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Seismic stability assessment of a steel plate fabricated column constructed on
liquefiable grounds with different soil-layer profiles
Évaluation de la stabilité sismique d'une colonne en plaques d'acier construite sur des sols
liquéfiables avec différents profils sol-couche
Nakai K., Xu B.
Nagoya University, Japan
Takaine T.
Asanuma Corporation, Japan
ABSTRACT: In this paper, the seismic stability of a steel fabricated column constructed on liquefiable grounds with different
stratigraphic compositions of the deep layers was evaluated using dynamic/static soil-water coupled finite deformation analysis taking
into consideration soil-structure interaction during an earthquake. Attention was paid to the variation in stratigraphic composition with
depth, which is not fully taken into consideration in the conventional liquefaction judgment. The results showed that when there was a
clay layer seated on the liquefiable layer, the acceleration was amplified in the clay layer, leading to an increase in the input
acceleration for the liquefiable layer, and that there was a risk that the oscillations of the structure would be increased. In particular,
when the thickness of the liquefiable layer was small, the attenuation of the acceleration in the liquefiable layer was small, so the
stability of the structure above was significantly reduced.
RÉSUMÉ : Dans cet article, la stabilité sismique d'une colonne en plaques d'acier construite sur des sols liquéfiables avec une
composition stratigraphique différente des couches profondes a été évaluée à l'aide d'une analyse de déformation dynamique / statique
sol-eau couplé en tenant compte de l'interaction sol-structure lors du séisme. L'attention est portée à la composition stratigraphique
dans les profondeurs qui n'est pas entièrement prise en compte dans les jugements de liquéfaction classiques. À partir du résultat,
quand il y avait une couche d'argile sur la couche liquéfiable, l'accélération a été amplifiée dans la couche d'argile ce qui a entraîné
une augmentation de l'accélération d'entrée pour la couche liquéfiable, et il y avait un risque que les oscillations de la structure soient
augmentées. En particulier, lorsque l'épaisseur de la couche liquéfiable est faible, l'atténuation de l'accélération dans la couche
liquéfiable est faible, de sorte que la stabilité de la structure posée en soit considérablement réduite.
KEYWORDS: soil-water coupled finite deformation analysis, stratigraphic composititon, liquefaction
1 INTRODUCTION.
In a gas company, in addition to earthquake-resistance of a gas
facilities and pipelines, the remote control equipment for
performing rapid gas stoppage at the time of a large-scale
disaster has been built, and, generally it consists of a governor
chamber that reduces the pressure and a steel fabricated column
that receives the wireless signals. Although the existing
equipments itself serves as design criteria supposing the
massive earthquake of the Great Hanshin-Awaji Earthquake
level, the earthquake loads were just applied to the structure as
static loads based on a Seismic Coefficient Method. And no
verification taking into consideration the soil-structure dynamic
interaction during an earthquake was performed.
Through several numerical examples, the paper aims to carry
out a numerical analysis to evaluate the seismic stability of a
steel fabricated column constructed on liquefiable grounds with
different soil layer depths and profiles employing elasto-plastic
seismic response analysis. The analysis code used was the soil-
water coupled finite deformation analysis code (Noda et al.
2008), which incorporates an elasto-plastic constitutive model
(SYS Cam-clay model; Asaoka et al. 2002) that allows
description of the behavior of soils ranging from sand to
intermediate soils and clay under the same theoretical
framework. One of the features of this study is solving the
ground deformation behavior during and after the earthquake
simultaneously taking into consideration of the dynamic soil-
structure interaction. Moreover, the attention is paid to
stratigraphic composition in the depth which is not fully taken
into consideration in the conventional liquefaction judgment.
2 ANALYSIS CONDITION
2.1
Determining the soil layer compositions
In view of the numerous remote control equipments,
constructed ground will range from stable grounds to weak soft
grounds. In this paper, the focus is on steel fabricated column
constructed on loose sand grounds that are highly susceptible to
liquefaction in order to verify the seismic stability by numerical
analysis. The analysis is not carried out on specific actually
constructed examples of the column, but instead, the seismic
stability of column installed on ground having different
stratigraphic compositions is analyzed, as shown in (1) to (3)
below.
(1) Influence of embedment depth of the column installed on
liquefiable ground on the seismic stability
(2) Influence of the soil properties of the surface layer (loose
sandy ground and weak clayey ground)
(3) Influence of the sequence of ground layers (effect of a weak
clay layer interposed below a liquefiable layer)
Fig. 1 shows 5 stratigraphic compositions and column
embedment depths for the above (1) to (3) items for
investigation. As can be seen, there are 4 stratigraphic
compositions, Type A to D. Apart from the embedment depth
using concrete, the various parameters of the column, material
constants and dimensions are the same in all analysis cases.
The elasto-plastic properties used for analysis are determined
by reproducing the mechanical behaviours of the undisturbed
specimen sampled from the original ground by the SYS Cam-
clay model (Noda et al. 2009). Table 1 presents the view of
material constants. It is assumed that 1) the grounds have
horizontally homogeneous layers; 2) within the same layer, the
