Report - PEER - University of California, Berkeley

5Ductility factor432100 0.2 0.4 0.6 0.8 1Storey drift factor (SDF)Figure 5. Correlation between ductility and the storey drift factor.4.2 Nonductile MRFMRF designed to earlier codes or without seismic detailing often suffer from poorconfinement of lap splices, lack of shear reinforcement in the beam-column joints andinadequate embedment length of the beam bottom reinforcement at the column. Theseframes behave in a nonductile manner and may fail in brittle failure modes. As anexample of the data used, the maximum interstorey drift is plotted against the damageindex in Figure 6. The behaviour of several frames when subjected to a number ofground motions contributed the data shown in the figure. For nonductile MRF, thedamage index corresponding to repairable damage limit is 0.4. This damage levelcorresponds to maximum interstory drift limit of 0.5%, which is considered to be thelimit of irreparable damage as suggested by experimental observation. The maximuminterstorey drift limits corresponding to various damage states of a nonductile MRFare listed in Table 2.1Damage index0.80.60.40.20Existing 3-storey frameExisting 9-storey frameData trend0 1 2 3 4Interstorey drift ratio %Figure 6. Relationship between maximum interstorey drift and damage forexisting nonductile frames.329