Report - PEER - University of California, Berkeley

Also, since the reparable damage ranges widely from slight to major, the Guidelinesconsiders two levels, i.e., the reparability limit states I and II. The first is the level ofdamage such that “slight repair might be needed but successive use will be possible,”and in terms of damage classification as minor and nearly minor-to-moderate. Thelatter is such that “although successive use might not be available, economicalrestoration is quite possible by repair or strengthening to some extent,” and damagelevel of moderate and nearly moderate-to-severe damage. There still left an enoughmargin to the actual safety limit deformation from these two limit states.The seismic performance of a building shall be evaluated independently on thethree principal directions of the structure for each of above performance objectives.4. PERFORMANCE INDEX AND EARTHQUAKESThe seismic performance level is expressed as a continuous value using the seismicperformance index. The value of the seismic performance index calculated indeterministic form as (1) below is the basic expression in the Guidelines, although (2),in probability form, may be used together with (1).(1) The index in terms of the intensity of the earthquake ground motion atbedrock when the building response attains to the limit states (i.e., serviceability,reparability or ultimate limit states), i.e., the intensity of the capacity earthquake,defined as the ratio to the intensity of the standard earthquake:Intensity of the capacity earthquakeSeismic performance index = (1)Intensity of the standard earthquake(2) The index in terms of the probability of the building response to exceed thelimit states, due to the earthquake ground motion that may occur on the site during theservice life of the building, i.e., the site earthquake motion.Particularly in the evaluation by the second probability form, many assumptionsare included in the models, because the state of knowledge on these fields is limited.Many would have to be revised as results from future research. Thus in the meantime,the method in the Guidelines is to be used for measuring the probabilistic significancerelatively and as interpretation on the deterministic index.In accordance with above two definitions, the expected earthquake groundmotions are also discriminated in two ways: the standard earthquake motion and thesite earthquake motion.The standard earthquake motion is defined at the engineering bedrock in terms ofthe elastic acceleration response spectrum with 5 percent of critical dampingcorresponding to the same level as the design earthquake specified by the BuildingStandard Law of Japan, namely as:Sa(T, h = 0.05) = 320 + 3000TSa(T, h = 0.05) = 800Sa(T, h = 0.05) = 512 / TifififT ≤ 0.160.16 ≤ T < 0.640.64 ≤ T < 5.0(2)30