Seismic responses of the supporting structure of FAST under multiple-support excitations

Seismic ground motions are spatial incoherent partly due to uncertainty in fault mechanism and wave propagation. The spatial coherency and its effect can be important and need to be investigated for multiple-support structures. In this study, an investigation of seismic responses of a five-hundred-meter aperture spherical telescope (FAST) is investigated. The structure is a cable net structure with multiple supports. For the structural analysis, parameters of an existing coherency model for excitations along the same orientation but considering the multi-component excitations and spatially separated locations are developed using the records from Taiwan. This coherency model together with adopted target power spectral density function and phase difference spectrum model are used to simulate multi-component seismic ground motions at 338 grid points covering the FAST. The simulated records are used as the basis to interpolate the time history of the ground motions at 2395 supports for the considered structure. The time-history responses of the structure under incoherent multiple-support excitations are evaluated and compared to that under uniform excitations. The results show that the influence of coherency on the supporting structure of the FAST in three excitation directions differs. The analysis results show that as compared to uniform excitations, the consideration of the seismic coherency in seismic excitations leads to, on average, 87% of increase in stress for 94% of the main cables, and 22% of increase in stress for 44% of the tie-down cables. It was also noted that the maximum tensile stress of the cable by considering the coherency is 835 MPa while that under uniform excitations is 671 MPa. In both cases, they are smaller than the characteristic tensile strength of the cables used for design and construction of the FAST.