6.4　Seismic Strength Verification Testing

6.4.1　For new type or significantly updated equipment，a shake-table test shall be conducted to verify its seismic capability.For equipment which is not suitable for overall test due to its dimensions，weight or complexity or which has passed relevant test and is not significantly remodeled，its seismic capability may be verified through sub-assemblage test or a combination of test and analysis.

6.4.2　The test specimen shall be mounted according to the operating conditions，and any fixing or connecting parts，which are only intended for the test purpose，shall not influence the dynamic performance of the test specimen.

6.4.3　The seismic strength verification testing of electrical facility shall involve stress testing at critical cross sections in the two principal axis directions.However，for axially symmetrical electrical equipment and device，symmetrical structure，the verification testing may be conducted in only one direction.

6.4.4　For long-span and long-cantilever electrical facilities，such as wall bushings，the verification testing should be conducted in both horizontal and vertical directions simultane ously.

6.4.5　The input ground motion type and peak acceleration for the seismic strength verification testing of electrical facilities shall be determined according to the following principles：

1　For verification testing of the prototype electrical equipment with support system and the prototype electrical device system，the input ground motion of shake table may be actual strong ground motion records or artificial ground motions meeting the seismic influence coefficient curve stated in Article 5.0.5 of this Code.The input peak acceleration shall be selected based on the design seismic precautionary intensity and Table 5.0.3-1 of this Code.When verification testing is only performed for the electrical equipment and devices or their components，the input peak acceleration shall be multiplied by the dynamic amplification factor stated in Article 6.2.6 of this Code.

2　When verification testing is only performed for the electrical equipment and devices of their components，the input ground motion of shake table may alternatively be sine beat composed of five resonant amplitude-modulated five-cycle sine waves，as shown in Figure 6.4.5.

The acceleration time history of each beat may be determined as follows：

When t≥5T，a=0；

When 0≤t＜5T，the value of a may be determined with the following formula：

Where，a——horizontal acceleration time history，g；

t——time，s；

T——fundamental period of the system in test direction，s；

as——horizontal peak ground acceleration，g；

ao——peak ground acceleration corresponding to the seismic precautionary intensity to be adopted in seismic design；

ω——natural circular frequency of the system in test direction，Hz.

To avoid the superposition of seismic response of each beat，the beat interval may be determined as follows：

Where，Tp——beat interval，s；

f——fundamental frequency of the system in test direction，Hz.

6.4.6　The monitoring points of test specimen shall be arranged depending on the structure of electrical facilities and the test requirements，and the measurements at all monitoring points shall be recorded and collected simultaneously.

6.4.7　The stress at critical cross sections measured in the verification testing shall be combined with the stresses due to gravity，internal pressure，terminal force，and 0.25 times the design wind load.Compliance with Article 6.3.8 of this Code implies that the product can meet the seismic requirements.