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12th International Conference on Structural Analysis of Historical Constructions
SAHC 2020
P. Roca, L. Pelà and C. Molins (Eds.)
POINT-LOAD TEST ASSESMENT AS STUDY OF THE SEISMIC
VULNERABILITY OF THE ADOBE BUILDINGS IN JOJUTLA DE
JUÁREZ, MÉXICO, AFTER THE 2017 EARTHQUAKES
A SANCHEZ1*, E. M. ALONSO1,2 AND J. A. BEDOLLA3
1Programa Interinstitucional de Doctorado en Arquitectura
Faculty of Architecture, Universidad Michoacana San Nicolás de Hidalgo
Gral. Francisco J. Múgica S/N, 58040 Morelia, Michoacán, México
e-mail: adria.sanchez.9@hotmail.com
2 Materials Department, Faculty of Civil Engineering, Universidad Michoacana San Nicolás de
Hidalgo,Gral. Francisco J. Múgica S/N, 58040 Morelia, Michoacán, México
email: eliamercedesalonso@gmail.com
3 Faculty of Architecture, Universidad Michoacana San Nicolás de Hidalgo
Gral. Francisco J. Múgica S/N, 58040 Morelia, Michoacán, México
email: bedollaalberto@gmail.com
Keywords: Adobe Masonry, Point-load test, Vernacular architecture, Seismic analysis
Abstract. The 2017 Puebla Earthquake on September 19 struck a big part of México causing
the loss of historic buildings in several states, being the state of Morelos one of the most
damaged in the whole country. Jojutla de Juarez was the most affected locality of Morelos
presenting important structural damages or total collapse in the built heritage, being the
traditional earthen buildings, made of adobe bricks, the most vulnerable buildings to seismic
efforts.
Some of the causes which contributed to the poor behaviour of the buildings were the
improper handling of the constructive systems and materials, the insufficient resistance of the
structures and the problems derivate by the foundations. The adobe houses of Jojutla
presented a mixture between the traditional building techniques and industrial materials like
concrete, cement and steel; also with irregular heights and plant layouts and inadequate
connections between the walls and foundations and roofs, resulting into a higher seismic
vulnerability when the earthquake impacted. Also the adobe bricks presented irregularities in
its composition and use of additives which resulted in completely different typologies and the
loss of the traditional construction techniques.
There was conducted a study to determine the earthquake resistance of the adobe bricks of
the houses in Jojutla, considering that the remaining structures were severely damaged and a
whole study of the seismic vulnerability would not be possible due the loss of the physical
buildings. The granulometry and composition of the adobe samples of the buildings were
determined as well as the natural aggregates like straw and its proportion. Also the
compressive strength of the pieces was tested by two methods: the compression test and the
point-load test, in order to obtain the indicative values which could be compared with other
patrimonial and vernacular study cases.
A. Sánchez, E. M. Guzmán, J. A. Bedolla
2
It was observed that the construction materials and therefore the adobe bricks of Jojutla
presented different compositions which caused an unpredictable behaviour during the
earthquake of September 19th. Loss of the traditional earthen construction techniques has
provoked a poor manufacture of the adobe houses, creating new scenarios where people do not
trust in the material and substitutes the earthen architecture by modern materials. The conduction of
point-load tests could be an alternative to study the mechanical properties of patrimonial samples
before its disappearance.
1 INTRODUCTION
México is a country with an important seismic history, experiencing huge earthquakes of
great magnitude which had a big impact in its population. The nearest states to the Trans-
Mexican Volcanic Belt, the Cocos Plate, Rivera Plate and Pacific Plate present high seismic
hazards, being prone to experiment earthquakes which had caused big damages in the cultural
heritage of México and its population. In the month of September of 2017 the country
suffered two big seismic events which had an enormous impact on the affected regions.
The first earthquake struck on September 7th of 2017 in the Gulf of Tehuantepec, near the
Mexican state of Chiapas, with a magnitude of 8.2 being originated in the Cocos Plate. This
natural disaster was marked by the multiple aftershocks which were detected on the following
days, causing damages mainly in Chiapas and Oaxaca. [1] (Servicio Sismológico Nacional,
2017) On the other hand, the second earthquake was reported by the Servicio Sismológico
Nacional of México on September 19th with a magnitude of 7.1 and a detected epicentre in the
boundaries between the states of Puebla and Morelos, located 12 Km southeast Axochiapan,
Morelos. [2] (Servicio Sismológico Nacional, 2017) In this case, the most affected states were
Puebla, Mexico State, Morelos, Tlaxcala, Guerrero and Mexico City.
Figure 1: Seismic intensity map of the 2017 Puebla Earquake. Source: Atlas Nacional de Riesgos, map
generated by Earthquake Institute of the National Autonomous University of México (UNAM)
The impact of the 2017 Puebla Earthquake on the region was especially destructive to the
colonial buildings which are part of the Mexican cultural heritage, resulting in severe
damages mainly in the states of Puebla and Morelos. In Morelos, the Instituto Nacional de
A. Sánchez, E. M. Guzmán, J. A. Bedolla
3
Antropología e Historia (INAH),
1
reported a total number of 259 buildings affected, suffering
damages classified as severe in the 47% of the whole ensemble. [3] (Meli Piralla, 2018) The
study case of Jojutla de Juarez, was the most affected locality of Morelos presenting important
structural damages or total collapse in the built heritage, being the traditional earthen
buildings, made of adobe bricks, the most vulnerable buildings to seismic efforts. (See Fig. 2)
1.1 Background
Despite the great impact of these events, the seismic memory of the population is short, the
state of alert only remains for a short period of time following the earthquake, disappearing
gradually, as the disaster ceases to seem an immediate danger. [4] (Blondet, 2011) In the
study case of the Estate of Morelos, the closest seismic events which had a deep impact in the
society were the 1985 Mexico City earthquake and the 1999 Tehuacan or Central Mexico
earthquake, with meaningful consequences on the architectonic and cultural heritage of the
region; however these two remained distant in the collective memory of the population. [5]
(Campos Goenaga, 2018)
The destructive effect in the architectonic and cultural heritage was translated into the
physical destruction of the buildings and monuments, being especially remarkable the
damages in the Mexican colonial churches, which are very meaningful elements for the local
culture and the identity of the communities. [5] Due to the importance of these constructions,
the damages were analysed, full-filling appropriate research jobs to understand the seismic
response of these structures. [6] (Díaz Fuentes, Baquedano Julià, D'Amato, & Laterza, 2019)
Figure 2: Municipality of Jojutla de Juárez after the 2017 Puebla Earthquake
Nonetheless, despite the reconstruction and restoration work done by the authorities and
responsible entities, the traditional housing, in particular the typologies with adobe walls,
were completely ignored. All the resources were invested in the restoration of the ancient
churches and monuments and the rehabilitation of homes and public structures as well as the
building of new housing with modern materials. Notwithstanding the great consequences for
the vernacular architecture, the organisations in charge decided to discredit this local culture,
1
The INAH, Instituto Nacional de Antropología e Historia, is the Mexican federal government bureau
established in 1939 to guarantee the research, preservation, protection, and promotion of the prehistoric,
archaeological, anthropological, historical and paleontological heritage of México.
A. Sánchez, E. M. Guzmán, J. A. Bedolla
4
calling adobe bricks as an unsafe material. [7] (Guerrero Baca, 2019) The result of these
disputed resolutions turned into the abandonment of the traditional techniques and the
reconstruction of the localities of the region with prefabricated concrete blocks and ceramic
brick walls and roof structures of metal casing.
1.2 Case study
The state of Morelos has a strong building tradition which can be observed from tis
vernacular architecture, being the adobe housing one of the most representative typologies
found. This architecture has resisted over time, withstanding important natural disasters. Most
of these traditional structures present earthquake-resistant features through several properties
in the materials, form, dimensions and functionality of the buildings. [8] (Guerrero Baca,
Meraz Quintana, & Soria López, 2014).These earthen constructions have suffered over time
the struck of historic earthquakes which had a big impact on the built heritage, withstanding
thanks to the qualities of the local architecture.
In the study case of Jojutla de Juarez, the traditional adobe houses of the locality were
fairly modified over the years, changing the ancient materials and construction systems for
modern ones; the vast majority of the buildings had important alterations to its morphology
too. Besides, the conservation and maintenance of the constructions were precarious, as a
result of the lack of knowledge and interest of the vernacular technologies, which always
responded to the natural environment. [9] (Jorquera, 2014) On the other hand, the traditional
houses which conserved their morphology, dimensions, materials and techniques; had a better
performance agains the 2017 Puebla earthquake, suffering non significant damages, as it has
been demonstrated in posterior research works. [7] [10] (Ríos Ramírez & Porcayo Victoriano,
15-18 de octubre de 2019)
Jojutla de Juarez shown a micro-seismic-regionalisation, especially in some of its colonies
or neighborhoods. The historic centre of the town was widely damaged, suffering important
losses in the built heritage, like the churches and main institutions, as well as the public
housing. The large majority of the adobe houses were located in the downtown colony, which
was the most affected zone with the Emiliano Zapata colony, this one was re-built more
recently. Both zones experienced severe damages, including the collapse of many buildings
and structures. [11] (del Campo Alatorre, Ochoa González, & Álvarez Partida, Abril 2018)
Figure 3: Damaged adobe building with mixed construction techniques
A. Sánchez, E. M. Guzmán, J. A. Bedolla
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2. METHODOLOGY
In order to study the seismic disaster affectation on the adobe buildings of Jojutla de
Juárez, several samples were collected to work with them. Considering that the remaining
structures were severely damaged and a whole study of the seismic vulnerability of the would
not be convenient due the loss of the traditional buildings, it was decided to apply these two
different destructive tests in order to obtain the indicative values of mechanical resistance,
which could be compared to other patrimonial and vernacular study cases.
2.1 Samples taking and soil studies
There were collected 11 representative shards of adobe bricks from 11 different traditional
houses of the downtown of Jojutla. These samples were collected before the demolition of the
buildings, which was shortly after the field trip. There also were taken samples of soils of the
region, concretely in the extraction area for the manufacture of adobe bricks and ceramic
bricks. The region is recognized by their rice production, even the Morelos rice is a trade
mark, and of course they have plenty of water. Taking into account the emergency state of
Jojutla de Juarez and the situation between the inhabitants and their damaged buildings, the
sample collection responded to the criteria of taking the maximum amount possible of
material before the demolition of the remaining houses and the consequently disappearing of
the earthen architecture. All the samples were classified by the Unified Soil Classification
System (USCS) to obtain the composition of the adobe bricks and the type of soils used for
construction materials in the region. There was also obtained the fibre percentage, straw in the
case of study, in each one of the adobes.
2.2 Compressive strength test
In order to performance the compressive strength of the samples, these had to be prepared.
Due to their precarious state most of them were found between the building remains of Jojutla
de Juarez, not all the originals were qualified for the compression strength test, as they didn’t
accomplish the minimum dimensions or were extremely inconsistent. From the 11 patrimonial
samples only 6 could be eligible for the mechanical characterisation trials, needing a previous
preparation. For being able to perform the analysis the samples were carved till obtain
appropriate dimensions, and later capped with melted sulphur, due to the irregularities
presented in their surface. Once prepared, they were introduced in the Tinius Olsen Universal
Test Machine to obtain their ultimate resistance to compressive strength.
Figure 4: Preparation and compressive testing of the adobe samples
A. Sánchez, E. M. Guzmán, J. A. Bedolla
6
2.3. Point-load test
Point-load test allows determining mechanical resistance of non-carved samples of several
types of masonries and rocks, both: natural or artificial, being especially designated for the
study of rocks. [12] (ASTM Standards ) Nevertheless, the materials researched in this work
are adobe bricks, being a first approximation to the characterisation of solid clay fragments
with this technique.
The equipment used for the point-load test was Digital rock strength index apparatus 100
kN cap of Controls Group, which has the advantage of being a portable equipment which
allows to test samples both in the laboratory or in field research, with the only preparation of
the measurement of each one of the fragments before performing the test.
The samples were tested under Compression strength, after cracking; the fragments were
also submitted to point-load test applying an incremental load leading to the failure of the
fragments, to compare the data. The equipment gave a rupture load value which needed to be
transformed by an equation system to the ultimate uniaxial compression resistance. The
methodology followed was according the standards and previous research works performed in
the materials laboratory. [12] [13] (Navarrete Seras, y otros, Mayo 2014)
Figure 5: Adobe sample in the point-load equipment
The point-load index without correction factor is calculated with the following equation:
Where:
Is = Point-load index, MPa.
P = Maximum load, kN.
De = Equivalent core diameter, mm.
The resistance index value (is a non-corrected value which varies depending on the
thickness of the fragments tested. To obtain the corrected resistance index ( it is
A. Sánchez, E. M. Guzmán, J. A. Bedolla
7
necessary to multiply the first index by the correction factor:
Depending on the size of the fragments, there will be used two different correction factors.
The election between one or the other will be the proximity of each sample to the standard
value of 50 mm. [12] For the specimens near to this 50 mm thickness (D), the correction
factor is calculated with the following equation:
Instead, when calculating fragments with thickness distant of 50 mm, the following
formula will be used:
The estimation to the compressive strength or UCS (Uniaxial Compressive Strength) is
obtained with the following equation:
The value is the main purpose which the point-load test follows and it is wanted to be
compared with other values of mechanical resistance obtained by other trials. Other
interesting aspect of the test is to observe the rupture mode of the fragments, finding relations
between the composition of the adobes, their morphology, size, fibres distribution or
aggregates. (See Figure 6)
Figure 6. Fracture in adobe fragments with point-load equipment
3. RESULTS
Figure 7 shows the classification of all the samples, including the adobes and the soils of
the region, by the Unified Soil Classification System (USCS); while Table 1 shows the results
of the soil classification and the grading of each one of the specimens which were subdued to
the mechanical analysis. M1 and M13, the two soil samples from the clay material quarry
were classified as high plasticity clays, while the adobes vary from clays of low plasticity to
mods. The low plasticity was probably due to the stabilization with other materials, for
example, lime was found in some specimens.
A. Sánchez, E. M. Guzmán, J. A. Bedolla
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Figure 7: Plasticity graphic and position of the adobes and soil samples
Table 1: USCS Classification of the specimens
Material
USCS Classification
M2
CL
Clay of low plasticity
M4
CL
Clay of low plasticity
M5
ML/OL
Silt / Organic silt
M9
ML/OL
Silt / Organic silt
M11
ML/OL
Silt / Organic silt
M12
ML/OL
Silt / Organic silt
The sieve analyses also permitted to separate and classify the mineral grains and vegetal
fibres in the adobes. It was calculated the percentage of straw, the only fibre used in this case,
from the weight (See Table 2). Some of the adobes did not have any amount of straw (sample
5) or an insignificant percentage (sample 9) or other fibres as reinforcement or strategy to
decrease the shrinkage, situation which contributes to expect the lower mechanical values
obtained.
Table 3: Fibre percentage results
Sample
Fibre percentage (% Weight)
2
0.38
4
0.68
5
-
9
0.06
11
0.27
12
0.23
A. Sánchez, E. M. Guzmán, J. A. Bedolla
9
3.1 Compressive strength
The mechanical resistance varies between 5-13 Kg/cm2, being the average of the adobe
bricks 7.26 Kg/cm2, a low value compared to the common resistance of the adobes, which
can also be very variable. [14] [15] [16] The proportion of the fibres does not seem to have a
direct relation with the resistance, as samples 5 and 9 had the lowest amount of straw,
otherwise reached some of the highest values during the test.
Table 3: Compressive strength results
Sample
Resistance (Kg/cm2)
2
5.97
4
9.35
5
12.33
9
5.08
11
9.13
12
7.09
3.2. Point-load
The point-load test allowed to trial some of the samples more times than the compressive
test, because fragments of lower dimensions can be tested with the equipment. The values
obtained were more variable with an extended range, being the average of all the adobes 5.30
Kg/cm2, lower than the compression strength results.
Table 4: Point-load values of the adobe samples of Jojutla de Juárez
Sample
σ (kg/cm2)2
2
3.24
4
3.64
5
5.78
9
4.62
11
3.91
12
2.52
The compressive strength and point-load values were compared (See Figure 8) in a graphic
to observe the correlation between the two tests. Considering the compressive strength values
slightly higher, most of the samples shown a lineal reciprocity, while some shown deviation.
2
The final value of the uniaxial compression resistance has been converted to kilogram per square centimetre.
The original value was found in megapascals.
A. Sánchez, E. M. Guzmán, J. A. Bedolla
10
Figure 8: Correlation between the Compressive strenght and the point-load tests
4. CONCLUSIONS
Point-load test could be a useful analytic tool for measuring the mechanical resistance of
patrimonial samples found in emergency situations like earthquakes or other natural hazards.
In these cases, where the specimens are corrupted, this test allows the characterisation of non-
complete fragments, like the ones found in Jojutla de Juarez, Morelos. It could be a support
for research works where it is impossible to access to the original constructive system. The
samples could be tested in situ, which is a great benefit, nevertheless it is recommended to
compare the values obtained with other mechanical resistance studies to achieve a more
complete research.
The mechanical resistance values obtained with the compression strength test and the
point-load test are lower than values from other researches which similar characteristic cases
in México. [7] [14] [15] [16] (Arroyo Matus, Sánchez Tizapa, & Catalán Quiroz, 2013) (Cruz
Farrera, 2018) (Ordaz Zapata, 16 de Mayo del 2019). These indicators show that the adobe
blocks of Jojutla presented a poor performance and manufacture. Also, the soil and grain size
classification of the adobes show insufficient or absent amount of fibres, however there
weren’t found significant proportions of sand or gravel in the pieces. The Figure 7 shows how
the healthy clays of the soil samples are in very different zone of the graphic than the adobe
samples. To diminish the plasticity of the adobes from high to light there could have been
some type of stabilization with local materials.
Nevertheless, this low values didn’t justify for itself the bad seismic behaviour of the
dwellings, which were very vulnerable due to multiple factors like the lack of reinforcements
and confinement of the structures, the incompatibility between the construction materials or
the poor maintenance of the buildings among others. In the study case, all these conditions
converged, resulting into the loss of most of its architectural heritage and infrastructures. The
adobe walls did not have any reinforcement, being this method unknown but the local
population, which prefer to substitute the traditional materials for modern ones representing
for them a better social status.
A. Sánchez, E. M. Guzmán, J. A. Bedolla
11
ACKNOWLEDGEMENTS
The authors acknowledge the Materials Laboratory “Ing. Luis Silva Ruelas” of the Faculty
of Civil Engineering of the UMSNH for the equipment support, the Postgraduation
coordination of the Faculty of Architecture of the UMSNH, the economic support given by
CONACYT and CIC-UMSNH, and the technical support of B.C.E.: D. Preciado Villicaña
and M. Ruiz Mendoza.
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