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Behavior of a multi-story building under seismic loads when taking into account the
viscoplasticity of the soil base.
L'interaction entre les constructions du bâtiment sous charges sismiques tout en tenant compte de
la viscoplasticité de la base du sol.
Boyko I.P., Sakharov O.S., Sakharov V.O.
KNUCA, Kyiv, Ukraine
ABSTRACT: This article presents an analysis of the dynamic behavior of the 3D “soil base – foundation – above-ground
construction” system that was conducted via the automotive system of scientific research (ASSR) “VESNA”. In particular, the
presented results show the effect of the use of elastic, visco-elastic and elastic-viscoplastic models on the behavior of the building
under seismic loads while taking into account a seismic isolation system. Taking into consideration the non-linearity of the soil’s
physical properties allowed the model to estimate the actual spatial position of the engineering structures after seismic action. The
model demonstrated that the greatest forces within the piles appeared below the pile heads.
RÉSUMÉ: Cet article présente une analyse du comportement dynamique de la «base au sol - fondation - construction du bâtiment" en
3 dimensions qui a été menée par les moyens du logiciel de recherche scientifique (ASSR) "VESNA". En particulier, les résultats
présentés montrent l'impact des modèles élastiques, visco-élastiques et élasto-viscoplastiques sur le comportement du bâtiment sous
des charges sismiques tout en tenant compte d'un système d'isolation sismique. Tenant compte de la non-linéarité des propriétés
physiques du sol, le modèle a permis d'estimer la position des constructions du bâtiment après l'action sismique. Le modèle a
démontré que les plus grands efforts dans les pieux sont révélés en-dessous des têtes de pieux.
.
KEYWORDS: Numerical modeling, dynamic, seismic, visco-plastic model, soil base, pile foundation, high-rise building, VESNA
1 INTRODUCTION
Seismic loads often result in additional stress in the building
which may exceed forces generated by the static and wind-
related load or even cause a completely different force
distribution picture. The dynamic stress-strain state of the “soil
base - foundation - building” system is substantially different
from the static one. Results of the interaction of the engineering
constructions with the soil base are largely dependent on the
characteristics of each element. This leads to the emergence of
new zones with a maximum load (vs static loading conditions).
The difficulty of a dynamic load assessment is caused by the
necessity of a detailed analysis of the dynamic behavior of all
the elements of the system. Seismic loads usually have a wide
range of frequencies, eliminating the possibility of predicting
the possible stress state of the system during the load.
1.1
Problem definition and the finite element model.
Existing spectral methods do not provide a complete picture
of the interaction between the solid base and engineering
constructions. In addition, methods based on Vinkler’s model of
the soil foundation base can not be considered satisfactory. In
this case it is impossible to correctly take into account the
inertial forces of the soil base. Foundations under tight pinching
conditions lead to even larger errors due to the difficulty of
precisely modeling interactions within the system.
The presented article contains an analysis of a real multi-
story building, located on a landslide slope in the seismically-
active area of the Crimean Republic. The building contains 16
floors with the lowest floor occupied by parking facilities.
Load-bearing constructions consist of 220mm floor slab, an
interior load-bearing column (with elevator shaft), diaphragm
(up to the 5th floor) and columns. The ground (parking) floor
uses a solid perimeter 400mm wall. The floor slab area steadily
decreases with each floor from 900 m
2
to 300 m
2
. Columns have
a section 400x400 mm with the contour inclined in accordance
with the generatrix.
The soil base is represented by a talus layer about 10-18 m
deep with a shifted mudstone layer (about 3-5 m deep) and an
argilite foundation below that.
The initial building design called for drilling piles
(
620 мм L35 м), embedded into the argilite bedrock. Also,
taking into account the high seismic activity (up to the XIII – IX
degree by MSK-64) and overall height of the building, the
design called for a grillage slab with a thickness of 2m.
3D modeling was performed using the automotive system of
scientific research (ASSR) “VESNA”. The finite element model
consists of multi-layer soil mass and engineering constructions
(Fig. 1). The size of the soil base was selected to minimize the
effect of boundary conditions on the construction elements.
Selected dimensions included 200 x 180m area with 155m
depth under foundation.
In order to reduce boundary effects caused by wave
reflection, boundary conditions were supplemented with
absorption conditions according to the Lysmer model
(J.Lysmer, R.L. Kuhlemeyer, 1969).
Seismic load action was modeled using 3D accelerogram
taken from the set of standard synthetic accelerograms (ДБН
В.1.1-12-2006) while taking into account the lowest
eigenfrequency of the construction.
a
b
Figure 1. Finite-element model of the system “soil base - foundation –
overhead construction” (a) and of the building construction (b) .
Construction eigenfrequencies and related forms were
calculated (selected) while accounting for the possible stiff shift
