Report - PEER - University of California, Berkeley

4.3 MRF with InfillsSeveral researchers have recently studied the behaviour of MRFs with infills (Lu2002). Quality experimental data is becoming available. An example illustrating theeffect of infills on the relationship between damage and maximum interstorey drift isshown in Figure 7. The load carrying capacity of infilled frame is higher than that of abare frame. A moment resisting frame with infills gives roughly half the interstoreydrift of a bare frame (Chiou et al. 1999) with twice the damage index. For example,0.35 damage index corresponds to interstorey drift of bare MRF of 0.8%. Interstoreydrift ratio of 0.8% corresponds to a damage index of a MRF with infills of 0.7, whichis near collapse. The behaviour of infilled frame may not return to the behaviour of aductile MRF after the failure of the masonry infills. The apparent lack of ductility forMRF with infills is because the pattern of masonry failure may cause brittle failure ofthe frame elements. This may be the case even for a well-designed frame that isductile when tested without the infills. The maximum interstorey drift limitscorresponding to various damage states of MRF with infills are listed in Table 2.0.8Damage index0.60.40.2Bare MRFMRF with infills00 1 2 3Interstorey drift ratio %Figure 7. Behaviour of bare portal MRF and MRF with infills.5. WALLSStructural walls may act predominantly in shear or flexure depending on their aspectratio and the applied loads. Squat walls may fail abruptly by one of several brittlemodes of failure. There is a comprehensive volume of experimental research and postearthquake observation on the behaviour of walls (Duffey et al. 1994; Khalil andGhobarah 2003; Kowalsky 2001; Wood 1991).330