TR.31.2.5 Chinese Static Seismic per GB500112001
General Format
The following general format should be used to generate loads in a particular direction.
DEFINE GB50011 2001 (ACCIDENTAL) LOAD
INTENSITY s1 { FREQUENT  RARE } GROUP i1 SCLASS i2 (DAMP f1) GFACTOR { 0.85  1.0 } (DELN f2) (SF f3) (PX f4) (PZ f5)
Where:
Generation of GB50011 Seismic Load
To apply the load in any load case, following command would be used
LOAD CASE i
GB LOAD { X  Y  Z } (f6) (ACC f7)
Where:
Parameter  Description 

LOAD i  load case number 
GB LOAD { X  Y  Z } f6  An optional factor to multiply horizontal seismic load. 
ACC f7  The multiplying factor for Accidental Torsion, to be used to multiply the accidental torsion load (default = 1.0). May be negative (otherwise, the default sign for MY is used based on the direction of the generated lateral forces). 
 When the seismic load is defined as per topic TR.32.12.2 Generation of Seismic Loads, then currently only the accidental torsion ACC is supported, DEC is not supported.
 If the ACCIDENTAL option is specified, the accidental torsion will be calculated per the GB 500112001 specifications. The value of the accidental torsion is based on the "center of mass" for each level. The "center of mass" is calculated from the selfweight, joint weights and member weights you have specified.
 The seismic load generator can be used to generate lateral loads in the X and Z directions for Y up and the X and Y directions for Z up; where Y up or Z up is the vertical axis parallel to the direction of gravity loads (See the SET Z UP command in TR.5 Set Command Specification).
 All vertical coordinates of the floors above the base must be positive and the vertical axis must be perpendicular to the floors.
 This method of seismic load generation is limited in use to buildings not taller than 40 meters, with deformations predominantly due to shear, and a rather uniform distribution of mass and stiffness in elevation. Alternately, for buildings modeled as a singlemass system, a simplified method such as this base shear method, may be used.
Gravity Loads for Design
In the computation of seismic action, the representative value of gravity load of the building shall be taken as the sum of characteristic values of the weight of the structure and members plus the combination values of variable loads on the structure. The combination coefficients for different variable loads shall be taken from the following table.
Type of Variable  land Combination coefficient  

Snow load  0.5  
Dust load on roof  0.5  
Live load on roof  Not considering  
Live load on the floor, calculated according to actual state  1.0  
Live load on the floor, calculated according to equivalent uniform state  Library, archives  0.8 
Other civil buildings  0.5  
Gravity for hanging object of crane  Hard hooks  0.3 
Soft hooks  Not considering 
Seismic Influence Coefficient
This shall be determined for building structures according to the Intensity, Siteclass, Design seismic group, and natural period and damping ratio of the structure. The maximum value of horizontal seismic influence coefficient shall be taken from Table 2.2; the characteristic period shall be taken as Table 2.3 according to Siteclass and Design seismic group, that shall be increased 0.05s for rarely earthquake of Intensity 8 and 9.
Earthquake influence  Intensity 6  Intensity 7  Intensity 8  Intensity 9 

Frequent earthquake  0.04  0.08 (0.12)  0.16(0.24)  0.32 
Rarely earthquake    0.50(0.72)  0.90(1.20)  1.40 
Earthquake Group  Site class  

I  II  III  IV  
1  0.25  0.35  0.45  0.65 
2  0.30  0.40  0.55  0.75 
3  0.35  0.45  0.65  0.90 
Calculation of Seismic Influence Coefficient
The design base shear is computed in accordance with the equations shown below.
The damping adjusting and forming parameters on the building seismic influence coefficient curve (Fig.2.1) shall comply with the following requirements:

The damping ratio of building structures shall select 0.05 except otherwise provided, the damping adjusting coefficient of the seismic influence coefficient curve shall select 1.0, and the coefficient of shape shall conform to the following provisions:
 Linear increase section, whose period (T) is less than 0.1 s;
 Horizontal section, whose period form 0. is thought to characteristic period, shall select the maximum value (α_{max});
 Curvilinear decrease section, whose period from characteristic period thought to 5 times of the characteristic period, the power index (γ) shall choose 0.9.
 Linear decrease section, whose period from 5 times characteristic period thought to 6s, the adjusting factor of slope (η_{1}) shall choose 0.02.
Seismic influence coefficient curve

When the damping adjusting and forming parameters on the seismic influence coefficient curve shall comply with the following requirements:

The power index of the curvilinear decreased section shall be determined according to the following equation E2.1
where$\gamma =\text{}0.9+\frac{0.05\zeta}{0.5+5\zeta}$ E2.1  γ
=  the power index of the curvilinear decrease section
 ξ
=  the damping ratio

The adjusting factor of slope for the linear decrease section shall be determined from following equation:
where${\eta}_{1}=0.02+\frac{0.05\zeta}{8}$ E2.2  η_{1}
=  the adjusting factor of slope for the linear decrease section, when it is less than 0, shall equal 0.

The damping adjustment factor shall be determined according to the following equation:
where${\eta}_{2}=1+\frac{0.05\zeta}{0.06+1.7\zeta}$ E2.3  η_{2}
=  the damping adjustment factor, when it is smaller than 0.55 shall equal 0.55.

Calculation of Horizontal Seismic Action
Characteristic Value of Horizontal Seismic Action
When the base shear force method is used, only one degree of freedom may be considered for each story; the characteristic value of horizontal seismic action of the structure shall be determined by the following equations:
${F}_{Ek}={\alpha}_{1}{G}_{eq}$  E2.4 
${F}_{i}=\frac{{G}_{i}{H}_{i}}{\stackrel{n}{\sum _{j=1}}{G}_{j}{H}_{j}}{F}_{Ek}(1{\delta}_{n})$  E2.5 
$\Delta {F}_{n}={\delta}_{n}{F}_{Ek}$  E2.6 
Calculation of horizontal seismic action
=  
=  
=  
=  
=  
=  
=  
= 
T_{g} (s)  T_{1} > 1.4T_{g}  T_{1} ≤ 1.4T_{g} 
T_{g} ≤ 0.35  0.08T_{1} + 0.07  0 
0.35 < T_{g} ≤ 0.55  0.08T_{1} + 0.01  
T_{g} > 0.55  0.08T_{1} − 0.02 
Horizontal Seismic Shear Force Verification
The horizontal seismic shear force at each floor level of the structure shall comply with the requirement of the following equation:
${V}_{Eki}>\lambda \stackrel{n}{\sum _{j=1}}{G}_{j}$  E2.7 
=  
=  
= 
Structures  Intensity 7  Intensity 8  Intensity 9 

structures with obvious torsion effect or fundamental period is less than 3.5s  0.16 (0.024)  0.032 (0.048)  0.064 
Structures with fundamental period greater than 5.0s  0.012 (0.018)  0.024 (0.032)  0.040 
Notes
 Structures having the oblique direction lateralforceresisting members and the oblique angel to major orthogonal axes is greater than 150, the horizontal seismic action along the direction of each lateralforceresisting member shall he considered respectively. So we could consider this though the item, the action of the oblique member could be multiplied by this factor as design force.

Eccentricity: similar to UBC code. The eccentricity value of gravity center on each floor should be e_{i }= ±0.05L_{i},
where e_{i}
=  Eccentricity value of gravity center on i^{th} floor.
 L_{i}
=  maximum width of calculated story of the building.
 Structures having obviously asymmetric mass and stiffness distribution, the torsion effects caused by both two orthogonal horizontal direction seismic action shall be considered; and other structures, it is permitted that a simplified method, such as adjusting the seismic effects method, to consider their seismic torsion effects.