Report - PEER - University of California, Berkeley

frame is usually able to resist the seismic loads after the infill fails. The pushovercurve can be modeled with a four-linear force-displacement relationship as shown inFig.6a. Based on an extensive statistical study of a SDOF mathematical model with afour-linear backbone curve and hysteretic behaviour typical for infill frames, aspecific R-µ-T relation was determined (Dolšek and Fajfar 2004a). The relationdepends on the basic parameters of the pushover curve (yield displacement D y andyield force F y , ductility at the beginning of softening of infills µ s , and the ratiobetween the force at which infills completely collapse and yielding force r u ) and thecorner periods of the acceleration spectrum T C and T D . T C represents the corner periodbetween the constant acceleration and constant velocity part of the spectrum of theNewmark-Hall type, and T D represents the corner period between the constantvelocity and constant displacement part of the spectrum.wherewithandwhere1( R R0 ) 0µ = − + µ(1)c⎧ ⎛ T ⎞⎪ 0.7 ⎜ ⎟ L R≤R( µs), T ≤TC⎪ ⎝TC⎠⎪ 0.7 + 0.3 ∆ T L R R( µ ),T T T≤ < ≤⎪1c = ⎨ ⎛ T ⎞ ru⎪ 0.7 ru ⎜ ⎟ L R> R( µs), T ≤TC⎪ ⎝TC⎠⎪⎪0.7 r ( 1 −∆ T) +∆ T L R> R( µ ),T < T ≤T⎪⎩>*s C D*u s C D*1 LT TD*T − TCTD = TD 2 − ru, ∆ T =T 2 −r −TD u C1 L R≤Rs( µ )( )⎪⎧µ0= ⎨⎪⎩ µsL R>R µsRR01 L R≤R( µs )( µ ) L > ( µ )⎧⎪= ⎨⎪⎩ RsR R( µ )ss(2), (3)⎧ ⎛ T ⎞0.7⎜ ⎟( µs− 1)+ 1 L T ≤TC⎪ TC=⎝ ⎠⎨. (6)*⎪( 0.7 + 0.3∆T)( µs− 1) + 1 L TC < T ≤TD⎪ *⎩ µsL T > TD(4)(5)364