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 GB (ACCIDENTAL) LOAD
INTENSITY s1 { FREQUENT  RARE } GROUP i1 SCLASS i2 (DAMP f1) (DELN f2) (SF f3) (AV f4) (PX f5) (PZ f6)
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 } (f7) (ACC f8)
Where:
Parameter  Description 

LOAD i  load case number 
GB LOAD { X  Y  Z } f7  optional factor to multiply horizontal seismic load. 
ACC f8  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). 
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).
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:
whereη_{1} = 0.02+(0.05ζ)/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:
${\eta}_{2}=1+\frac{0.05\zeta}{0.06+1.7\zeta}$where η_{2}
=  the damping adjustment factor, when it is smaller than 0.55 shall equal 0.55.

Calculation 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 (Fig. 2.2):
F_{Ek} = α_{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 
ΔF_{n} = δ_{n}F_{Ek}  E2.6 
Calculation of horizontal seismic action
=  
=  
=  
=  
=  
=  
=  
= 
Table 2.4 Additional seismic action factors at top of the building
The horizontal seismic shear force at each floor level of the structure shall comply with the requirement of the following equation:
=  
=  
= 
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 
Calculation of vertical seismic action
For tall buildings for Intensity 9, the characteristic value of vertical seismic action shall be determined by the following equations (figure 2.3). The effects of vertical seismic action at floor level may be distributed in proportion of representative value of gravity load acting on the members, which should multiply with the amplified factor 1.5:
F_{Evk} = α_{vmax}G_{eq}  E2.8 
${F}_{i}=\frac{{G}_{i}{H}_{i}}{\stackrel{n}{\sum _{j=1}}{G}_{j}{H}_{j}}{F}_{Evk}$  E2.9 
=  
=  
=  
= 
Sketch for the computation of vertical seismic action
Complementarities
 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.
Example Output
***************************************************************************** * * * EQUIV. SEISMIC LOADS AS PER SEISMIC DESIGN CODE FOR BUILDINGS * * (GB500112001) OF CHINA ALONG X * * T CALCULATED = 0.252 SEC. T USER PROVIDED = 1.200 SEC. * * T USED = 1.200 SEC. * * MAX. HORIZONTAL SEISMIC INFLUENCE COEFFICIENT = 0.240 * * CHARACTERISTIC PERIOD = 0.750 SEC. * * DAMPING RATIO = 0.030 POWER INDEX (GAMMA) = 0.931 * * DAMPING ADJUSTMENT FACTOR (ETA2) = 1.180 * * ADJUSTING FACTOR (ETA1) = 0.022 * * HORIZONTAL SEISMIC INFLUENCE COEFFICIENT (ALPHA1) = 0.183 (18.288%) * * MINIMUM SHEAR FACTOR AS PER SEC. 5.2.5 (LAMBDA) = 0.050 ( 5.000%) * * TOTAL HORIZONTAL SEISMIC ACTION = * * = 0.183 X 285.529 = 52.218 KIP * * DESIGN BASE SHEAR = 0.750 X 52.218 * * = 39.164 KIP * * ADDITIONAL SEISMIC ACTION FACTOR (DELTAN) = 0.020 * * VERTICAL SEISMIC INFLUENCE COEFFICIENT (ALPHA,VMAX) = 0.108 * * TOTAL VERTICAL SEISMIC ACTION = * * = 0.108 X 285.529 = 30.837 KIP * * TOTAL DESIGN VERTICAL LOAD = 0.750 X 30.837 * * = 23.128 KIP * * * ***************************************************************************** CHECK FOR MINIMUM LATERAL FORCE AT EACH FLOOR [GB500112001:5.2.5] LOAD  1 FACTOR  0.750 FLOOR LATERAL GRAVITY LAMBDA LAMBDA ADJUSTMENT HEIGHT (KIP ) LOAD (KIP ) LOAD (KIP ) (%) MIN (%) FACTOR       30.000 23.406 79.045 29.61 5.00 1.00 20.000 19.208 180.888 10.62 5.00 1.00 10.000 9.604 282.731 3.40 5.00 1.47 JOINT LATERAL TORSIONAL VERTICAL LOAD  1 LOAD (KIP ) MOMENT (KIP FEET) LOAD (KIP ) FACTOR  0.750     17 FX 0.541 MY 0.000 FY 0.221 18 FX 0.663 MY 0.000 FY 0.271 19 FX 0.663 MY 0.000 FY 0.271 20 FX 0.541 MY 0.000 FY 0.221 21 FX 0.663 MY 0.000 FY 0.271 22 FX 0.785 MY 0.000 FY 0.321 23 FX 0.785 MY 0.000 FY 0.321 24 FX 0.663 MY 0.000 FY 0.271 25 FX 0.663 MY 0.000 FY 0.271 26 FX 0.785 MY 0.000 FY 0.321 27 FX 0.785 MY 0.000 FY 0.321 28 FX 0.663 MY 0.000 FY 0.271 29 FX 0.541 MY 0.000 FY 0.221 30 FX 0.663 MY 0.000 FY 0.271 31 FX 0.663 MY 0.000 FY 0.271 32 FX 0.541 MY 0.000 FY 0.221    TOTAL = 10.602 0.000 0.221 AT LEVEL 10.000 FEET