Centrifuge modeling of rocking-isolated inelastic RC bridge piers

2015

A preceding experimental study carried out at the University of Dundee, as well as independent experimental and numerical research results, have shown the improved seismic performance of rocking shallow foundations in comparison to conventional, conservatively designed foundations, for bridges. By properly reducing the size of the footing, rocking behaviour due to seismic loading can occur about the footing base. It has been shown that rocking foundations can reduce seismic ductility demand on bridge columns and improve bridge performance so much so as to enable them to safely resist very strong seismic motions which lead to collapse of alternative conventional systems. Yet, key concern is the potential for significant settlement accumulation, especially in relatively poor soil conditions. Therefore, current research objectives focus on exploring possible innovative foundation systems that will optimise the seismic performance of rocking foundations. To this end, a series of dynamic...

2005

Shallow foundations supporting building structures might be loaded well into their nonlinear range during intense earthquake loading. The nonlinearity of the soil may act as an energy dissipation mechanism, potentially reducing shaking demands exerted on the building. This nonlinearity, however, may result in permanent deformations that also cause damage to the building. Five series of tests on a large centrifuge, including 40 models of shear wall footings, were performed to study the nonlinear load-deformation characteristics during cyclic and earthquake loading. Footing dimensions, depth of embedment, wall weight, initial static vertical factor of safety, soil density, and soil type (dry sand and saturated clay) were systematically varied. The moment capacity was not observed to degrade with cycling, but due to the deformed shape of the footing-soil interface and uplift associated with large rotations, stiffness degradation was observed. Permanent deformations beneath the footing continue to accumulate with the number of cycles of loading, though the rate of accumulation of settlement decreases as the footing embeds itself.

The behaviour of inclined pile foundations under seismic actions is not thoroughly investigated. This paper provides new experimental data on the responses of inclined pile foundations tested using the centrifuge modelling technique. The experiments are designed to investigate soil-structure interaction. Different mock-ups are subjected to several earthquakes with low intensities and the evolution of their frequency components is identified. Experimental results are analyzed in terms of response frequencies and section forces in the piles. Numerical simulation of the soil-structure systems is conducted in the linear viscoelastic domain. Comparison of the experimental and the numerical response both in the frequency and in the time domain is satisfactory. From both the experimental and numerical results preliminary conclusions can be drawn concerning the dynamic characteristics of the soil-structure systems and the effects of inclined piles. Blank line 10 pt

Nuclear Engineering and Design, 2007

Proper understanding of the role of unbounded soil in the evaluation of dynamic soil structure interaction (SSI) problem is very important for structures used in the nuclear industry. In this paper, the results from a series of dynamic centrifuge tests are reported. These tests were performed on different types of soil stratifications supporting a rigid containment structure. Test results indicate

Proceedings of the 13th …, 2004

In this paper, an attempt is made to validate the numerical response of a soil-structure system with observations from physical modeling, using data from high gravity centrifuge testing that have been carried out on portal frames founded on uniform soil strata. The preliminary ...

Earthquake Engineering & Structural Dynamics, 1989

This paper presents a centrifuge model that is capable of realistically representing soil-structure systems subjected to earthquake-like excitation. The model is validated by performing (i) free field soil tests, (ii) dynamic soil-structure interaction tests and (iii) a numerical analysis of the experimental results. The free field experiments show that the simulated earthquake, which is generated by the hammer-exciter plate method, is similar in amplitude and frequency content to a real earthquake. The experiments also demonstrate that a confined soil sample can satisfactorily model a horizontal soil stratum of infinite lateral extent when the containment walls are lined with an absorptive material to attenuate wave reflections that would otherwise occur. Measurements of the acceleration at different locations on the free soil surface indicate that the surface motion is fairly uniform over a relatively large area. This is further confirmed by a comparison made between the measured free and scattered field motions for a surface foundation. Next, a series of soil-structure interaction tests are performed which examine the dependence of radiation damping on the natural frequencies of the structure relative to the fundamental frequency of the soil stratum. The experimental results are shown to be consistent with established theories. Finally, the experimental results are used to compute the stiffness and damping parameters of a two degree of freedom numerical model of the soil-structure system. The experimental parameters are shown to be in good agreement with calssical text book formulae. This study demonstrates that the centrifuge model consistently behaves as expected for simple, but realistic, dynamic soil and soil-structure systems, and can, therefore, be used with confidence to examine more complicated systems that are not yet fully understood.

Soils and Foundations, 2018

A series of dynamic centrifuge model tests was conducted to investigate the effects of reinforcement on the seismic behaviour of hillside embankments consisting of sandy soils and resting on stiff base slopes. In total, three types of seismic reinforcements, namely, largescale gabions, drainage-reinforcing piles, and ground anchors with pressure plates, were employed in the tests. The test results showed that: (1) the seismic performance of both lower and higher embankments was remarkably improved by installing large-scale gabions at the toe as they restrained the completion of the formation of sliding planes; (2) the installation of drainage-reinforcing piles at the embankment toe was rather effective in reducing the overall earthquake-induced deformation due to their high permeability and restraint effect against sliding displacement at the reinforced region; and (3) the embankments improved by ground anchors with pressure plates were not vulnerable to earthquake-induced damage due to their constraint effects even under high water table conditions. The improvement effects by the above-mentioned three types of reinforcements were presented by evaluating the global safety factors based on the results of a series of triaxial compression tests.

Soil Dynamics and Earthquake Engineering, 2017

Liquefaction-induced settlement and bearing capacity failure have been reported as leading causes of damages in shallow foundations during earthquakes. Previous studies of this problem have mainly focused on the performance of isolated shallow foundations. In urban areas, however, foundations are generally located in close proximity. In this study, three series of centrifuge tests were conducted to investigate the effect of foundationsoil-foundation interaction (FSFI) on the seismic and post-seismic settlement of shallow foundations on saturated sand. Two rigid foundations with different surcharge loads (as heavy and light foundations) were placed with different spacing. Multiple shaking events were applied to achieve different extents of soil liquefaction. The results indicate that significant part of foundation settlement occurred before soil reconsolidation. Furthermore, the time period after shaking, wherein excess pore water pressure sustains, plays an important role in the total settlement of foundations. The acceleration responses experienced by the foundations were significantly larger than those observed in the free-field. The heavy foundation fluctuated more strongly than the light one. Moreover, adjacency considerably affected the seismic response of foundations whereas stronger acceleration response on the ground level was observed for the closer cases. The Clear asymmetric settlement was observed for the adjacent foundations. It is demonstrated that settlement of foundations not only is dependent on foundations' proximity but also is a function of shaking intensity. Influence of foundations' spacing on the generation-dissipation mechanism of excess pore water pressure (EPWP) and liquefaction extent was described by the time-dependent contours plotted by interpolation of the recorded data.

Bulletin of Earthquake Engineering, 2015

Although batter pile foundations are widely used in civil engineering structures, their behavior under seismic loadings is not yet thoroughly understood. This paper provides insights about the differences in the behavior of batter and vertical piles under seismic soil-pile-superstructure interaction. An experimental dynamic centrifuge program is presented, where the influences of the base shaking signal and the height of the gravity center of the superstructure are investigated. Various seismic responses are analyzed (displacement and rotation of the pile cap, total shear force at the pile cap level, overturning moment, residual bending moment, total bending moment and axial forces in piles). It is found that in certain cases batter piles play a beneficial role on the seismic behavior of the pile foundation system. The performance of batter piles depends not only on the characteristics of the earthquakes (frequency content and amplitude) but also on the type of superstructures they support. This novel experimental work provides a new experimental database to better understand the behavior of batter pile foundations in seismic regions.

International Journal of Physical Modelling in Geotechnics, 2010

Drum centrifuge tests on circular footings resting on medium dense silica sand subjected to combined vertical, moment and horizontal loading are reported and compared with existing data from similar studies carried out at 1g. Vertical loading tests and displacement-controlled horizontal and rotational swipe tests were carried out; the results are reported in terms of load-displacement relationships and yield surfaces in (V, M/D, H) load space. The centrifuge test results from this study are well described using the existing theoretical framework of strain-hardening plasticity applied to surface footings on sand, developed on the basis of experimental data from 1g tests. Attention is given to the embedment effect, which can be especially pointed out by centrifuge testing.