Vulnerability and Expected Seismic
Performance
of Palestinian common Buildings
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Jalal Al-Dabbeek
Abdel Hakim
Al-Jawhari
Associate
Professor
Civil
Engineering/ M.Sc
1- Introduction .
Over the
last three decades, natural disasters particularly earthquakes, have become
increasingly destructive as they affect larger concentrations of population and
property. The cost of replacing and repairing earthquake – damaged buildings is
a significant drain on the economies of earthquake – prone countries.
Therefore, it is imperative to achieve methods of reducing earthquake damage to
an economically supportable level.
Estimates of seismic risk can be of considerable use
to physical and economic planners concerned with investment and settlement in
seismic areas. Also to those concerned with insurance against such losses and
to civil defense officials whose task is to prepare plans for rescue, relief
and rehabilitation after a possible future earthquake disaster.
Although there have been many studies of the
assessment of seismic hazard, there have been relatively few attempts to assess
the probability of damage or destruction of existing buildings. This is
probably due to the lack of precise information on the vulnerability of
existing buildings, i.e on the degree of damage or proportional loss of value
that they are likely to suffer when subjected, to ground motion of various
intensities.
2- Basic Methodology
It is hard to find two identical buildings, in order
to be able to derive information of prognostic value from the inspection of
earthquake damage, buildings must therefore be classified into a limited number
of structural types. The definition of each type must not be only narrow enough
to ensure some degree of uniformity in seismic response of all buildings within
the type but wide enough to ensure that the number of buildings in each type is
large enough for statistical analysis. Therefore it is necessary to define the
relation between buildings types (in addition to the architectural and
structural building configurations) and vulnerability classes, also between
vulnerability classes and damage grades. The studies of vulnerability of
buildings in West Bank were done according to the EMS-98 (European Macro
seismic Scale).
3- Buildings Types
The buildings in West Bank were divided into categories
according to the construction system:
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Stone
masonry.
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Brick masonry.
-
Reinforced
concrete beam-column –slab system (Joist system).
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Reinforced
concrete braced (infield) frame structures.
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Reinforced
concrete shear wall structures.
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Bearing
wall structures.
4- Factors Affecting the
seismic Vulnerability of Buildings: -
There is A number of different factors affect the
overall vulnerability of a structure besides construction type. These factors
are generally applicable to all types of structures.
According to the site and building investigations,
the following factors have been considered: -
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Site
conditions.
-
Regularity
and configuration of structural and architectural elements.
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Position:
severe damage can occur to two adjacent buildings if they don’t have enough
spacing (seismic joint).
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Strengthening
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Earthquake
resistant design (ERD).
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Importance:
the importance of a building is determined by the number of occupants or
visitors, the use of buildings or the danger for public and environment in the
case of the building's failure.
5-Assigning the
Vulnerability Classes
Assessing the vulnerability classes of buildings
structures was been done according to the EMS-98.
For Reinforced concrete
frame buildings without earthquake resistant design ERD, vulnerability
classes B to C are probable with C
being most likely. For RC frame buildings with serious defects (such as soft
storeys, weak columns, lack of stiffening elements, long or very long
cantilevers with heavy loads at the end …..etc) vulnerability class B or even A
maybe appropriate for regular RC buildings without ERD, but incorporating a certain level of
lateral resistance (due to wind load design or stability verification)
vulnerability class D might be representative of exceptional cases.
For reinforced concrete wall
structures without ERD, vulnerability classes C to D are probable, with C being
the most likely one. For RC walls with serious defects, a vulnerability class B
can be regarded as the exceptional case. One should notice that defects will
not lead to a such drastic decrease of vulnerability which can be observed in
case of RC frame structures.
To emphasize the necessary
data required for assigning the vulnerability class of Palestinian buildings,
most of cities were investigated by collecting information and data, depending
on the following parameters:
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Slop
of the site.
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Existence
of basements.
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Soil
type.
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Number
of storeys .
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Slenderness
ratio.
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Age
of building.
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State
of concrete.
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Construction
over existing old building.
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Adjacent
to other building.
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Building
type.
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Structural
system.
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Existence
cantilever structural system.
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Soft
storey.
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Symmetry
of stiffness in horizontal plan.
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Variation
of stiffness horizontally and vertically.
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Staircase
location.
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Stair
case structural system.
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Entrance
and exist of buildings.
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Symmetry
in horizontal configuration.
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Symmetry
in vertical configuration.
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Symmetry in mass horizontally.
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Formation
of short column.
The outputs or results obtained from investigations
depending on the pre-mentioned
parameters were arranged in standard tables for all the cities included in the
study.
For each city, a representative zone or more were
chosen to be investigated, the number of buildings in each zone varied between 80
and 120 buildings.
In addition to the a above mentioned tables which
include the data related to the Palestinian buildings and all are documented in
the main Vulnerability filed in the Earth Sciences & seismic Engineering
Center.
Find enclosed representative photos for selected Buildings
in Palestinian Cities, Based on data collected and the analysis done according
to EMS 98, the following vulnerability classes have been obtained.
Table-1 Vulnerability Classes
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City |
Vulnerability Classes |
No.of buildings |
|||
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A |
B |
C |
D |
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Nablus |
35.5 % |
42% |
18% |
4.5% |
700 |
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Ramallah
& Abudis |
32% |
39% |
22% |
7% |
120 |
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Hebron |
43% |
31% |
26% |
0 |
120 |
|
Jenin |
45% |
43% |
12% |
0% |
100 |
|
Qalqilia |
34% |
45% |
21% |
0% |
100 |
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Tulkarim |
41% |
37% |
19% |
3% |
80 |
|
Bethlahim |
42% |
39% |
19% |
0 |
100 |
6- Damage Grades:-
Combining the influence of intensity with the
vulnerability obtained, the expected grades of damage according to EMS-98 can
be summarized as shown in table 2.
7- Comments and Conclusions
The main aspects of the study are:
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It
dose worth to mention that many of the buildings included in the investigations
were relatively new.
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Absence
of codes is the major problem, and if a certain code is adopted, it is applied
in a way that dose not represent the real performance of the building or code
guidelines. This was clarified when the study has been done according to the
equivalent static method (see report No.1 the results of applying different
codes on Palestinian buildings using equivalent static method ).
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Codes
are generally applied depending on the personal judgements of engineers, which
in many cases produce a wide variation in the results. For instance, the codes
are usually applied on buildings having soft storey, although it is quite clear
that applying codes using equivalent static method on such buildings is not
valid.
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Considering
the results obtained from this report (vulnerability), and those obtained from
the last report (Report No.1), it is essential to make dynamic analysis for
different types of Palestinian buildings. This is important to identify the
variation in the results obtained from the static method, also to try to find
relevant values for the critical building characteristic, such as: Natural
period of structural systems of buildings, properties of building materials,
end conditions of structural elements, and spectral analysis.