Transactions on the Built Environment vol 26, © 1997 WIT Press, www.witpress.com, ISSN 1743-3509
The behaviour of the monuments of Seville under
the action of earthquakes
J.L. Justo, A. Jaramillo & P. Gentil
Abstract
Seville has suffered, along its history, important earthquakes that have damaged its monuments.
The working-out of models of these monuments by the finite element method, and the probabilistic
estimate of the accelerogram, allow us to estimate the damage, and to compare it with the harm
indicated in the chronicles. We can modify the design accelerogram so as to approach the
estimated and reported damage, and, in this way, improve the estimate of this accelerogram. This
will allow to foresee the harm produced by future earthquakes, and will permit the design of
adequate strengthening. Three monuments from the XII till the XV Century have been discretized;
each of them has suffered many well documented earthquakes. The finite element program SAP
90 has been used, and the contours of maxima tensile, compression and shear stresses have been
studied. Also tests on the materials have been earned out, and conclusions about the appearance
of damage have been reached.
1 Introduction
Seville has suffered, along its history, important earthquakes that have hit its
monuments.
A study of their effects has a double interest: on one hand the comparison of
the damage produced by different tremors to a same monument may help in the
evaluation of the Intensity of each of them; on the other hand, the modeling of the
monument by the finite element method (FEM) and the estimate of the design
accelerogram allow the calculation of the harm and the comparison with the
damage described in the chronicles. Modifying the design accelerogram we can
approach the calculated and described damage, and so improve the design
earthquake. This will allow the prediction of the damage produced by future
earthquakes to our monument and the design of adequate strengthening.
We shall review the damage produced by several important quakes to three
very important monuments: the Giralda, the Golden Tower and the Cathedral.
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2 The quakes
We shall review the effect of the following quakes:
- The earthquake of August the 24th 1356. It is the oldest well documented
tremor of the Iberian peninsula. Its Magnitude may be similar to that in the
Lisbon earthquake (1755), and it has been studied by Justo and Gentil [1] who
have published an isoseismal map. The Intensity (MSK) in Seville was VIII.
- The earthquake of the 24th April 1431.
- The Carmona earthquake (5 April 1504). Gentil and Justo [2] have published
an isoseismal map. The Intensity in Seville was VIII.
- The Malaga earthquake (9 October 1680). The Intensity in Seville was VI-VII
- The Lisbon earthquake (1st of November 1755). Figure 1 compares the
isoseismals of this earthquake and those of the event of 28/2/69.
- The tremor that took place the 20th October 1883.
28-02-1969 TANG I EFN?G'BR ALTAR
Figure 1: Overlapping of the isoseismal maps corresponding to the earthquakes
of the 1st November 1755 (Lisbon) ans 28th February 1969 (Elmrabet et al. [3]).
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459
-
The Andalucian earthquake of 25 December 1884. The Intensity in Seville was
V to VI (Gentil [4]).
- The earthquake of 28 February 1969 (fig. 1). The Intensity in Seville was VI
(Gentil [4]).
3 Damage to the monuments
Only three monuments of Seville will be reviewed here:
1 The Giralda was constructed in brick and stone as the minaret of the main
mosque of Seville, and was ended in 1198 as indicated in the left hand side of
figure 2. An inside ramp allows the ascent to the top of the tower. The golden
balls at the upper part of the tower fell down during the earthquake that
occurred in 1356, when Seville was already under the Christians. The tower
was provisionaly repaired as indicated at the right hand side, and after the
restoration of Hernan Ruiz acquired the aspect indicated at the centre, when it
reached a height of 93,93 m including the upper bronze figure.
a)
b)
Figure 2: States of the Giralda at different times:
a) At the end of construction (1198) as observatory and alminar
b) After the restoration of Hernan Ruiz (1568) and the latter of 1890.
c) After the restoration subsequent to the fall of the balls produced by the
earthquake of 1356.
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2. The Golden Tower (figure 3) was constructed in 1221 with only the two lower
bodies and incorporated into the wall of defence of Seville. It is another
outstanding example of the Almohade architecture. The third and upper body
was added in 1760 with the restoration that followed the Lisbon earthquake.
The height is, at present, 36.75 m
One pillar of the upper
tower has fallen and
another is tumbling.
The upper and lower vaults
are broken and loosened.
The walls are also broken
from the soil up to the
upper tower.
Figure 3: The Golden Tower today, showing damage produced by the Lisbon
earthquake.
3. After the conquest of Seville by the Christians in 1248 the main mosque was
converted into a cathedral. In 1434 the state of the old mosque was so bad
(owing in part to the earthquake of 1356) that it was decided to build a new
cathedral. The construction took one century. It is the larger gothic cathedral
and the third larger church in the world (after St. Peter in Rome and St. Paul
in London).
We are going to review now the damage produced by different earthquakes to
these three monuments.
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3.1. The Giralda
The balls that topped the tower were joined by a central iron shaft, fixed to the
upper part of it, weighting according to different accounts from 575 up to 1725 kg
(Jimenez [5]). The shaft resisted the drive of the wind during one century and a
half, which indicates that it was properly built. This stem was cut off by the
earthquake that occurred in 1356, and the balls fell down. The chronicle of
Archbishop Don Rodrigo [6] indicates that "the tower nearly fell".
Galvez [7] refers to the earthquake that occurred in 1504 in the following
terms: "The tower moved so strongly from side to side that the bells rang up to five
or more times, and the four corners of the tower split; and some people say that an
Angel was seen embracing the tower to avoid its fall". This account was written
between the 21st June and the 26th July 1504, about three months after the
earthquake, and the fantastic description about the Angel might reflect the awe
produced by the earthquake.
Before the Lisbon earthquake, the aspect of the tower was as indicated in figure
Ib. There are two detailed accounts of the state of the tower after the earthquake
[4,5]. Thefirstis written the 3rd of November, two days after the earthquake, and
the main conclusions are collected in figure 4. When the report was written, the
main shock and the former five aftershocks had occurred. The second report has
the date of 15 December, when all the aftershocks had occurred. It coincides with
the former account but is much more detailed and explains the damage (the pillars
had fallen or were leaning) and repair of the last but one body.
The tower is a structure type B according to the M.S.K. scale. During the 1356
earthquake there was fall of free-standing elements (type 3 damage). In the 1504
earthquake large bells rang and cracks in the walls appeared (type 3 damage). The
Intensity, in both cases, might range from VII to VIII. Finally the Lisbon
earthquake produced cracks in the walls and loss of links between different parts
of the construction; this joined to what we know about the destructive effects of
the earthquake in the rest of Seville (Gentil [4]) gives clearly Intensity VIII.
The Andalucia earthquake of 1884 produced some damage [4] and the event
of 28/2/69 produced the fall one of the bronze white lilies (fig. 2 and 4). This is
class 1 damage.
3.2. The Golden Tower
We do notfindany account on damage to the tower up to the Lisbon earthquake
Notwithstanding in the report made in 1757 about the damage produced by this
event it is indicated that "several repairs have been made in the past to the low and
high vaults... and the tower is hooped and tied".
In September 1757, the tower is visited jointly by three Master builders.
However they do not agree in their conclusions and present two different reports.
One Master builder describes the harm shown in figure 3, that he ascribes to both,
the "weakness of its foundation" and the new cause due to the earthquake. He
recommended the demolition of the tower, owing to its state and also adducing
urbanistic reasons. Fortunately the two other Master builders maintained that this
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Structural Studies, Repairs and Maintenance of Historical Buildings
outstanding monument could be repaired. The structure is type B, the harm described corresponds to class 3 of the M.S.K. scale, and the Intensity assigned is VIII.
During the 28/2/69 earthquake, the small dome that tops the tower was
displaced from its base (I = VI).
Some tilting
Little damage
The la£>tL_but one body next to ruin
white lily
NO DAMAGE
The four main arches of the bellfry
and the masonry vaults that cover
them are next to ruin
the four facades, from the first
row of balconies till the bellfry
have split, so that the inside ramp
is, in several parts, next to ruin
Figure 4: Section of the Giralda showing the conclusions of the report of the 3rd
of November 1755.
3.3. The Cathedral
Gentil [4] describes the damage produced by the earthquakes of 1481 and 1504 to
the cathedral that was, then, under construction.
During this last quake, the building suffered severe harm, and cracked in many
parts. Two years later, the 10th of October 1506 the dome (figure 5) was ended,
and the church was finished in May 1507. As the quake had lessened the stability
of some pillars, the dome fell the 28th December 1511, wrecking the vaults of the
transept and the choir (figure 5). In a report made in 1513 on the effects of the
earthquake it is proposed to repair the affected pillars, specially pillar PI (figure 5).
The damage produced by the Lisbon earthquake has been described, in detail
by Gentil [4]: damage in the diagonal arches, in front of the Chalices Chapel and
Saint Christopher gate (figure 5), in both cases broken and loosened stones;
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pyramids and balustrades from the terrace have fallen on the vaults, which exhibit
harm in the transept, in the choir entrance and elsewhere. The balustrade of the
terrace of the attached church of El Sagrario is partly ruined.
Figure 5: Plan of the cathedral.
D = dome
T = transept
C = choir
CH = Chalices chapel
S = church of El Sagrario SC = Saint Christopher gate
The structure is type B. The damage may be class 4 for the 1504 earthquake
and class 3 for the Lisbon earthquake, and the Intensity VIII in both cases.
4 Aplications of the finite element method
The dynamic FEM SAP90 has been used. The former calculations have been made
assuming plane stress with the Giralda, Golden Tower and Cathedral. The EW
component of the acceleration register in Lisbon of the earthquake that occurred
the 28th February 1969 has been used as input. As indicated in figure 1 this
earthquake was quite similar to the Lisbon event, although with much less
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Structural Studies, Repairs and Maintenance of Historical Buildings
Magnitude. Unfortunately we have no register in Seville. A factor of 5.7 was
applied to the accelerogram to arrive to the accelerogram that would correspond
to Intensity VIII according to our preliminary seismic risk studies.
Figure 6 shows the simplified discretization of Giralda, some openings have
been eliminated, and so as to take this into account the modulus of Elasticity of the
corresponding elements was consequently decreased. Figure 7 shows the
discretization of the Golden Tower; it has been simplified establishing a symmetry
which actually is not complete (compare with figure 3). Finally figure 8 shows the
discretization of the cathedral.
Figure 6: Discretization of the Giralda.
Respect to the Giralda, two dynamic studies have been carried out. one conside
ring the tower fixed to the ground surface, and the second discretizing also a block
of foundation under the tower (figure 9). In this second case the displacements are
larger and the stresses smaller. A modulus of 3.158 MPa has been measured.
The following outputs have been obtained in the three monuments: maximum
displacement, contours of major and minor main stresses, horizontal and vertical
normal stress and shear stress. Table 1 collects the main results.
The maxima compressions are always allowable.
The results are encouraging, but there is still much work to be done. We have
made three-dimensional calculations of Giralda and Golden Tower, that will be
Transactions on the Built Environment vol 26, © 1997 WIT Press, www.witpress.com, ISSN 1743-3509
Structural Studies, Repairs and Maintenance of Historical Buildings
presented in a fothcoming paper.
Figure 7: Discretization of the Golden Tower
Figure 8: Discretization of the Cathedral
Table 1: Main outputs (maxima)
Monument
Horizontal displacement Tensile stress Shear stress
mm
kPa
kPa
Giralda
Golden Tower
Cathedral
a = allowable
423
13
15
2340 (e)
206 (a)
693 (e)
e = excesive
1030 (e)
124 (a)
674 (e)
465
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Figure 9: Vibration of the Giralda assuming a deformable block of foundation
References
1. Justo, J.L. & Gentil, P. El terremoto peninsular del 24 de agosto de 1356.
Ingenieria Civil, 1990, 74, 34-40.
2. Gentil, P & Justo, J.L. Terremoto de Carmona de 1504, Sismicidad Historica
de la Peninsula Iberica, pp. 9-16, Asociacion Espanola de Ingenieria Sismica,
Madrid, 1983.
3. Elmrabet, T , Levret, A., Ramdani, M & Tadili, B Historical seismicity in
Morocco: Methodological aspects and cases of multidisciplinary evaluation,
Seismicity, Seismotectonics and Seismic Risk of the Ibero-Maghrevian Region,
pp. 115-129, Instituto Geografico Nacional, Madrid, 1991.
4. Gentil, P. El Riesgo Sismico de Sevilla, Servicio de Publicaciones de la
Universidad de Sevilla, 1989.
5. Jimenez, A & Cabeza, J.M*. Turns Fortissima, Colegio Oficial de
Aparejadores, Sevilla, 1988.
6. Cronica del arzobispo don Rodrigo, continuada desde 1242 a 1395. Biblioteca
Colombina, Sevilla.
7. Ortiz de Zuniga, D. Anales Eclesidsticos y Seculares de la mny Noble...
Ciudadde Sevilla, 5 vol., Madrid, 1975.