Document Type : Regular Article
Authors
^{1} Assistant Professor, Department of Civil Engineering, King Khalid University, KSA. On leave from Sudan University for Science and Technology, Khartoum, Sudan
^{2} Assistant Professor, Department of Civil Engineering, King Khalid University, KSA. On leave from Structural Engineering Department, Zagazig University, Zagazige, Egypt
^{3} Lecturer, Department of Civil Engineering, King Khalid University, KSA
Abstract
Highlights
Keywords
Main Subjects
Haql is a town in the northwest of Saudi Arabia near the head of the Gulf of Aqaba, adjacent to Aqaba across the Jordanian border. The coasts of Egypt, Israel and Jordan can be seen from Haql. Haql city is located in the most active seismic zone region of the Kingdom of Saudi Arabia where there is a complicated geological structures and tectonics. This paper is an attempt to study the effect of seismic loads on RC residential buildings located in the most active seismic zone region of the Kingdom of Saudi Arabia. Saudi Arabia is not free from earthquakes. It has experienced many earthquakes during the recent history, and the previous studies in this field demonstrated this argument. Most of existing buildings in Saudi Arabia do not meet the current design standards due to design shortage or construction shortcomings.
The last major event was the 1995 Haql earthquake in the Gulf of Aqaba (magnitude 7.3) which caused significant damage on both sides of the Gulf and was felt hundreds of kilometres away. As far as Saudi Arabia is concerned, the most active area is along the Gulf of Aqaba (Dead Sea transform fault). On 19 May, 2009, 19 earthquakes of M4.0 or greater took place in the volcanic area of Harrat Lunayyir to the north of Yanbu, including a M5.4 event that caused minor damage to structures [4]. The 1995 Gulf of Aqaba earthquake (also known as Nuweiba earthquake) occurred in November 22 at 06:15 local time (04:15 UTC) and registered 7.3 on the moment magnitude scale. The epicentre was located in the central segment of the Gulf of Aqaba. The earthquake occurred along the Dead Sea Transform (DST) fault system, an active tectonic plate boundary with seismicity that is characterized by longrunning quiescent periods with occasional large and damaging earthquakes, along with intermittent earthquake swarms. It was the strongest tectonic event in the area for many decades and caused injuries, damage, and deaths throughout the Levant and is also thought to have remotely triggered a series of small to moderate earthquakes 500 kilometres (310 miles) to the north of the epicentre. In the aftermath of the quake, several field investigations set out to determine the extent of any surface faulting, and the distribution of aftershocks was analyzed. Areas affected: Egypt, Israel, Jordan and Saudi Arabia as shown in Figure 1[4]. Recent studies, historical evidences, geological and geophysical observations indicate that parts of the Kingdom fall within seismic risk regions. In western Saudi Arabia, a design peak ground acceleration (PGA) ranging from 0.03g to 0.26g for an economic life of 50 years was suggested. Seismic zonation was established with zone numbers 0, 1, 2A, and 2B [5]. Saudi Arabia is not free from earthquakes. It has experienced many earthquakes during the recent history, and the previous studies in this field demonstrated this argument. Most of existing buildings in Saudi Arabia do not meet the current design standards due to design shortage or construction shortcomings. Therefore, buildings should be designed regarding their capacity for resisting expected seismic effects. The seismic hazard analysis for the Kingdom was performed [6, 7]. Seismograph stations of the Saudi National Seismic Network as shown in Figure 2 [8], was developed for the Kingdom based on the peak ground acceleration, PGA, values calculated for 50 years service lifetime with 10% probability of being exceeded.
Fig. 1. 1995 Gulf of Aqaba earthquake [4]
Fig. 2. Seismograph stations of the Saudi National Seismic Network [8]
A sixstorey residential buildings with plan and elevations as shown in Figures 3 to 6 is considered for study. The building is composed of moment resisting RC frame with solid slab, 140mm thickness, situated in the most active seismic zone region of the Kingdom of Saudi Arabia. The structure members are made of insitu reinforced concrete .The overall plan of building is square with dimensions 14.5x15m as shown in Figure 3. Height of the building is 16 m and storey height for each floor is 3.2 m. Columns and beams sizes are shown in Table 1. The building is approximately symmetric in both directions. The plan and some frames of the studied building as shown in Figures 3 to 5. Beams and columns have been modelled as frame elements while inplane rigidity of the slab is simulated using rigid diaphragm action. The columns are assumed to be fixed at the base. The building is analyzed.
as per seismic provisions provided by SBC 3012007.
Table 1. The cross section of beams and columns
Building 
Beams 
Level 
Columns 
Reinforcement 
mm 
mm 


6 Stories 
600*250 
1st floor 2nd floor 
600*250 
12 Φ 16 
(10 Φ 16) 
3nd floor4rd floor 
500*250 
10 Φ 16 

5th floor 5th floor 
450*250 
10 Φ 16 
Fig. 3. Architectural plan of the studied building
Fig. 4. YZ elevation @ X=5.5 m of the studied building
Fig. 5. XZ elevation @ Y=9.5 m of the studied building
Fig. 6. XY Plan of studied building
It is a common practice in The Kingdom of Saudi Arabia to design buildings without any consideration of seismic loads. Therefore, the one typical case study has been studied first under the effect of gravity loads and without consideration of seismic loads in order to check the current design. Dead and live loads are following the equations and tables given in the SBC3012007(Saudi Arabia) and second under the effect of seismic loads.
Most buildings and structures in the kingdom of Saudi Arabia have not yet been designed and constructed in compliance with earthquake provisions or given any consideration for earthquake effect.
The horizontal seismic loads are defined according to Saudi Buildings Code (SBC3032007). The lateral force effect on the structure can be translated to equivalent lateral force at the base of the structure which can be distributed to different stories. According to Saudi Buildings Code (SBC3032007), the total seismic base shear force V is determined as follows:
V = Cs*W )1(
Where: Cs is the seismic coefficient, W is the total weight and V is the base shear. The seismic design coefficient (Cs) shall be determined in accordance with the following equation:
Cs = SDS / (R / I) )2(
Where, SDS = Design spectral response acceleration in the short period range
R = Response modification factor
I = Occupancy importance factor determined
The value of the seismic response coefficient, (Cs), need not be greater than the following equation:
Cs = SD1 / [T. (R / I)] )3(
But shall not be taken less than.
T = 0.1N )4(
Where N = Number of stories
Cs = 0.044SDS I )5(
Where, SDS = Design spectral response acceleration at a period of 1 sec
T = Fundamental period of the structure (sec)
Design earthquake spectral response acceleration at short periods, SDS, and at 1sec period, SD1, shall be as follows.
SMS= Fa*SS )6(
SM1= Fv*S1 )7(
SDS= 2/3*SMS )8(
SD1= 2/3*SM1 )9(
Where:
SS: the maximum spectral response acceleration at short periods
S1: the maximum spectral response acceleration at a period of 1 sec
Fa: accelerationbased site coefficient
Fv: velocitybased site coefficient
SMS: the maximum spectral response acceleration at short periods adjusted for site class
SM1: the maximum spectral response acceleration at a period of 1 sec adjusted for site class
SDS: the design spectral response acceleration at short periods
SD1: the design spectral response acceleration at a period of 1 sec
The buildings are subjected to a lateral load distributed across the height of the buildings
based on the following formula specified by Saudi Buildings Code (SBC3032007):
Where, Fx is the applied lateral force at level ‘x’, W is the storey weight, h is the storey height and V is the design base shear, and N is the number of stories. The summation in the denominator is carried through all storey levels. This results in an inverted triangular distribution when k is set equal to unity. A uniform lateral load distribution consisting of forces that are proportional to the storey masses at each storey level.
k = an exponent related to the structure period as follows:
For structures having a period of 0.5 sec or less, k = 1
For structures having a period of 2.5 sec or more, k= 2
As per SBC301 section 2.3, following load combinations should be considered for design of structures, components, and foundations.
1.4 (D + F)
1.2 (D + F + T) + 1.6 (L + H) + 0.5 (Lr or R)
1.2 D + 1.6 (Lr) + (f1L)
1.2D + f1L + 0.5 (Lr)
1.2D + 1.0 E + f1L
0.9D ± 1.0E
Where:
E = ρQE + 0.2SDSD
1.0 ≤ ρ ≤ 1.5
f1 = 1.0 for areas occupied as places of public assembly, for live loads in excess of 5.0 kN/m2, and for parking garage live load.
f1 = 0.5 for other live loads.
SDS = the design spectral response acceleration in the short period range as determined from Section.
QE = the effect of horizontal seismic (earthquakeinduced) forces.
Table 6.1 shows the design parameters taken from both codes for analysis of buildings.
The Saudi Buildings Code (SBC3032007) provides seismic maps for the Kingdom of Saudi Buildings, as shown in Figures 7 and 8.
Fig. 7. Maximum Considered Earthquake Ground Motion for the Kingdom of 1 SEC Spectral Response Acceleration (S1 in %g) (5 Percent of Critical Damping), Site Class B. (Region 1) [1].
Fig. 8. Maximum Considered Earthquake Ground Motion for the Kingdom of 0.2 SEC Spectral Response Acceleration (Ss in %g) (5 Percent of Critical Damping), Site Class B. (Region 1) [1].
The design parameters that are used in the equivalent static method are illustrated as following: The parameters Ss and S1 shall be determined from the 0.2 and 1 second spectral response accelerations shown on country maps
Where S1 is less than or equal to 0.04 and Ss is less than or equal 0.15, the structure is permitted to be assigned to seismic design category A So,
S1= the mapped spectral accelerations for a 1 second period
Ss= the mapped spectral accelerations for short period.
v On lack of a map of spectral accelerations of S1 and SS, the following can be assumed: S1= 1.25 Z, Ss= 2.5 Z (amendment no. 3 to SI 413 (2009)) or from maps as shown in Figures 7 and 8.
Figures 9 and 10 shows the label of columns and beams of the selected frames
Fig. 9. Label of beams and columns in direction XZ@Y=9.5 m
Fig 10. Label of beams and columns in direction YZ@X= 5.5 m
This part presents the results of analysis and design of considered RC buildings due to gravity loads. We selected one frame in each direction X and Y as shown in figures 9 and 10 for columns and beams.
1. Beams
Table 2 shows the Straining action of some beams in the selected frames at direction YZ @ X = 5.5
Table 2. The Straining action of some beams in the selected frames at direction YZ @ X = 5.5
Direction YZ @ X=5.5 

Load Case Ultimate (1.4DL+1.6LL) 

Beam No. 
SHEAR 
MOMENT 33 (KN.m) 

KN 
END 
START 

B03 
9.81 
0.24 
6,81 
B09 
21.7 
29.54 
1.62 
B11 
11.91 
4.5 
10.15 
B17 
21.42 
29.11 
1.61 
B19 
13.16 
7.37 
12.3 
2. Columns
Tables 3 shows the Straining action of some columns in the selected frames at direction YZ @ X = 5.5
Table 3. The Straining action of some columns in the selected frames at direction YZ @ X = 5.5
Direction YZ @ X=5.5 

Load Case Ultimate (1.4DL+1.6LL) 

Column No. 
AXIAL 
SHEAR 
MOMENT 33 (KN.m) 

KN 
END 
START 

C01 
907.8 
0.61 
0.62 
2.57 
C03 
1307.75 
10.94 
21.51 
13.51 
C09 
586.33 
0.56 
1.46 
0.33 
C11 
855.93 
15.98 
26.44 
24.68 
C17 
285.18 
0.63 
1.17 
0.84 
C19 
421.77 
11.1 
18.29 
17.22 
This part presents the results of analysis and design of considered RC buildings due to seismic loads. Using the Saudi Buildings Code (SBC3012007) provisions, the following parameters have been calculated to be used as input data for seismic analysis of the selected model with notice that the Haql City falls in region 6. The calculated results of these parameters are as follows:
Table 4. Seismic parameter for Haql City according to SBC301
SDS 
0.14 
CS = 
0.0714 
SD1 
0.04 
CS (max.) = 
0.0678 
I 
1.00 
CS(min.) = 
0.0057 
R 
2.00 

W= 
812.0 KN 
V= 
55.1 TON 
Take CS= 0.678 
Table 5. Calculation of Base Shear and lateral load distribution with height
Storey 
W (ton) 
h (m) 
w*h 
cv 
Fx (TON) 
Sixth Floor 
16.66 
21 
350 
0.015 
0.9 
Fifth Floor 
142.67 
18 
2568 
0.114 
6.3 
Fourth Floor 
268.69 
15 
4030 
0.179 
9.8 
Third Floor 
394.70 
12 
4736 
0.210 
11.6 
Second Floor 
520.72 
9 
4686 
0.208 
11.4 
First Floor 
646.73 
6 
3880 
0.172 
9.5 
Ground Floor 
772.75 
3 
2318 
0.103 
5.7 
SUM(W*H) 
22570 
SUM FX 
55.1 
1. Beams
Tables 6 shows the Straining action of some beams in the selected frames at direction YZ @ X = 5.5 m due to load case GroupY
Table 6. The Straining action of some beams in the selected frames at direction YZ @ X = 5.5 m due to load case GroupY
Direction YZ @ X=5.5 m 

Load case: GroupY 

Beam No. 
SHEAR 
MOMENT 33 (KN.m) 

KN 
END 
START 

B03 
53.39 
93.73 
90.13 
B09 
22.07 
30.12 
1.65 
B11 
49.02 
86.03 
82.88 
B17 
21.78 
29.68 
1.64 
B19 
32.05 
52.51 
49.84 
Where:
Load Case GroupY is load combination included seismic loads at Y direction.
Load Case Ultimate is load combination included dead and live loads only
2. Columns
Tables 7 shows the Straining action of some columns in the selected frames at direction YZ @ X = 5.5 m
Table 7. The Straining action of some Columns in the selected frames at direction YZ @ X = 5.5 m due to load case GroupY
Direction YZ @ X=5.5 

Load Case: GroupY 

Column No. 
AXIAL 
SHEAR 
MOMENT 33 (KN.m) 

KN 
END 
START 

C01 
922.95 
1.23 
2.68 
2.62 
C03 
1331.32 
11.18 
21.93 
13.8 
C09 
596.12 
1.74 
3.28 
2.3 
C11 
871.43 
18.32 
27.01 
25.21 
C17 
289.96 
0.74 
1.33 
1.04 
C19 
429.44 
11.33 
18.68 
17.59 
The reinforced concrete sections were designed according to the BSI 8110 [9] using the limit state design method (Mosley and Bungey, 1997) [10].
(a) Calculation of internal forces in columns
The columns were designed to resist axial compression forces and bending moment due to gravity load. The design forces in columns obtained from the computer analysis program SAP2000 are shown in Table 8.
*Direction YZ@X=5.5
Table 8. Internal forces in columns due to gravity loads
Column No. 
Output Case 
Shear Force (KN) 
Bending Moment (KN.m) 
Axial Force (KN) 
C04 
1.4DL+1.6LL 
11.26 
13.99 
1372.02 
C03 
1.4DL+1.6LL 
10.94 
13.51 
1307.75 
C02 
1.4DL+1.6LL 
1.64 
3.78 
997.52 
C01 
1.4DL+1.6LL 
0.61 
2.57 
907.80 
(b) Design of columns before adding seismic loads
* Direction YX@X=5.5
The design of columns has been performed using a computer program called ISACOL [5]. Figures 11 and 13 show the main window of ISACOL program and sample of a column design.
Fig. 11. ISACOL program results for C40 [3].
Table 9. Design of columns before adding seismic Loads
Column No. 
Original design 
Present design 

Dimensions 
Reinforcement 
Dimensions 
Reinforcement 

C04 
250 X 500 
12 Φ 16 
250 X 500 
10 Φ 16 
C03 
250 X 500 
12 Φ 16 
250 X 500 
10 Φ 16 
C02 
250 X 500 
12 Φ 16 
250 X 500 
10 Φ 16 
C01 
250 X 500 
12 Φ 16 
250 X 500 
10 Φ 16 
250*500 250*500
12 Φ 16 10 Φ 16
Fig. 12. Design of some columns before adding seismic Loads
As for the beams the internal forces due to gravity loads have been calculated first .Then the BSI [9], has been used to check the existing design .It has been found that the existing design is adequate.
The reinforced concrete sections were designed according to the BSI 8110 [9] using the limit state design method (Mosley and Bungey, 1997) [10].
(a) Calculation of internal forces in columns
The columns were designed to resist seismic and gravity load. The design forces in columns obtained from the computer analysis program SAP2000 are shown in Table 10.
* Direction YZ@X=5.5 m
Table 10. Internal forces in columns due to seismic loads.
Column No. 
Output Case 
Shear Force (KN) 
Bending Moment (KN.m) 
Axial Force (KN) 
C04 
GROUPX 
159.27 
298.95 
1397.14 
C03 
GROUPX 
137.69 
256.36 
1331.32 
C02 
GROUPX 
125.60 
223.55 
1041.80 
C01 
GROUPX 
96.96 
173.70 
922.95 
(b) Design of columns after adding seismic loads
The design of columns has been performed using a computer program called ISACOL [3]. Figures 12 and 14 show the design of some columns before and after adding seismic loads.
Fig. 13. ISACOL program results for C04 [3].
Table 11. Shows the design of columnsafter adding seismic loads.
Table 11. Design of columns after adding seismic loadsdirection (y)
Column No. 
Original design 
Including seismic loads 

Dimensions 
Reinforcement 
Dimensions 
Reinforcement 

C04 
250 X 500 
10 Φ 16 
250*1550 
18 Φ 20 
C03 
250 X 500 
10 Φ 16 
250*1250 
14 Φ 20 
C02 
250 X 500 
10 Φ 16 
250*1200 
14 Φ 20 
C01 
250 X 500 
10 Φ 16 
250*850 
12 Φ 20 
250*1200 250*850
14 Φ 20 12 Φ 20
Fig.14. Design of some columns after adding seismic loads
This paper provides set of seismic analysis and design of RC buildings located in the most active seismic zone region in Saudi Arabia. The building was analyzed and designed before and after considering earthquake loads applied in two directions; XX and YY. From the results obtained it can be clearly seen that:
1. There are slight changes in the values of the bending moments and shear forces on the beams before and after considering earthquake loads as shown in Tables 2 and 6. There is increase in some internal beams, such as B3, B11 and B19.
2. The values of the bending moments and shear forces on the columns due to seismic loads are nearly five times that due to gravity loads as shown in Tables 8 and 10.
3. The values of the axial forces on the columns due to seismic loads are approximately similar to gravity loads as shown in Tables 8 and 10.
4.As an overall trend the results showed that the current design of RC buildings located in the most active seismic zone region of the Kingdom of Saudi Arabia, Haql city were found unsafe, inadequate and unsatisfied to mitigate seismic loads.
The present study represents the first attempt to investigate the seismic resistance of residual buildings in Haql city in Saudi Arabia. Due to the lack of knowledge about the seismic activity in this country some buildings are designed and constructed without any seismic load consideration. Seismicity of The Saudi Arabia may be considered as moderate. Hence, all buildings should be checked against earthquake resistance. The present paper proposes a simple procedure to check the seismic resistance of such buildings.
The obtained results emphasize the following conclusions:
1 Current design of some residual buildings in the Saudi Arabia does not consider earthquake loads.
2 It has been found that the current design of residual buildings in the Haql city is unsafe for the current seismicity of the Haql city.
The author would like to express his gratitude to King Khalid University, Saudi Arabia for providing administrative and technical support.