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Roofs covering buildings in the city of Bam, Iran prior to the earthquake of 26 December 2003 can be categorized into three main groups: traditional masonry dome or vault, steel I-beam jack-arch system, and concrete beamhollow block system. The collapse of nonengineered masonry roofs and floor slabs during the earthquake was the single largest contributor to the large number of fatalities. This paper discusses the seismic performance of each type of roofing and their strengths and weaknesses. The poor seismic performance of traditional domes and vault roofs and unanchored jack-arch slabs are noted and the seismic merits of the anchored jack-arch slabs and concrete beam-hollow block slabs are discussed.
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Performance of Building Roofs in the
2003 Bam, Iran, Earthquake
Mahmoud R. Maheria
Roofs covering buildings in the city of Bam, Iran prior to the earthquake of
26 December 2003 can be categorized into three main groups: traditional
masonry dome or vault, steel I-beam jack-arch system, and concrete beam-
hollow block system. The collapse of nonengineered masonry roofs and floor
slabs during the earthquake was the single largest contributor to the large
number of fatalities. This paper discusses the seismic performance of each
type of roofing and their strengths and weaknesses. The poor seismic
performance of traditional domes and vault roofs and unanchored jack-arch
slabs are noted and the seismic merits of the anchored jack-arch slabs and
concrete beam-hollow block slabs are discussed. DOI: 10.1193/1.2098859
Unreinforced masonry buildings with load-bearing walls or lowrise steel-framed
buildings constituted the majority of buildings in the city of Bam at the time of the
earthquake. The unreinforced masonry buildings were roofed by either traditional ma-
sonry domes or vaults, or nonengineered, unanchored, jack-arch flooring systems. The
lowrise steel-framed buildings were mainly floored by anchored jack-arch slabs. In some
of the more recently constructed buildings, floors consisted of concrete beam-hollow
block slabs.
A large number of buildings in the older quarters of Bam were traditional unrein-
forced masonry structures with masonry dome or vault roofs. These buildings are gen-
erally characterized by weak, brittle materials, weak element connections and excessive
weight. Construction materials and techniques have remained unchanged for hundreds
of years. Beginning around the middle of twentieth century, a new type of floor con-
struction in the form of the steel beam jack-arch slab was introduced into Iran from Eu-
rope. The new flooring system, considered a nonengineered construction, became very
popular in Iran such that the majority of existing buildings in provincial towns and vil-
lages and a vast number of buildings in Tehran are floored with this type of construction.
In the jack-arch flooring method, a number of parallel steel I-beams are placed di-
rectly on the load-bearing walls at between 80 cm to 1.0 m spacing and spanning from
one wall to the other. The space between the two adjacent I-beams is then filled with a
series of shallow brick arches Figure 1. The process is repeated until the whole slab
area is covered. A layer of lime-clay mortar or concrete is then placed on the brick
arches to create a flat surface. The slab is subsequently plastered underneath to create a
aProfessor of Civil Engineering, Shiraz University, P.O. Box 71345/1676, Shiraz, Iran; e-mail:
Earthquake Spectra, Volume 21, No. S1, pages S411–S424, December 2005; © 2005, Earthquake Engineering Research Institute
at ceiling. Due to a number of advantages including ease of construction, speed, and
low cost, the jack-arch system is still popular in Iran Maheri 2004.
The jack-arch ooring system is stable under normal static conditions. The brick
arches transfer the gravity loads, mainly in compression, to the supporting steel beams.
The load is then transferred via the steel beams in exure and shear to the load-bearing
walls. However, reports of slab damage and collapse in recent earthquakes in Eastern
Europe and Iran Razani and Lee 1973; Maheri 1990, 1992, 1998reect the weakness
of the unanchored slab under dynamic loading. To overcome this problem, it is sug-
gested that the slab beams be joined together at their ends by either transverse beams or
by steel tie bars Moinfar 1968. This form of anchored jack-arch slab has a better seis-
mic response because the relative movements of the slab beams are somewhat prevented.
Figure 1. aGeneral layout of steel beam, jack-arch ooring system, and banchored jack-
arch slab made with lightweight perforated bricks.
In recent years, there has been a notable trend away from the jack-arch construction
in favor of the more robust concrete beam/hollow block oors. This ooring system is
similar in principle to the steel beam jack-arch system, but uses different materials and
construction techniques. In this method, the steel I-beams are replaced by a small section
of pre-cast reinforced concrete beams. The concrete beams are, however, placed more
closely to each, other at about 40 cm intervals. The gaps between the adjacent concrete
beams are lled with purpose-cast hollow concrete or earthenware blocks. The beams
are inverted T-shaped in cross-section so that the hollow blocks can be supported on the
bottom anges Figure 2. The resulting beam-block slab is then reinforced by the ad-
dition of a 5-10 cm thick reinforced concrete slab. In this way, a relatively light and in-
sulated reinforced concrete composite at slab is constructed without using scaffolding.
The relatively poor performance of traditional masonry buildings roofed with ma-
sonry domes and cylindrical vaults under earthquake forces, observed in numerous past
Iranian earthquakes, is well documented Maheri 1998; Ambraseys 1963; Ambraseys
and Tchalenko 1969. Low material strength, including weak mortar and the brittleness
of sun-dried or traditionally red bricks, poor workmanship, and lack of proper connec-
tions between perpendicular walls and between walls and roof and nonhomogeneous
roofs are but a few parameters that contribute to the general weakness of these buildings.
In addition, the excessive weight of the structure resulting from the thick walls and mas-
sive roofs causes an increased seismic load on the structure. The majority of these build-
ings in the Bam, Iran earthquake disintegrated into heaps of dried mud and brick rubble,
causing many casualties. The inherent seismic weaknesses of this type of construction
were further emphasized by their performance during the Bam earthquake.
The majority of traditional masonry buildings in the city of Bam were roofed with
masonry vaults, spanning between shared parallel load-bearing walls in a cluster of ad-
joining buildings. The typical mode of failure of the vault-roofed buildings was ob-
served to be the partial or total collapse of the freestanding end walls under their own
inertia followed by failure of the load-bearing supporting walls of the vault. Failure in
walls with larger openings was more profound. The survival or failure of the roof itself
Figure 2. Concrete beam, hollow block ooring system.
appeared to be dependant on the state of the supporting walls. So long as the walls re-
mained in place, the roof also stayed in place Figure 3. Conversely, when a part of the
load-bearing wall collapsed, the heavy roof also collapsed.
The main points of weakness of the traditional masonry curved roofs that contrib-
uted to poor seismic response can be summarized as follows:
1. Inability of the roof to act as a diaphragm: Masonry dome and vault roofs are
incapable of diaphragm action. This is due to their curved geometries, the
load- carrying mechanisms and the weak and brittle materials. The load-
carrying mechanism of these types of roofs is primarily in compression. The
nonhomogeneous masonry of the roofs is unable to carry tensile or exural
loads. As a result, they are not capable of restraining the top of their support-
ing walls during ground shaking, nor are they capable of transferring exces-
sive horizontal inertia forces. These curved roofs do not provide the neces-
sary support for the load-bearing walls. Furthermore, they induce a pre-
earthquake static horizontal force at the top of the walls as they transfer their
compressive load to the walls. In the shared load-bearing walls, the thrust
from the two adjoining vaults cancel each other out. However, in end vaults
this force causes an unbalanced outward thrust on the wall.
2. Vault roof construction has the added weakness of having a relatively small
support ratio and a one-directional support system. As a result, it has per-
formed poorly when compared with the dome roof construction, which has a
two-directional support system.
Figure 3. Survival of masonry vault roof.
3. Poor quality of material and bad workmanship: The majority of the older
buildings in the city of Bam were of mud brick adobe construction. Poor
quality of the adobe units, together with the use of mud as mortar had re-
sulted in weak, brittle material, which as time went by, became weaker. At the
onset of ground shaking, many of these buildings simply disintegrated into a
heap of dried mud rubble. Added to the poor quality of material, bad work-
manship was also noted in the construction of roofs, with uneven placing of
the mud bricks in the arches and without proper overlaps. When roofs were of
better quality red bricks and lime mortar with good workmanship, such as
the large vault of the old mill shown in Figures 4 and 5, they performed more
favorably in the earthquake.
4. Heavy weight of the roof: Perhaps the most important seismic weakness of
the masonry domes and vaults is their excessive weight. The masonry curved
roofs are, by nature heavy, as a minimum roof thickness is required to enable
the successful transfer of the gravity load in an arch action. Added to the
weight of the roof structure is a layer of straw-reinforced mud plaster known
locally as kahgel for waterproong the roof. This layer varies in thickness be-
tween 5cmto 7cm. The effective life of this waterproong course is limited
to about one year and each year a new layer should be applied to the roof.
Before the application of the new layer, ideally, the half-washed older layer
should be removed, but in most cases the new plaster is simply laid over the
existing layer. This practice results in an ever-increasing weight of the roof as
the building ages. As was noted in Bam, it is not uncommon to have tradi-
tional curved roofs having thicknesses in excess of 50 cm Figures 3 and 4.
In recent years, a number of large mosques have been constructed in Bam, keeping
to the tradition of using domes to cover the main halls. A typical construction of this
Figure 4. Good performance of better quality brick masonry vault of the old mill in Bam.
type is shown in Figure 6. In these buildings, the domes are supported by ring beams and
are reinforced by steel frames. In fact, the steel frames act as the main load-carrying
elements of the roof, reducing the role of brick masonry to mere inlls. Expectedly,
these domes performed much better during the earthquake than their traditional unsup-
ported counterparts. They all stayed in place during the earthquake, suffering only minor
local failures. The performance of these domes highlights the notion that the use of steel
or concrete ring beams under the dome, together with steel ribs, will greatly enhance the
seismic strength of curved masonry roofs.
A large number of the residential and commercial buildings in Bam were roofed
with masonry jack-arch slabs. These slabs may be divided into two groups: unanchored
jack-arch slabs, and anchored jack-arch slabs.
In buildings oored with this type of slab, depending on the response of the load-
bearing walls and the construction details of the slab, different modes of failure could be
1. Short bearing length of the slab beams: In many instances it was noted that
the bearing length of slab beams over the load-bearing walls was minimal,
and in some cases the ends of the beams were simply resting on the edge of
the walls. This short supported length of beams caused increased concentra-
tion of stresses in regions of the walls already highly stressed. At the onset of
ground shaking, local support failures under the slab beams resulted in the
Figure 5. Flexural failure in the vault of the old mill.
movement of the beams, causing the subsequent collapse of the masonry
arches. As the unrestrained load-bearing walls moved away from the slab un-
der ground shaking, the beams simply separated from their supporting walls
and collapsed Figure 7.
2. Use of end walls to support end brick arches: To reduce construction costs, it
appeared common practice to omit the slab beam over the end walls and use
the end walls to support the end jack-arches. Since there are no proper con-
nections between the perpendicular walls, separation of the end walls from
the load-bearing walls was a common mode of failure, resulting in the col-
lapse of the end masonry arches Figure 8.
3. Inability of the slab to act as a diaphragm: The poorly-connected composite
Figure 6. Favorable performance of the steel-framed high dome of a recently constructed
mosque in Bam.
Figure 7. Collapse of jack-arch steel beams due to inadequate bearing length.
Figure 8. Collapse of masonry arches due to the movement of end support wall.
form of the unanchored slab does not allow for a diaphragm action, as is re-
quired for good seismic performance. It was observed that when a part of the
load-bearing wall or supporting beam failed under earthquake loading, the
unsupported section of the slab had also failed.
4. Failure of the masonry arches due to the earthquake induced in-plane forces:
In traditional one-way slabs, the in-plane axial and shear loads are transferred
mainly by the brick arches. The brick arches are, however, ill-suited to trans-
fer these forces.
5. Weak slab materials: The type of brick and mortar used for construction of
arches is of prime importance for good seismic response. The bricks used in
construction of the arches were traditionally red, heavy solid bricks with low
strength to weight ratios. Using this type of brick not only does not increase
the strength of the arch, but results in a heavy slab, increasing the gravity and
seismic loads.
6. Poor workmanship: Poor workmanship was another shortcoming of the older
unanchored jack-arch slabs. The ability of the brick arch to transfer the load
in compression depends on the rise of the arch. As it was noted in Bam, the
masons tend to reduce the rise of arch as much as possible to almost a at
brick slab so that the amount of plaster required to make a at surface is re-
duced to a minimum. This changes the load-carrying behavior of the brick
arch into one of a at brick inll, susceptible to exural failure under small
The above general points of weakness, as was observed repeatedly in the response of
buildings in the Bam earthquake, make the unanchored traditional jack-arch system un-
suitable for earthquake-prone areas. Considering the apparent popularity of the jack-arch
system, Iranian seismic code BHRC 1988proposes to anchor the ends of the slab
beams to their supporting walls through concrete or steel ring beams and join the par-
allel beams together by steel bars. Although observations made during recent earth-
quakes, including the 2003 Bam, Iran earthquake, have shown the inadequacy of the
code recommendations, better seismic performance of anchored slabs was noted. In fact,
some observed performance of the anchored jack-arch slabs conrm previous numerical
and experimental ndings regarding the seismic capabilities and resilience of the an-
chored slab.
A good example of the resilience of anchored jack-arch slab can be seen in Figure 9.
This gure shows the collapse of the second oor jack-arch slab of a two-story steel-
frame building due to the failure of the main beam/column connections on one line of
support. The slab beams are joined together by transverse beams acting as girders. The
conned brick arches survived both the earthquake shaking and the collapse of the slab.
Also note in the same gure that the rst oor jack-arch slab of the building had also
survived the earthquake loads and the massive shock caused by the collapse of the upper
oor slab.
The jack-arch slabs are considered nonductile, brittle composite systems. However,
the behavior of a large number of jack-arch slabs during the Bam earthquake showed a
different response. It was noted that the masonry arches, when conned, underwent large
deformations along with their supporting steel beams and remained intact.
A large number of buildings that survived the earthquake had anchored jack-arch
slabs. In many instances the oor slabs were so intact that even minor failures in the
form of cracks in plaster could not be seen. The code-designed single-story masonry
building with concrete ring beams shown in Figure 10 is but one example of such be-
havior. Some of the anchored jack-arch slabs had construction materials and details and
workmanship similar to the slabs of the building already seen in Figure 1b. This unn-
ished building also survived the Bam earthquake. The brick arches of the slab consist of
lightweight perforated brick units and lime/clay mortar. The lightweight perforated
bricks are far more suitable for jack-arch construction, as they reduce the weight of the
slab and provide a better bond between the mortar and bricks. The parallel load-bearing
beams of the slab are also well restrained by transverse beams at their ends.
It should be noted that the contemporary jack-arch slab construction in Iran is still
considered a nonengineered slab in the Iranian seismic code, and there are no particular
design procedures for their engineered design. Simple methods of increasing the seismic
performance of the slab in the form of inter-span transverse beams have been proposed
and their effectiveness investigated both experimentally and numerically Maheri and
Imanipour 1999; Maheri 2001. Finally, procedures for engineered design and construc-
tion were introduced Maheri and Rahmani 2003. Although these design procedures
were not applied in the construction of the jack-arch slabs in the city of Bam, some ex-
isting anchored slabs had details comparable to the proposed engineered version of the
Figure 9. Integrity of the anchored jack-arch slab under earthquake loading and after collapse.
slab. An example of the effectiveness of the use of mid-span transverse beams can be
seen in Figure 11. It can be seen that the portion of the slab in which inter-span trans-
verse beams were used to join the main beams together has remained in place, whereas
the front section of the slab that lacks similar transverse beams has disintegrated and
Figure 10. No damage was observed to this code-designed masonry building with ring-beam-
supported jack-arch slab.
Figure 11. Effectiveness of inter-span transverse beams in keeping the integrity of the slab.
In recent years, the concrete beam-hollow block roong system has become popular
in ooring framed structures. As a result, a number of buildings in the city of Bam, Iran
were oored with this type of construction. The seismic performance of concrete beam/
hollow block roong systems was generally more favorable than the jack-arch slabs. The
materials and construction details of the oor provide homogeneous slabs capable of
diaphragm action. Although the concrete beam/hollow block oor is inherently robust
and has favorable seismic response, poor workmanship was identied as the main reason
behind the failure and collapse of a number of oors of this type during the Bam earth-
quake Figure 12.
Figure 12. Poor workmanship in construction of concrete beam/hollow block slab.
The performance of different types of roofs and oor slabs observed following the
2003 Bam, Iran earthquake are summarized below:
1. As far as the performance of the dome and vault roofs are concerned, it was
observed that although they are incapable of providing sufcient anchorage
for the walls, as long as the supporting walls remained in place, they did not
2. Domes with two-directional support systems appeared to perform better than
one- directional vault roofs. Also, the good performance of large masonry
domes supported by ring beams and steel ribs indicate the importance of
these reinforcing elements in the successful transfer of seismic loads.
3. The nonengineered unanchored type of jack-arch slabs also performed poorly
during the earthquake. However, ample examples of the potential of this
ooring system as an earthquake-resistant slab could be seen when the slab
was anchored. It is noted that the seismic performance of existing unan-
chored and anchored jack-arch slabs may be greatly enhanced by the provi-
sion of transverse beams at the ends and at the inter-span of the main beams
according to the design provisions detailed in other publications.
4. The concrete beam/hollow block slabs are well suited for earthquake resistant
construction. However, good workmanship is a key factor for the realization
of their good seismic response.
Ambraseys, N. N., 1963. The Buyin-Zara Iranearthquake of Sept. 1962: A eld report, Bull.
Seismol. Soc. Am. 53 4.
Ambraseys, N. N., and Tchalenko, J. S., 1969. The Dasht-e-Bayaz Iranearthquake of August
31 1968, a eld report, Bull. Seismol. Soc. Am. 59 5.
Building and Housing Research Centre BHRC, 1988. Iranian Code for Seismic Resistant De-
sign of Buildings, Standard 2800, Publication No. 82 in Persian.
Maheri, M. R., 1990. Engineering Aspects of the Manjil, Iran Earthquake of 20 June 1990, re-
port published by EEFIT Earthquake Engineering Field Investigation Team,Society for
Earthquake and Civil Engineering Dynamics. United Kingdom.
Maheri, M. R., 1992. Manjil, Iran earthquake of June 1990, some aspects of structural re-
sponse, Struct. Eng. Rev. 41, 1-16.
Maheri, M. R., 1998. Lessons from Golbaf, Kerman earthquake of 14 March 1998, Proceed-
ings,1st Iran-Japan Workshop on Recent Earthquakes in Iran and Japan. Tehran, Iran. pp.
1Publication of this special issue on the Bam, Iran earthquake was supported by the Learning from Earthquakes
Program of the Earthquake Engineering Research Institute, with funding from the National Science Foundation
under grant CMS-0131895. Any opinions, ndings, conclusions, or recommendations expressed herein are the
authorsand do not necessarily reect the views of the National Science Foundation, the Earthquake Engineer-
ing Research Institute, or the authorsorganizations.
Maheri, M. R., 2001. The Gravity and Seismic Design of Jack-arch Slabs, Iranian National Re-
search Report No. NRCI-ZL-479 in Persian.
Maheri, M. R., 2004. Performance of roofs and oor slabs during Bam earthquake of 26 De-
cember 2003, J. Seismol. Earthquake Eng., Special Issue on Bam Earthquake.
Maheri, M. R., and Imanipour, A., 1999. Seismic evaluation of a proposed two-way jack-arch
slab, Proceedings, 3rd International Conf. Earthq. Engineering and Seismology, Vol. III, Te-
hran, Iran.
Maheri, M. R., and Rahmani, H., 2003. Static and seismic design of one-way and two-way jack-
arch masonry slabs, Eng. Struct. 25, 16391654.
Moinfar, A. A., 1968. Seismic activities and conditions of rural houses in countries of the re-
gion, Proceedings, CENTO Conf. on Earthquake Hazard Mitigation, Turkey.
Razani, R., and Lee, K. L., 1973. The Engineering Aspects of the Qir Earthquake of April 10,
1972 in Southern Iran, National Academy of Engineering, Washington D.C.
Received 26 September 2004; accepted 29 April 2005
... Despite the wide spread use of the jack-arch slabs and their advantages, there are no particular procedures for their engineered design and there is no mention of the system in codes of practice. Indeed, a search of literature reveals no reference to any particular scientific research directed at studying this slab system or any attempts made to provide an engineering basis for its design and construction prior to the works carried out by the author and his colleagues [Maheri, et-al 1999, 2003and Maheri 2004. The jack arch flooring system is stable under normal static conditions. ...
... Collapse of a large number of jack arch slabs and damage sustained by many more was reported from the Romanian earthquake of 1990 [EEFIT, 1990]. The Manjil, Iran earthquake of 1990 [Maheri, 1990[Maheri, , 1992 and Bam, Iran earthquake of 2003 [Maheri, 2005] are of particular interest in this regard. They provided real testing grounds for different forms of the one-way jack arch system. ...
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The performance of the traditional one-way jack-arch slabs in a number of recent earthquakes in Eastern Europe and the Middle East has been generally poor. Collapse of a large number of jack-arch slabs and damage in many more were reported from the Romanian earthquake of 1990, the Manjil, Iran earthquake of 1990 and the more recent Bam, Iran earthquake of December 2003. Subsequent to the Romanian earthquake, some of the surviving jack-arch floors were retrofitted by adding a reinforced concrete layer over the slab. This method, also adopted for some retrofitting cases in Iran, is costly and the extra weight of the concrete layer necessitates expensive upgrading of the entire building. In this paper, a simple and efficient method of retrofitting jack-arch floors is discussed. The method entails using transverse steel sections to join the main beams at a number of locations along their span, hence creating a steel grid. This steel grid will act as the main load-carrying element of the floor, capable of transferring both the in-plane and out-of-plane loads. Details of the proposed retrofitting method is also discussed.
... Most of the main compounds of mosques, having single dome with multiple semi-spherical domes, were generally intact or suffered very slight damage [1][2]. On the other hand, the losses occurred during recent earthquakes have proven that there is an urgent need for improved knowledge of the seismic behavior of these parts of buildings [2][3][4][5][6][7][8][9][10][11]. In order to have proper rehabilitation schemes, a better understanding of the structural behavior of such parts under lateral loads is needed. ...
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After the industrial revolution, the use of jack arch slabs (JAS) was quite common in many historical structures with the availability of iron and steel in structural engineering field. JAS is a composite system of steel I-beams and masonry bricks, which are placed between steel I-beams. This study focuses on the structural failures and weaknesses of masonry structures with JAS. The aims of this paper are to deeply illustrate the structural vulnerability of masonry JAS and to summarize the positive and negative effects of JAS on structural behavior. Within the scope of this study, this study focuses on historical American Boarding School for Girls in Merzifon, Turkey, which has one-way masonry JAS. It essentially assesses the structural behavior of the school and investigates the seismic vulnerability of JASs. For this purpose, the mechanical properties of the structural materials have been primarily evaluated with experimental tests. Then the finite element analyses have been carried out with the use of three dimension numerical model in order to investigate the structural behavior of the structure.
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This paper presents the results of an experimental work in order to evaluate the performance of a novel proposed retrofitting technique on a typical dome-roof adobe building by shaking table tests. For this purpose, two specimens, scaled 2:3, were subjected to a total of nine shaking table tests. The unretrofitted specimen, constructed by common practice, is designed to evaluate seismic performance and vulnerability of dome-roof adobe houses. The retrofitted specimen, exactly duplicating the first specimen, is retrofitted based on the results obtained from unretrofitted specimen tests, and the improvement in seismic behavior of the structure is investigated. Zarand earthquake (2005) Chatrood Station is selected as the input ground motion that was applied consecutively at 25, 100, 125, 150 and 175% of the design-level excitation. At 125% excitation level, the roof of the unretofitted specimen collapsed due to the walls' out-of-plane action and imbalanced forces. The retrofitting elements consist of eight horizontal steel rods drilled into the walls, passed through the specimen and bolted on the opposite wall surfaces. To improve walls in-plane seismic performance, welded steel mesh without using mortar, covered less than half area of walls on the external face of the walls, is used. In addition to strain gauges for recording steel rod responses, several instrumentations including acceleration and displacement transducers are implemented to capture response time histories of different parts of the specimens. The corresponding full-scaled retrofitted prototype tolerated peak acceleration of 0.62 g almost without any serious damage. Copyright
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This article addresses three large earthquake disasters in Iran: Tabas in 1978, Rudbar in 1990, and Bam in 2003. Lessons and “Lessons Learned” from these three earthquake disasters were investigated together with their contributions over time towards earthquake disaster risk reduction in Iran. Many lessons from 1978 Tabas, 1990 Rudbar, and 2003 Bam did not become “Lessons Learned” and they were identified again within the dramatic context of other earthquake disasters in various places of Iran. Both lessons and “Lessons Learned” from Tabas, Rudbar, Bam, and other earthquake disasters in Iran require a sustainable long-term framework—an earthquake culture.
Conference Paper
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Considering the widespread use of jack arch roofs and the need for seismic retrofitting of this system of flooring in Iran the behaviour of the retrofitted form of these slabs is unknown. The Iranian building codes also do not deal sufficiently with this type of roofing and as a result little control is applied on their method of construction. The retrofitting method of adding a concrete layer (CL) is a method which was first introduced in Romania after the earthquake of 1990. This paper reports on an experimental investigation of this method and comparison with other retrofitting methods. For this purpose, a number of slabs with different methods of retrofitting such as the Romanian method, the method recommended by the Iranian Standard 2800, the two way method and a slab without retrofitting were constructed. Then, the slabs were loaded step by step in out of plane direction and the load-displacement pushover curves for the slabs were obtained. Using these curves, the seismic strength parameters of different slabs are determined and compared.
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Following the destructive Bam earthquake of 2003, the Iranian government initiated a vast program of seismic retrofitting for existing school buildings throughout the country. As a result of the school retrofitting program, an extensive amount of field test data is available on the shear strength of brick walls of buildings from different parts of the country having different climates. A large portion of the available data is utilised in this paper to determine the effects of environmental conditions, particularly those of humidity and temperature, on the shear strength of brick walls. The effects of other factors including the type of material and age of the building are also investigated. Results of the statistical analyses highlight the important effects of the location humidity level. A nearly three folds increase in strength was noted for walls constructed of solid brick units in wetter northern parts of the country compared to those constructed in the drier central parts. Another important factor is found to be the absorption rate of bricks used in constructing the wall. On the other hand, the effect of overall environment temperature is found to be minimal. The daily temperature gradient of the location, however, may affect the strength by causing some long-term fatigue. It is recommended that for assessing the vulnerability of unreinforced brick walls, regionalization is considered and an appropriate ‘climate factor’ is adopted.
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Collapse of non-engineered roofs and floor slabs during the Bam earthquake of December 2003 was the single major contributor to the large fatalities during that earthquake. Different floor systems of buildings in the city of Bam can be categorised into three types namely; the traditional masonry dome or vault, the steel I-beam jack arch system and the concrete beam-hollow block system. In this paper the seismic performance of each type of flooring as observed after the Bam earthquake is discussed and their points of weakness and strength are highlighted. Also the poor seismic performance of the traditional dome and vault roofs and the unanchored jack arch slabs are noted and the seismic merits of the anchored jack arch slabs and concrete beam-hollow block slabs are discussed.
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Steel I-beam, brick jack arch slabs have long been used to floor and roof industrial and residential buildings in many parts of the world. Collapse of a large number of these non-homogeneous one-way slabs during past earthquakes has highlighted their poor seismic performance. However, due to their easy construction together with low cost, the jack-arch slab is still widely used in many countries. In this article, the weaknesses inherent in the traditional one-way jack-arch slabs are explored. To overcome these shortcomings, a new two-way system is proposed. Results of static and dynamic tests on full scale two-way and one-way jack-arch slabs and finite element numerical analyses, aimed at investigating the effectiveness of the proposed two-way system, are presented with favourable conclusions. Following these investigations the static and seismic design of jack arch slabs are discussed. The proposed, allowable stress design method is based on designing for the steel grid and controlling the stresses in brick arches. Parameters necessary for an equivalent static seismic load calculation are first determined. Finite element numerical analyses are then conducted to investigate the effects of a number of parameters on the design of the slab and the necessary design factors are evaluated. In addition, appropriate tables and figures are presented to facilitate the design of the one-way and two-way jack arch slabs. It is concluded that the jack arch slab system, designed and constructed as presented in this article, provides a viable, low cost alternative to other forms of flooring in seismic zones and elsewhere.
Results are presented of a reconnaissance investigation of the earthquake which occurred on Apr 10, 1974 with a magnitude of 7, totally destroyed the town of Qir and destroyed or severely damaged more than eighty smaller villages in the surrounding area. The general seismic behavior of engineered, and traditional adobe and masonry structures is discussed; their most common modes of failure, their areas of weakness, and the lessons learned from this earthquake are described. Some recommendations with regard to future construction and seismic protection in rural and urban areas of Iran are given.
Seismic evaluation of a proposed two-way jack-arch slab
  • M R Maheri
  • A Imanipour
Maheri, M. R., and Imanipour, A., 1999. Seismic evaluation of a proposed two-way jack-arch slab, Proceedings, 3 rd International Conf. Earthq. Engineering and Seismology, Vol. III, Tehran, Iran.
The Dasht-e-Bayaz Iran earthquake of
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  • J S Tchalenko
Ambraseys, N. N., and Tchalenko, J. S., 1969. The Dasht-e-Bayaz Iran earthquake of August 31 1968, a field report, Bull. Seismol. Soc. Am. 59 5. Building and Housing Research Centre BHRC, 1988. Iranian Code for Seismic Resistant Design of Buildings, Standard 2800, Publication No. 82 in Persian.
The Gravity and Seismic Design of Jack-arch Slabs
  • M R Maheri
Maheri, M. R., 2001. The Gravity and Seismic Design of Jack-arch Slabs, Iranian National Research Report No. NRCI-ZL-479 ͑in Persian͒.