1

FRAGILITY ASSESSMENT OF PRE-SEISMIC CODE BUILDINGS AND

EMERGENCY FACILITIES IN THE UAE

Anas ISSA1 and Aman MWAFY2

ABSTRACT

High levels of investments and population densities are represented in the building inventory in the

UAE. The number of buildings in the existing inventory that may be at risk because of the inefficient

seismic design provisions at the time they were constructed cannot be underestimated. Moreover, a

crucial role in the recovery period following an earthquake is played by emergency facilities. Hence,

this study focuses on the seismic fragility assessment of buildings representing substandard and

emergency structures when subjected to potential earthquake scenarios in the UAE. Nine reference

buildings representing the building inventory in a highly populated seismically active area in the UAE

are selected based on an on-ground survey. Detailed structural design and fibre-based modelling are

carried out for the reference structures, and forty earthquake records are selected to represent potential

earthquake scenarios in the study area. A wide range of local and global response parameters are

monitored from static pushover and incremental dynamic analyses. Previous studies are reviewed and

compared with the performance criteria obtained from the present study. Fragility relationships and

damage state probabilities are generated for the nine reference structures under the effect of two seismic

scenarios for the direct implementation in a loss estimation system for the UAE. While the results reflect

the acceptable performance of emergency facilities, particularly under near-field events, they reveal the

need for implementing mitigation measures for pre-code structures to reduce seismic losses.

INTRODUCTION

The United Arab Emirates (UAE) was known to be a region of low seismicity even though being in

close proximity to high seismic zones. Recent earthquakes recorded within the region have emphasized

the significance of investigating the impacts of anticipated seismic scenarios on different types of

structures. Due to the rapid development of the construction industry in the UAE, significant attention

has been drawn to the risk posed by earthquakes to the buildings and infrastructure. More importantly,

since pre-seismic code buildings were constructed when the knowledge regarding the seismicity and

seismic code regulations was limited, they may be vulnerable. This knowledge has advanced since then

and reflected on the improved seismic performance of modern code-design structures. The poor

performance of pre-seismic code buildings will prevent such structures from reaching the desired

seismic performance objectives (ATC, 1996; Buratti et al., 2010). In addition, serious attention should

be paid to the emergency facilities to assess their performance as they play a crucial role in the

earthquake recovery period and should be fully functioning. A great attention has been paid to the

emergency facilities around the world. For instance, the State of California has taken steps in that

1 Graduate Teaching Assistant, United Arab Emirates University, Al Ain, UAE, 200734567@uaeu.ac.ae 2 Associate Professor, United Arab Emirates University, Al Ain, UAE, amanmwafy@uaeu.ac.ae

also Professor of Structural Engineering, Zagazig University, Egypt (on leave)

2

direction by enacting a decree to retrofit emergency facilities by 2030 to allow them to be fully

operational subsequent an earthquake (Bruneau and Reinhorn, 2007).

Catastrophic consequences are expected if the seismic risk of the building stock is neglected,

particularly for substandard and emergency facilities. The repeated reports of seismic activities in the

UAE and the devastating social and economic impacts of strong seismic events that have been recorded

in neighbouring territories emphasize the significance of adopting reliable loss estimation and hazard

mitigation strategies for the built environment in this region. This study thus focuses on the probabilistic

seismic vulnerability assessment of buildings representing pre-seismic code and emergency structures,

which enables the direct implementation of a wide range of fragility relationships representing different

structures and earthquake scenarios in a loss estimation and mitigation system for the UAE.

REFERENCE STRUCTURES AND GROUND MOTIONS

Selection of Earthquake Records based on Possible Seismic Scenarios:

A diverse set of earthquake records representing the study area are selected for inelastic dynamic

simulations. Both the PEER Ground Motion Database (Chiou and Youngs, 2008) and the European

Strong-Motion Database (Ambraseys et al., 2004) are thoroughly searched to select 40 natural records

that represent two earthquake scenarios recommended for the study area, namely far-field records and

near-source events (Mwafy et al., 2006). The main criteria of selecting input ground motions are: (i)

epicentral distance, (ii) magnitude, (iii) soil condition, (iv) a/v ratio, and (v) PGA. Table 1 shows a

summary of the selected near source records. The response spectra of the selected records are developed

and scaled to the recommended design intensity of the study area (i.e. a PGA of 0.16g; Mwafy et al.,

2006). Figure 1 compares the response spectra of the 40 input ground motions that represent the two

seismic scenarios with the current design spectra for Dubai for soil classes C and D.

Table 1. Summary of near-field earthquake records

Ref Earthquake Station Comp. Date Mag. (Mw)

Site class

Ep. Dist. (km)

Duration (sec)

PGA (m-s2)

a/v g-ms-1

a/v class.

NF01 Coyote Lake San Juan Bautista, 24 polk St 213 06-08-1979 5.74 v. dense 19.7 15 0.991 1.424 NF02 Livermore-02 Livermore-Morgan Terr Park 355 27-01-1980 5.42 v. dense 14.1 14 2.235 2.581 NF03 Hollister-04 City Hall 271 28-11-1974 5.14 v. dense 9.8 21 1.651 1.480 NF04 Whittier Narrows-01 Brea Dam (L Abut) 130 10-01-1987 5.99 v. dense 24.0 26 1.299 1.460 NF05 Whittier Narrows-01 LA-Centry City CC North 90 10-01-1987 5.99 stiff 29.9 9.9 0.851 1.788 NF06 Whittier Narrows-01 LB-Orange Ave 2280 10-01-1987 5.99 stiff 24.5 20 2.111 1.468 NF07 Northridge-06 Panorama City-Roscoe 90 20-03-1994 5.28 stiff 11.8 30 1.141 1.916 NF08 Montenegro Petrovac-Hotel Oliva Y 15-04-1979 5.80 v. dense 24.0 15 0.873 1.426 NF09 Umbria Ma. Castelnuovo-Assisi NE 26-09-1997 6.04 v. dense 16.0 12 1.600 1.254 NF10 Lazio Abr. Y Cassino-Sant Elia EW 07-05-1984 5.93 v. dense 16.0 11 1.123 1.590 NF11 Mammoth Lakes-02 Mammoth Lakes H. S. 344 25-05-1980 5.69 v. dense 3.49 28 4.064 1.957 NF12 Mammoth Lakes-06 Fish & Game (FIS) 0 27-05-1980 5.94 stiff 12.02 7.2 3.979 2.753 high NF13 Coalinga-04 Anticline Ridge Free-Field 270 07-09-1983 5.18 v. dense 6.34 45 3.220 2.048 NF14 Coalinga-04 Anticline Ridge Pad 270 07-09-1983 5.18 v. dense 6.34 20 3.246 2.350 NF15 Coalinga-05 Burnett Construction 360 22-07-1983 5.77 stiff 12.38 30 2.915 1.988 NF16 Whittier Narrows-01 Alhambra - Fremont School 180 10-01-1987 5.99 v. dense 6.77 21 3.806 1.514 NF17 Whittier Narrows-01 Garvey Res. - Control Bldg 60 10-01-1987 5.99 v. dense 2.86 26 3.775 2.432 NF18 Whittier Narrows-01 LA - 116th St School 360 10-01-1987 5.99 stiff 21.26 38 3.343 1.888 NF19 Whittier Narrows-01 LA - Obregon Park 360 10-01-1987 5.99 stiff 9.05 25 4.161 1.748 NF20 Friuli Breginj-Fabrika IGLI Y 15-09-1976 6 v. dense 21.0 30 4.956 2.333

a/v: PGA/PGV, a/v classification (<0.8 Low & >1.2 high), Vs30 of very dense soil = 360-760 m/s, and for stiff soil = 180-360 m/s

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 0.5 1 1.5 2 2.5 3 3.5 4

Spec. Acc. (g)

Period (s)

Natural Records

Design Code Spectrum (D)

Design Code Spectrum (C)

Mean

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 0.5 1 1.5 2 2.5 3 3.5 4

Spec. A

cc. (g)

Period (s)

Natural Records

Design Code Spectrum (D)

Design Code Spectrum (C)

Mean

Figure 1. Response spectra of near-field (left) and far-field (right) earthquake records along with their mean and

the current design spectra for Dubai for soil classes C and D

A.Issa and A.Mwafy 3

Selection of Pre-seismic Code and Emergency Structures:

A fundamental step in this study is selecting representative structures for the study area. On-ground

surveying was carried out with several site visits for Dubai, Sharjah and Ajman, which is a highly

populated and seismically active area in the UAE (Figure 2), to select a set of nine reference structures

representing the pre-seismic code buildings and emergency facilities (Mwafy, 2012). Table 2 shows a

summary of the selected representative buildings. Three-dimensional (3D) finite element (FE) models

are developed for the investigated buildings using the structural analysis and design program ETABS

(CSI, 2011). Figure 3 depicts the layouts and 3D models for the set of the reference buildings. For the

pre-code wall structures, the height of all stories is 3.2 m except for the ground storey, which is 4.5 m.

For the pre-code frame structures, the height of all stories is 3.5 m except for the ground storey, which

is 5.0 m. The total heights of the nine reference buildings are shown in Table 2.

Point North East

A

B

C

D

E

F

G

H

Dubai

Ajman

Sharjah A 25o 04’ 17’’55o 07’ 30’’

B 25o 03’ 40’’55o 08’ 15’’

C 25o 05’ 48’’55o 10’ 57’’

D 25o 04’ 35’’55o 12’ 43’’

E 25o 12’ 25’’55o 18’ 57’’

F 25o 13’ 47’’55o 17’ 26’’

G 25o 17’ 23’’55o 21’ 33’’

H 25o 25’ 41’’55o 31’ 14’’

Figure 2. Study area

Table 2. Summary of the selected buildings

Category

Number Buildings description Building Reference Building Height (m)

Selection according to construction date

1

Pre-seismic code structures

BO-02 8

2 BO-08 28.5

3 BO-18 58.9

4 BO-26 84.5

5 BO-40 129.3

Selection according to function

6 Fire station FS 9.5

7 Police station PS 9

8 School SC 13

9 Hospital HO 24.5

Pre

-code

Str

uct

ure

s

BO-02, 2 story BO-08, 8 story BO-18 & BO-26,18 & 26 story BO-40, 40 story

Em

ergem

cy

FS, Fire Station PS, Police Station SC, School HO, Hospital

P

CORE

Figure 3. Three-dimensional design models

4

Design of Reference Buildings:

The five pre-seismic code reference buildings are designed and detailed specifically for the purpose of

the current study according to the building codes that were implemented at the construction time

(BS8110, 1986). Pre-seismic code buildings are defined in this study as those built in the study area

before 1990 when seismic design provisions might be disregarded. It is worth noting that the Uniform

Building Code (UBC, 1997) recommended the use of Seismic Zone ‘0’ for the cities of Abu Dhabi and

Dubai, UAE. Revised seismic design criteria have been adopted in the UAE after the recommendations

of recent seismic hazard studies (e.g. Abdalla and Al-Homoud, 2004; Mwafy et al., 2006). Therefore,

wind loads are the only lateral loads considered in design to represent the real situation before 1990.

The permanent loads used in design include the self-weight and a superimposed dead load of 4.0 kN/m2.

The live load is 2.0 kN/m2 except for stairs and exit ways, which is 4.8 kN/m2. Wind loads are calculated

based on a basic wind speed of 45 m/s (BS-6399-2, 1998). The design is carried out for each building

carefully to obtain the optimum cross sections for different structural elements. Table 3 shows sample

design results for the 26-story building. To accurately represent the pre-code structures, the material

properties that were utilized at the time of construction are considered. The concrete strength ranges

between 20 and 40 MPa, while mild steel is used with a yield strength of 240 MPa. Pre-code buildings

with such material properties are likely to be more vulnerable to earthquake loads due to the large cross

sections, heavy mass and inadequate detailing as compared to modern code-designed structures.

The four emergency buildings are designed and detailed in the current study according to modern

building codes (ACI-318, 2011; ASCE-7, 2010). Wind loads are estimated using ASCE-7 (2010) based

on a basic wind speed of 45 m/s and an exposure category C. The seismic loads are also estimated using

ASCE-7 (2010) with a soil class C, as per the recommendations of recent hazard assessment studies and

design provisions for the UAE. The adopted live load is 3.80 kN/m2, while the permanent loads used in

design include the self-weight of structural members in addition to a uniformly distributed load on slab

of 4.0 kN/m2, which is intended to account for superimposed dead loads. Taking into consideration the

moderate seismicity of the UAE, intermediate moment resisting frames are employed in the design of

such buildings. The design information is used in the numerical modelling phase, as explained below.

Table 3: Design summary of the vertical structural members of the 26-story building

Pier P

Location of section Foundation Floor no. 3 Floor no. 8 Floor no. 12 Floor no. 17

Vertical steel ratio, % 3.9 3.11 1.72 1.34 1.00

VL. Reinforcement 66#40 52#40 42#32 36#26 36#20

HL. Reinforcement #12@200mm #12@200mm #8@200mm #8@200mm #8@200mm

Links #12@510mm #12@510mm #8@380mm #8@340mm #8@260mm

Design/Capacity (D/C) Ratio 0.998 0.996 0.995 0.922 0.969

Pier section, mm x mm 600x3500 600x3500 550x3500 550x3500 400x3500

Concrete strength (fc'), MPa 28 24 24 24 20

CORE

Location of section Foundation Floor no. 8 Floor no. 17

Vertical steel ratio 1.1% 1.0% 1.0%

Vertical Reinforcement 160#20 121#20 97#20

Horizontal Reinforcement #10@200mm #8@200mm #8@200mm

links #10@430mm #8@300mm #8@190mm

Design/Capacity (D/C) Ratio 0.999 0.849 0.572

Core thickness, mm 300 250 200

Concrete strength (fc'), MPa 28 24 20

Modelling and Verifications:

The fibre modelling technique is used to idealize the reference structures for the multi-degree-of-

freedom Inelastic Pushover Analysis (IPA) and Incremental Dynamic Analysis (IDA) using the inelastic

analysis platform Zeus-NL (Elnashai et al., 2012). Reinforcing steel, confined and unconfined concrete

are effectively idealized to enable monitoring of stresses and strains during the inelastic simulations.

Figure 4 illustrates the numerical models of the selected buildings. Each structural member is divided

into three segments to allow for more accurate representation of longitudinal reinforcement and

prediction of steel yielding, concrete crushing, and shear capacity of structural members (Elnashai and

Mwafy, 2002). The verifications of numerical models is conducted by comparing the periods of

A.Issa and A.Mwafy 5

vibration of different models used in both design and inelastic analyses. Table 4 summarizes the obtained

periods of the nine reference buildings as well as those associated with the first two mode shapes for a

sample building (HO). It is clear that the periods of the design models are slightly longer (within 10%

difference) than the periods of the fibre-based models. This difference is justified by the consideration

of actual material strength values and steel reinforcement in the fibre-based models, which increase

stiffness and shorten periods. These sample results verify the numerical models and lend weight to the

results obtained from the present study.

a. Pre-seismic code structures b. Fiber-based model (Elnashai and Mwafy, 2002) c. Critical Facilities

Wall

Slab

Core wall

Rigid arm

Figure 4. Fiber-based numerical models developed for two set of reference buildings

Table 4. Summary of buildings fundamental periods (T1) from fibre-based and design models

Building T1, Fibre-based Models T1, Design models

BO-02 0.780 0.880

BO-08 1.344 1.396

BO-18 1.432 1.572

BO-26 2.370 2.457

BO-40 3.901 3.755

FS 0.746 0.764

PS 0.656 0.702

SC 0.817 0.891 Fiber-based model Design model

HO 1.294 1.365 First two mode shapes for the Hospital (HO)

SELECTION OF LIMIT STATES

Seismic performance criteria of structures, which are related to the level of non-structural and structural

damage, have received focused attention. The performance levels considered in this study are as follows

(ASCE-41, 2007; SEAOC, 1995):

(i) Collapse Prevention (CP): which allows for a small margin of safety against collapse during a severe

earthquake.

(ii) Life Safety (LS): which indicates a significant damage to the building's lateral force resisting system,

but keeps a large margin against collapse.

(iii) Immediate Occupancy (IO): where a relatively minor damage may occur to the building, and the

lateral force-resisting elements retain their initial strength and much of their original ductility.

Studying the structural performance at both the global and local response levels would provide a

clear understanding about the behaviour of the structure during an earthquake. The local and global

seismic behaviour of the reference structures are therefore assessed using IPA and IDA to provide

insights into the performance limit states. Figure 5 depicts sample IPA results including mapping the

6

local response with the global response for one of the reference buildings (BO-08). The 10% reduction

in ultimate strength is also shown on the IPA curve which is observed at 2.96% Interstorey Drift (ID).

It is shown from the results that the steel yielding starts in beams and followed by columns. The global

yielding takes place at 1.16% ID. First concrete crushing occurs in beams at 1.86% ID. Mapping the

plastic hinge distributions of a sample building shows a wide spreading of yielding unlike concrete

crushing which is limited to four locations. Despite the acceptable overstrength, plastic hinge

distributions and sequence, which are attributable to considering wind loads in design, the results

confirm the rapid strength degradation of pre-seismic code buildings.

Inelastic dynamic simulations are performed using the set of earthquake records selected

previously. Post-processors and spreadsheets are utilized for monitoring the local and global

performance criteria during IDAs. Figure 6(a) presents the distributions of concrete crushing and plastic

hinges for the 2-story frame building. Figure 6(b) also presents sample results for the shear demand

versus capacity of an internal column. The experimentally verified shear strength model used to check

the shear failure possibility in structural members was proposed by Priestley et al. (1994). The shear

strength obtained using the design code is also shown as a reference (BS8110, 1986). The results of the

former model show a significant drop in shear strength due to increasing ductility to the level that

matches the code shear strength. It is clear that from these sample results that columns are dominated

by flexure, rather than shear as the demand does not exceed either of the Priestley or the code shear

strength models. The results obtained from monitoring the local and global response of the nine

reference structures are used for selecting the required limit states for developing fragility curves.

0

1000

2000

3000

4000

5000

6000

0 200 400 600 800 1000

Base Shear (kN)

Top Disp. (mm)

Design

∆∆∆∆max

Vd

Vy

∆∆∆∆y

Vd

ID=1.16

ID=1.86

ID=2.96

First beam yielding ● First column yielding �

Global yielding � Global failure ▲

First beam crushing × First column crushing ○

10% reduction

in strength

Figure 5. Sample IPA results for the 8-story pre-code building (BO-08); mapping the local response with the

global capacity curve (left), plastic hinge distributions (middle) and distributions of concrete crushing (right)

(a) (b)

0

50

100

150

200

250

0 5 10 15 20 25 30

Shear Deaman

d &

Supply (KN)

Time Step (s)

V(Demand)

V(Design Strength)

V(Priestley)

Figure 6. Sample IDA results for the 2-story frame building (BO-02): (a) mapping the distributions of plastic

hinges and concrete crushing, and (b) shear response of an internal column

A literature review is also carried out to confirm the limit states used for deriving fragility curves.

The adopted performance criteria thus take into consideration those recommended by code provisions

and previous experimental and analytical studies as well as the IPA and IDA results obtained from the

current study. For the pre-code frame and wall structures, the IO limit states are determined from the

A.Issa and A.Mwafy 7

IDA curves based on the 16 percentile of the ID values at the first indication of nonlinear response

(Vamvatsikos and Cornell, 2002). The CP limit state of pre-code frames is determined from IPA based

on the 10% strength reduction of ultimate capacity, which is the most conservative CP performance

indicator observed in the present study (Mwafy and Elnashai, 2001; Park, 1988). For pre-code wall

structures, the CP performance limit is determined from Time History Analysis (THA) based on the 16

percentile of the ID values at the first indication of crushing in the confined concrete of shear walls. The

strain corresponding to the crushing of confined concrete is obtained as per Mander et al. (1988). Finally,

for emergency facilities, the IDA results indicated a significantly high limit states compared with

previous studies. Therefore, the IO limit state is selected based on another study that covered a wide

range of well-designed structure with different characteristics (Ashri and Mwafy, 2014). The CP limit

state is determined according to the statistical analysis of several previous test results (Dymiotis et al.,

1999). The LS performance level is generally considered 50% of the CP value (ASCE-41, 2007). Table

5 summarizes the literature review and results of the present study, which are used to select limit states.

All of the selected performance criteria are consistent with the results obtained from the current study,

previous experimental studies (e.g. Dymiotis et al., 1999; Ghobarah et al., 1998; Wood, 1991), previous

analytical studies (Ghobarah et al., 1999; Liel et al., 2010; Ramamoorthy et al., 2008), and the code

provisions (ASCE-41, 2007). Additional information regarding the adopted limit states is available

elsewhere (Issa, 2014).

Table 5. Summary of interstory drift (ID) ratios for different limit states

Selection Approach

Reference Structure

Pre-code Frames Pre-code Walls Emergency Facilities

Limit State - Interstory Drift (%)

IO LS* CP IO LS* CP IO LS* CP

ASCE-41, 2007 0.50 1.00 2.00 1.00 2.00 4.00

Ex

per

imen

tal

stu

die

s Ghobarah, 1998 1.00 2.00 3.28

Wood, 1991 - 16% 1.36

Wood, 1991 - 50% 1.88

Wood, 1991 - 84% 2.60

Dymiotis et.al., 1999 - 16% 1.90

Dymiotis et.al., 1999 - 50% 4.00

Dymiotis et.al., 1999 - 84% 6.70

An

aly

tica

l

stu

die

s

Ghobarah et.al., 1999 0.70 1.10 2.50 0.40 1.80 3.00

Ramamoorthy et.al., 2008 - 16 % 0.33 0.56

Ramamoorthy et.al., 2008 - 50 % 0.50 0.98

Ramamoorthy et.al., 2008 - 84 % 0.75 1.71

Liel et.al., 2010 - 16 % 3.26

Liel et.al., 2010 - 50 % 4.17

Liel et.al., 2010 - 84 % 5.34

Cu

rren

t st

udy

IPA, first yield and crushing 0.67 3.74 0.33 1.59 0.85 3.67

IPA, 10% strength reduction 2.96

THA - 16% 0.40 2.71 0.32 1.78 0.77 2.91

THA - 50% 0.48 3.30 0.39 2.27 0.98 3.16

THA - 84% 0.57 4.02 0.48 2.89 1.24 3.44

IDA - 16% 0.39 4.13 0.34 2.83 0.65 6.49

IDA - 50% 0.57 5.43 0.62 3.83 1.00 8.79

IDA - 84% 0.84 7.14 1.13 5.18 1.54 11.91

Selected Limit State 0.39 1.48 2.96 0.34 0.89 1.78 1.00 2.00 4.00 IO: Immediate Occupancy, LS: Life Safety, CP: Collapse Prevention

IPA: Pushover Analysis, THA: Time History Analysis, IDA: Incremental Dynamic Analysis * LS limit state is considered 50% of the CP counterpart

FRAGILITY ASSESSMENT

A large number of IDAs are performed to derive the vulnerability relationships of the nine reference

structures. In addition to monitoring global response parameters such as ID ratio, top displacement, and

base shear, the developments of plastic hinges and concrete crushing in different structural members are

8

monitored to provide more understanding into the level of structural damage. As shown in Figure 7, 280

response points (PGA versus ID ratio) are plotted for each of the nine buildings from each of the

considered seismic scenarios. Regression analyses are performed for IDA results to develop fragility

relationships. The presented set of regression analysis results shown in Figure 7 are for three reference

buildings.

y = 1.1432x1.0726

R² = 0.7828

0.00

5.00

10.00

15.00

20.00

0.00 1.00 2.00 3.00 4.00 5.00

ID (

%)

PGA (g)

Fire Station (Short)

y = 4.9707x1.3399

R² = 0.9421

0.00

2.00

4.00

6.00

8.00

10.00

12.00

0.00 0.20 0.40 0.60 0.80 1.00 1.20

ID (

%)

PGA (g)

Fire Station (Long)

y = 0.6434x0.9268

R² = 0.8208

0.00

1.00

2.00

3.00

4.00

5.00

6.00

0.00 1.00 2.00 3.00 4.00 5.00

ID (

%)

PGA (g)

18-Story (Short)

y = 3.3225x1.0141

R² = 0.8886

0.00

1.00

2.00

3.00

4.00

5.00

6.00

0.00 0.20 0.40 0.60 0.80 1.00 1.20

ID (

%)

PGA (g)

18-Story (Long)

y = 0.4084x + 0.187

R² = 0.5713

0.00

1.00

2.00

3.00

4.00

0.00 1.00 2.00 3.00 4.00 5.00

ID (

%)

PGA (g)

40-Story (Short)

y = 3.1294x0.9625

R² = 0.8871

0.00

1.00

2.00

3.00

4.00

5.00

6.00

0.00 0.20 0.40 0.60 0.80 1.00 1.20

ID (

%)

PGA (g)

40-Story (Long)

Figure 7. Regression analysis for sample buildings using two seismic scenarios

(short: near-field records; long: far-filed records)

The statistical distributions shown in Figure 7 are employed to estimate the probability of

exceeding each of the selected limit states at different ground motion intensity levels. The vulnerability

curves are derived by plotting the calculated probability values versus PGAs. The derived fragility

relationships of the reference structure are shown in Figure 8. The results are presented to enable the

comparison of the vulnerability curves derived from the two seismic scenarios used in the current study.

The results show that the steepness of the fragilities decreases as the limit state changes from IO to CP.

For pre-seismic code buildings, the probability of exceeding different limit states are higher for low-rise

frame buildings. This indicates that earthquakes have less impact on high-rise wall structures. This

statement is confirmed under the effect of both severe distant and moderate close events. This is

attributable to the efficiency of shear walls in controlling drift and to the lower contribution of the

fundamental mode of vibration to seismic response with increasing the building height.

The vulnerability curves of the five pre-code structures reflect the differences between the

fragilities obtained from the two seismic scenarios employed in the present study. The slopes are sharper

A.Issa and A.Mwafy 9

and the probability of exceeding various limit states is much higher under the effect of the far-field

ground motions compared with near-source events. The seismic response of the pre-code high-rise

buildings (i.e. 18, 26 and 40 storeys) is acceptable at the design PGA when subjected to the near-source

records. The results confirm that the earthquake magnitude and distance have a significant influence on

the seismic risk of multi-story buildings. The findings support the observations discussed above about

the vulnerability of the pre-code buildings to severe distant earthquakes compared with moderate close

events. The low impacts of short-period records on seismic performance is noticeable and it follows the

findings of previous analytical studies (Mwafy, 2012).

The four emergency facilities show satisfactory seismic performance under the two seismic

scenarios considered herein. As discussed above in pre-code structures, far-field records have the highest

impact on emergency facilities. In spite of the good performance of modern code designed emergency

buildings, and taking into consideration their important role during and after an earthquake, it is

preferable to perform a precautionary retrofit for such facilities to minimize seismic losses.

0

0.2

0.4

0.6

0.8

1

0 0.5 1 1.5

P(L

imit State|G

MI)

PGA (g)

IO-Long

LS-Long

CP-Long

IO-Short

LS-Short

CP-Short

0

0.2

0.4

0.6

0.8

1

0 0.5 1 1.5

P(L

imit State|G

MI)

PGA (g)

IO-Long

LS-Long

CP-Long

IO-Short

LS-Short

CP-Short

0

0.2

0.4

0.6

0.8

1

0 0.5 1 1.5

P(L

imit State|G

MI)

PGA (g)

IO-Long

LS-Long

CP-Long

IO-Short

LS-Short

CP-Short

BO-02, 2-storey BO-08, 8-storey BO-18, 18-storey

0

0.2

0.4

0.6

0.8

1

0 0.5 1 1.5

P(L

imit State|G

MI)

PGA (g)

IO-Long

LS-Long

CP-Long

IO-Short

LS-Short

CP-Short

0

0.2

0.4

0.6

0.8

1

0 0.5 1 1.5

P(L

imit State|G

MI)

PGA (g)

IO-Long

LS-Long

CP-Long

IO-Short

LS-Short

CP-Short

0

0.2

0.4

0.6

0.8

1

0 0.5 1 1.5

P(L

imit State|G

MI)

PGA (g)

IO-Long

LS-Long

CP-Long

IO-Short

LS-Short

CP-Short

BO-26, 26-storey BO-40, 40-storey FS, Fire Station

0

0.2

0.4

0.6

0.8

1

0 0.5 1 1.5

P(L

imit State|G

MI)

PGA (g)

IO-Long

LS-Long

CP-Long

IO_Short

LS-Short

CP-Short

0

0.2

0.4

0.6

0.8

1

0 0.5 1 1.5

P(L

imit State|G

MI)

PGA (g)

IO-Long

LS-Long

CP-Long

IO-Short

LS-Short

CP-Short

0

0.2

0.4

0.6

0.8

1

0 0.5 1 1.5

P(L

imit State|G

MI)

PGA (g)

IO-Long

LS-Long

CP-Long

IO-Short

LS-Short

CP-Short

PS, Police Station SC, School HO, Hospital

Figure 8. Fragility curves of nine reference structures using two seismic scenarios (short: near-field records;

long: far-filed records)

To provide more representative results from the derived fragility curves, limit states probabilities

are estimated at the design and twice the design PGAs for far-field records, twice and four times the

design for near-source records (Figure 9). Two main observations are evident; the first observation is

that pre-code structures are significantly more vulnerable compared with emergency facilities. The

second observation is that far-field records have much higher impact on the reference structures over

the near-source records. The large increase in the probabilities of various limit states is also clear when

the buildings are subjected to twice and four times the design intensities for far-field and short-period

records, respectively.

10

0

0.2

0.4

0.6

0.8

1

BO-02

(1D)

BO-02

(2D)

BO-08

(1D)

BO-08

(2D)

BO-18

(1D)

BO-18

(2D)

BO-26

(1D)

BO-26

(2D)

BO-40

(1D)

BO-40

(2D)

Pro

ba

bil

ity

(%

)

Building

IO LS CP

0

0.2

0.4

0.6

0.8

1

BO-02

(2D)

BO-02

(4D)

BO-08

(2D)

BO-08

(4D)

BO-18

(2D)

BO-18

(4D)

BO-26

(2D)

BO-26

(4D)

BO-40

(2D)

BO-40

(4D)

Pro

ba

bil

ity

(%

)

Building

IO LS CP

Pre-code buildings,

Far-field records at the design (1D) and at twice the design

(2D)

Pre-code buildings,

Near-source records at twice the design (2D) and at four times

the design (4D)

0

0.2

0.4

0.6

0.8

1

FS (1D) FS (2D) PS (1D) PS (2D) S (1D) S (2D) H (1D) H (2D)

Pro

ba

bil

ity

(%

)

Building

IO LS CP

0

0.2

0.4

0.6

0.8

1

FS (2D) FS (4D) PS (2D) PS (4D) S (2D) S (4D) H (2D) H (4D)

Pro

ba

bil

ity

(%

)

Building

IO LS CP

Emergency facilities,

Far-field records at the design (1D) and at twice the design

(2D)

Emergency facilities,

Near-source records at twice the design (2D) and at four times

the design (4D)

Figure 9. Limit state probabilities of the nine reference buildings

CONCLUSIONS

Pre-code structures and emergency facilities are of high significance in the potential consequences from

natural hazard events since they represent high levels of vulnerability and readiness of service,

respectively. Due to the significance of such structures along with increasing the frequency of seismic

activities, a detailed vulnerability assessment of seismic risk in the earthquake prone areas of the UAE

is necessary in order to effectively estimate and mitigate earthquake losses. This comprehensive study

enabled the derivation of a wide range of dynamic response simulation-based fragility relationships for

pre-seismic code buildings and emergency facilities. The study included the selection, structural design

and developing verified fibre-based simulation models for nine reference structures representing a wide

range of the pre-code structures and emergency facilities in the UAE. The selection and scaling of 40

input ground motions representing the near-field and far-field earthquake scenarios anticipated in a

highly populated seismically prone area of the UAE were briefly discussed. The limit state criteria

employed for deriving fragility curves were selected based on the mapping of local and global response

parameters from inelastic pushover analyses (IPAs) and incremental dynamic analyses (IDAs) as well

as from previous studies. The measured seismic response from a large number of IDAs was related to

ground motion intensity to derive the fragility relationships of the nine reference structures.

The probability of exceeding limit states was much higher and the slopes were sharper under the

effect of the far-field earthquake scenario compared with the near-source counterpart. The latter seismic

scenario had low impacts on the seismic response of the reference buildings, especially the emergency

facilities at the design and twice the design intensity. The high impacts of the far-field seismic scenario

are attributed to the higher spectral amplifications and effective durations of the long period input ground

motions. At the design intensity, the seismic response of the pre-seismic code wall structures and

emergency facilities was acceptable under the near-field seismic scenario. On the other hand, the

presented study confirmed the vulnerability of a wide range of pre-code buildings to the far-field seismic

A.Issa and A.Mwafy 11

scenario anticipated in the earthquake-prone areas of the UAE. It also showed the lower vulnerability of

emergency buildings due to the adoption of modern code provisions in the design of such facilities. The

results support implementing a mitigation strategy for reducing the seismic risk of pre-code structures

by means of various rehabilitation techniques. Such measures include but not limited to, reinforced

concrete jacketing, fibre-reinforced polymers (FRP) wrapping, and buckling-restrained braces (BRB). In spite of the acceptable performance of modern code designed emergency buildings under near-field

events, and taking into consideration their crucial role following an earthquake, it is recommended to

perform a precautionary retrofit for such facilities to minimize seismic losses, particularly under the

effect of the far-field seismic scenario. The developed fragility functions in this study are an essential

component for the estimation of possible earthquake losses in the UAE. The outcomes of the present

study motivates interdisciplinary research activities in future to develop a comprehensive earthquake

loss assessment and mitigation system to preserve the large investments in the construction industry in

this region.

AKCNOWLEDGEMENT

This work was supported by the United Arab Emirates University under research grants no. 31N132 and

31N007.

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