Seismic Isolation Design For Simply-Supported Beam Bridges Based On The Energy Balance Method Under Near-Fault Ground Motions

The S(EI)smically isolated simply-supported beam bridge (SISBB) with the S(EI)smic isolation bearing (SIB) is converted into an equivalent bilinear single-degree-of-freedom system. Then, by inputting the 139 near-fault ground motion (GM) records into the equivalent system, the parametric study on the near-fault S(EI)smic input energy spectra (S-EI) of the SISBB is conducted by considering the equivalent system parameters and the near-fault GM characteristics. So, it can be found that: the increase of post-yield stiffness ratio (eta(e)) can slightly increase the peak values of the near-fault S-EI, and eta(e) = 0.2 can be used to calculate the near-fault S-EI design spectra of the SISBB; with the increase of the damping ratio (eta(e)) (or ductility ratio (mu e)), the spectral values of the near-fault S-EI increases, the hysteretic energy dissipation capacity of the SIB decreases, and the damping energy dissipation capacity of the equivalent system increases; when mu(e) > 10, the effect of mu(e) on the near-fault S-EI can be ignored; the softer the site soil or the smaller the Joyner-Boore distance to rupture plane (R-jb) is, the greater the near-fault S-EI is; if the near-fault S-EI with a standard peak ground acceleration (PGA) is known, the near-fault S-EI with other PGAs can be obtained by multiplying the (PGA(Other)/PGA(Standard))(2) by the spectral values of the near-fault S-EI with a standard PGA. Finally, the near-fault S-EI design spectra of the SISBB are obtained, and the seismic isolation design for SISBB based on the energy balance method is proposed, the feasibility of which is verified by a case study.