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Proceedings of the 4
th
International Conference on Seismic Retrofitting, Tabriz, Iran, 2-4 May 2012
Paper Code.4127
Seismic Retrofitting of Historical Buildings
A.Bahar
𝟏
, M.Saffari Tabalvandani
𝟐
𝟏
University of Guilan, Rasht, Iran. bahar@guilan.ac.ir
𝟐
University of Science and Culture, Rasht, Iran. M.Saffari@gmail.com
ABSTRACT
Monuments have preserved the cultural identity of ancient peoples, therefore, these valuable
structures should be retrofitted to withstand earthquakes. Note that each monument has its own
characteristics and requires special considerations depending on its features. The vulnerable parts of
important sites must be identified and recognized; finally, the procedures for retrofitting and
maintenance are presented. New technologies can effectively help retrofit historic buildings with
minimal or no changes to their exterior appearance. The main objective of this article is to present
the devastating effects of earthquakes on monuments and the methods for seismic retrofitting.
Key Words: Monument, Historical Building, Retrofitting, Earthquake Resistant.
1 INTRODUCTION
Monuments and historic buildings are the identity of a nation and the people who live in
them, showing the cultures, customs and traditions of the people who lived there many years ago.
The importance of these monuments is closely related to their age, which shows the existence of a
nation for centuries, for example “Persepolis” in Shiraz, Iran or “Ghal’e Rudkhan” and “Masuleh”
in Guilan province, Iran (Figs. 1-3).
Monumental buildings are existing structures with important cultural values (historical
meanings, typological aspects and material aspects within a general architectural interest), that is,
with valuable evidence of ancient times that deserve to be preserved [1]. In addition, the
preservation of a community's cultural heritage not only helps to protect economically valuable
material assets, but also to preserve its practices, history, and environment, as well as a sense of
continuity and identity [2]. They also help us understand the building techniques and materials of
the past [3]. Cultural heritage is affected by a primary risk, which is the direct damage caused by a
natural disaster [2]. Destructive natural disasters include earthquakes, floods, tsunamis, etc. In this
Figure
1- Masuleh, photo by M.Saffari
Figure
2- Ghal'e Rudkhan, photo by M.Saffari
Figure
3- Persepolis, photo by M.Saffari
research work, we are mainly concerned with earthquakes and their harmful effects on monuments
and historic buildings, and seismic retrofitting methods. The earthquakes we cannot predict in time
and intensity, may cause major structural damage, and the collapse of historical buildings and
monuments [3].
Local planning departments and disaster managing agencies are responsible for implementing
disaster management and urban development plans. They should be involved when heritage
conservation issues arise in a post-disaster situation, as should historical societies committed to
protecting the affected cultural assets, academic institutions entangled in heritage research, and
local government arts and cultural agents. Heritage conservation may guide by national-level
policies and public agencies, such as the Iranian Cultural Heritage Organization [2].
2 EARTHQUAKES
Research and experience give us knowledge about earthquakes and how catastrophic and
costly they can be. For example, in the last 25 years Italy has suffered casualties and severe damage
to property and cultural heritage due to earthquakes. The ratio of induced damage to earthquakes
released energy is a factor that shows how vulnerable structures in a given region are. This ratio is
much higher in Italy than in other seismic regions such as California or Japan [1]. Records of
earthquakes in Turkey also show very violent collapses of historic buildings. They prove that
monuments were ruined or partially destroyed. Looking at the history of earthquakes in Istanbul,
there were major earthquakes in which thousands of people lost their lives and buildings were
destroyed. According to the Turkish Earthquake Foundation (TDV), 13 major earthquakes occurred
in the years 325 to 1999 [3].
Iran was also affected by this phenomenon a lot. Iran is located in the earthquake belt of the
Alps and the Himalayas (Fig.4) and has experienced many catastrophic earthquakes in the past,
including the Tabas earthquake in 1978 (18,000 deaths), the Manjil earthquake in 1990 (40,000
deaths), the Bam earthquake in 2003 (40,000 deaths), and the Dahoeieh-Zarand earthquake in 2005
(650 deaths) [4].
Figure 4- Global seismic hazard map, by GSHAP
In December 2003, an Mw = 6.5 earthquake struck the ancient city of Bam in Iran, almost
completely destroying the city and its surroundings. Unfortunately, the historical monument of Arg-
e-Bam, some of which is 2000 years old, was severely damaged (Fig.5) [5]. The newly rebuilt city
of Bam, Iran, has few features of the architectural structure of the ancient city that existed before
the 2003 earthquake (Fig.6). During the reconstruction of the city, the entire landscape was
significantly altered.
Figure 5- Arg-e Bam, [5] Figure 6- New Arg-e Bam, photo by A.Mojtahedi
The changes were mainly due to pressure to speed up reconstruction through the use of
prefabricated steel frame structures and conventional building materials. Other factors that
influenced these changes were; (1) fear for the safety of the old mud-brick construction techniques,
(2) lack of skills to apply the old construction techniques in a way that would ensure risk mitigation,
(3) lack of a recognized national building code or guidelines to promote mud-brick construction
(Iran's 2800 building codes and national building regulations discourage mud-brick construction),
and, (4) the slow process of building with mud-brick techniques compared to conventional
construction techniques [6]. All these sad news cited above highlight the importance of general
awareness and certain adjustments to protect our monuments against earthquakes, and it must be
stated that earthquake prevention is one of the most important measures and works related to
sustainable development in earthquake areas and prone countries.
All these sad news quoted above highlight the importance of general awareness and certain
adjustments to protect our monuments against earthquakes, and it must be noted that earthquake
prevention is one of the most important measures and works related to sustainable development in
earthquake zones and earthquake-prone countries.
3 TYPOLOGY OF MONUMENTS
It should be noted that the construction methods, building materials and design of rural
buildings in each region generally reflect the vernacular of the houses in that particular zone.
M.A.Ghannad et al. conducted a field survey to classify the existing rural buildings in Iran.
According to them, the rural buildings were classified into the following nine groups:
Type 1: Adobe walls with wooden apartment roofs, they are very popular and usually found
in the mountainous areas in the northeast and northwest of Iran. It is the predominant type of rural
construction in Khorasan, Azerbaijan and Ardebil.
Type 2: Adobe walls with vaulted roofs are found in arid and semi-arid regions, especially the
deserts of central Iran, provinces: Kerman, Yazd and south of Khorasan.
Type 3: stone walls with wooden apartment roof especially in mountainous and cold regions
such as Fars, Azerbaijan and Khorasan.
Types 4 and 5: Wooden walls with sloping roof and cement block walls with sloping roof,
they are found on the Caspian coast in northern Iran, in provinces such as Guilan, Mazandaran and
Golestan.
Type 6: Brick/cement block walls with wooden apartment roof, usually found in regions
where wood is available.
Type 7: Brick/cement block walls with arched roof, which are found in arid and semi-arid
regions.
Types 8 and 9: Brick/cement block walls with pointed arch roof (without tie beam) and
brick/cement block walls with pointed arch roof (with tie beam), they are found almost in all rural
regions [4].
According to this classification, it can be assumed that most of the rural buildings and also the
historical buildings can be classified as wood and masonry buildings. Another research in Turkey
also confirms the existence of wood and masonry buildings vernacular architecture of this country
[3]. Our fieldwork in Guilan Province confirmed this pattern when we found rural buildings in the Masuleh
Mountains with stone and mud thatch walls and apartment wooden roofs covered with mud, even though the
new regulations do not allow the construction of traditional buildings with old building materials (Figs. 7, 8).
4 TYPES OF SEISMIC RETROFITTING
4.1. Retrofitting of masonry, stone and adobe buildings
In many historic buildings, load-bearing walls are the predominant type of construction. This
fact results from the absence of a steel or reinforced concrete skeleton in old technologies and the
accessibility of other traditional materials. Most masonry buildings have adequate load-bearing
capacity, but when out-of-plane lateral loads occur, they eventually fail. Compared to concrete,
masonry has some compressive strength but less tensile, shear and flexural strength. Therefore, the
integrity of masonry, especially plain masonry, is very poor, the load-bearing capacity is rather low,
and it is prone to cracking under external loads [13].
Figure 4- Stone wall in Masuleh, Iran, photo by M.Saffari Figure 5- Wood structure building, Rasht, Iran, photo by M.Saffari
In this type of building, the repair and reinforcement of masonry cracks is very important.
Cracks occur due to uneven settlement, thermal expansion and cold shrinkage, lack of bearing
capacity and earthquakes. The proposed methods in these cases are:
a. Grouting can be used for large walls with few cracks.
b. If the walls have cracks so severe that grouting is useless, reconstruction may be
appropriate, and in this case it is better to use compression grouting to fill the closed
cracks.
c. The retrofit method of adding local cement mortar layers with a reinforcing mat is
available when the wall cracks are densely distributed. [7]
5 TYPES OF SEISMIC RETROFITTING
5.1. Retrofitting a brick wall by adding concrete paste with mat reinforcement
When a brick wall has a serious lack of compressive or shear strength and low lateral
stiffness, retrofitting with a mat reinforcement course is very useful [7].
5.2. Strengthening the integrity of masonry structures
Experimental research and project practice have shown that adding reinforced concrete
columns, ring beams, and steel tension bars is quite effective in improving the integrity of
buildings. The methods for adding reinforced concrete can vary depending on the needs of the
project. If the original building has no structural columns, ring beams or sufficient ring beams, it
can be retrofitted by adding structural columns, ring beams or steel tie rods [7]. It is clear that
changing the appearance of historic buildings and monuments is not very acceptable, as it makes
them lose their originality and the aspect of uniqueness, but in very difficult situations retrofit
solutions are better than restorations.
5.3. Retrofitting of wooden structures
Wooden structures can better resist earthquakes [7, 3]. Therefore, the key to seismic
retrofitting of buildings with wooden structures lies in their structural systems, so the seismic
resistance of wooden frames should be improved [7]. The following methods can be used to retrofit
wood-framed buildings: Strengthening of wood structural members such as beams, columns, trusses
and purlins, etc. Strengthening and adding columns or braces, and 3. Strengthening the connections
of wood structural members [7].
6 INNOVATIVE RETROFITTING METHODS
Modern materials and new technologies offer many opportunities to improve the performance
of historic buildings without altering the fabric of the building. In this section, we present some
common techniques for retrofitting monuments.
6.1. Post tensioning
Post-tensioning is considered one of the most potentially efficient retrofit options for
reinforced concrete or masonry buildings that provide strength and ductility on the overall structure
with minimal intervention, since masonry has high compressive strength but low tensile strength.
Therefore, this method can be used to provide the necessary strength and ductility [8].
6.2. Micro piles
Micropiles play the role of the roots of a tree and can be used in foundation rehabilitation and
earthquake mitigation projects to improve foundation capacity and reduce deflections [8].
6.3. Composites
Composite jackets, carbon fiber jackets, GFRP, and FRP are used to strengthen and increase
the ductility of masonry components or concrete structures. They are useful because they provide
additional support. For example, GFRP layers can be applied to desired building components to
increase tensile and flexural strength, or fiberglass mats can be applied to conventional walls and
covered with clay straw to provide sufficient continuity, tensile strength, and integrity. [8,9] For
buildings with large seismic deficiencies, a combination of conventional and FRP strengthening
techniques may prove effective retrofit solution [10]. FRP composites can be used to retrofit wood
and masonry structures, as they are our preferred buildings due to their dominance. In a case study
on the retrofit of the Bell Tower, a historic building, it was demonstrated that the use of FRP
composites can improve the structure's performance against earthquakes [11].
6.4. Seismic isolator
Seismic or base isolation keeps buildings, bridges and other important structures fully
functional after a major earthquake. This isolation effectively reduces forces and displacements by
absorbing energy in base isolators. Seismic isolators can reduce up to 80% of the seismic energy
transmitted to the structure. These isolators are suitable for critical facilities such as hospitals,
bridges, communication centers, historic structures or buildings with valuable contents, etc. [12].
It is very notable that seismic isolators (Fig. 9) are a very acceptable choice because they do
not make any external changes to historic buildings, but only improve the connections between
foundation and building. In this context, the base isolation system (BIS) has recently been proposed
as an innovative retrofit strategy and adopted for seismic retrofit of some large monumental
buildings in the U.S. because it can efficiently improve the seismic capacity of the building with
minimal degradation of architectural features [13].
6.5. Traditional seismic isolators
Seismic isolation is not so long ago, but observations, studies and research on some rural
buildings in Iran's Guilan Province show that people understood the harmful effects of earthquakes
many years ago and constructed wooden seismic isolators to protect their traditional wooden houses
from seismic loads. The rural houses in the Guilan Rural Heritage Museum bear witness to this
wonderful design and technology. However, at that time, there was no computer-aided design or
such new technologies as we find in the construction industry today.
Figure 6- Seismic isolators
Figure 7- Traditional seismic isolators, Rural Heritage Museum, Rasht, Iran, photo by M.Saffari
7 CONCLUSION
In summary, monuments and historic buildings can be the identities of a nation and the people
who live in it. Therefore, it is critical that the historic buildings and monuments that need seismic
retrofitting are properly identified and appropriate methods are used based on the objectives. We
also need to raise public awareness so that monuments can be better preserved and maintained. The
history of earthquakes shows catastrophic collapses of buildings and monuments that have cost
many lives, but also many costs for rehabilitation, restoration and repairs in the affected areas. In
this regard, earthquake-prone countries need to make serious adjustments to strengthen and retrofit
monuments against seismic loads. Modern technologies must respect the cultural significance of
historic buildings and alter the appearance of their traditional fabric as little as possible, unless this
is impossible. New and modern technologies such as composite sheathing and seismic isolators are
good options for retrofitting monuments.
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