Issue 29

L. Facchini et alii, Frattura ed Integrità Strutturale, 29 (2014) 139-149; DOI: 10.3221/IGF-ESIS.29.13 146                     1 2 , , 1 , , , , , k k k k k k k k mx t cx t kg z g z z t x t h x z x t h x z zz h x x x x                          (11) Figure 9: Response   x t evaluated for    k E k . Figure 10: Sensitivity of the response   k x t . Moreover, a further differentiation with respect to k gives the equation of motion of the second derivative of BW response to the earthquake, as follows:                                 1 2 2 2 11 12 22 1 2 , 2 , 1 , 2 , , , , , , 2 , , , , , , , , kk kk kk kk k k kk kk k k k k k k k kk kk mx t cx t kg z g z z t x t h x z x t h x z x h x z z x t h x z x h x z x z h x z z h x z x h x x x z z                                            (12)