SYRIAN SEISMIC CODE 20041:
Two static methods have been issued in Syrian building code 2004 to calculate the lateralseismic forces in the building.
The First Static Method:
It is the same method in the previous code (1995) with few modifications. It is based ondetermination of a design base shear force (V), which is then distributed in a specificpattern over the height of the structure for structure analysis of lateral load resistance.
The total design base shear in a given direction (V) is given by:

V = ( ZIKCS)*W

Seismic Zone Factor (Z):It is represent the peak ground acceleration in studied site as a percentage of gravity
acceleration g (9.81 m/sec2). Z factor for each zone is shown in the table below:
Seismic Zone
Z factor00

10.075

2A
0.15

2B
0.20

2C
0.25

30.3

Importance factor (I):
Occupancy CategoryI

All important structures which are required for continued operating
during earthquakes such as: hospitals, fire and police stations, …..etc.

1.50

All Structures with occupancy more than 300 persons.

1.25

All others structures.

1.00

I value not less than 2 for atomic structures and all hazardous structures.
Ductility Factor (K):
Building Type or description

KAll buildings not mentioned in this table
Bearing wall system

1.00
1.30

Building Frame System or Mixed System according to the following designing case:-Frames can bear 25% of the total lateral loads.
-Frames can bear 50% of the total lateral loads.

11.00
0.80

High tanks of water and similar which carried by a group of columns not less thanfour.

2.50

Special Building such as: Chimneys, T.V towers …..

2.00

The original Code is in Arabic and it has been translated to English by Eng. Hussam Eldein Zaineh,
National Earthquake Center (NEC).

Dynamic Factor (C):It represents the percentage between equivalent acceleration of the structure to the groundacceleration and it defined from this equation:
C=1
2

10T 3
Where:
T: is the fundamental period of the structure (sec) in a given direction, calculated by:
1- approximate determination in case of shear wall system structures:T(sec) = 0.08 N
Where, N is the number of stories.
2- approximate determination in case of frame system structures:

T = 0.1N
3- also, T must be estimated by using this approximate equation:3

T = γ t .(hn ) 4
Where:

hn : building height from the base up to level n in meters.

γ t =0.0853 for steel frame.

γ t =0.0731 for RC frame.
γ t =0.0488 for other buildings.
Note 1: T is the minimum value from previous three equations.
Note 2: C is equal to 0.15 for buildings consist of only one or two stories.
Note 3: in other cases C must be less than 0.18.
Note 4: in all cases, K.C must be less than 0.38 and more than 0.09.
Soil Coefficient (S):

1- in case ofT≤ 1:
Ts⎛T ⎞TS = 1.0 + − 0.5⎜⎜ ⎟⎟Ts⎝ Ts ⎠2

2- in case ofT> 1:
Ts⎛T ⎞TS = 1.2 + 0.6 − 0.3⎜⎜ ⎟⎟Ts⎝ Ts ⎠2

Ts: the characteristic site period (sec).
Total weight (W): is equal to all dead loads and 25% of live loads.
Lateral Loads distribution:

1-Regular structures or structural frame system:
The total lateral force (V) shall be distributed over the height of the structure inconformance with formulas:nV = Ft + ∑ Fii =1

Ft: The concentrated force at the top of the structure shall be determined from theformula:Ft = 0.07 × T × V
The value of (Ft) need not exceed (0.25 V) and may be considered as zero where T is
0.70 sec or less.
T: the fundamental period of the structure (sec) in the considered direction.
The remaining portion of the base shear (V- Ft) shall be distributed over the height of thestructure According to the following formula:
Fx =(V − Ft ) wx hxn∑w hi =1i i

Where:
wx: the vertical concentrated load at level x which equal to the weight of this level.
wi: the portion of (w) located at assigned to level i.
hx: height above the base to level x.
hi: height above the base to level i.
Fx: design seismic force applied at level x in the gravity center of this level.

2- Irregular structures:
The dynamic lateral-force procedure shall be used to analysis these kind of structures.

The Second Static Method:
It is based on determination of a design base shear force (V), which is then distributed
in a specific pattern over the height of the structure for structure analysis of lateral loadresistance.
The total design base shear in the considered direction (V) is given by:

V=Cv IW
RTThe total design base shear need not exceed the following:V =2.5C a IWR

The total design base shear shall not be less than the following:V = 0.11C a IW
In addition, for Seismic Zone 4, the total base shear shall also not be less than thefollowing:

V =0.8ZN v I
W
R

Where Ca, Cv, Na and Nv from tables (3-9), (3-10), (3-11) and (3-12) respectively.

Seismic Zone Factor (Z):Seismic Zone Factor as it mentioned in the first method.

Importance factor (I):
Importance factor (I) as it mentioned in the first method.

Structure period (T):The value of T shall be determined from one of the following methods:

1. Method A: For all buildings, the value T may be approximated from the following
formula:3

T = C t (hn ) 4
Where:

hn : building height from the base up to level n in meters.
C t =0.0853 for steel moment resisting frames.
C t = 0.0731 for reinforced concrete moment-resisting frames and eccentrically bracedframes.
C t =0.0488 for all other buildings.

Alternatively, the value of C t for structures with concrete or masonry shear walls may betaken as:

C t = 0.0743

Ac

Where Ac in m2 and shall be determined from the following formula:
Ac = ∑ Ae [0.2 + ( De / hn ) 2 ]The value of De/hn used in previous formula shall not exceed 0.9.
2. Method B: The fundamental period T may be calculated using the structural propertiesand deformational characteristics of the resisting elements in a properly substantiatedanalysis. The analysis shall be in accordance with the requirements of Section 4.2.2. The
value of T from Method B shall not exceed a value 30 percent greater than the value of T
obtained from Method A in Seismic Zone 4, and 40 percent in Seismic Zones 1, 2 and 3.
The fundamental period T may be computed by using the following formula:nni =1i =1

T = 2π (∑ wi δ i2 ) ÷ ( g ∑ f i δ i )The values of fi represent any lateral force distributed approximately in accordance withthe principles of Formulas (4-13), (4-14) and (4-15) or any other rational distribution.
The elastic deflections, δi, shall be calculated using the applied lateral forces, Fi.

The elastic deflections, δi
Simplified design base shear:a. General: Structures conforming to the requirements of section 3-9-2 may bedesigned using this procedure below.
b. Base shear: The total design base shear in a given direction shall be determinedfrom the following formula:

V=3.0C aW
RWhere, the value of Ca shall be based on Table 9-3 regarding the soil profile type.
When the soil properties are not known in sufficient detail to determine the soil
profile type, Type SD shall be used in Seismic Zones 3 and 4, and Type SE shall be
used in Seismic Zones 1, 2A and 2B. In Seismic Zone 4, the Near-Source Factor, Na,need not be greater than 1.3 if none of the following structural irregularities arepresent: Type (1, 4 or 5) of Table (3-4), or Type (1) or (4) of Table (3-5).
c. Vertical distribution: The forces at each level shall be calculated using thefollowing formula:

Fx =3.0C awiR

Where, the value of Ca shall be determined in Subsection (4-3-3-b).
d. Applicability: Sections (4-2-2), (4-2-3), (4-3-1), (4-3-2), (4-6), (4-10), (4-11) and5 shall not apply when using the simplified procedure.

EXCEPTION: For buildings with relatively flexible structural systems, the building official may
require consideration of P-∆ effects and drift in accordance with Sections (4-2-3), (4-10) and (411). While ∆s shall be calculated using design seismic forces from Subsection (4-3-3-b).

Where used, ∆M shall be taken equal to 0.01 times the story height of all stories.
In Section (7-11-8), Formula (7-2) shall read:F px =3.0C aw px
RAnd need not exceed (1.Ca.wpx), but shall not be less than (0.5.Ca.wpx). R shall betaken from Table (3-6).
Vertical Distribution of Force:

The total force shall be distributed over the height of the structure in conformance with
Formulas (4-13), (4-14) and (4-15) in the absence of a more accurate procedure.
nV = Ft + ∑ Fi

(4 − 13)i =1

The concentrated force Ft at the top, which is in addition to Fn shall be determined fromthe formula:Ft = 0.07T .V(4 − 14)

The value of T used for the purpose of calculating Ft shall be the period that correspondswith the design base shear as computed using Formula (4-4). Ft need not exceed 0.25V
and may be considered as zero where T is 0.7 second or less. The remaining portion ofthe base shear shall be distributed over the height of the structure, including Level n,according to the following formula:
Fx =(V − Ft ) wx hxn∑w hi =1i(4 − 15)i

At each level designated as x, the force Fx shall be applied over the area of the building inaccordance with the mass distribution at that level. Structural displacements (figure 4-2)
and design seismic forces (figure 4-3) shall be calculated as the effect of forces Fx and Ft
applied at the appropriate levels above the base.

Figure (4-2): Structural displacements

Figure (4-3): Design Seismic Forces

Dynamic Analysis Procedures:

1. General:

Dynamic analyses procedures, when used, shall conform to the criteria established in thissection. The analysis shall be based on an appropriate ground motion representation andshall be performed using accepted principles of dynamics. Structures that are designed inaccordance with this section shall comply with all other applicable requirements of theseprovisions.
2. Ground Motion:

The ground motion representation shall, as a minimum, be one having a 10-percent
probability of being exceeded in 50 years, shall not be reduced by the quantity R and may
be one of the following:
2.1. An elastic design response spectrum constructed in accordance with Figure 5-1,
using the values of Ca and Cv consistent with the specific site. The design acceleration
ordinates shall be multiplied by the acceleration of gravity (9.815 m/sec2).
2.2. A site-specific elastic design response spectrum based on the geologic, tectonic,seismologic and soil characteristics associated with the specific site. The spectrum shallbe developed for a damping ratio of 0.05, unless a different value is shown to beconsistent with the anticipated structural behavior at the intensity of shaking established
for the site.
2.3. Ground motion time histories developed for the specific site shall be representativeof actual earthquake motions. Response spectra from time histories, either individually orin combination, shall approximate the site design spectrum conforming to Section 5-2-2.
2.4. For structures on Soil Profile Type SF, the following requirements shall apply whenrequired by Subsection (3-9-4-d):2.4.1 The ground motion representation shall be developed in accordance with Items 2and 3.
2.4.2 Possible amplification of building response due to the effects of soil-structureinteraction and lengthening of building period caused by inelastic behavior shall beconsidered.
2.5. The vertical component of ground motion may be defined by scaling corresponding
horizontal accelerations by a factor of two thirds. Alternative factors may be used whensubstantiated by site-specific data. Where the Near Source Factor, Na, is greater than 1.0,
site-specific vertical response spectra shall be used in lieu of the factor of two-thirds.
3. Mathematical Model:

A mathematical model of the physical structure shall represent the spatial distribution of
the mass and stiffness of the structure to an extent that is adequate for the calculation of
the significant features of its dynamic response. A three-dimensional model shall be used
for the dynamic analysis of structures with highly irregular plan configurations such as
those having a plan irregularity defined in Table (3-5) and having a rigid or semi-rigid
diaphragm. The stiffness properties used in the analysis and general mathematicalmodeling shall be in accordance with Section 4-2-2.
4. Description of Analysis Procedures:

4.1. Response spectrum analysis: An elastic dynamic analysis of a structure utilizing thepeak dynamic response of all modes having a significant contribution to total structural
response. Peak modal responses are calculated using the ordinates of the appropriate
response spectrum curve which correspond to the modal periods. Maximum modalcontributions are combined in a statistical manner to obtain an approximate total
structural response.

4.2. Time-history analysis: An analysis of the dynamic response of a structure at eachincrement of time when the base is subjected to a specific ground motion time history.

Figure (5-1): Design Response Spectrum

Table (4-2) shows the value of R factor for most common structural systems in Syria.
No.
12345Lateral Force resisting System Description
Special Moment Resisting Frame Systems.
Dual System With Special Moment Resisting Frames which are capable toresist at least 50% of Prescribed Seismic Force.
Dual System With Special Moment Resisting Frames which are capable toresist at least 25% of Prescribed Seismic Force.
Dual System With Special Moment Resisting Frames which are capable toresist at least 10% of Prescribed Seismic Force.
Bearing Shear Wall System without Special Moment Resisting Frames

R
8.0
7.5
6.5
5.5
4.5

Table (3-9), Seismic Coefficient Ca
Soil ProfileTypeSASBSCSDSESF

Z = 0.075
0.06
0.08
0.09
0.12
0.19Seismic Zone Factor, Z
Z = 0.15
Z = 0.2
Z = 0.3
0.12
0.16
0.24
0.15
0.20
0.30
0.18
0.24
0.33
0.22
0.28
0.36
0.30
0.34
0.36
1See Footnote

Z = 0.4
0.32 Nv
0.40 Nv
0.40 Nv
0.44 Nv
0.36 Nv

1
Site-specific geotechnical investigation and dynamic site response analysis shall be performed todetermine seismic coefficient for Soil Profile Type SF

Table (3-10), Seismic Coefficient Cv

1Soil Profile
TypeSASBSCSDSESF

Z = 0.075
0.06
0.08
0.13
0.18
0.26

Seismic Zone Factor, ZZ = 0.15
Z = 0.2
Z = 0.3
0.12
0.16
0.24
0.15
0.20
0.30
0.25
0.32
0.45
0.32
0.40
0.54
0.50
0.64
0.84
See Footnote1

Z = 0.4
0.32 Nv
0.40 Nv
0.56 Nv
0.64 Nv
0.96 Nv

Site-specific geotechnical investigation and dynamic site response analysis shall be performed todetermine seismic coefficient for Soil Profile Type SF

Table (3-11) NEAR- SOURCE FACTOR Na1

1Seismic Source
TypeABC

Closest Distance to Known Seismic Source2≤ 2 km
5 km≥ 10 km
1.5
1.2
1.0
1.3
1.0
1.0
1.01.01.0

The Near-Source Factor may be based on the linear interpolation of values for distances other than thoseshown in the table.
2The closest distance to seismic source shall be taken as the minimum distance between the site and thearea described by the vertical projection of the source on the surface (i.e, surface projection of fault plane).
The surface projection need not include portions of the source at depths of 10 km or greater. The largest
value of the Near-Source Factor considering all sources shall be used for design.

Table (3-12) NEAR- SOURCE FACTOR NV11Seismic Source
TypeABC≤ 2 km
2.0
1.6
1.0

Closest Distance to Known Seismic Source25 km
10 km
1.6
1.2
1.2
1.0
1.0
1.0

≥ 15 km
1.0
1.0
1.0

The Near-Source Factor may be based on the linear interpolation of values for distances other than thoseshown in the table2
the closest distance to seismic source shall be taken as the minimum distance between the site and the area
described by the vertical projection of the source on the surface (i.e, surface projection of fault plane). Thesurface projection need not include portions of the source at depths of 10 km or greater. The largest valueof the Near-Source Factor considering all sources shall be used for design.

Table (3-13) SEISMIC SOURCE TYPE1
Seismic source Type

Seismic source Description

Seismic source Definition
Maximum Moment
Magnitude, M

Slip Rate, SR(mm/year)

AFaults that are capable ofproducing large magnitude
events and that have a highrate of seismic activity

M ≥ 7.0SR ≥ 5B

All faults other than type A
and CM ≥ 7.0
M < 7.0
M ≥ 6.5

SR < 5SR > 2
SR < 2CFaults that are not capableof producing large
magnitude earthquakes andthat have a relatively low
rate of seismic activity

M < 6.5SR ≤ 2

PGA distribution for 10% probability of exceeding in 50 years (Return Period 475 years)