1 Seismic Design Criteria

1.1 Based on Saudi Building Code

In accordance with Saudi Building Code 301 chapter 9, figure 9.4.1(a), Jeddah is in Region 6.

Figure 2.1a: Regions for Determination of the Maximum Considered Earthquake Ground Motion in the Kingdom of Saudi Arabia ( Figure 9.4.1(a) of SBC-301)

Ss, 0.2 sec Spectral Response Acceleration (% of g) for 5% critical damping and site class B = 25% g = 0.25g - refer figure 9.4.1(h).

S1, 0.1 sec Spectral Response Acceleration (% of g) for 5% critical damping and site class B = 10% g = 0.10g - refer figure 9.4.1 (p).

Site Class – D assuming stiff soil (refer Table 14.1.1).

Site Coefficients values are as follows based on Table 9.4.3 a & b of Saudi Building Code 301:

Fa 1.6 Ss ≤ 0.25 and Site Class D

Fv 2.4 S1 ≤ 0.10 and Site Class D

The maximum considered earthquake spectral response acceleration for short period

SMS = Fa Ss = 1.6 x 0.25g = 0.40g

The maximum considered earthquake spectral response acceleration for 1 sec period

SM1 = Fv S1 = 2.4 x 0.10g = 0.24g

Figure 2.1b: Maximum Considered Earthquake Ground Motion for the Kingdom of 0.2 SEC Spectral Response Acceleration (Ss in %g) 5 percent Critical Damping, Site Class B. (Region 6)-( Figure 9.4.1(h) of SBC-301)

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Figure 2.1c: Maximum Considered Earthquake Ground Motion for the Kingdom of 1 SEC Spectral Response Acceleration (S1 in %g) 5 percent Critical Damping, Site Class B. (Region 6)-( Figure 9.4.1(p) of SBC-301)

1.1.1 Design Spectral Response Acceleration Parameter

Design Spectral Response Acceleration Parameters are as follows based on section 9.4.4 of Saudi Building Code 301:

SDS = 2/3 x SMS 0.27g

SD1 = 2/3 x SM1 0.16g

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1.1.2 Design Response Spectrum

Based on Saudi Building Code 301 section 9.4.5, the design response spectrum is as follows.

Figure 2.1.2: Saudi Building Code Region 4 design response spectrum – site class A

where,

Sa = The design Spectral Response Acceleration

T = The fundamental period of structure

To = 0.2 SD1/SDS = 0.119 sec

Ts = SD1/SDS = 0.593 sec

For T ≤ To, Sa = SDS (0.4+0.6 T/To)

For To≤T≤Ts, Sa = SDS

For T>Ts, Sa = SD1/T

1.1.3 Occupancy Importance Factor

Based on Saudi Building Code 301 table 1.6-1, the Sky Villa is under Category II which suggests I = 1.0 in accordance with table 9.5.

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Sa = SD1/T

T0 Ts

SD1

SDS

1.1.4 Seismic Design Category

Based on section 9.6.1, as SDS is equal to 0.27g which is greater than 0.167g but less than 0.33g and the building is under the occupancy category II, the seismic design category of the structure is B. SD1 is equal to 0.16g which is greater than 0.20g but less than 0.133g and the building is under the occupancy category II, the seismic design category of the structure is C.

For seismic design category C the following analytical procedures are permitted based on Table 10.6.1 for regular or irregular structure:

(a) Equivalent Lateral Force Analysis – Section 10.9

(b) Modal Response Spectrum Analysis – Section 10.10

For Building Frame System with ordinary reinforced concrete shear walls which is not limited for seismic design category C, the following design parameters have used for the sky villa lateral analysis under seismic load.

Response Modification Coefficient, R

4

SBC -Table 10.2System Overstrength

Factor, Ωo2.5

Deflection Amplification Factor, Cd

4.5

Reliability Factor ρ 1.0SBC- Section 10.3.3.1

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1.1.5 Seismic Base Shear for the Building

The fundamental time period of the building has been determined based on section 10.9.3.

The maximum limit of T = Cu Ta where Cu = 1.58 from Table 10.9.3.1 based on SD1 = 0.16g and Ta = Ct hn^x from equation 10.9.3.2-1.

Ct = 0.055 from Table 10.9.3.2 for all other structural system and x = 0.75 where as hn, the height above the base to the highest level of the structure i.e, from B1 to level 3 = 19.3 m.

Ta = 0.055 x (180)^0.75 = 2.7 sec. & Ta,max = 1.58 x 2.7 = 4.27 sec.

Based on Saudi Building Code 301 section 10.9 using equivalent lateral force procedure V = Cs W where Cs is the seismic response coefficient.

Cs

SDS

R/I

0.27

4.0/1.0= 0.0675

Cs, max SD1

T (R/I)

0.16

4.27 x (4.0/1.0)= 0.0094

Cs, min

0.044 SDS I 0.044 x 0.27 x 1.0 = 0.012

Vdesign = 0.012 x W

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2 Load CombinationsIn accordance with Saudi Building Code 301 section 2.3 load combinations for strength design have been used as follows.

(a) 1.2D+1.0E+f1 L – (Eq. 2.3.2-5)

(b) 0.9D+1.0E+1.6H – (Eq. 2.3.2-7)

where f1=1.0 for areas as places of public assembly, for live load in excess of 5.0 kPa, and for parking garrage live load

f1 = 0.5 for other live load

D = dead load

E = Earthquake load = ρ QE + 0.2 SDS D = 1.0 QE + 0.2 x 0.27 x D = QE + 0.054 D – to be used for Eq. 2.3.2-5

E = Earthquake load = ρ QE - 0.2 SDS D = 1.0 QE - 0.2 x 0.27 x D = QE - 0.054 D – to be used for Eq. 2.3.2-7

H = load due to lateral earth pressure, ground water pressure or pressure of bulk materials

L = live load

Lr = roof live load

Specific strength design load combinations are to be used :

(i) 1.254D+1.0EQx+0.3EQy+0.5L

(ii) 1.254D-1.0EQx-0.3EQy+0.5L

(iii) 1.254D+1.0EQy+0.3EQx+0.5L

(iv) 1.254D-1.0EQy-0.3EQx+0.5L

(v) 0.846D+1.0EQx+0.3EQy

(vi) 0.846D-1.0EQx-0.3EQy

(vii) 0.846D+1.0EQy+0.3EQx+0.5L

(viii) 0.846D-1.0EQy-0.3EQx+0.5L

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