Archaeoseismology and Palaeoseismology in the Alpine ... - Tierra

1 st INQUA‐IGCP‐567 International Workshop on Earthquake Archaeology and Palaeoseismology
DYNAMIC RESPONSE OF SIMPLE STRUCTURES
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K.G. Hinzen (1)
(1) Earthquake Geology Group, Cologne University, Vinzenz‐Pallotti‐Str. 26, 51429 Bergisch Gladbach. GERMANY.
hinzen@uni‐koeln.de
Abstract: Two discrete element models, a three‐part structured column and a 52‐block wall, with the size of archaeological remains found in
Susita, Israel, and Selinute, Italy, are used to study principal aspects of the dynamic behaviour during earthquake related ground motions.
Systematic variation of frequency and maximum amplitude of ground motion shows that the impact pattern of a simply structured,
uncemented wall reveals limited information about the nature of the ground motion. When activated by modified measured earthquake
ground motion, the column model exhibits chaotic behaviour similar to coupled pendulums. Very small changes in initial conditions and/or
time‐dependent input forces produce unpredictable behaviour. The longer the input motion lasts, the more complex‐structured the resultant
ground motion becomes. Knowledge of the mechanics and dynamics of building elements typical for classical archaeological structures is an
essential tool to test the seismogenic hypothesis of documented damages.
Key words: Column, Block Wall, Discrete Element Model, Archaeoseismology.
INTRODUCTION
One of the main challenges for carrying out archaeo‐
seismic field studies is the deduction of damage scenarios.
Even for cases that seem obvious concerning the nature
of the damaging process, all other possible scenarios have
to be taken into account. In order to further understand
the reaction of archaeologically excavated structures to
external forces such as earthquakes and other natural
dynamic or anthropogenic sources, we studied simple
structural elements.
Here we present some results from the investigation of
simple columns and block walls motivated by the toppled
columns of the so‐called ‘cathedral’ in Susita (Fig. 1a)
above the banks of the Sea of Galilee and the toppled
block wall of the Triolo temple in Selinute (Fig. 1b), Sicily.
We used similar‐sized structural elements for the basic
model.
MODELING PROCEDURE
Several previous studies have shown that much can be
learned from numeric experiments with block structures
using finite and discrete element techniques (i.e. Augusti
and Sinopoli,1992; Konstantinidis and Makris, 2005;
Psycharis, 2007; Hinzen, 2009). While finite element (FE)
models, a standard in civil engineering, are able to predict
dynamic stability and failure limits, discrete element (DE)
models are suitable for modelling post failure movements
of building parts. In archaeoseismology we are forced to
deal with the ‘final result’ of the damage process,
(a) (b)
Fig. 1: (a) Row of toppled columns of the ‘cathedral’ in Susita,
Israel (Photo: Hinzen); (b) fallen block wall of the Triolo
temple at Selinute, Sicily (from Bottari, 2008)
therefore the consideration of post failure movements of
building parts is of special interest and speaks for the use
of DE models. However, this limits the analysis to
situations where the elastic properties and material
strength are not crucial as for free standing columns and
block structures without mortar or complex clamping
devices. These are ideal candidates for DE modelling.
The aim of this study is the evaluation of the principal
behaviour of simple structures, not the development of
appropriate scenarios for the two archaeological sites.
Therefore, only rough measures were taken from
photographs and published plans of the church columns
and the temple wall and non site‐specific ground motions
are used.
Column Model
Fig. 2a shows the column model in two versions, (1)
completely rotational symmetric with round pedestal and
capital and (2) with square base of the pedestal and
capital top like those in Figure 1a. Total height is in both
cases 5.8 m with contributions of 0.3, 4.7 and 0.8 m from
the pedestal, the shaft and the capital, respectively. With
a density of 2.7 Mg/m 3 , the weight of the three parts is
490, 3570, and 760 kg. Joints between the column parts
and between the pedestal and the base block have six
degrees of freedom. Contact forces are of stick slip type
with static and dynamic coefficients of 0.7 and 0.6,
respectively and a contact frequency of 200 Hz.
(a) (b)
5.8 m
0.60 m
3.25 m
5.55 m
Fig. 2: Discrete element model of (a) rotational symmetric
three part column (left) and a column with square pedestal
and capital (right); (b) a 52‐block wall.