5　Earthquake Action for Electrical Facilities

5.0.1　The earthquake action for electrical facilities shall be determined according to the following principles：

1　The seismic calculation of electrical facilities shall involve calculation of the horizontal earthquake actions in at least two horizontal axis directions，and the horizontal earthquake action in each direction shall be resisted by lateral force resisting members in the direction.

2　For structures with asymmetrical mass and stiffness distribution，the torsional effect under horizontal earthquake action shall be taken into consideration.

3　When the seismic precautionary intensity is 8 or 9 degree，the vertical earthquake action shall be checked for long-span facilities and long-cantilever structures.

5.0.2　The seismic analysis for electrical facilities may be performed using the static method，equivalent base shear method，mode analysis response spectrum method，or time history analysis method.

5.0.3　The seismic influence coefficient of earthquake action shall be determined according to the relevant requirements of the current national standard Seismic Ground Motion Parameters Zonation Map of China GB 18306，site classification，natural period of vibration，damping ratio，and Article 1.0.9 of this Code，and shall comply with the following requirements：

1　The maximum value of horizontal seismic influence coefficient shall be selected from Table 5.0.3-1 based on the design basic acceleration of ground motion.The design basic acceleration of ground motion shall be the seismic peak ground acceleration at the place where the electrical facility is located according to Seismic Ground Motion Parameters Zonation Map of China GB 18306.

2　The characteristic period of horizontal seismic influence coefficient shall be the characteristic period of response spectrum at the place where the electrical facility is located according to Seismic Ground Motion Parameters Zonation Map of China GB 18306，and is subject to adjustment based on the site classification.Alternatively，it may be determined according to Table 5.0.3-2 in the current national standard Code for Seismic Design of Buildings GB 50011 depending on the design earthquake group and the site classification of the place where the electrical facility is located.The characteristic period is increased by 0.05s in the case of rare earthquake.

Note：The seismic influence coefficient of structures whose period is larger than 6.0s shall be subjected to special studies.

5.0.4　For cities with established seismic microzonation or sites which have been evaluated for seismic safety，the seismic influence coefficient shall be determined based on the approved design ground motion parameters.

5.0.5　The shape parameter of seismic influence coefficient curve shall comply with the following requirements：

1　For ClassⅡsite，the shape parameter of seismic influence coefficient curve of earthquake action（Figure 5.0.5）shall be calculated in accordance with the following requirements：

1）Linear increase section：whose period is shorter than 0.1s；

2）Horizontal section：whose period is from 0.1s to the characteristic period；

3）Curvilinear decrease section：whose period is from the characteristic period to five times the characteristic period；

4）Linear decrease section：whose period is from five times the characteristic period to 6s；

5）The seismic influence coefficient curve is expressed as follows：

Where，α——seismic influence coefficient；

αmax——maximum value of seismic influence coefficient；

Tg——characteristic period；

T——natural period of vibration of structure；

ζ——damping ratio of structure；

γ——attenuation index；

η1——adjustment factor of the slope of linear decrease section.When the calculated value of η1＜0，η1 shall be taken as zero；

η2——adjustment factor of damping.When the calculated value of η2＜0.55，η2 shall be taken as 0.55.

2　For sites of other classes，the shape parameter of seismic influence coefficient curve shall be determined using the formula below：

Where，αs——seismic influence coefficient for different site classes；

α——seismic influence coefficient calculated according to Formula（5.0.5-1）；

η3——Site adjustment factor for the maximum value of seismic influence coefficient，see Table 5.0.5.

5.0.6　When base shear method is used to calculate the horizontal earthquake action on structure as shown in Figure 5.0.6，the characteristic values of the total horizontal earthquake action and the horizontal earthquake action at various mass points shall be calculated using the following formula：

1　The characteristic value of the total horizontal earthquake action on structure shall be calculated using the formula below：

Where，FEk——characteristic value of total horizontal earthquake action on structure；

α1——horizontal seismic influence coefficient corresponding to the natural period of vibration of structure，whose value shall be determined according to Article 5.0.5 of this Code；

Geq——equivalent total gravity load of structure，which shall be taken as the representative value of total gravity load for structures with single mass point and may be taken as 85% of the representative value of total gravity load for structures with several mass points.

2　The characteristic value of horizontal earthquake action at various mass points shall be calculated using the formula below：

Where，Fi——characteristic value of horizontal earthquake action on mass point i；

Gi，Gj——representative value of gravity load at mass points i and j；

Hi，Hj——calculation height of mass points i and j；

δn——additional earthquake action coefficient at the top of structure，which may be determined according to Table 5.0.6.

3　The additional horizontal earthquake action at top of structure shall be calculated with the following formula：

Where，ΔFn——additional horizontal earthquake action at top of structure，which shall comply with Table 5.0.6.

5.0.7　When mode analysis response spectrum method is adopted，the number of vibration modes shall ensure that the participating mass is not less than 90% of the total mass.The earthquake action and its effect shall comply with the following requirements：

1　The characteristic value of the horizontal earthquake action at mass point i of the jth mode shall be determined according to the following formulae：

Where，Fji——characteristic value of horizontal earthquake action at mass point i of the jth vibration mode；

αj——horizontal seismic influence coefficient corresponding to the natural period of vibration of the jth mode，whose value shall be determined in accordance with Article 5.0.5 of this Code；

γj——participation coefficient of the jth mode；

Xji——horizontal relative displacement of mass point i of the jth mode；

Gi——representative value of the gravity load at mass point i，including all dead loads，gravity load of fixed equipment，and other gravity loads applied on the mass point.

2　When the period ratio of adjacent modes is less than 0.9，the horizontal earthquake action effect（bending moment，shear force，axial force and deformation）of each vibration mode shall be calculated using the formula below：

Where，SEk——horizontal earthquake action effect；

Sj——horizontal earthquake action effect of the jth mode.

3　When the period ratio of adjacent modes is greater than 0.9，the horizontal earthquake action effect（bending moment，shear force，axial force and deformation）of each vibration mode shall be calculated using the formula below：

Where，SEk——horizontal earthquake action effect；

Sj，Sk——earthquake action effect of the jth and kth modes；

ζj，ζk——damping ratio of the jth and kth modes；

ρjk——coupling coefficient between the jth and kth modes；

λT——ratio of the natural period of vibration between the kth and jth modes.