Page 507 - Advanced Design Examples of Seismic Retrofit of Structures

450 Advanced Design Examples of Seismic Retrofit of Structures

FIG. 6.49 Collapse of the unretrofitted specimen at 125% level of excitation (plan view). (Photos
taken by Mohammad Yekrangnia.)

probability of occurrence in 50years’ lifetime of the building). Also, the spec-
trum related to 175% of excitation level is compared with 150% of the codified
DBE spectrum which represents the Maximum Credible Earthquake (MCE)
with the return period of 2475years (or 2% probability of occurrence in
50years’ lifetime of the building). For the tested building model in shaking table
tests, the natural period of the first mode of the building (noted as T 1 in
Fig. 6.55) was 0.11s. Based on the codified spectral scaling procedure for per-
forming time history analysis, the excitation spectrum intensity should not be
lower than 0.9 of the codified spectrum between 0.2T 1 and 1.5T 1 [36]. Based
on this procedure, the spectra of 100% and 175% of excitation levels meet
the requirements for scaling according to DBE and MCE, respectively. Based
on this figure, the unretrofitted specimen did not satisfy the Life Safety (LS)
Performance Level during DBE. However, thanks to the implemented retrofit
measures, the corresponding retrofitted specimen not only satisfied the LS
during DBE, but also met the requirement of the Collapse Prevention (CP) Per-
formance Level during MCE.