Report - PEER - University of California, Berkeley

5.2 Performance Levels and Limit States of StructureThe performance objective given by the Chinese “Code for seismic design ofbuildings” (GBJ11-89) is as follows. For frequently occurring earthquakes ofintensity lower than the seismic strengthening intensity of the region, buildingsdesigned according to the code shall not be damaged and/or shall be able to be inservice; for occasionally occurring earthquakes of intensity corresponding to theseismic strengthening intensity of the region, buildings may be damaged but shouldbe restorable to service with minor repairs; for rarely occurring earthquakes ofintensity higher than the seismic strengthening intensity of the region, buildings shallnot collapse or incur severe life-threatening damage. So, on the basis of the seismicstrengthening objective, three performance levels are specified: for frequentlyoccurring, occasionally occurring and rarely occurring earthquakes, which are the socalled“no damage during frequently occurring earthquakes, repairable duringoccasionally occurring earthquakes, and no collapse during rarely occurringearthquakes”.In order to conduct reliability analysis, the limit states of a structure need to begiven. Usually, five limit states are considered: representing initial cracking damage,slight damage, moderate damage, severe damage and collapse of the structure. Wecan see from the definition of three performance levels as mentioned above that thefirst one corresponds to the initial cracking damage; the second one corresponds toslight to moderate damage; the third one corresponds to severe damage.In this analysis, the limit state of a structure is defined in terms of the structuralductility factor. For each limit state, a corresponding capacity in terms of the ductilityfactor can be established. The ductility factor of the brick wall is defined as the ratioof the maximum deformation to the cracking deformation. The structural capacity canbe usually modeled by a lognormal distribution. According to Zhang (2002), on thebasis of the cracking features of walls in each hysteretic skeleton curve stage andcompared with the true earthquake damage degree of buildings, the median µ~R andlogarithmic standard deviation σ can be obtained, as shown in Table 3.RTable 3. Ductility factor capacityLimit statesBrick wall withoutconstructional columnBrick wall withconstructional column~ µRσ RRσRµ ~Initial cracking damageSevere damageCollapse1.0 0.31.6 0.32.6 0.31.0 0.32.6 0.34.8 0.3414