resisting systems. As a result, it is not uncommon that the building load path becomes asymmetric. When subjected to lateral wind or seismic load, building asymmetry could produce a coupled response between its lateral and torsional modes, which greatly complicates the analysis of the system. Researchers have realized this issue and proposed approximate analytic solutions [e.g. 1, 2], or developed simplified numerical methods for estimating the seismic demand to these structures [e.g. 3-5]. These and other studies highlight another key aspect of the asymmetry, namely that axial

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Characterization of rocking shallow foundations using centrifuge model tests

Cited by 91 publications

References 23 publications

Static and cyclic undrained response of square embedded foundations

Static and cyclic undrained response of square embedded foundations

Experimental assessment of contact forces on a rigid base following footing uplift

Effect of earthquake‐induced axial load fluctuations on asymmetric frame–wall–rocking foundation systems

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